@article{karnauskas_aiyyer_camargo_capitanio_feakins_fulweiler_ganju_giannini_gu_huber_et al._2025, title={Thank You to Our 2024 Reviewers}, volume={52}, ISSN={["1944-8007"]}, url={https://doi.org/10.1029/2025GL115360}, DOI={10.1029/2025GL115360}, abstractNote={Abstract On behalf of the journal, AGU, and the scientific community, the editors of Geophysical Research Letters would like to sincerely thank those who reviewed manuscripts in 2024. The hours reading and commenting on manuscripts not only improve the manuscripts but also increase the scientific rigor of future research in the field. With the advent of AGU's data policy, many reviewers have also helped immensely to evaluate the accessibility and availability of data, and many have provided insightful comments that helped to improve the data presentation and quality. We greatly appreciate the assistance of the reviewers in advancing open science, which is a key objective of AGU's data policy. We particularly appreciate the timely reviews in light of the demands imposed by the rapid review process at Geophysical Research Letters. We received 5,225 submissions in 2024, and 5,597 reviewers contributed to their evaluation by providing 9,697 reviews in total. We deeply appreciate their contributions. We would also like to acknowledge the passing of our beloved colleague, Harihar Rajaram. An AGU Fellow and longtime affiliate of AGU's Hydrology Section, Hari was the Editor‐in‐Chief of Geophysical Research Letters since 2019, a former editor on Water Resources Research, and served on the AGU Publications Committee.}, number={4}, journal={GEOPHYSICAL RESEARCH LETTERS}, author={Karnauskas, Kris and Aiyyer, Anantha and Camargo, Suzana and Capitanio, Fabio and Feakins, Sarah and Fulweiler, Robinson and Ganju, Neil and Giannini, Alessandra and Gu, Yu and Huber, Christian and et al.}, year={2025}, month={Feb} }
 @article{hwang_schreck_aiyyer_sankarasubramanian_2025, title={Understanding the organizing scales of winter flood hydroclimatology and the associated drivers over the coterminous United States}, url={https://doi.org/10.1016/j.hydroa.2025.100200}, DOI={10.1016/j.hydroa.2025.100200}, journal={Journal of Hydrology X}, author={Hwang, Jeongwoo and Schreck, Carl J., III and Aiyyer, Anantha and Sankarasubramanian, Arumugam}, year={2025}, month={May} }
 @article{hasan_larson_mcmonigal_robinson_aiyyer_2024, title={Hemisphere-Dependent Impacts of ENSO and Atmospheric Eddies on Hadley Circulation}, volume={37}, ISSN={["1520-0442"]}, DOI={10.1175/JCLI-D-24-0112.1}, abstractNote={Abstract The variability of the Hadley circulation strength (HCS), crucial to tropical climate variability, is attributed to both oceanic and atmospheric forcings. El Niño-Southern Oscillation (ENSO) and variations in the extratropical upper tropospheric eddies are known drivers of the interannual HCS variability. However, the relative contributions of these oceanic and atmospheric forcings to the hemispheric HCS variability are not well understood. In particular, how much anomalous wind stress-driven ocean dynamics, including ENSO, impact HCS variability remains an open question. To address these gaps, we investigate the drivers of the interannual HCS variability using global coupled model experiments that include or exclude anomalous wind stress-driven ocean circulation variability. We find that the anomalous wind stress-driven ocean circulation variability significantly amplifies HCS variability in the Southern Hemisphere (SH). ENSO is the leading modulator of the SH HCS variability, which offers the potential to improve the predictability of HC-related hydrological consequences. On the other hand, the Northern Hemisphere (NH) HCS variability is predominantly influenced by the eddy-driven internal atmospheric variability with little role for ocean dynamics.We hypothesize that the large eddy variability in the NH and concentrated ENSO-associated heating and precipitation in the SH lead to the hemisphere-dependent differences in the interannual HCS variability.}, number={24}, journal={JOURNAL OF CLIMATE}, publisher={American Meteorological Society}, author={Hasan, Mahdi and Larson, Sarah m. and Mcmonigal, Kay and Robinson, Walter a. and Aiyyer, Anantha}, year={2024}, month={Dec}, pages={6533–6548} }
 @article{rajaram_aiyyer_camargo_cappa_dombard_donohue_feakins_flesch_fulweiler_ganju_et al._2024, title={Thank You to Our 2023 Peer Reviewers}, volume={51}, ISSN={["1944-8007"]}, url={https://doi.org/10.1029/2024GL109626}, DOI={10.1029/2024GL109626}, abstractNote={Abstract On behalf of the journal, AGU, and the scientific community, the editors of Geophysical Research Letters would like to sincerely thank those who reviewed manuscripts for us in 2023. The hours reading and commenting on manuscripts not only improve the manuscripts, but also increase the scientific rigor of future research in the field. With the advent of AGU's data policy, many reviewers have also helped immensely to evaluate the accessibility and availability of data, and many have provided insightful comments that helped to improve the data presentation and quality. We greatly appreciate the assistance of the reviewers in advancing open science, which is a key objective of AGU's data policy. We particularly appreciate the timely reviews in light of the demands imposed by the rapid review process at Geophysical Research Letters. We received 4,512 submissions in 2023 and 5,112 reviewers contributed to their evaluation by providing 8,587 reviews in total. We deeply appreciate their contributions.}, number={9}, journal={GEOPHYSICAL RESEARCH LETTERS}, author={Rajaram, Harihar and Aiyyer, Anantha and Camargo, Suzana and Cappa, Christopher D. and Dombard, Andrew J. and Donohue, Kathleen A. and Feakins, Sarah and Flesch, Lucy and Fulweiler, Robinson and Ganju, Neil and et al.}, year={2024}, month={May} }
 @article{aiyyer_schreck_2023, title={Surface Wind Speeds and Enthalpy Fluxes During Tropical Cyclone Formation From Easterly Waves: A CYGNSS View}, volume={50}, ISSN={["1944-8007"]}, url={https://doi.org/10.1029/2022GL100823}, DOI={10.1029/2022GL100823}, abstractNote={Abstract We examined the Cyclone Global Navigation Satellite System (CYGNSS) retrievals of surface wind speeds and enthalpy fluxes in African easterly waves that led to the formation of 30 Atlantic tropical cyclones during 2018–2021. Lag composites show a cyclonic proto‐vortex as early as 3 days prior to tropical cyclogenesis. The enthalpy flux distribution does not vary substantially before cyclogenesis, but subsequently, there is a marked increase in the extreme upper values. In the composites, a negative radial gradient of enthalpy fluxes becomes apparent 2–3 days before cyclogenesis. These results—based on novel data blending satellite retrievals and global reanalysis—support the findings from recent studies that the spin‐up of tropical cyclones is associated with a shift of peak convection toward the vortex core and an inward increase of enthalpy fluxes.}, number={6}, journal={GEOPHYSICAL RESEARCH LETTERS}, author={Aiyyer, Anantha and Schreck, Carl}, year={2023}, month={Mar} }
 @article{dhavale_aiyyer_2023, title={The Impact of the Madden-Julian Oscillation on the Formation of the Arabian Sea Monsoon Onset Vortex}, volume={50}, ISSN={["1944-8007"]}, url={https://doi.org/10.1029/2023GL104156}, DOI={10.1029/2023GL104156}, abstractNote={Abstract During certain years, a synoptic scale vortex called the monsoon onset vortex (MOV) forms within the northward advancing zone of precipitating convection over the Arabian Sea. The MOV does not form each year and the reason is unclear. Since the Madden‐Julian Oscillation (MJO) is known to modulate convection and tropical cyclones in the tropics, we examined its role in the formation of the MOV. While the convective and transition phases of the MJO do not always lead to MOV formation, the suppressed phase of the MJO hinders the formation of the MOV more consistently. This asymmetric relationship between the MJO and MOV can be partially explained by the modulation of the large‐scale environment, measured by a tropical cyclone genesis index. It also suggests that the Arabian Sea is generally near a critical state that is favorable for MOV formation during the monsoon onset period.}, number={17}, journal={GEOPHYSICAL RESEARCH LETTERS}, author={Dhavale, Shreyas and Aiyyer, Anantha}, year={2023}, month={Sep} }
 @article{dhavale_aiyyer_2023, title={The impact of the Madden-Julian Oscillation on the formation of the Arabian Sea Monsoon Onset Vortex}, url={https://doi.org/10.22541/essoar.168276016.62888353/v1}, DOI={10.22541/essoar.168276016.62888353/v1}, abstractNote={During some years, a synoptic scale vortex called the Monsoon Onset Vortex (MOV) forms within the northward advancing zone of precipitating convection over the Arabian Sea. The MOV does not form each year and the reason is unclear. Since the Madden-Julian Oscillation (MJO) is known to modulate convection and tropical cyclones in the tropics, we examined its role in the formation of the MOV. While the convective and transition phases of the MJO do not always lead to MOV formation, the suppressed phase of the MJO hinders the formation of the MOV more consistently. This non-linear relationship between the MJO and MOV can be partially explained by the modulation of the large-scale environment, measured by a tropical cyclone genesis index. It also suggests that the Arabian Sea is generally near a critical state that is favorable for MOV formation during the monsoon onset period.}, author={Dhavale, Shreyas and Aiyyer, Anantha}, year={2023}, month={Apr} }
 @article{aiyyer_wade_2021, title={Acceleration of Tropical Cyclones As a Proxy For Extratropical Interactions: Synoptic-Scale Patterns and Long-Term Trends}, url={https://doi.org/10.5194/wcd-2021-4}, DOI={10.5194/wcd-2021-4}, abstractNote={Abstract. It is well known that rapid changes in tropical cyclone motion occur during interaction with extratropical waves. While the translation speed has received much attention in the published literature, acceleration has not. Using a large data sample of Atlantic tropical cyclones, we formally examine the composite synoptic-scale patterns associated with tangential and curvature components of their acceleration. During periods of rapid tangential acceleration, the composite tropical cyclone moves poleward between an upstream trough and downstream ridge of a developing extratropical wavepacket. The two systems subsequently merge in a manner that is consistent with extratropical transition. During rapid curvature acceleration, a prominent downstream ridge promotes recurvature of the tropical cyclone. In contrast, during rapid tangential or curvature deceleration, a ridge is located directly poleward of the tropical cyclone. Locally, this arrangement takes the form of a cyclone-anticyclone vortex pair somewhat akin to a dipole block. On average, the tangential acceleration peaks 18 hours prior to extratropical transition while the curvature acceleration peaks at recurvature. These findings confirm that rapid acceleration of tropical cyclones is mediated by interaction with extratropical baroclinic waves. Furthermore, The tails of the distribution of acceleration and translation speed show a robust reduction over the past 5 decades. We speculate that these trends may reflect the poleward shift and weakening of extratropical Rossby waves.}, author={Aiyyer, Anantha and Wade, Terrell}, year={2021}, month={Jan} }
 @article{aiyyer_wade_2021, title={Acceleration of tropical cyclones as a proxy for extratropical interactions: synoptic-scale patterns and long-term trends}, url={https://doi.org/10.5194/wcd-2-1051-2021}, DOI={10.5194/wcd-2-1051-2021}, abstractNote={Abstract. It is well known that rapid changes in tropical-cyclone motion occur during interaction with extratropical waves. While the translation speed has received much attention in the published literature, acceleration has not. Using a large data sample of Atlantic tropical cyclones, we formally examine the composite synoptic-scale patterns associated with tangential and curvature components of their acceleration. During periods of rapid tangential acceleration, the composite tropical cyclone moves poleward between an upstream trough and downstream ridge of a developing extratropical wave packet. The two systems subsequently merge in a manner that is consistent with extratropical transition. During rapid curvature acceleration, a prominent downstream ridge promotes recurvature of the tropical cyclone. In contrast, during rapid tangential deceleration or near-zero curvature acceleration, a ridge is located directly poleward of the tropical cyclone. Locally, this arrangement takes the form of a cyclone–anticyclone vortex pair. On average, the tangential acceleration peaks 18 h prior to extratropical transition, while the curvature acceleration peaks at recurvature. These findings confirm that rapid acceleration of tropical cyclones is mediated by interaction with extratropical baroclinic waves. Furthermore, the tails of the distribution of acceleration and translation speed show a robust reduction over the past 5 decades. We speculate that these trends may reflect the poleward shift and weakening of extratropical Rossby waves.}, journal={Weather and Climate Dynamics}, author={Aiyyer, Anantha and Wade, Terrell}, year={2021}, month={Nov} }
 @article{white_aiyyer_2021, title={African easterly waves in an idealized general circulation model: instability and wave packet diagnostics}, volume={2}, url={https://doi.org/10.5194/wcd-2-311-2021}, DOI={10.5194/wcd-2-311-2021}, abstractNote={Abstract. We examine the group dynamic of African easterly waves (AEWs) generated in a realistic, spatially non-homogeneous African easterly jet (AEJ) using an idealized general circulation model. Our objective is to investigate whether the limited zonal extent of the AEJ is an impediment to AEW development. We construct a series of basic states using global reanalysis fields and initialize waves via transient heating over West Africa. The dominant response is a localized, near-stationary wave packet that disperses upstream and downstream. The inclusion of a crude representation of boundary layer damping stabilizes the waves in most cases, consistent with other studies in the past. In some basic states, however, exponential growth occurs even in the presence of damping. This shows that AEWs can occasionally emerge spontaneously. The key result is that, whether triggered by an external forcing or generated internally, the wave packet can remain within the AEJ for multiple wave periods instead of being swept away. Drawing from other studies, this also suggests that even the damped waves can grow if coupled with additional sources of energy such as moist convection and dust radiative feedback. The wave packet in the localized AEJ appears to satisfy a condition for absolute instability, a form of spatial hydrodynamic instability. However, this needs to be verified more rigorously. We conclude that the limited zonal extent of the AEJ is not an impediment. Our results also suggest that the intermittent nature of AEWs is mediated, not by transitions between convective and absolute instability, but likely by external sources such as propagating equatorial wave modes.}, number={2}, journal={Weather and Climate Dynamics}, publisher={Copernicus GmbH}, author={White, Joshua and Aiyyer, Anantha}, year={2021}, month={Apr}, pages={311–329} }
 @article{mantripragada_schreck_aiyyer_2021, title={Energetics of Interactions between African Easterly Waves and Convectively Coupled Kelvin Waves}, volume={149}, ISSN={["1520-0493"]}, DOI={10.1175/MWR-D-21-0003.1}, abstractNote={Abstract Perturbation kinetic and available energy budgets are used to explore how convectively coupled equatorial Kelvin waves (KWs) impact African easterly wave (AEW) activity. The convective phase of the Kelvin wave increases the African easterly jet’s meridional shear, thus enhancing the barotropic energy conversions, leading to intensification of southern track AEWs perturbation kinetic energy. In contrast, the barotropic energy conversion is reduced in the suppressed phase of KW. Baroclinic energy conversion of the southern track AEWs is not significantly different between Kelvin waves’ convective and suppressed phases. AEWs in the convective phase of a Kelvin wave have stronger perturbation available potential energy generation by diabatic heating and stronger baroclinic overturning circulations than in the suppressed phase of a Kelvin wave. These differences suggest that southern track AEWs within the convective phase of Kelvin waves have more vigorous convection than in the suppressed phase of Kelvin waves. Barotropic energy conversion of the northern track AEWs is not significantly different between Kelvin waves’ convective and suppressed phases. The convective phase of the Kelvin wave increases the lower-tropospheric meridional temperature gradient north of the African easterly jet, thus enhancing the baroclinic energy conversion, leading to intensification of northern track AEWs perturbation kinetic energy. In contrast, the baroclinic energy conversion is reduced in the suppressed phase of KW. These results provide a physical basis for the modulation of AEWs by Kelvin waves arriving from upstream.}, number={11}, journal={MONTHLY WEATHER REVIEW}, author={Mantripragada, Rama Sesha Sridhar and Schreck, C. J., III and Aiyyer, Anantha}, year={2021}, month={Nov}, pages={3821–3835} }
 @article{white_aiyyer_russell_2021, title={The Impact of Orography on the African Easterly Wave Stormtrack}, volume={126}, ISSN={["2169-8996"]}, url={https://doi.org/10.1029/2020JD033749}, DOI={10.1029/2020JD033749}, abstractNote={We examined the sensitivity of African easterly waves (AEWs) to elevated terrain over North Africa using a numerical weather prediction model. We formed five ensembles of simulated AEW activity with orographic features independently reduced in four key regions. The ensemble members consisted of 10 consecutive AEW seasons simulated separately. From the ensembles, the southern AEW stormtrack was most sensitive to the reduction of the Ethiopian highlands. Energy budgets showed that diminished diabatic heating associated with precipitating convection was the likely driver of the weaker AEWs. Baroclinic overturning was the dominant pathway for this response. The northern AEW stormtrack was most sensitive to the reduction of the Hoggar and Tibesti mountains. In this case, a reduction in the vertical shear and diminished baroclinic energy conversions from the background state was associated with weaker AEWs. Through terrain reduction, our results provide a view of thermodynamic and dynamic feedback in AEWs that is complementary to what has been shown in past studies.}, number={9}, journal={JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES}, publisher={American Geophysical Union (AGU)}, author={White, J. D. and Aiyyer, A. and Russell, J. O. H.}, year={2021}, month={May} }
 @article{chalise_aiyyer_sankarasubramanian_2021, title={Tropical cyclones contribution to seasonal precipitation and streamflow using station-based data in Southeastern and Southcentral United States}, volume={48}, ISSN={["1944-8007"]}, url={https://doi.org/10.1029/2021GL094738}, DOI={10.1029/2021GL094738}, abstractNote={Abstract Studies have quantified the contribution of tropical cyclones (TCs) toward seasonal precipitation, but limited analysis is available on TC contribution toward seasonal streamflow over the southeastern and southcentral (SESC) United States (U.S.). Using an extensive network of hydroclimatic data that consists of 233 TC tracks and daily precipitation and streamflow, we estimate TC contribution toward precipitation and streamflow during the hurricane season over the SESC U.S. We found that TCs account for 12% of seasonal streamflow and 6% of seasonal precipitation over the region. Florida, North Carolina, and Louisiana have the highest fractional occurrence of TC‐generated annual maximum precipitation (∼20%–32%) and streamflow (∼15%–27%). We also found the fractional occurrence of TCs associated with peak‐over threshold precipitation (streamflow) events ranges from 5% to 8% in coastal regions (10%–20% over FL and 5%–10% over coastal NC). Increased antecedent moisture results in increased TCs contribution to streamflow leading to different land‐surface responses for similar hurricane events.}, number={15}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Chalise, D. and Aiyyer, A. and Sankarasubramanian, A.}, year={2021}, month={Aug}, pages={e2021GL094738} }
 @article{russell_aiyyer_dylan white_2020, title={African Easterly Wave Dynamics in Convection-Permitting Simulations: Rotational Stratiform Instability as a Conceptual Model}, volume={12}, ISSN={["1942-2466"]}, url={https://doi.org/10.1029/2019MS001706}, DOI={10.1029/2019MS001706}, abstractNote={Abstract We examine the upscale effect of moist convection on African easterly waves (AEWs) by limiting condensational heating and initial ambient moisture in convection‐permitting simulations. Moist convection is fundamental in maintaining and destabilizing AEWs. The contribution from barotropic‐baroclinic instability, albeit important, is relatively smaller. Mesoscale convective systems (MCSs) are initiated downstream of the AEW troughs and are associated with extensive trailing stratiform cloud regions. Using a potential vorticity (PV) budget, we show that the attendant diabatic heating profile reinforces the AEW. A model for destabilization is proposed that relies on the phasing of stratiform heating and the PV anomaly of the AEW. It qualitatively resembles stratiform instability and stretched building blocks hypotheses introduced in previous studies. The generation of PV by deep moist convection in the vicinity of the trough counters the shearing effect of the background flow. This helps maintain an upright PV column, which is conducive for formation of tropical cyclones. AEW propagation is dominated by advective processes and intermittently modified by moist convection when large MCSs move ahead of the AEW.}, number={1}, journal={JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS}, publisher={American Geophysical Union (AGU)}, author={Russell, James O. H. and Aiyyer, Anantha and Dylan White, J.}, year={2020}, month={Jan} }
 @article{white_aiyyer_2020, title={African Easterly Waves in an Idealized General Circulation Model: Instability and Wavepacket Diagnostics}, url={https://doi.org/10.5194/wcd-2020-47}, DOI={10.5194/wcd-2020-47}, abstractNote={Abstract. We examine the group dynamic of African easterly waves (AEW) generated in a realistic, spatially non-homogeneous African easterly jet (AEJ) using an idealized general circulation model. Our objective is to investigate whether the limited zonal extent of the AEJ is an impediment to AEW development. We construct a series of basic states using global reanalysis fields and initialize waves via transient heating over West Africa. The dominant response is a localized wavepacket that disperses upstream and downstream. The inclusion of a crude representation of boundary layer damping stabilizes the waves in most cases. In some basic states, however, exponential growth occurs even in the presence of damping. This shows that AEWs can occasionally emerge spontaneously. The key result is that the wavepacket in almost all cases remains within the AEJ instead of being swept away. Drawing from other studies, this also suggests that even the damped waves can grow if coupled with additional sources of energy such as moist convection and dust radiative feedback. The wavepacket in the localized AEJ appears to satisfy a condition for absolute instability, a form of spatial hydrodynamic instability. However, this needs to be verified more rigorously. Our results also suggest that the intermittent nature of AEWs is mediated, not by transitions between convective and absolute instability, but likely by external sources such as propagating equatorial wave modes.}, author={White, Joshua and Aiyyer, Anantha}, year={2020}, month={Sep} }
 @article{russell_aiyyer_2020, title={The Potential Vorticity Structure and Dynamics of African Easterly Waves}, volume={77}, ISSN={["1520-0469"]}, DOI={10.1175/JAS-D-19-0019.1}, abstractNote={Abstract The dynamics of African easterly waves (AEWs) are investigated from the perspective of potential vorticity (PV) using data from global reanalysis projects. To a leading order, AEW evolution is governed by four processes: advection of the wave-scale PV by background flow, advection of background PV by the AEW, diabatic forcing due to wave-scale moist convection, and coupling between the wave and background diabatic forcing. Moist convection contributes significantly to the growth of AEWs in the midtroposphere, and to both growth and propagation of AEWs near the surface. The former is associated with stratiform clouds while the latter with deep convection. Moist convection helps maintain a more upright AEW PV column against the background shear, which makes the wave structure conducive for tropical cyclogenesis. It is also argued that—contrary to the hypothesis in some prior studies—the canonical diabatic Rossby wave model is likely not applicable to AEWs.}, number={3}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, publisher={American Meteorological Society}, author={Russell, James O. H. and Aiyyer, Anantha}, year={2020}, month={Mar}, pages={871–890} }
 @article{hannah_aiyyer_2017, title={Reduced African Easterly Wave Activity with Quadrupled CO2 in the Superparameterized CESM}, volume={30}, DOI={10.1175/jcli-d-16-0822.1}, abstractNote={Abstract African easterly wave (AEW) activity is examined in quadrupled CO2 experiments with the superparameterized CESM (SP-CESM). The variance of 2–10-day filtered precipitation increases with warming over the West African monsoon region, suggesting increased AEW activity. The perturbation enstrophy budget is used to investigate the dynamic signature of AEW activity. The northern wave track becomes more active associated with enhanced baroclinicity, consistent with previous studies. The southern track exhibits a surprising reduction of wave activity associated with less frequent occurrence of weak waves and a slight increase in the occurrence of strong waves. These changes are connected to changes in the profile of vortex stretching and tilting that can be understood as interconnected consequences of increased static stability from the lapse rate response, weak temperature gradient balance, and the fixed anvil temperature hypothesis.}, number={20}, journal={Journal of Climate}, publisher={American Meteorological Society}, author={Hannah, Walter M. and Aiyyer, Anantha}, year={2017}, month={Sep}, pages={8253–8274} }
 @article{russell_aiyyer_white_hannah_2017, title={Revisiting the connection between African Easterly Waves and Atlantic tropical cyclogenesis}, volume={44}, ISSN={["1944-8007"]}, DOI={10.1002/2016gl071236}, abstractNote={Abstract African Easterly Waves (AEWs) are the primary precursor for Atlantic tropical cyclones (TCs). We update the statistics on this relationship using reports from the U.S. National Hurricane Center. Sixty‐one percent of TCs originate directly from AEWs. Indirectly, AEWs are implicated in the formation of an additional 11% of TCs. AEW activity is quantified by eddy kinetic energy (EKE). The correlation between seasonal mean EKE and TC genesis is maximized in the lower troposphere below the southern AEW storm track, instead of where the canonical AEW is maximized. Therefore, midlevel AEW activity is a poor predictor of TC genesis, whereas its lower tropospheric circulation exerts stronger control. In most seasons, AEW activity is supercritical, and therefore, EKE is only a controlling factor in seasons when the low‐level EKE is weak. Predicting 1000–800 hPa EKE below the southern AEW track may be useful for seasonal TC prediction.}, number={1}, journal={GEOPHYSICAL RESEARCH LETTERS}, author={Russell, James O. and Aiyyer, Anantha and White, Joshua D. and Hannah, Walter}, year={2017}, month={Jan}, pages={587–595} }
 @article{diaz_aiyyer_2015, title={Absolute and Convective Instability of the African Easterly Jet}, volume={72}, ISSN={["1520-0469"]}, DOI={10.1175/jas-d-14-0128.1}, abstractNote={Abstract The stability of the African easterly jet (AEJ) is examined using idealized numerical simulations. It is found that a zonally homogeneous representation of the AEJ can support absolute instability in the form of African easterly waves (AEWs). This finding is verified through a local energy budget, which demonstrates the presence of both upstream and downstream energy fluxes. These energy fluxes allow unstable wave packets to spread upstream and downstream relative to their initial point of excitation. This finding is further verified by showing that the ground-relative group velocity of these wave packets has both eastward and westward components. In contrast with normal-mode instability theory, which emphasizes wave growth through energy extraction from the basic state, the life cycle of the simulated AEWs is strongly governed by energy fluxes. Convergent fluxes at the beginning of the AEW storm track generate new AEWs, whereas divergent fluxes at the end of the storm track lead to their decay. It is argued that, even with small normal-mode growth rates and a short region of instability, the presence of absolute instability allows AEWs to develop through the mixed baroclinic–barotropic instability mechanism, because upstream energy fluxes allow energy extracted through baroclinic and barotropic conversion to be recycled between successive AEWs.}, number={5}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, publisher={American Meteorological Society}, author={Diaz, Michael and Aiyyer, Anantha}, year={2015}, month={May}, pages={1805–1826} }
 @article{tyner_aiyyer_blaes_hawkins_2015, title={An Examination of Wind Decay, Sustained Wind Speed Forecasts, and Gust Factors for Recent Tropical Cyclones in the Mid-Atlantic Region of the United States}, volume={30}, ISSN={["1520-0434"]}, DOI={10.1175/waf-d-13-00125.1}, abstractNote={Abstract In this study, several analyses were conducted that were aimed at improving sustained wind speed and gust forecasts for tropical cyclones (TCs) affecting coastal regions. An objective wind speed forecast analysis of recent TCs affecting the mid-Atlantic region was first conducted to set a benchmark for improvement. Forecasts from the National Digital Forecast Database were compared to observations and surface wind analyses in the region. The analysis suggests a general overprediction of sustained wind speeds, especially for areas affected by the strongest winds. Currently, National Weather Service Weather Forecast Offices use a software tool known as the Tropical Cyclone Forecast/Advisory (TCM) wind tool (TCMWindTool) to develop their wind forecast grids. The tool assumes linear decay in the sustained wind speeds when interpolating the National Hurricane Center 12–24-hourly TCM product to hourly grids. An analysis of postlandfall wind decay for recent TCs was conducted to evaluate this assumption. Results indicate that large errors in the forecasted wind speeds can emerge, especially for stronger storms. Finally, an analysis of gust factors for recent TCs affecting the region was conducted. Gust factors associated with weak sustained wind speeds are shown to be highly variable but average around 1.5. The gust factors decrease to values around 1.2 for wind speeds above 40 knots (kt; 1 kt = 0.51 m s−1) and are in general insensitive to the wind direction, suggesting local rather than upstream surface roughness largely dictates the gust factor at a given location. Forecasters are encouraged to increase land reduction factors used in the TCMWindTool and to modify gust factors to account for factors including the sustained wind speed and local surface roughness.}, number={1}, journal={WEATHER AND FORECASTING}, publisher={American Meteorological Society}, author={Tyner, Bryce and Aiyyer, Anantha and Blaes, Jonathan and Hawkins, Donald Reid}, year={2015}, month={Feb}, pages={153–176} }
 @article{rasheed_aneja_aiyyer_rafique_2015, title={Measurement and Analysis of Fine Particulate Matter (PM2.5) in Urban Areas of Pakistan}, volume={15}, ISSN={["2071-1409"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84925941359&partnerID=MN8TOARS}, DOI={10.4209/aaqr.2014.10.0269}, abstractNote={In order to assess the extent of air quality within the major urban environments in Pakistan, PM2.5 pollutant has been analyzed during the period 2007–2011 in Islamabad; and 2007 to 2008 in Lahore, Peshawar and Quetta (high elevation, 1680 m MSL). Seasonal and diurnal variations of PM2.5 mass concentration formation and accumulation within these areas have been analyzed. Air quality monitoring data and meteorological data (both QA/QCed) were obtained from Federal and Provincial Pakistan Environmental Protection Agencies. In Islamabad, the annual average PM2.5 mass concentrations were 81.1 ± 48.4 µg/m3, 93.0 ± 49.9 µg/m3, 47.8 ± 33.2 µg/m3, 79.0 ± 49.2 µg/m3, and 66.1 ± 52.1 µg/m3 during 2007 to 2011 respectively. Comparison of the four cities during summer 2007 to spring 2008 shows that all the four cities had PM2.5 concentration exceeding the Pakistan National Environmental Quality Standards (annual average concentration of 25 µg/m3; and 24 hourly average concentration of 40 µg/m3) for ambient air. During the same time period, the highest seasonal PM2.5 mass concentrations for Islamabad were observed as 98.5 µg/m3 during spring 2008; 150.4 ± 87.9 µg/m3; 104.1 ± 51.1 µg/m3 and 72.7 ± 55.2 µg/m3 for Lahore, Peshawar, and Quetta during fall 2007, respectively. Wind speed and temperature have a negative correlation with the mass concentration of PM2.5. Diurnal profile for all the cities suggests an association of PM2.5 with vehicular traffic. Back trajectory analysis conducted using the NOAA HYSPLIT model indicates that air trajectories, during high pollution episodes, influencing the urban regions commonly originate from either western India, especially in summer as part of the prevailing monsoon circulation; or are located in eastern Afghanistan. The source areas in Western India i.e., states of Gujarat, Rajasthan and Punjab have high concentration of industrial activities and crop residue burning, and are likely sources of enhanced PM2.5 concentrations, in addition to the local sources.}, number={2}, journal={AEROSOL AND AIR QUALITY RESEARCH}, author={Rasheed, Anjum and Aneja, Viney P. and Aiyyer, Anantha and Rafique, Uzaira}, year={2015}, month={Apr}, pages={426–439} }
 @article{aiyyer_2015, title={Recurving western North Pacific tropical cyclones and midlatitude predictability}, volume={42}, ISSN={["1944-8007"]}, DOI={10.1002/2015gl065082}, abstractNote={Abstract Data from an ensemble prediction system are used to examine the impact of recurving tropical cyclones on downstream midlatitude forecasts. The ensemble spread, normalized by its climatology, increases after recurvature and peaks approximately 4–5 days later. It returns to climatological levels within a week after recurvature. Initially, the spread increases around the position of the tropical storm. Subsequently, it increases after extratropical transition, and it is associated with a developing wave packet in the midlatitude storm track. The enhanced spread propagates downstream approximately at the group speed of the wave packet. These results suggest that relative to the model's baseline, recurvature‐related increase in loss of forecast skill is spatially and temporally localized. Further, energy dispersion of the developing wave packet may constrain the rate at which the forecast errors propagate downstream.}, number={18}, journal={GEOPHYSICAL RESEARCH LETTERS}, publisher={American Geophysical Union (AGU)}, author={Aiyyer, A.}, year={2015}, month={Sep}, pages={7799–7807} }
 @article{rasheed_aneja_aiyyer_rafique_2014, title={Measurements and analysis of air quality in Islamabad, Pakistan}, volume={2}, ISSN={2328-4277}, url={http://dx.doi.org/10.1002/2013EF000174}, DOI={10.1002/2013EF000174}, abstractNote={Abstract Ambient air quality of Islamabad, Pakistan, reveals that annual average mass concentration of particulate matter ( PM 2 .5 ) (∼45 to ∼95 µg m −3 ) and nitric oxide ( NO ) (∼41 to ∼120 µg m −3 ) exceeds the Pakistan's National Environmental Quality Standards ( NEQS ). The annual ozone ( O 3 ) concentration is within the permissible limits; however, some of the hourly concentration exceeds the NEQS mostly during the summer months. Correlation studies suggest that carbon monoxide ( CO ) has a significant ( p ‐value ≤ 0.01) positive correlation with NO and NO y′ ; whereas, with O 3 , a significant ( p ‐value ≤ 0.01) negative correlation is observed. The regression analysis estimates the background CO concentration to be ∼300 to ∼600 ppbv in Islamabad. The higher ratio of CO / NO (∼10) suggests that mobile sources are the major contributor to NO concentration. On the other hand, the ratio analysis of sulfur dioxide ( SO 2 )/ NO for Islamabad (∼0.011) indicates that the point sources are contributing to SO 2 in the city. NO and SO 2 correlation indicates contribution of direct sulfur emission sources. Ratios of [ CO ] to [ NO ] and [ SO 2 ] to [ NO ], based on ambient air quality measurements, provide a test for emission inventories. The ratios of these pollutants in the available Islamabad emission inventories are consistent with ambient values for these pollutants. The correlation of PM 2 .5 and NO suggests that a fraction of secondary PM 2 .5 is produced by chemical conversion of NO into nitrates. The regional background O 3 concentration for Islamabad has been determined to be ∼31 ppbv. This study suggests that there is an increase in O 3 concentration with increases in photochemical conversion of NO to reservoir NO y′ species.}, number={6}, journal={Earth's Future}, publisher={American Geophysical Union (AGU)}, author={Rasheed, Anjum and Aneja, Viney P. and Aiyyer, Anantha and Rafique, Uzaira}, year={2014}, month={Jun}, pages={303–314} }
 @article{mallard_lackmann_aiyyer_hill_2013, title={Atlantic Hurricanes and Climate Change. Part I: Experimental Design and Isolation of Thermodynamic Effects}, volume={26}, ISSN={["1520-0442"]}, DOI={10.1175/jcli-d-12-00182.1}, abstractNote={Abstract The Weather Research and Forecasting (WRF) model is used in a downscaling experiment to simulate a portion of the Atlantic hurricane season both in present-day conditions and with modifications to include future thermodynamic changes. Temperature and moisture changes are derived from an ensemble of climate simulations from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) A1B scenario and added to analyzed initial and lateral boundary conditions, leaving horizontal temperature gradients and vertical wind shear unaltered. This method of downscaling excludes future changes in shear and incipient disturbances, thereby isolating the thermodynamic component of climate change and its effect on tropical cyclone (TC) activity. The North Atlantic basin is simulated with 18- and 6-km grid spacing, and a four-member physics ensemble is composed by varying microphysical and boundary layer parameterization schemes. This ensemble is used in monthly simulations during an active (2005) and inactive (2009) season, and the simulations are able to capture the change in activity between the different years. TC frequency is better reproduced with use of 6-km grid spacing and explicitly simulated convection, relative to simulations with 18-km grid spacing. A detailed comparison of present-day and future ensemble results is provided in a companion study.}, number={13}, journal={JOURNAL OF CLIMATE}, publisher={American Meteorological Society}, author={Mallard, Megan S. and Lackmann, Gary M. and Aiyyer, Anantha and Hill, Kevin}, year={2013}, month={Jul}, pages={4876–4893} }
 @article{mallard_lackmann_aiyyer_2013, title={Atlantic Hurricanes and Climate Change. Part II: Role of Thermodynamic Changes in Decreased Hurricane Frequency}, volume={26}, ISSN={["1520-0442"]}, DOI={10.1175/jcli-d-12-00183.1}, abstractNote={Abstract A method of downscaling that isolates the effect of temperature and moisture changes on tropical cyclone (TC) activity was presented in Part I of this study. By applying thermodynamic modifications to analyzed initial and boundary conditions from past TC seasons, initial disturbances and the strength of synoptic-scale vertical wind shear are preserved in future simulations. This experimental design allows comparison of TC genesis events in the same synoptic setting, but in current and future thermodynamic environments. Simulations of both an active (September 2005) and inactive (September 2009) portion of past hurricane seasons are presented. An ensemble of high-resolution simulations projects reductions in ensemble-average TC counts between 18% and 24%, consistent with previous studies. Robust decreases in TC and hurricane counts are simulated with 18- and 6-km grid lengths, for both active and inactive periods. Physical processes responsible for reduced activity are examined through comparison of monthly and spatially averaged genesis-relevant parameters, as well as case studies of development of corresponding initial disturbances in current and future thermodynamic conditions. These case studies show that reductions in TC counts are due to the presence of incipient disturbances in marginal moisture environments, where increases in the moist entropy saturation deficits in future conditions preclude genesis for some disturbances. Increased convective inhibition and reduced vertical velocity are also found in the future environment. It is concluded that a robust decrease in TC frequency can result from thermodynamic changes alone, without modification of vertical wind shear or the number of incipient disturbances.}, number={21}, journal={JOURNAL OF CLIMATE}, publisher={American Meteorological Society}, author={Mallard, Megan S. and Lackmann, Gary M. and Aiyyer, Anantha}, year={2013}, month={Nov}, pages={8513–8528} }
 @article{diaz_aiyyer_2013, title={Energy Dispersion in African Easterly Waves}, volume={70}, ISSN={["1520-0469"]}, DOI={10.1175/jas-d-12-019.1}, abstractNote={Abstract The existence of an upstream (eastward) group velocity for African easterly waves (AEWs) is shown based on single-point lag regressions using gridded reanalysis data from 1990 to 2010. The eastward energy dispersion is consistent with the direction of ageostrophic geopotential flux vectors. A local eddy kinetic energy (EKE) budget reveals that, early in the life cycle of AEWs, growth rate due to geopotential flux convergence exceeds baroclinic and barotropic growth rates. Later in the life cycle, EKE decay due to geopotential flux divergence cancels or exceeds baroclinic and barotropic growth. A potential vorticity (PV) budget is used to diagnose tendencies related to group propagation. Although both upstream and downstream group speeds are possible because of the reversal in the mean meridional PV gradient, upstream propagation associated with the positive poleward PV gradient dominates wave packet evolution. Analogous to the concept of downstream development of midlatitude baroclinic waves, new AEWs develop preferentially upstream of the older ones, thus providing a mechanism for seeding new waves. It is suggested that these results are also relevant to AEW intermittency and storm-track structure.}, number={1}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, publisher={American Meteorological Society}, author={Diaz, Michael and Aiyyer, Anantha}, year={2013}, month={Jan}, pages={130–145} }
 @article{diaz_aiyyer_2013, title={The Genesis of African Easterly Waves by Upstream Development}, volume={70}, ISSN={["1520-0469"]}, DOI={10.1175/jas-d-12-0342.1}, abstractNote={Abstract A genesis mechanism for African easterly waves (AEWs) is proposed. In the same manner that new troughs and ridges in the midlatitudes form downstream of existing ones through a mechanism known as downstream development, it is proposed that new AEWs can be generated upstream of existing AEWs. A local eddy kinetic energy budget of the AEW that ultimately became Hurricane Alberto (2000) demonstrates that upstream development explains its genesis more convincingly than previous theories of AEW genesis. The energetics and ageostrophic secondary circulation of a composite AEW are consistent with a new AEW forming as a result of this mechanism. Some strengths and weaknesses of upstream development as a paradigm for AEW genesis are discussed with respect to other potential mechanisms.}, number={11}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, publisher={American Meteorological Society}, author={Diaz, Michael and Aiyyer, Anantha}, year={2013}, month={Nov}, pages={3492–3512} }
 @article{schreck_molinari_aiyyer_2012, title={A Global View of Equatorial Waves and Tropical Cyclogenesis}, volume={140}, ISSN={["0027-0644"]}, DOI={10.1175/mwr-d-11-00110.1}, abstractNote={Abstract This study investigates the number of tropical cyclone formations that can be attributed to the enhanced convection from equatorial waves within each basin. Tropical depression (TD)-type disturbances (i.e., easterly waves) were the primary tropical cyclone precursors over the Northern Hemisphere basins, particularly the eastern North Pacific and the Atlantic. In the Southern Hemisphere, however, the number of storms attributed to TD-type disturbances and equatorial Rossby waves were roughly equivalent. Equatorward of 20°N, tropical cyclones formed without any equatorial wave precursor most often over the eastern North Pacific and least often over the western North Pacific. The Madden–Julian oscillation (MJO) was an important tropical cyclone precursor over the north Indian, south Indian, and western North Pacific basins. The MJO also affected tropical cyclogenesis by modulating the amplitudes of higher-frequency waves. Each wave type reached the attribution threshold 1.5 times more often, and tropical cyclogenesis was 3 times more likely, within positive MJO-filtered rainfall anomalies than within negative anomalies. The greatest MJO modulation was observed for storms attributed to Kelvin waves over the north Indian Ocean. The large rainfall rates associated with tropical cyclones can alter equatorial wave–filtered anomalies. This study quantifies the contamination over each basin. Tropical cyclones contributed more than 20% of the filtered variance for each wave type over large potions of every basin except the South Pacific. The largest contamination, exceeding 60%, occurred for the TD band near the Philippines. To mitigate the contamination, the tropical cyclone–related anomalies were removed before filtering in this study.}, number={3}, journal={MONTHLY WEATHER REVIEW}, publisher={American Meteorological Society}, author={Schreck, Carl J., III and Molinari, John and Aiyyer, Anantha}, year={2012}, month={Mar}, pages={774–788} }
 @article{tyner_aiyyer_2012, title={Evolution of African Easterly Waves in Potential Vorticity Fields}, volume={140}, DOI={10.1175/mwr-d-11-00170.1}, abstractNote={Abstract The evolution of African easterly waves (AEWs) leading to tropical cyclones (TCs) in the Atlantic during 2000–08 is examined from isentropic potential vorticity (PV) and Lagrangian streamline perspectives. Tropical cyclone formation is commonly preceded by axisymmetrization of PV, scale contraction of the wave, and formation of a closed circulation within the wave. In these cases, PV associated with the synoptic-scale wave is irreversibly deformed and subsumed within the developing vortex. Less commonly, filamentation of the PV leads to separation and independent propagation of the wave and the TC vortex. In an example presented here, the remnant wave with a closed circulation persisted for several days after separation from the TC. A second TC did not result, consistent with several past studies that show that a midtropospheric closed gyre is not sufficient for TC genesis. Sometimes, an AEW and a weak TC remain coupled for a few days, followed by the dissipation of the TC and the continued propagation of the wave. Merger of tropical and extratropical PV anomalies is also often observed and likely helps maintain some waves. The results of this study are broadly consistent with recent Lagrangian analyses of AEW evolution during TC genesis.}, number={11}, journal={Monthly Weather Review}, publisher={American Meteorological Society}, author={Tyner, Bryce and Aiyyer, Anantha}, year={2012}, month={Nov}, pages={3634–3652} }
 @article{aiyyer_mekonnen_schreck_2012, title={Projection of Tropical Cyclones on Wavenumber-Frequency-Filtered Equatorial Waves}, volume={25}, ISSN={["0894-8755"]}, DOI={10.1175/jcli-d-11-00451.1}, abstractNote={Abstract The impact of localized convection associated with tropical cyclones (TCs) on activity ascribed to equatorial waves is estimated. An algorithm is used to remove outgoing longwave radiation (OLR) signal in the vicinity of observed tropical cyclones, and equatorial wave modes are extracted using the standard wavenumber–frequency decomposition method. The results suggest that climatological activity of convection-coupled equatorial waves is overestimated where TC tracks are densest. The greatest impact is found for equatorial Rossby (ER)- and tropical depression (TD)-type waves followed by the Madden–Julian oscillation (MJO). The basins most affected are the eastern and western North Pacific Ocean where, on average, TCs may contribute up to 10%–15% of the climatological wave amplitude variance in these modes. In contrast, Kelvin waves are least impacted by the projection of TCs. The results are likely relevant for studies on the climatology of equatorial waves in observations and global climate model simulations and for those examining individual cases of TC genesis modulated by equatorial wave activity.}, number={10}, journal={JOURNAL OF CLIMATE}, publisher={American Meteorological Society}, author={Aiyyer, Anantha and Mekonnen, Ademe and Schreck, Carl J., III}, year={2012}, month={May}, pages={3653–3658} }
 @article{aiyyer_thorncroft_2011, title={Interannual-to-Multidecadal Variability of Vertical Shear and Tropical Cyclone Activity}, volume={24}, ISSN={["1520-0442"]}, DOI={10.1175/2010jcli3698.1}, abstractNote={Abstract Spatiotemporal patterns of tropics-wide vertical shear variability are extracted after separating a 58-yr data record into high-frequency (HF, periods of 1.5–8 yr) and low-frequency (LF, periods greater than 8 yr) components. The HF vertical shear variability is dominated by circulation anomalies associated with the El Niño–Southern Oscillation (ENSO). The LF variability is primarily contained in two multidecadal patterns and a near-decadal pattern. The multidecadal modes are strongest within the tropical Atlantic and are correlated with Sahel precipitation and interhemispheric sea surface temperature (SST) anomalies. The results suggest that the multidecadal variability of vertical shear over the Atlantic is linked to atmospheric circulation anomalies forced by the variability in Sahel precipitation. The decadal mode is strongest within the central Pacific and is correlated with Pacific decadal oscillation (PDO)-like SST anomalies. The circulation associated with this anomalous shear pattern appears to be consistent with the atmospheric response to the PDO-related diabatic heating anomaly over the central Pacific. The relationship between vertical shear and seasonal tropical cyclone activity, as defined by the accumulated cyclone energy (ACE), is examined for the Atlantic, eastern Pacific, and western Pacific Oceans. The results show that global modes of vertical shear and seasonal average ACE are not consistently related in all three regions. It is only in the Atlantic Ocean that seasonal ACE is most consistently limited by vertical shear. This calls into question the utility of vertical shear as an independent predictor of seasonal tropical cyclone activity, particularly over the western Pacific Ocean.}, number={12}, journal={JOURNAL OF CLIMATE}, publisher={American Meteorological Society}, author={Aiyyer, Anantha and Thorncroft, Chris}, year={2011}, month={Jun}, pages={2949–2962} }
 @article{novak_colle_aiyyer_2010, title={Evolution of Mesoscale Precipitation Band Environments within the Comma Head of Northeast US Cyclones}, volume={138}, ISSN={["1520-0493"]}, DOI={10.1175/2010mwr3219.1}, abstractNote={Abstract This paper explores the mesoscale forcing and stability evolution of intense precipitation bands in the comma head sector of extratropical cyclones using the 32-km North American Regional Reanalysis, hourly 20-km Rapid Update Cycle analyses, and 2-km composite radar reflectivity data. A statistical and composite analysis of 36 banded events occurring during the 2002–08 cool seasons reveals a common cyclone evolution and associated band life cycle. A majority (61%) of banded events develop along the northern portion of a hook-shaped upper-level potential vorticity (PV) anomaly. During the 6 h leading up to band formation, lower-tropospheric frontogenesis nearly doubles and the conditional stability above the frontal zone is reduced. The frontogenesis increase is primarily due to changes in the kinematic flow associated with the development of a mesoscale geopotential height trough. This trough extends poleward of the 700-hPa low, and is the vertical extension of the surface warm front (and surface warm occlusion when present). The conditional stability near 500 hPa is reduced by differential horizontal potential temperature advection. During band formation, layers of conditional instability above the frontal zone are present nearly 3 times as often as layers of conditional symmetric instability. The frontogenetical forcing peaks during band maturity and is offset by an increase in conditional stability. Band dissipation occurs as the conditional stability continues to increase, and the frontogenesis weakens in response to changes in the kinematic flow. A set of 22 null events, in which band formation was absent in the comma head, were also examined. Although exhibiting similar synoptic patterns as the banded events, the null events were characterized by weaker frontogenesis. However, statistically significant differences between the midlevel frontogenesis maximum of the banded and null events only appear ~2 h prior to band formation, illustrating the challenge of predicting band formation.}, number={6}, journal={MONTHLY WEATHER REVIEW}, publisher={American Meteorological Society}, author={Novak, David R. and Colle, Brian A. and Aiyyer, Anantha R.}, year={2010}, month={Jun}, pages={2354–2374} }
 @article{meskhidze_remer_platnick_juarez_lichtenberger_aiyyer_2009, title={Exploring the differences in cloud properties observed by the Terra and Aqua MODIS sensors}, volume={9}, DOI={10.5194/acp-9-3461-2009}, abstractNote={Abstract. The aerosol-cloud interaction in different parts of the globe is examined here using multi-year statistics of remotely sensed data from two MODIS sensors aboard NASA's Terra (morning) and Aqua (afternoon) satellites. Simultaneous retrievals of aerosol loadings and cloud properties by the MODIS sensor allowed us to explore morning-to-afternoon variation of liquid cloud fraction (CF) and optical thickness (COT) for clean, moderately polluted and heavily polluted clouds in different seasons. Data analysis for seven-years of MODIS retrievals revealed strong temporal and spatial patterns in morning-to-afternoon variation of cloud fraction and optical thickness over different parts of the global oceans and the land. For the vast areas of stratocumulus cloud regions, the data shows that the days with elevated aerosol abundance were also associated with enhanced afternoon reduction of CF and COT pointing to the possible reduction of the indirect climate forcing. A positive correlation between aerosol optical depth and morning-to-afternoon variation of trade wind cumulus cloud cover was also found over the northern Indian Ocean, though no clear relationship between the concentration of Indo-Asian haze and morning-to-afternoon variation of COT was established. Over the Amazon region during wet conditions, aerosols are associated with an enhanced convective process in which morning shallow warm clouds are organized into afternoon deep convection with greater ice cloud coverage. Analysis presented here demonstrates that the new technique for exploring morning-to-afternoon variability in cloud properties by using the differences in data products from the two daily MODIS overpasses is capable of capturing some of the major features of diurnal variations in cloud properties and can be used for better understanding of aerosol radiative effects.}, number={10}, journal={Atmospheric Chemistry and Physics}, author={Meskhidze, N. and Remer, L. A. and Platnick, S. and Juarez, R. N. and Lichtenberger, A. M. and Aiyyer, Anantha}, year={2009}, pages={3461–3475} }
 @article{meskhidze_remer_platnick_juárez_lichtenberger_aiyyer_2009, title={Exploring the differences in cloud properties observed by the Terra and Aqua MODIS sensors}, volume={1}, DOI={10.5194/acpd-9-1489-2009}, abstractNote={Abstract. The aerosol-cloud interaction in different parts of the globe is examined here using multi-year statistics of remotely sensed data from two MODIS sensors aboard NASA's Terra (morning) and Aqua (afternoon) satellites. Simultaneous retrievals of aerosol loadings and cloud properties by the MODIS sensor allowed us to explore intra-diurnal variation of liquid cloud fraction (CF) and optical thickness (COT) for clean, moderately polluted and heavily polluted clouds in different seasons. Data analysis for six-years of MODIS retrievals revealed strong temporal and spatial patterns in intra-diurnal variation of cloud fraction and optical thickness over different parts of the global oceans and the land. For the vast areas of stratocumulus cloud regions, the data shows that the presence of aerosols can more than double afternoon reduction of CF and COT pointing to the possible predominance of semi-direct over the indirect effects of aerosols in stratocumulus clouds. A positive relationship between AOD and morning-to-afternoon variation of trade wind cumulus cloud cover was also found over the northern Indian Ocean, though no clear correlation between the concentration of Indo-Asian haze and intra-diurnal variation of COT was established. Over the Amazon region during wet conditions, aerosols are associated with an enhanced convective process in which morning shallow warm clouds are organized into afternoon deep convection with greater ice cloud coverage. Analysis presented here demonstrates that the new technique for exploring intra-diurnal variability in cloud properties by using the differences in data products from the two daily MODIS overpasses is capable of capturing some of the major features of morning-to-afternoon variations in cloud properties and can be used for improved understanding of aerosol radiative effects.}, publisher={Copernicus GmbH}, author={Meskhidze, N. and Remer, L. A. and Platnick, S. and Juárez, R. Negrón and Lichtenberger, A. M. and Aiyyer, A. R.}, year={2009}, month={Jan} }
 @article{galarneau_bosart_aiyyer_2008, title={Closed Anticyclones of the Subtropics and Midlatitudes: A 54-Yr Climatology (1950–2003) and Three Case Studies}, volume={33}, DOI={10.1175/0065-9401-33.55.349}, abstractNote={Abstract The pioneering large-scale studies of cyclone frequency, location, and intensity conducted by Fred Sanders prompt similar questions about lesser-studied anticyclone development. The results of a climatology of closed anticyclones (CAs) at 200, 500, and 850 hPa, with an emphasis on the subtropics and midlatitudes, is presented to assess the seasonally varying distribution and hemispheric differences of these features. To construct the CA climatology, a counting program was applied to twice-daily 2.5° NCEP–NCAR reanalysis 200-, 500-, and 850-hPa geopotential height fields for the period 1950–2003. Stationary CAs, defined as those CAs that were located at a particular location for consecutive time periods, were counted only once. The climatology results show that 200-hPa CAs occur preferentially during summer over subtropical continental regions, while 500-hPa CAs occur preferentially over subtropical oceans in all seasons and over subtropical continents in summer. Conversely, 850-hPa CAs occur preferentially over oceanic regions beneath upper-level midocean troughs, and are most prominent in the Northern Hemisphere, and over midlatitude continents in winter. Three case studies of objectively identified CAs that produced heal waves over the United States, Europe, and Australia in 1995, 2003, and 2004, respectively, are presented to supplement the climatological results. The case studies, examining the subset of CAs than can produce heat waves, illustrate how climatologically hot continental tropical air masses produced over arid and semiarid regions of the subtropics and lower midlatitudes can become abnormally hot in conjunction with dynamically driven upper-level ridge amplification. Subsequently, these abnormally hot air masses are advected downstream away from their source regions in conjunction with transient disturbances embedded in anomalously strong westerly jets.}, number={55}, journal={Meteorological Monographs}, publisher={American Meteorological Society}, author={Galarneau, Thomas J. and Bosart, Lance F. and Aiyyer, Anantha R.}, year={2008}, month={Nov}, pages={349–392} }
 @article{mekonnen_thorncroft_aiyyer_kiladis_2008, title={Convectively Coupled Kelvin Waves over Tropical Africa during the Boreal Summer: Structure and Variability}, volume={21}, ISSN={["1520-0442"]}, DOI={10.1175/2008JCLI2008.1}, abstractNote={Abstract The structure and variability of convectively coupled Kelvin waves during the boreal summer are explored using satellite-observed brightness temperature data and ECMWF reanalyses. Kelvin wave activity is most prominent between the central and eastern Pacific, across Africa, and the Indian Ocean. Composite analysis shows that over sub-Saharan Africa Kelvin wave convection is peaked north of the equator, while the dynamical fields tend to be symmetric with respect to the equator. Convectively coupled Kelvin waves propagate faster over the Pacific and western Atlantic (∼24 m s−1), and slow down over tropical Africa (∼14 m s−1), consistent with stronger coupling between the dynamics and convection over tropical Africa. The Kelvin waves observed over Africa generally propagate into the region from anywhere between the eastern Pacific and the Atlantic, and decay over the eastern Indian Ocean basin. Results show marked interannual variability of Kelvin wave activity over Africa. Anomalously high Kelvin wave variance tends to occur during dry years, while low variance occurs during wet years. African Kelvin wave activity is positively correlated with SST anomalies in the equatorial east Pacific. The same warm SST anomalies that are favorable for enhanced Kelvin wave activity suppress the mean rainfall over tropical Africa via a more slowly varying teleconnection and associated subsidence. A brief analysis of an intense Kelvin wave in August 1987 (a dry year) shows a clear impact of the wave on convective development and daily rainfall over tropical Africa. This Kelvin wave was also associated with a series of easterly wave initiations over tropical Africa.}, number={24}, journal={JOURNAL OF CLIMATE}, publisher={American Meteorological Society}, author={Mekonnen, Ademe and Thorncroft, Chris D. and Aiyyer, Anantha R. and Kiladis, George N.}, year={2008}, month={Dec}, pages={6649–6667} }
 @article{archambault_bosart_keyser_aiyyer_2008, title={Influence of Large-Scale Flow Regimes on Cool-Season Precipitation in the Northeastern United States}, volume={136}, DOI={10.1175/2007mwr2308.1}, abstractNote={Abstract The influence of large-scale flow regimes on cool-season (November–April) northeastern U.S. (Northeast) precipitation is investigated for the period 1948–2003 from statistical and synoptic perspectives. These perspectives are addressed through (i) a statistical analysis of cool-season Northeast precipitation associated with the North Atlantic Oscillation (NAO) and Pacific–North American (PNA) regimes (one standard deviation or greater NAO or PNA daily index anomalies persisting several days), and (ii) a composite analysis of the synoptic signatures of major (two standard deviation) 24-h cool-season Northeast precipitation events occurring during NAO and PNA regimes. The statistical analysis reveals that negative PNA regimes are associated with above-average cool-season Northeast precipitation and an above-average frequency of light and moderate precipitation events, whereas the opposite associations are true for positive PNA regimes. In comparison with PNA regimes, NAO regimes are found to have relatively little influence on the amount and frequency of cool-season Northeast precipitation. The composite analysis indicates that a surface cyclone flanked by an upstream trough over the Ohio Valley and downstream ridge over eastern Canada and upper- and lower-level jets in the vicinity of the Northeast are characteristic signatures of major cool-season Northeast precipitation events occurring during NAO and PNA regimes. Negative NAO and positive PNA precipitation events, however, are associated with a more amplified trough–ridge pattern and greater implied Atlantic moisture transport by a low-level jet into the Northeast than positive NAO and negative PNA precipitation events. Furthermore, a signature of lateral upper-level jet coupling is noted only during positive and negative PNA precipitation events.}, number={8}, journal={Mon. Wea. Rev.}, publisher={American Meteorological Society}, author={Archambault, Heather M. and Bosart, Lance F. and Keyser, Daniel and Aiyyer, Anantha R.}, year={2008}, month={Aug}, pages={2945–2963} }
 @article{aiyyer_molinari_2008, title={MJO and tropical cyclogenesis in the Gulf of Mexico and eastern Pacific: Case study and idealized numerical modeling}, volume={65}, ISSN={["0022-4928"]}, DOI={10.1175/2007JAS2348.1}, abstractNote={Abstract The role of the Madden–Julian oscillation (MJO) in modulating the frequency and location of tropical cyclogenesis over the eastern Pacific and the Gulf of Mexico during August–September 1998 is examined. During the nonconvective phase of the MJO, convection and low-level cyclonic vorticity occurred primarily in conjunction with the intertropical convergence zone (ITCZ). During the convective phase, convection, low-level cyclonic vorticity, and convergence expanded into the northeastern Pacific and the Gulf of Mexico. This was accompanied by enhanced eddy kinetic energy and barotropic energy conversions as compared to the nonconvective phase, consistent with previous research. During the nonconvective phase of the MJO, vertical shear was relatively weaker but tropical cyclones tended to form mainly within the ITCZ. On the contrary, during the convective phase, vertical wind shear exceeded 10 m s−1 over much of this region and tropical cyclone development occurred north of the ITCZ, near the Mexican Pacific coast and the Gulf of Mexico. Idealized numerical experiments are conducted using a barotropic model with time-invariant basic states representative of the nonconvective and convective phases of the MJO. The simulations indicate that the propagation paths as well as the amplification of the eddies differ substantially between the two phases. During the nonconvective phase, the waves tend to propagate westward into the eastern Pacific. During the convective phase, stronger southerlies steer the waves into the Gulf of Mexico. The MJO-related modulation of tropical cyclogenesis in the eastern Pacific and Gulf of Mexico thus appears to involve anomalous convergence, cyclonic vorticity, vertical wind shear, and differing tracks of easterly waves.}, number={8}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, publisher={American Meteorological Society}, author={Aiyyer, Anantha and Molinari, John}, year={2008}, month={Aug}, pages={2691–2704} }
 @article{holder_yuter_sobel_aiyyer_2008, title={The mesoscale characteristics of tropical oceanic precipitation during Kelvin and mixed Rossby-gravity wave events}, volume={136}, ISSN={["1520-0493"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000259295200015&KeyUID=WOS:000259295200015}, DOI={10.1175/2008MWR2350.1}, abstractNote={Abstract Precipitation structures within Kelvin and mixed Rossby–gravity (MRG) wave troughs near Kwajalein Atoll during the 1999–2003 rainy seasons are analyzed using three-dimensional ground-based radar data and upper-air sounding data. Consistent with previous work, wave troughs are preferred locations for precipitation and typically yield 1.3 times more rain area compared to the overall rainy season climatology. Although the contiguous areas of cold cloudiness associated with tropical wave troughs are large and long lived, the underlying precipitation structure is most frequently small, isolated convection from mixed-phase clouds. This mismatch in instantaneous cold cloudiness area versus radar-observed precipitation area indicates differences in the rate and nature of evolution between the mesoscale anvil cloud and the underlying precipitating portion of the cloud. Mesoscale convective systems (MCSs) were identified during portions of 32 of the 39 wave trough events examined. Convective cells are frequently embedded within stratiform regions. Reflectivity holes or pores in contiguous radar echo have been frequently observed in other regions but are quantified for the first time in this study. Based on characteristics such as total size of precipitating area and occurrence of convective lines, MCSs within Kelvin troughs are slightly more organized than those occurring within MRG troughs. Similar to the west Pacific warm pool region, there is a well-defined separation between observed and unobserved stratiform area fraction and convective precipitation area, each as a function of total precipitation area. At precipitation area sizes near 40% of the radar domain, the maximum observed convective area changes from increasing to decreasing with increasing precipitation area. The maximum observed convective precipitation area occupied ∼20% of the radar domain. These characteristics suggest that the atmosphere in the west Pacific can sustain a limited area of updrafts capable of supporting precipitation growth by collision/coalescence and riming.}, number={9}, journal={MONTHLY WEATHER REVIEW}, author={Holder, Christopher T. and Yuter, Sandra E. and Sobel, Adam H. and Aiyyer, Anantha R.}, year={2008}, month={Sep}, pages={3446–3464} }
 @article{atallah_bosart_aiyyer_2007, title={Precipitation distribution associated with landfalling tropical cyclones over the eastern United States}, volume={135}, ISSN={["0027-0644"]}, DOI={10.1175/MWR3382.1}, abstractNote={Abstract Tropical cyclones (TCs) making landfall over the United States are examined by separating those associated with precipitation predominantly left of their tracks from those with the same to the right of their tracks. Composites of atmospheric variables for these two TC categories are performed and analyzed using potential vorticity (PV) and quasigeostrophic (QG) frameworks. Dynamical signatures are retrieved from these composites to help understand the evolution of precipitation in these storms. Results indicate that a left of track precipitation distribution (e.g., Floyd 1999) is characteristic of TCs undergoing extratropical transition (ET). In these cases, a positively tilted midlatitude trough approaches the TC from the northwest, shifting precipitation to the north-northwest of the TC. Potential vorticity redistribution through diabatic heating leads to enhanced ridging over and downstream of the TC, resulting in an increase in the cyclonic advection of vorticity by the thermal wind over the transitioning TC. A right of track precipitation distribution is characteristic of TCs interacting with a downstream ridge (e.g., David 1979). When the downstream ridge amplifies in response to TC-induced diabatic heating ahead of a weak midlatitude trough, the PV gradient between the TC and the downstream ridge is accentuated, producing a region of enhanced positive PV advection (and cyclonic vorticity advection by the thermal wind) over the TC. The diabatic enhancement of the downstream ridge is instrumental in the redistribution of precipitation about the transitioning TCs in both cases and poses a significant forecast challenge.}, number={6}, journal={MONTHLY WEATHER REVIEW}, publisher={American Meteorological Society}, author={Atallah, Eyad and Bosart, Lance F. and Aiyyer, Anantha R.}, year={2007}, month={Jun}, pages={2185–2206} }
 @article{hopsch_thorncroft_hodges_aiyyer_2007, title={West African Storm Tracks and Their Relationship to Atlantic Tropical Cyclones}, volume={20}, DOI={10.1175/jcli4139.1}, abstractNote={Abstract The automatic tracking technique used by Thorncroft and Hodges has been used to identify coherent vorticity structures at 850 hPa over West Africa and the tropical Atlantic in the 40-yr ECMWF Re-Analysis. The presence of two dominant source regions, north and south of 15°N over West Africa, for storm tracks over the Atlantic was confirmed. Results show that the southern storm track provides most of the storms that reach the main development region where most tropical cyclones develop. There exists marked seasonal variability in location and intensity of the storms leaving the West African coast, which may influence the likelihood of downstream intensification and longevity. There exists considerable year-to-year variability in the number of West African storm tracks, both in numbers over the land and continuing out over the tropical Atlantic Ocean. While the low-frequency variability is well correlated with Atlantic tropical cyclone activity, West African rainfall, and SSTs, the interannual variability is found to be uncorrelated with these. In contrast, variance of the 2–6-day-filtered meridional wind, which provides a synoptic-scale measure of African easterly wave activity, shows a significant, positive correlation with tropical cyclone activity at interannual time scales.}, number={11}, journal={Journal of Climate}, publisher={American Meteorological Society}, author={Hopsch, Susanna B. and Thorncroft, Chris D. and Hodges, Kevin and Aiyyer, Anantha}, year={2007}, month={Jun}, pages={2468–2483} }
 @article{mekonnen_thorncroft_aiyyer_2006, title={Analysis of Convection and Its Association with African Easterly Waves}, volume={19}, DOI={10.1175/jcli3920.1}, abstractNote={Abstract The association between convection and African easterly wave (AEW) activity over tropical Africa and the tropical Atlantic during the boreal summer is examined using satellite brightness temperature (TB) and ECMWF reanalysis datasets. Spectral analysis using 18 yr of TB data shows significant variance in the 2–6-day range across most of the region. Within the regions of deep convection, this time scale accounts for about 25%–35% of the total variance. The 2–6-day convective variance has similar amplitudes over western and eastern Africa, while dynamic measures of AEW activity show stronger amplitudes in the west. This study suggests that weak AEW activity in the east is consistent with initial wave development there and indicates that convection triggered on the western side of the mountains over central and eastern Africa, near Darfur (western Sudan) and Ethiopia, has a role in initiating AEWs westward. The subsequent development and growth of AEWs in West Africa is associated with stronger coherence with convection there. Results show large year-to-year variability in convection at the 2–6-day time scale, which tends to vary consistently with the mean convection and dynamical measures of AEW activity over West Africa and the Atlantic, but not over central and eastern Africa. The Darfur region is particularly important for providing convective precursors that propagate westward and trigger AEWs downstream. During wet years, convection over eastern Africa (western Ethiopian highlands) can be a significant source of AEW initiation. In addition to being important for precursors of AEWs, the Darfur region is also a source of convection that propagates eastward toward Ethiopia.}, number={20}, journal={J. Climate}, publisher={American Meteorological Society}, author={Mekonnen, Ademe and Thorncroft, Chris D. and Aiyyer, Anantha R.}, year={2006}, month={Oct}, pages={5405–5421} }
 @article{aiyyer_thorncroft_2006, title={Climatology of Vertical Wind Shear over the Tropical Atlantic}, volume={19}, DOI={10.1175/jcli3685.1}, abstractNote={Abstract The spatiotemporal variability of the 200–850-hPa vertical wind shear over the tropical Atlantic is examined for a period of 46 yr. This work extends and updates past studies by considering a longer data record as well as a tropospheric-deep measure of vertical wind shear. Composite fields are constructed to illustrate the spatial pattern of the large-scale circulation associated with the mean and extreme cases of vertical shear within the tropical Atlantic. The contemporaneous relationship of vertical shear with El Niño–Southern Oscillation (ENSO) and Sahel precipitation are also examined. While the ENSO–shear correlation appears to have slightly strengthened during the past decade, the Sahel–shear correlation has become significantly degraded. A combined empirical orthogonal function (EOF) analysis of the zonal and meridional components of the vertical shear reveals interannual and multidecadal modes. The leading EOF exhibits mainly interannual variability and is highly correlated with ENSO. The second EOF is associated with a multidecadal temporal evolution and is correlated with Sahel precipitation. Both EOFs correlate at the same level with tropical cyclones in the main development region of the tropical Atlantic.}, number={12}, journal={J. Climate}, publisher={American Meteorological Society}, author={Aiyyer, Anantha R. and Thorncroft, Chris}, year={2006}, month={Jun}, pages={2969–2983} }
 @article{corbosiero_molinari_aiyyer_black_2006, title={The Structure and Evolution of Hurricane Elena (1985). Part II: Convective Asymmetries and Evidence for Vortex Rossby Waves}, volume={134}, DOI={10.1175/mwr3250.1}, abstractNote={Abstract A portable data recorder attached to the Weather Surveillance Radar-1957 (WSR-57) in Apalachicola, Florida, collected 313 radar scans of the reflectivity structure within 150 km of the center of Hurricane Elena (in 1985) between 1310 and 2130 UTC 1 September. This high temporal and spatial (750 m) resolution dataset was used to examine the evolution of the symmetric and asymmetric precipitation structure in Elena as the storm rapidly strengthened and attained maximum intensity. Fourier decomposition of the reflectivity data into azimuthal wavenumbers revealed that the power in the symmetric (wavenumber 0) component dominated the reflectivity pattern at all times and all radii by at least a factor of 2. The wavenumber 1 asymmetry accounted for less than 20% of the power in the reflectivity field on average and was found to be forced by the environmental vertical wind shear. The small-amplitude wavenumber 2 asymmetry in the core was associated with the appearance and rotation of an elliptical eyewall. This structure was visible for nearly 2 h and was noted to rotate cyclonically at a speed equal to half of the local tangential wind. Outside of the eyewall, individual peaks in the power in wavenumber 2 were associated with repeated instances of cyclonically rotating, outward-propagating inner spiral rainbands. Four separate convective bands were identified with an average azimuthal velocity of 25 m s−1, or ∼68% of the local tangential wind speed, and an outward radial velocity of 5.2 m s−1. The azimuthal propagation speeds of the elliptical eyewall and inner spiral rainbands were consistent with vortex Rossby wave theory. The elliptical eyewall and inner spiral rainbands were seen only in the 6-h period prior to peak intensity, when rapid spinup of the vortex had produced an annular vorticity profile, similar to those that have been shown to support barotropic instability. The appearance of an elliptical eyewall was consistent with the breakdown of eyewall vorticity into mesovortices, asymmetric mixing between the eye and eyewall, and a slowing of the intensification rate. The inner spiral rainbands might have arisen from high eyewall vorticity ejected from the core during the mixing process. Alternatively, because the bands were noted to emanate from the vertical shear-forced deep convection in the northern eyewall, they could have formed through the axisymmetrization of the asymmetric diabatically generated eyewall vorticity.}, number={11}, journal={Mon. Wea. Rev.}, publisher={American Meteorological Society}, author={Corbosiero, Kristen L. and Molinari, John and Aiyyer, Anantha R. and Black, Michael L.}, year={2006}, month={Nov}, pages={3073–3091} }
 @article{lapenis_shvidenko_shepaschenko_nilsson_aiyyer_2005, title={Acclimation of Russian forests to recent changes in climate}, volume={11}, DOI={10.1111/j.1365-2486.2005.001069.x}, abstractNote={Assessments made over the past few decades have suggested that boreal forests may act as a sink for atmospheric carbon dioxide. However, the fate of the newly accumulated carbon in the living forest biomass is not well understood, and the estimates of carbon sinks vary greatly from one assessment to another. Analysis of remote sensing data has indicated that the carbon sinks in the Russian forests are larger than what has been estimated from forest inventories. In this study, we show that over the past four decades, the allometric relationships among various plant parts have changed in the Russian forests. To this end, we employ two approaches: (1) analysis of the database, which contains 3196 sample plots; and (2) application of developed models to forest inventory data. Within the forests as a whole, when assessed at the continental scale, we detect a pronounced increase in the share of green parts (leaves and needles). However, there is a large geographical variation. The shift has been largest within the European Russia, where summer temperatures and precipitation have increased. In the Northern Taiga of Siberia, where the climate has become warmer but drier, the fraction of the green parts has decreased while the fractions of aboveground wood and roots have increased. These changes are consistent with experiments and mathematical models that predict a shift of carbon allocation to transpiring foliage with increasing temperature and lower allocation with increasing soil drought. In light of this, our results are a possible demonstration of the acclimation of trees to ongoing warming and changes in the surface water balance. Independent of the nature of the observed changes in allometric ratios, the increase in the share of green parts may have caused a misinterpretation of the satellite data and a systematic overestimation by remote sensing methods of the carbon sink for living biomass of the Russian forest.}, number={12}, journal={Global Change Biol}, publisher={Wiley-Blackwell}, author={LAPENIS, ANDREI and SHVIDENKO, ANATOLY and SHEPASCHENKO, DMITRY and NILSSON, STEN and AIYYER, ANANTHA}, year={2005}, pages={2090–2102} }
 @article{nagarajan_aiyyer_2004, title={Performance of the ECMWF Operational Analyses over the Tropical Indian Ocean}, volume={132}, DOI={10.1175/1520-0493(2004)132<2275:poteoa>2.0.co;2}, abstractNote={The quality of the ECMWF operational analyses is evaluated against independent upper-air sounding data collected during the Joint Air–Sea Monsoon Interaction Experiment (JASMINE; April–May 1999) and the Indian Ocean Experiment (INDOEX; February–March 1999). Statistics of the difference between observations and analyses are compiled for temperature, humidity, and wind speed. The results show that the analyzed temperature has a cold bias between 1000 and 750 hPa. However, in the upper troposphere, a warm bias occurs between 350 and 150 hPa, while a cold bias is seen above 150 hPa. Compared to the observations, the analyzed humidity is lower between 1000 and 950 hPa and higher between 950 and 750 hPa. The analyzed wind speeds are close to observations over much of the troposphere, except near the tropopause, where they are overestimated by 1–2 m s−1 in the analyses. The low-level (1000– 750 hPa) biases in moisture and temperature in the ECMWF analyses over the Indian Ocean are similar to those reported for the tropical Pacific Ocean in past studies. The occurrence of a cold and dry bias in the lowest 50 hPa indicates reduced convective available potential energy, which will render difficult the initiation and development of convection in numerical models initialized with these analyses. The moisture biases arise most likely because of the poor fit to humidity observations by the four-dimensional variational data assimilation scheme. This suggests that a better fit to humidity observations will yield an improved water vapor climatology over the Arabian Sea and Indian Ocean.}, number={9}, journal={Mon. Wea. Rev.}, publisher={American Meteorological Society}, author={Nagarajan, Badrinath and Aiyyer, Anantha R.}, year={2004}, month={Sep}, pages={2275–2282} }