@article{horvath_lin_ivanican-picek_2008, title={Classification of cyclone tracks over the Apennines and the Adriatic Sea}, volume={136}, ISSN={["1520-0493"]}, DOI={10.1175/2007MWR2231.1}, abstractNote={Abstract Cyclones that appear in the Adriatic Sea basin strongly influence the climate and weather conditions in the area. In particular, apart from the usually mild climate, cyclone activity in the Adriatic and the central Mediterranean Sea provide both the main hydrological forcing and the trigger mechanisms for a range of extreme weather phenomena. Therefore, a basic understanding of the cyclogenesis over the Adriatic Sea is essential. In particular, the classification of different types of cyclogenesis in the area is fundamental because it will help the understanding and prediction of the relevant weather phenomena. In this study, based on the analysis of the 4-yr (2002–05) operational European Centre for Medium-Range Weather Forecasts T511 dataset, various types of cyclone tracks are classified and the mesocyclogenesis areas in the vicinity of the Adriatic Basin are isolated. This analysis indicates that the following four types of cyclogenesis over the Adriatic Sea can be identified: 1) type A: cyclones connected with preexisting Genoa cyclones [with two subcategories, (A-I) continuous track: Genoa cyclones crossing over the Apennines to the Adriatic Sea, and (A-II) discontinuous track: new surface cyclones generated over the Adriatic Sea under the influence of a parent cyclone generated in the Gulf of Genoa (Genoa cyclones) and moving toward the Adriatic but blocked by the Apennines]; 2) type B: cyclones developed in situ over the Adriatic Sea without any connections with other preexisting cyclones in the surrounding area; 3) type AB: mixed types A and B cyclones, including cases where two cyclones coexist and stride over the Apennines (twin or eyeglass cyclones); and 4) type C: cyclones moving from the Mediterranean Sea, but not from the Gulf of Genoa (non-Genoa cyclones) [with 2 subcategories: (C-I) continuous track: a non-Genoa cyclone is able to cross over the Apennines to the Adriatic Sea continuously, and (C-II) discontinuous track: a non-Genoa cyclone is blocked by the Apennines and a new surface cyclone is generated over the Adriatic Sea]. The relevant dynamics of the above types of cyclones are discussed along with characteristics of the cyclones and their synoptic situations at the lower and upper troposphere.}, number={6}, journal={MONTHLY WEATHER REVIEW}, author={Horvath, Kristian and Lin, Yuh-Lang and Ivanican-Picek, Branka}, year={2008}, month={Jun}, pages={2210–2227} }
 @article{reeves_lin_rotunno_2008, title={Dynamic forcing and mesoscale variability of heavy precipitation events over the Sierra Nevada mountains}, volume={136}, ISSN={["0027-0644"]}, DOI={10.1175/2007MWR2164.1}, abstractNote={Abstract The aim of this research is to investigate the causes for an isolated maximum in precipitation that is typically found along the northern half of the Sierra Nevada mountains of California, in the vicinity of Plumas National Forest (PNF), during moderate to heavy precipitation events. Particular attention was paid to the role various mesoscale (i.e., <200 km) terrain features may have played in localizing the precipitation at PNF. Numerical simulations and sensitivity experiments for two cases of heavy precipitation at PNF reveal that the extent to which terrain acts to focus precipitation is case sensitive. In the first case, the upstream flow was characterized by a strong horizontal gradient in wind speed and moisture. This gradient led to differential deflection of airstreams incident to the range and, consequently, localized convergence and enhanced rain rates at PNF. This localized enhancement occurred regardless of whether any terrain variations were present in the simulations or not. The second case was characterized by more a horizontally uniform upstream flow and showed a much stronger sensitivity to terrain variations, in particular, short- and long-wavelength undulations along the leading (west) edge of the Sierra Nevada range. When these undulations were removed, no localized maxima in precipitation occurred.}, number={1}, journal={MONTHLY WEATHER REVIEW}, author={Reeves, Heather Dawn and Lin, Yuh-Lang and Rotunno, Richard}, year={2008}, month={Jan}, pages={62–77} }
 @article{huang_lin_2008, title={The influence of mesoscale mountains on vortex tracks: shallow-water modeling study}, volume={101}, ISSN={["1436-5065"]}, DOI={10.1007/s00703-007-0284-1}, number={1-2}, journal={METEOROLOGY AND ATMOSPHERIC PHYSICS}, author={Huang, C. -Y. and Lin, Y. -L.}, year={2008}, month={Sep}, pages={1–20} }
 @article{reeves_lin_2007, title={The effects of a mountain on the propagation of a preexisting convective system for blocked and unblocked flow regimes}, volume={64}, ISSN={["1520-0469"]}, DOI={10.1175/JAS3959.1}, abstractNote={Abstract Observations and previous research of squall lines impinging on mountain ranges have revealed that the squall lines sometimes stall upstream of the mountains for several hours leading to copious accumulations of precipitation. It has been hypothesized that squall-line stagnation may be more prone to occur in flows where the Froude number (F = U/Nh, where U is the basic-state wind, N is the Brunt–Väisälä frequency, and h is the mountain height) is low. This hypothesis is tested herein through a series of idealized, two-dimensional experiments where a convective system was triggered upstream of a mesoscale mountain in conditionally unstable flow. For simulations with relatively low Froude numbers, stagnation of the preexisting convective system was not observed. In the simulations with high values of F, squall lines were noted to stagnate between 100 and 200 km upstream of the mountain. This result indicates that squall-line stagnation may be more favored for moderate to large values of F for conditionally unstable flow. The mechanisms leading to the formation of the stationary convective system upstream of the mountain in the unblocked flows were explored and it was found that evaporative cooling played a pivotal role in the stagnation of the squall line.}, number={7}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Reeves, Heather Dawn and Lin, Yuh-Lang}, year={2007}, month={Jul}, pages={2401–2421} }
 @article{kaplan_charney_waight_lux_cetola_huffman_riordan_slusser_kiefer_suffern_et al._2006, title={Characterizing the severe turbulence environments associated with commercial aviation accidents. A real-time turbulence model (RTTM) designed for the operational prediction of hazardous aviation turbulence environments}, volume={94}, ISSN={["0177-7971"]}, DOI={10.1007/s00703-005-0181-4}, abstractNote={In this paper, we will focus on the real-time prediction of environments that are predisposed to producing moderate-severe (hazardous) aviation turbulence. We will describe the numerical model and its postprocessing system that is designed for said prediction of environments predisposed to severe aviation turbulence as well as presenting numerous examples of its utility. The purpose of this paper is to demonstrate that simple hydrostatic precursor circulations organize regions of preferred wave breaking and turbulence at the nonhydrostatic scales of motion. This will be demonstrated with a hydrostatic numerical modeling system, which can be run in real time on a very inexpensive university computer workstation employing simple forecast indices. The forecast system is designed to efficiently support forecasters who are directing research aircraft to measure the environment immediately surrounding turbulence. The numerical model is MASS version 5.13, which is integrated over three different grid matrices in real-time on a university workstation in support of NASA-Langley’s B-757 turbulence research flight missions. The model horizontal resolutions are 60, 30, and 15 km and the grids are centered over the region of operational NASA-Langley B-757 turbulence flight missions. The postprocessing system includes several turbulence-related products including four turbulence forecasting indices, winds, streamlines, turbulence kinetic energy, and Richardson numbers. Additionally there are convective products including precipitation, cloud height, cloud mass fluxes, lifted index, and K-index. Furthermore, soundings, sounding parameters, and Froude number plots are also provided. The horizontal cross section plot products are provided from 16,000–46,000 feet in 2,000 feet intervals. Products are available every three hours at the 60 and 30 km grid interval and every 1.5 hours at the 15 km grid interval. The model is initialized from the NWS ETA analyses and integrated two times a day.}, number={1-4}, journal={METEOROLOGY AND ATMOSPHERIC PHYSICS}, author={Kaplan, M. L. and Charney, J. J. and Waight, K. T., III and Lux, K. M. and Cetola, J. D. and Huffman, A. W. and Riordan, A. J. and Slusser, S. D. and Kiefer, M. T. and Suffern, P. S. and et al.}, year={2006}, month={Nov}, pages={235–270} }
 @article{lin_witcraft_kuo_2006, title={Dynamics of track deflection associated with the passage of tropical cyclones over a mesoscale mountain}, volume={134}, ISSN={["0027-0644"]}, DOI={10.1175/MWR3263.1}, abstractNote={Abstract In this study, the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) was used to simulate Supertyphoon Bilis (in 2000) and Typhoon Toraji (in 2001) in order to investigate the dynamics of track deflection caused by the Central Mountain Range (CMR) of Taiwan. The MM5 predicted the track of each storm reasonably well. Bilis was stronger and had a relatively faster forward motion, which helped make the track continuous as it crossed the CMR. The use of a “bogus” vortex in the initialization process helped produce a storm closer to the observed strength. Bilis is a classic example of a typhoon crossing Taiwan with a continuous track. For comparison, Typhoon Toraji, a typical typhoon having a discontinuous track, was also studied. Toraji was weaker and had a relatively slower forward speed, which prevented the original low center from crossing over the CMR and forced more air parcels to go around the northern tip of the CMR. As a result, it produced a vortex and a secondary low center on the lee. Potential vorticity banners on the north side of the CMR acted to organize the secondary low and the lee vortex. With time, the low-level circulation extended into the upper levels, completing the formation of the secondary center. Remnants of the initial center crossed over the CMR and were entrained into the secondary center. Nondimensional control parameters for track continuity and deflection from idealized studies are calculated for Bilis and Toraji. The results are consistent with the theory proposed in Lin et al. For tropical cyclones (TCs) approaching Taiwan from the southeast, the conceptual model proposed by Lin et al. for continuous and discontinuous tracks was applied. For continuous tracks over the CMR, the blocking effect on the outer circulation of the vortex is weak and the vorticity advection around the northern tip is strong due to an intense TC. Weak TCs tend to be totally blocked by the CMR.}, number={12}, journal={MONTHLY WEATHER REVIEW}, author={Lin, Yuh-Lang and Witcraft, Nicholas C. and Kuo, Ying-Hwa}, year={2006}, month={Dec}, pages={3509–3538} }
 @article{reeves_lin_2006, title={Effect of stable layer formation over the Po valley on the development of convection during MAP IOP-8}, volume={63}, ISSN={["1520-0469"]}, DOI={10.1175/JAS3759.1}, abstractNote={Abstract During intensive observation period (IOP)-8 of the Mesoscale Alpine Program, there was a stable layer of air in the lowest levels of the Po Valley and just upstream of the Apennines. In this study, the effects of the stable layer on the formation of convection in the southern Alpine region were investigated through a series of two-dimensional, idealized experiments. The goals of this study were twofold: 1) to determine if stable layer strength affected the placement of convection and 2) to test the notion that the stable layer during IOP-8 behaved as an effective mountain. To accomplish the first objective, three simulations were compared in which the strength of the inversion and low-level cooling in the Po Valley and upstream of the Apennines was varied. The results of these simulations show that the stronger the inversion and low-level cooling, the farther south the convection was positioned. Additionally, it was found that convection developed as a result of the formation of a broad region of moist instability over the stable layer. Cellular convection developed in this region of moist instability. The second objective was tested through a simulation where the cold pool was replaced by terrain (MMTN). As in the reference (or STB10) simulation, the upslope of the terrain in the MMTN simulation was characterized by a wide zone of moist instability. However, wave structures to the lee of the Apennines were markedly different in the STB10 and MMTN simulations. This led to different convective and precipitation patterns, with the MMTN simulation exhibiting heavier convection over the Po Valley while the heaviest convection in STB10 was upstream of the Apennines. These results suggest that, at best, the stable layer in the STB10 simulation can only be roughly approximated by terrain.}, number={10}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Reeves, Heather Dawn and Lin, Yuh-Lang}, year={2006}, month={Oct}, pages={2567–2584} }
 @article{hoggarth_reeves_lin_2006, title={Formation and maintenance mechanisms of the stable layer over the Po valley during MAP IOP-8}, volume={134}, ISSN={["0027-0644"]}, DOI={10.1175/MWR3251.1}, abstractNote={Abstract During intensive observation period 8 (IOP-8) of the Mesoscale Alpine Program, a strong stable layer formed over Italy’s Po Valley and the northern Ligurian Sea. This stable layer has been shown in previous research to be important for the formation of convection over the Ligurian Sea and the lack thereof over the Po Valley and southern slopes of the Alps. The purpose of this study is to investigate the mechanisms that acted to form and maintain the stable layer during IOP-8. This aim is accomplished through inspection of observed data as well as numerical simulations and sensitivity experiments. Observations and reanalysis data show that starting on 17 October 1999, a relatively cool, stable air mass was advected around the eastern side of the Alps into the lower atmosphere of the Po Valley. Both observational data and model output show this air mass as being blocked as it encountered the western Alps, thus resulting in an accumulation of cool, stable air at low levels in the Po Valley during the ensuing 60 h. When southerly flow approached northern Italy beginning on 20 October 1999, both the western Alps and the northern Alps appeared to help retain the low-level, cool, stable air over the Po Valley. A trajectory and sounding analysis shows that warmer, less stable air originating from over the southern Mediterranean Sea was advected atop the low-lying stable layer within the Po Valley. It is hypothesized that this differential advection, as well as blocking by the western and northern flanks of the Alps, were responsible for the longevity of the stable layer. A series of numerical simulations and sensitivity experiments were performed to test the above hypotheses. These tests support the hypotheses. Other mechanisms were also considered, including blocking of solar radiation by clouds, friction, and evaporative cooling. These simulations revealed that all three processes were critical for the longevity of the stable layer and point to the importance of accurate model representation of subgrid-scale processes.}, number={11}, journal={MONTHLY WEATHER REVIEW}, author={Hoggarth, Allison M. and Reeves, Heather Dawn and Lin, Yuh-Lang}, year={2006}, month={Nov}, pages={3336–3354} }
 @article{kaplan_huffman_lux_charney_riordan_lin_2005, title={Characterizing the severe turbulence environments associated with commercial aviation accidents. Part 1: A 44-case study synoptic observational analyses}, volume={88}, ISSN={["1436-5065"]}, DOI={10.1007/s00703-004-0080-0}, number={3-4}, journal={METEOROLOGY AND ATMOSPHERIC PHYSICS}, author={Kaplan, ML and Huffman, AW and Lux, KM and Charney, JJ and Riordan, AJ and Lin, YL}, year={2005}, month={Apr}, pages={129–152} }
 @article{kaplan_huffman_lux_cetola_charney_riordan_lin_waight_2005, title={Characterizing the severe turbulence environments associated with commercial aviation accidents. Part 2: Hydrostatic mesoscale numerical simulations of supergradient wind flow and streamwise ageostrophic frontogenesis}, volume={88}, DOI={10.1007/s00703-004-0079-6}, number={04-Mar}, journal={Meteorology and Atmospheric Physics}, author={Kaplan, M. L. and Huffman, A. W. and Lux, K. M. and Cetola, J. D. and Charney, J. J. and Riordan, A. J. and Lin, Y. L. and Waight, K. T.}, year={2005}, pages={153–173} }
 @article{lin_chen_hill_huang_2005, title={Control parameters for the influence of a mesoscale mountain range on cyclone track continuity and deflection}, volume={62}, ISSN={["0022-4928"]}, DOI={10.1175/JAS3439.1}, abstractNote={Abstract In this study prospective control parameters are identified for diagnosing the continuity and deflection of cyclone tracks across a mesoscale mountain range. Based on idealized simulations of a westward-moving cyclone, it was found that the cyclone track becomes a discontinuous (continuous) track and the cyclone experiences more (less) deflection with a combination of small (large) values of Vmax/Nh, U/Nh, R/Ly, U/fLx, and Vmax/fR, and large (small) value of h/Lx. The symbols are defined as follows: Vmax the maximum tangential wind, N the Brunt–Väisälä frequency, h the mountain height, U the basic wind speed, R the radius of Vmax, f the Coriolis parameter, and Lx and Ly the horizontal scales of the mountain in x and y directions, respectively. A conceptual model is proposed to explain track deflection and continuity for a westward-moving cyclone encountering idealized topography representative of the Central Mountain Range of Taiwan. With weak orographic blocking, a cyclone crosses over the mountain range with some northward deflection. With moderate orographic blocking, northward deflection of a cyclone is greater upstream of the mountain range and a secondary, leeside vortex forms to the southwest of the mountain range, indicative of discontinuity in the cyclone track. With strong orographic blocking, a westward-moving cyclone is deflected southward and a secondary cyclone forms to the northwest of the mountain range. The northward or southward deflection of a cyclone track is explained by the orographic blocking on the outer circulation of the cyclone.}, number={6}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Lin, YL and Chen, SY and Hill, CM and Huang, CY}, year={2005}, month={Jun}, pages={1849–1866} }
 @article{witcraft_lin_kuo_2005, title={Dynamics of orographic rain associated with the passage of a tropical cyclone over a mesoscale mountain}, volume={16}, DOI={10.3319/TAO.2005.16.5.1133(A)}, number={5}, journal={Terrestrial, Atmospheric, and Oceanic Sciences}, author={Witcraft, N. C. and Lin, Y. L. and Kuo, Y. H.}, year={2005}, pages={1133–1161} }
 @article{chen_lin_2005, title={Effects of moist froude number and CAPE on a conditionally unstable flow over a mesoscale mountain ridge}, volume={62}, ISSN={["1520-0469"]}, DOI={10.1175/JAS-3380.1}, abstractNote={Abstract In this study, idealized simulations are performed for a conditionally unstable flow over a two-dimensional mountain ridge in order to investigate the propagation and types of cloud precipitation systems controlled by the unsaturated moist Froude number (Fw) and the convective available potential energy (CAPE). A two-dimensional moist flow regime diagram, based on Fw and CAPE, is proposed for a conditionally unstable flow passing over a two-dimensional mesoscale mountain ridge. The characteristics of these flow regimes are 1) regime I: flow with an upstream-propagating convective system and an early, slowly moving convective system over the mountain; 2) regime II: flow with a long-lasting orographic convective system over the mountain peak, upslope, or lee slope; 3) regime III: flow with an orographic convective or mixed convective and stratiform precipitation system over the mountain and a downstream-propagating convective system; and 4) regime IV: flow with an orographic stratiform precipitation system over the mountain and possibly a downstream-propagating cloud system. Note that the fourth regime was not included in the flow regimes proposed by Chu and Lin and Chen and Lin. The propagation of the convective systems is explained by the orographic blocking and density current forcing associated with the cold-air outflow produced by evaporative cooling acting against the basic flow, which then determines the propagation and cloud types of the simulated precipitation systems.}, number={2}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Chen, SH and Lin, YL}, year={2005}, month={Feb}, pages={331–350} }
 @article{lin_reeves_chen_chiao_2005, title={Formation mechanisms for convection over the Ligurian Sea during MAP IOP-8}, volume={133}, ISSN={["0027-0644"]}, DOI={10.1175/MWR2970.1}, abstractNote={Abstract The dynamical impacts of an unusually strong stable layer that developed over the Po Valley and northern Ligurian Sea during Mesoscale Alpine Program (MAP) intensive observation period 8 (IOP-8) on the formation of convection over the Ligurian Sea are explored. Based on numerically simulated equivalent potential temperature, wind vectors, and by a trajectory analysis of parcels both beneath and above the stable layer, it is shown that the stable layer behaved as a material surface or “effective mountain” to the airstreams impinging on it from the south. Additional analyses show that the leading edge of the stable layer was collocated with maxima in upward motion and a strong positive moisture flux. Hence, it was further argued and demonstrated through inspection of soundings upstream of the cold dome and trajectory analyses that lifting by the stable layer enhanced convective activities over the Ligurian Sea. Finally, processes contributing to the maintenance of the stable layer during IOP-8 were explored. It was found that the differential advection of a warm, less stable air mass on top of a cooler, more stable air mass helped maintain the stable layer. The Ligurian Apennines made a secondary contribution to the stagnation of the cool air in the Po Valley by partially blocking this air mass from exiting the valley to the south.}, number={8}, journal={MONTHLY WEATHER REVIEW}, author={Lin, YL and Reeves, HD and Chen, SY and Chiao, S}, year={2005}, month={Aug}, pages={2227–2245} }
 @article{lin_robertson_hill_2005, title={Origin and propagation of a disturbance associated with an African easterly wave as a precursor of Hurricane Alberto (2000)}, volume={133}, ISSN={["1520-0493"]}, DOI={10.1175/MWR3035.1}, abstractNote={Abstract In this study, it is proposed that mesoscale convective complexes (MCCs) and a mesovortex (MV) were embedded within a wavelike disturbance over North Africa that led to the genesis of Hurricane Alberto (2000). The wavelike disturbance observed may be classified as an African easterly wave (AEW). Based on the cloud-top area and brightness values observed from infrared satellite data, four genesis and three lysis stages are identified within a cycle of moist convection associated with the pre-Alberto disturbance. The availability of water vapor is the most essential factor controlling the convective cycle of the pre-Alberto disturbance over the African continent. The presence of significant topography also contributes to the generation or decay of the associated MCCs through regulation of the water vapor supply. Further analysis of Meteosat satellite imagery reveals that the incipient disturbances for 23 of 34 eastern Atlantic tropical cyclones originated from the Ethiopian highlands (EH) region during the period of 1990–2001. The pre-Alberto disturbance was found to have exhibited characteristics of an AEW. At the EH, there existed two modes of disturbance development: a stationary mode and a propagating mode. The stationary mode corresponded with the generation of moist convection over the EH triggered by diurnally variant sensible heating, while the propagating mode corresponded with the generation and propagation of MVs and mesoscale convective systems (MCSs) from the lee side of the EH over a period of about 2 to 3 days. These components of the disturbance propagated westward together within an AEW train at an average speed of 11.6 m s−1. The average wavelength was roughly estimated to be about 2200 km. To prove that disturbances generated at the EH are indeed AEWs, the NCAR Regional Climate Model Version 3.0 is adopted to simulate the event. The simulated fields showed that both the propagating wave and stationary mountain wave modes were present, the convection was generated over the EH, and the pre-Alberto disturbance was generated near the lee of the EH. In addition, the convective cycle detected from NCEP reanalysis data was also reflected in the simulated fields. The simulated AEW possesses similar wave characteristics as the observed pre-Alberto disturbance.}, number={11}, journal={MONTHLY WEATHER REVIEW}, author={Lin, YL and Robertson, KE and Hill, CM}, year={2005}, month={Nov}, pages={3276–3298} }
 @article{chen_lin_2005, title={Orographic effects on a conditionally unstable flow over an idealized three-dimensional mesoscale mountain}, volume={88}, number={02-Jan}, journal={Meteorology and Atmospheric Physics}, author={Chen, S. H. and Lin, Y. L.}, year={2005}, pages={21-} }
 @article{chiao_lin_kaplan_2004, title={Numerical study of the orographic forcing of heavy precipitation during MAP IOP-2B}, volume={132}, ISSN={["1520-0493"]}, DOI={10.1175/1520-0493(2004)132<2184:NSOTOF>2.0.CO;2}, abstractNote={Abstract This paper investigates the local circulation associated with a heavy orographic rainfall event during 19–21 September 1999 [Mesoscale Alpine Programme Intensive Observing Period 2B (MAP IOP-2B)]. This event was simulated with a 5-km horizontal grid spacing using the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5). The MM5 simulation reproduced the basic features such as the timing and location of the deep trough and the associated precipitation evolution, though the total amount of precipitation is slightly higher than that measured by rain gauges (∼30% in 24 h). The near-surface flow was dominated by an easterly jet originally from the Adriatic Sea and a southerly jet from the Gulf of Genoa. A significant westward turning occurred when the southerly flow approached the south side of the Alps. This deflection was caused by boundary layer friction and rotation, as well as mountain blocking effects. Flow was generally from the south above the surface. Precipitation was ma...}, number={9}, journal={MONTHLY WEATHER REVIEW}, author={Chiao, S and Lin, YL and Kaplan, ML}, year={2004}, month={Sep}, pages={2184–2203} }
 @article{hill_lin_2003, title={Initiation of a mesoscale convective complex over the Ethiopian Highlands preceding the genesis of Hurricane Alberto (2000)}, volume={30}, number={5}, journal={Geophysical Research Letters}, author={Hill, C. M. and Lin, Y. L.}, year={2003}, pages={1232–1} }
 @article{chiao_lin_2003, title={Numerical modeling of an orographically enhanced precipitation event associated with Tropical Storm Rachel over Taiwan}, volume={18}, ISSN={["0882-8156"]}, DOI={10.1175/1520-0434(2003)018<0325:NMOAOE>2.0.CO;2}, abstractNote={Abstract An orographic rainfall event that occurred on 6–7 August 1999 during the passage of Tropical Storm (TS) Rachel over Taiwan is investigated by performing triply nested, nonhydrostatic numerical simulations using the Naval Research Laboratory's (NRL) Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) model. By examining both observational data and numerical model output, it is found that this orographic rainfall event may be separated into three distinct stages. During the first stage (0000–1200 UTC 6 August), TS Rachel was located in the South China Sea and tracked northeastward to Taiwan. Meanwhile, TS Paul was steered by the subtropical high over southwest Japan. During the second stage (1200 UTC 6 August–0000 UTC 7 August), the southwesterly monsoon current as well as the circulation of TS Rachel over southwest Taiwan strengthened and formed a low-level jet (LLJ) with high equivalent potential temperature when TS Rachel moved closer to Taiwan. In comparing the control and sensitivity...}, number={2}, journal={WEATHER AND FORECASTING}, author={Chiao, S and Lin, YL}, year={2003}, month={Apr}, pages={325–344} }
 @article{lin_ensley_chiao_huang_2002, title={Orographic influences on rainfall and track deflection associated with the passage of a tropical cyclone}, volume={130}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(2002)130<2929:OIORAT>2.0.CO;2}, abstractNote={In this study, a nonhydrostatic mesoscale model [Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS)] was adopted to simulate Supertyphoon Bilis (2000) and investigate the dynamics of orographic rain and track deflection accompanying the storm as it passes the Central Mountain Range (CMR) of Taiwan. Both the storm track and its associated orographic rainfall distribution are well predicted by the numerical model. The intensity of the storm is underpredicted, resulting in a discontinuous track, due to the lack of specifying a “bogus” vortex at the time of model initialization. Cyclonic curvature of the storm track over the island topography track as well as major circulation features are similar to previous studies of landfalling typhoons affecting Taiwan. The model overpredicts the total amount of accumulated rainfall. Generalization of the flux model proposed in a 2001 study by Lin and coauthors is used to help predict and understand the observed rainfall distribution by calculating both the orographic and general vertical moisture fluxes from COAMPS model-predicted wind and moisture fields. The vertical moisture flux calculated from the 15-km-resolution simulation compares reasonably well to the actual, storm-observed rainfall distribution. Results of the flux model using 5-km COAMPS model output are not necessarily better than those using the coarser 15-km-resolution results. The overall consistency between the observed rainfall distribution and that predicted by the moisture flux model of Lin and coauthors indicates that the rainfall occurring in the vicinity of the topography was strongly controlled by orographic forcing, rather than being associated with the original rainbands accompanying the typhoon as it moved onshore. Analysis of simulation control parameters from previous studies of tropical cyclones (TCs) passing over Taiwan's CMR implies that track continuity is strongly linked to Vmax/Nh and Vmax/Rf, where Vmax and R are the maximum tangential wind and radius of the tropical cyclone, N the Brunt–Väisälä frequency, h the maximum mountain height, and f the Coriolis parameter. It appears that track continuity (discontinuity) is associated with higher (lower) values of these two control parameters. Numerical estimates of these two control parameters from observational data and the numerical simulation results for Supertyphoon Bilis produce results consistent with the findings shown here. Physically, Vmax/Nh represents the vortex-Froude number (linearity) of the outer circulation of the vortex, and Vmax/Rf represents the intensity (inertial stability) of the vortex. It is hypothesized that when these two control parameters are small, orographic blocking forces a greater percentage of flow around the mountain, instead of allowing the flow to pass over the topography. The vortex becomes unstable, subsequently resulting in a discontinuous surface and near-surface storm track. Analysis of control parameters from previous studies of landfalling typhoons affecting Taiwan also indicates that a westward-moving TC tends to be deflected to the north (south) when Vmax/Nh is large (small). The dependence of TC track deflection on the basic-flow Froude number (U/Nh) is not revealed by parameter analysis of the previous studies.}, number={12}, journal={MONTHLY WEATHER REVIEW}, author={Lin, YL and Ensley, DB and Chiao, S and Huang, CY}, year={2002}, month={Dec}, pages={2929–2950} }
 @article{lin_joyce_2001, title={A further study of the mechanisms of cell regeneration, propagation, and development within two-dimensional multicell storms}, volume={58}, ISSN={["0022-4928"]}, DOI={10.1175/1520-0469(2001)058<2957:AFSOTM>2.0.CO;2}, abstractNote={The mechanisms of cell regeneration, development, and propagation within a two-dimensional multicell storm proposed by Lin, Deal, and Kulie (hereafter LDK) were further investigated by conducting a series of sensitivity tests. LDK’s advection mechanism was reexamined by performing simulations utilizing a plateau with five additional wind profiles having a wider range of shear. All five cases gave results that show that the cell regeneration period decreases with the storm-relative midlevel inflow, similar to that proposed by LDK. It was also found that a rigid lid is not an appropriate upper boundary condition for multicell storm simulations. In order to test whether the advection mechanism is responsible for cell regeneration with a different sounding, an idealized sounding was used. A multicell storm was produced along with a strong density current and gust front updraft. Investigation of this storm supports the advection mechanism within the growing mode and a gravity wave mechanism in the propagation mode, as proposed by LDK. From further investigation, the relaxation mechanism proposed by Fovell and Tan was shown to exist within these simulations yet found to be dependent on the advection mechanism to cause cell regeneration. To avoid some problems that occurred when using a plateau, a prescribed heat sink was used to produce a more realistic density current. This experiment demonstrates that the advection mechanism is responsible for cell regeneration and the gravity wave mechanism is responsible for cell propagation within the storm. It was found that without precipitation loading, an individual cell is still able to split. In this case, the compensating downdraft produced by vertical differential advection is responsible for cell splitting and merging.}, number={20}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Lin, YL and Joyce, LE}, year={2001}, pages={2957–2988} }
 @article{koch_zhang_kaplan_lin_weglarz_trexler_2001, title={Numerical simulations of a gravity wave event over CCOPE. Part III: The role of a mountain-plains solenoid in the generation of the second wave episode}, volume={129}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(2001)129<0909:NSOAGW>2.0.CO;2}, abstractNote={Mesoscale model simulations have been performed of the second episode of gravity waves observed in great detail in previous studies on 11–12 July 1981 during the Cooperative Convective Precipitation Experiment. The dominant wave simulated by the model was mechanically forced by the strong updraft associated with a mountain–plains solenoid (MPS). As this updraft impinged upon a stratified shear layer above the deep, well-mixed boundary layer that developed due to strong sensible heating over the Absaroka Mountains, the gravity wave was created. This wave rapidly weakened as it propagated eastward. However, explosive convection developed directly over the remnant gravity wave as an eastward-propagating density current produced by a rainband generated within the MPS leeside convergence zone merged with a westward-propagating density current in eastern Montana. The greatly strengthened cool pool resulting from this new convection then generated a bore wave that appeared to be continuous with the movement of the incipient gravity wave as it propagated across Montana and the Dakotas. The nonlinear balance equation and Rossby number were computed to explore the role of geostrophic adjustment in the forecast gravity wave generation, as suggested in previous studies of this wave event. These fields did indicate flow imbalance, but this was merely the manifestation of the MPS-forced gravity wave. Thus, the imbalance indicator fields provided no lead time for predicting wave occurrence. Several sensitivity tests were performed to study the role of diabatic processes and topography in the initiation of the flow imbalance and the propagating gravity waves. When diabatic effects owing to precipitation were prevented, a strong gravity wave still was generated in the upper troposphere within the region of imbalance over the mountains. However, it did not have a significant impact because moist convection was necessary to maintain wave energy in the absence of an efficient wave duct. No gravity waves were present in either a simulation that disallowed surface sensible heating, or the “flat terrain” simulation, because the requisite MPS forcing could not occur. This study highlights difficulties encountered in attempting to model the generation of observed gravity waves over complex terrain in the presence of strong diabatic effects. The complex interactions that occurred between the sensible heating over complex terrain, the incipient gravity wave, and convection highlight the need for much more detailed observations between wave generation regions over mountains and the plains downstream of such regions.}, number={5}, journal={MONTHLY WEATHER REVIEW}, author={Koch, SE and Zhang, FQ and Kaplan, ML and Lin, YL and Weglarz, R and Trexler, CM}, year={2001}, pages={909–933} }
 @article{lin_chiao_wang_kaplan_weglarz_2001, title={Some common ingredients for heavy orographic rainfall}, volume={16}, ISSN={["0882-8156"]}, DOI={10.1175/1520-0434(2001)016<0633:SCIFHO>2.0.CO;2}, abstractNote={The purpose of this paper is to synthesize some common synoptic and mesoscale environments conducive to heavy orographic rainfall. Previous studies of U.S. and Alpine cases and new analyses of some Alpine and east Asian cases have shown the following common synoptic and mesoscale environments are conducive to heavy orographic rainfall: 1) a conditionally or potentially unstable airstream impinging on the mountains, 2) a very moist low-level jet (LLJ), 3) a steep mountain, and 4) a quasi-stationary synoptic system to slow the convective system over the threat area. A deep short-wave trough is found to approach the threat area in the U.S. and European cases, but is not found in the east Asian cases. On the other hand, a high convective available potential energy (CAPE) value is observed in east Asian cases, but is not consistently observed in the U.S. and European cases. The enhancement of low-level upward motion and the increase of instability below the trough by the approaching deep short-wave trough in the U.S. and Alpine events may partially compensate the roles played by high CAPE in the East Asian events. In addition, the concave mountain geometry plays an important role in helping trigger the convection in Alpine and Taiwanese cases. Based on an ingredient argument, it is found that a heavy orographic rainfall requires significant contributions from any combinations of the above four common synoptic and mesoscale environments or ingredients, and high precipitation efficiency of the incoming airstream, strong upward motion, and large convective system. These ingredients are also used to help explain the synoptic and mesoscale environments observed in some orographic flooding and heavy rainfall events in other regions, such as in New Zealand, China, and India. An index, U(∂h/∂x)q, where U is the flow velocity perpendicular to the mountain range, ∂h/∂x the mountain slope, and q the water vapor mixing ratio, is also proposed to help predict the occurrence of heavy orographic rainfall. Estimates of this proposed index indicate that it may serve as a good indicator for predicting east Asian heavy orographic rainfall events.}, number={6}, journal={WEATHER AND FORECASTING}, author={Lin, YL and Chiao, S and Wang, TA and Kaplan, ML and Weglarz, RP}, year={2001}, pages={633–660} }
 @article{kaplan_lin_charney_pfeiffer_ensley_decroix_weglarz_2000, title={A terminal area PBL prediction system at Dallas-Fort Worth and its application in simulating diurnal PBL jets}, volume={81}, ISSN={["0003-0007"]}, DOI={10.1175/1520-0477(2000)081<2179:ATAPPS>2.3.CO;2}, abstractNote={A state-of-the-science meso-β-scale numerical weather prediction model is being employed in a prototype forecast system for potential operational use at the Dallas–Fort Worth International Airport (DFW). The numerical model is part of a unique operational forecasting system being developed to support the National Aeronautics and Space Administration's (NASA) Terminal Area Productivity Program. This operational forecasting system will focus on meso-β-scale aviation weather problems involving planetary boundary layer (PBL) turbulence, and is named the Terminal Area PBL Prediction System (TAPPS). TAPPS (version 1) is being tested and developed for NASA in an effort to improve 1–6-h terminal area forecasts of wind, vertical wind shear, temperature, and turbulence within both stable and convective PBLs at major airport terminal areas. This is being done to enhance terminal area productivity, that is, aircraft arrival and departure throughput, by using the weather forecasts as part of the Aircraft Vortex Spacing System (AVOSS). AVOSS is dependent upon nowcasts or short-period forecasts of wind, temperature, and eddy dissipation rate so that the drift and dissipation of wake vortices can be anticipated for safe airport operation. This AVOSS system will be demonstrated during calendar year 2000 at DFW. This paper describes the numerical modeling system, which has three basic components: the numerical model, the initial data stream, and the postprocessing system. Also included are the results of several case study simulations with the numerical model from a field program that occurred in September 1997 at DFW. During this field program, detailed local measurements throughout the troposphere, with special emphasis on the PBL, were taken at and surrounding DFW in an effort to verify the numerical model simulations. Comparisons indicate that the numerical model is capable of an accurate simulation of the vertical wind shear structure during the diurnal evolution of the PBL when compared directly to specific local observations. The case studies represent unambiguous examples of the dynamics of the Great Plains diurnal low-level jet stream. This diurnal jet stream represents the dominant low-level wind shear–production mechanism during quiescent synoptic-scale flow regimes. Five consecutive daily case studies, during which this phenomenon was observed over and in proximity to DFW, are compared to the products derived from TAPPS.}, number={9}, journal={BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY}, author={Kaplan, ML and Lin, YL and Charney, JJ and Pfeiffer, KD and Ensley, DB and DeCroix, DS and Weglarz, RP}, year={2000}, month={Sep}, pages={2179–2204} }
 @article{doyle_durran_chen_colle_georgelin_grubisic_hsu_huang_landau_lin_et al._2000, title={An intercomparison of model-predicted wave breaking for the 11 January 1972 Boulder windstorm}, volume={128}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(2000)128<0901:AIOMPW>2.0.CO;2}, abstractNote={Two-dimensional simulations of the 11 January 1972 Boulder, Colorado, windstorm, obtained from 11 diverse nonhydrostatic models, are intercompared with special emphasis on the turbulent breakdown of topographically forced gravity waves, as part of the preparation for the Mesoscale Alpine Programme field phase. The sounding used to initialize the models is more representative of the actual lower stratosphere than those applied in previous simulations. Upper-level breaking is predicted by all models in comparable horizontal locations and vertical layers, which suggests that gravity wave breaking may be quite predictable in some circumstances. Characteristics of the breaking include the following: pronounced turbulence in the 13–16-km and 18–20-km layers positioned beneath a critical level near 21-km, a well-defined upstream tilt with height, and enhancement of upper-level breaking superpositioned above the low-level hydraulic jump. Sensitivity experiments indicate that the structure of the wave breaking was impacted by the numerical dissipation, numerical representation of the horizontal advection, and lateral boundary conditions. Small vertical wavelength variations in the shear and stability above 10 km contributed to significant changes in the structures associated with wave breaking. Simulation of this case is ideal for testing and evaluation of mesoscale numerical models and numerical algorithms because of the complex wave-breaking response.}, number={3}, journal={MONTHLY WEATHER REVIEW}, author={Doyle, JD and Durran, DR and Chen, C and Colle, BA and Georgelin, M and Grubisic, V and Hsu, WR and Huang, CY and Landau, D and Lin, YL and et al.}, year={2000}, month={Mar}, pages={901–914} }
 @article{chu_lin_2000, title={Effects of orography on the generation and propagation of mesoscale convective systems in a two-dimensional conditionally unstable flow}, volume={57}, ISSN={["0022-4928"]}, DOI={10.1175/1520-0469(2001)057<3817:EOOOTG>2.0.CO;2}, abstractNote={Abstract Effects of orography, cold-air outflow, and gravity waves on the generation and propagation of convective systems in a conditionally unstable airstream over a mesoscale mountain are studied using a two-dimensional cloud model. Based on the propagation of convective systems, three regimes are identified: (I) an upstream propagating convective system, (II) a quasi-stationary convective system, and (III) quasi-stationary and downstream propagating systems. In regime I [low moist Froude number (Fw)], the convective cells are generated by upstream deceleration associated with orographic forcing, by gravity waves associated with convective cells over the upslope area at earlier stages, and by the upstream propagating density current at later stages when the density current is fully developed. In this flow regime, quasi-continuous and heavy rainfall is produced over the upslope and plain areas as individual convective cells develop farther upstream at the head of the density current and then propagate d...}, number={23}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Chu, CM and Lin, YL}, year={2000}, month={Dec}, pages={3817–3837} }
 @article{wang_lin_2000, title={Effects of shear and sharp gradients in static stability on two-dimensional flow over an isolated mountain ridge}, volume={75}, ISSN={["0177-7971"]}, DOI={10.1007/s007030070017}, number={1-2}, journal={METEOROLOGY AND ATMOSPHERIC PHYSICS}, author={Wang, TA and Lin, YL}, year={2000}, pages={69–99} }
 @article{han_lin_schowalter_arya_2000, title={Large eddy simulation of aircraft wake vortices within homogeneous turbulence: Crow instability}, volume={38}, ISSN={["0001-1452"]}, DOI={10.2514/2.956}, abstractNote={Ambient atmospheric turbulence effects on aircraft wake vortices are studied using a validated large eddy simulationmodel. Our results conŽ rm that the most ampliŽ ed wavelength of the Crow instability and the lifetime of wake vortices are signiŽ cantly in uenced by ambient turbulence (Crow, S. C., “Stability Theory for a Pair of TrailingVortices,” AIAA Journal, Vol. 8, No. 12, 1970,pp. 2172–2179). The Crow instabilitybecomeswell developed in most atmospheric turbulence levels, but in strong turbulence the vortex pair deforms more irregularly due to turbulence advection. The most ampliŽ ed wavelength of the instability decreases with increasing dimensionless turbulence intensity , although it increases with increasing turbulence integral length scale. The vortex lifespan is controlled primarily by and decreases with increasing , whereas the effect of integral scale of turbulence on vortex lifespan is of minor importance. The lifespan is estimated to be about 40% larger than Crow and Bate’s predicted value (Crow, S. C., and Bate, E. R., “Lifespan of Trailing Vortices on a Turbulent Atmosphere,” Journal of Aircraft, Vol. 13, No. 7, 1976, pp. 476–482) but in agreement with Sarpkaya’s recent modiŽ cation (Sarpkaya, T., “Decay of Wake Vortices of Large Aircraft,” AIAA Journal, Vol. 36, No. 9, 1998, pp. 1671–1679) to Crow and Bate’s theory. This larger lifespan is also supported by data from water tank experiments and direct numerical simulations. There appears to be a possibility that the scatter in vortex lifespans due to ambient turbulence alone decreases with increasing Reynoldsnumber, whereas larger scatter of lifespans in  ight tests may result from other factors such as stratiŽ cation, wind shear, and inhomogeneous ambient turbulence.}, number={2}, journal={AIAA JOURNAL}, author={Han, JG and Lin, YL and Schowalter, DG and Arya, SP}, year={2000}, month={Feb}, pages={292–300} }
 @article{egentowich_kaplan_lin_riordan_2000, title={Mesoscale simulations of dynamical factors discriminating between a tornado outbreak and non-event over the southeast US - Part I: 84-48 hour precursors}, volume={74}, ISSN={["0177-7971"]}, DOI={10.1007/s007030070030}, number={1-4}, journal={METEOROLOGY AND ATMOSPHERIC PHYSICS}, author={Egentowich, JM and Kaplan, ML and Lin, YL and Riordan, AJ}, year={2000}, pages={129–157} }
 @article{egentowich_kaplan_lin_riordan_2000, title={Mesoscale simulations of dynamical factors discriminating between a tornado outbreak and non-event over the southeast US - Part II: 48-6 hour precursors}, volume={74}, ISSN={["0177-7971"]}, DOI={10.1007/s007030070031}, number={1-4}, journal={METEOROLOGY AND ATMOSPHERIC PHYSICS}, author={Egentowich, JM and Kaplan, ML and Lin, YL and Riordan, AJ}, year={2000}, pages={159–187} }
 @article{egentowich_kaplan_lin_riordan_2000, title={Mesoscale simulations of dynamical factors discriminating between a tornado outbreak and non-event over the southeast US - Part III: 6 hour precursors}, volume={74}, ISSN={["0177-7971"]}, DOI={10.1007/s007030070032}, number={1-4}, journal={METEOROLOGY AND ATMOSPHERIC PHYSICS}, author={Egentowich, JM and Kaplan, ML and Lin, YL and Riordan, AJ}, year={2000}, pages={189–215} }
 @article{han_lin_arya_proctor_2000, title={Numerical study of wake vortex decay and descent in homogeneous atmospheric turbulence}, volume={38}, ISSN={["1533-385X"]}, DOI={10.2514/2.1006}, abstractNote={Numerical simulations are performed to isolate the effect of ambient turbulence on the wake vortex decay rate within a neutrally stratified atmosphere. Simulations are conducted for a range of turbulence intensities by injecting wake vortex pairs into an approximately homogeneous and isotropic turbulence field. Consistent with field observations, the decay rate of the vortex circulation increases clearly with increasing levels of ambient turbulence. Based on the results from the numerical simulations, simple decay models for the vortex pair are proposed as functions of nondimensional ambient turbulence intensity, nondimensional radial distance, and nondimensional time. For strong atmospheric turbulence, the model predictions are in reasonable agreement with the observational data. For weak turbulence with stable stratification, the model, based on turbulence dissipation alone, underestimates circulation decay with consistent overestimation of vortex descent, unless stratification effects are included}, number={4}, journal={AIAA JOURNAL}, author={Han, J and Lin, YL and Arya, SP and Proctor, FH}, year={2000}, month={Apr}, pages={643–656} }
 @article{shen_lin_1999, title={Effects of critical levels on two-dimensional back-sheared flow over an isolated mountain ridge on an f plane}, volume={56}, number={18}, journal={Journal of the Atmospheric Sciences}, author={Shen, B. W. and Lin, Y. L.}, year={1999}, pages={3286–3302} }
 @article{lin_han_hamilton_huang_1999, title={Orographic influence on a drifting cyclone}, volume={56}, ISSN={["0022-4928"]}, DOI={10.1175/1520-0469(1999)056<0534:OIOADC>2.0.CO;2}, abstractNote={In this study, a primitive equation numerical model is adopted to investigate the orographic influence on a drifting cyclone over an idealized topography similar to that of Taiwan. For a cyclone propagating from the east and impinging on the central portion of the mountain, a northerly surface jet tends to form upstream of the mountain between the primary cyclone and the mountain due to blocking and channeling effects. Two pressure ridges and one trough are also produced. When the cyclone approaches the mountain, the low-level vorticity and low pressure centers decelerate and turn southward upstream of the mountain due to orographic blocking. At the same time, the upstream low-level vorticity is blocked by the mountain. The abrupt increase of surface vorticity and the contraction of cyclone scale on the lee side are explained by the generation of new potential vorticity (PV) due to wave breaking associated with the severe downslope wind and hydraulic jump. The generation of this new PV is evidenced by the transition from the regime dominated by flow splitting to the regime dominated by wave breaking and the dominance of mixing and diffusion term in the vorticity and PV budgets. At this stage, the cyclone and low pressure centers appear to accelerate or jump over the mountain. At the same time, the surface low shifts to the south of the original westward track, which is primarily influenced by strong adiabatic warming associated with the downslope wind. The primary surface cyclone then resumes its original westward movement and symmetric circulation on the lee side once it moves away from the mountain. The deflection of the cyclone and low pressure centers at midlevels, such as σ = 3 km, are similar to those at the surface. Both vorticity and PV budgets are calculated to help understand the contributions from individual terms at different stages when a cyclone drifts over an idealized topography.}, number={4}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Lin, YL and Han, JG and Hamilton, DW and Huang, CY}, year={1999}, month={Feb}, pages={534–562} }
 @article{wang_lin_1999, title={Wave ducting in a stratified shear flow over a two-dimensional mountain. Part I: General linear criteria}, volume={56}, ISSN={["1520-0469"]}, DOI={10.1175/1520-0469(1999)056<0412:WDIASS>2.0.CO;2}, abstractNote={A linear theory for wave ducting is developed by solving a three-layer, steady-state nonrotating flow over a two-dimensional mountain analytically. The reflection coefficient (Ref), transmission coefficient, and the strongest horizontal wind speed at the surface are calculated based on the linear theory as functions of the Richardson number (Ri) and the depth of the lowest layer, with uniform wind speed. The relationship between the low-level response and reflectivity is also investigated. Based on this linear theory, a more general linear criteria is proposed for wave ducting, with the case considered by R. Lindzen and K.-K. Tung being only its subset. The linear theory is then applied to investigate the wave-ducting mechanism for long-lasting propagating waves in the atmosphere through a series of nonlinear numerical simulations. In the presence of a critical level, wave ducting may occur over a relatively wider range of Ri, once Ref is close to 1. That is, it is not necessary to have Ri < 0.25 in the shear layer for wave ducting to occur. The effects of varying N2/N1, N3/N1, and −U3/U1 on the low-level response in a three-layer atmosphere have also been investigated. When a stable lower layer of thickness 0.25 + n/2 times the vertical wavelength is capped by a nearly neutral layer with 0.01 < Ri < 100, it may act as a wave duct due to the reflection from the interface of sharp gradients in static stability. This wave duct exists even if there exists no vertical shear in the wind profile. The wave-ducting criteria derived from the present linear theory could be applicable even to a nonlinear flow regime, although the ducted wave may be strengthened by nonlinearity and new ducted wave modes may be induced.}, number={3}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Wang, TA and Lin, YL}, year={1999}, month={Feb}, pages={412–436} }
 @article{wang_lin_1999, title={Wave ducting in a stratified shear flow over a two-dimensional mountain. Part II: Implications for the development of high-drag states for severe downslope windstorms}, volume={56}, ISSN={["1520-0469"]}, DOI={10.1175/1520-0469(1999)056<0437:WDIASS>2.0.CO;2}, abstractNote={Abstract In this study, it is found that the discrepancies among earlier studies of severe downslope windstorms are caused by the use of the critical level height (zc), instead of the low-level uniform flow–layer depth (z1), as an indicator to determine the optimal conditions for the occurrence of high-drag states. It is determined that once the wave breaking occurs, it induces a critical level and establishes a flow configuration favorable for wave ducting in the lower uniform wind layer, which determines the phase of reflected waves. Flow regimes of high- and low-drag states for a two-dimensional, nonrotating flow with uniform static stability and a basic-state critical level over a mountain were also determined as functions of nondimensional mountain height (h), Richardson number (Ri), and nondimensional z1 in the terrain-following coordinates (σ1). The authors found that 1) the critical h for high-drag state increases as Ri increases when σ1 is fixed, 2) the critical h for high-drag state increas...}, number={3}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Wang, TA and Lin, YL}, year={1999}, month={Feb}, pages={437–452} }
 @article{lee_park_lin_1998, title={A numerical modeling study of mesoscale cyclogenesis to the east of the Korean peninsula}, volume={126}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(1998)126<2305:ANMSOM>2.0.CO;2}, abstractNote={Numerical simulations and the analysis of observational data are employed to understand the mesoscale cyclogenesis in a polar airstream that occurred over the sea to the east of the Korean peninsula on 28–29 January 1995. The observational analysis shows that a mesoscale low develops over the southeastern East Sea (Japan Sea) on 29 January 1995. Satellite imagery also indicates that a meso-β-scale vortex forms on the lee side of the northern Korean mountain complex (KMC), which is located in the northern Korean peninsula, and that a meso-α-scale cyclone develops over the southeastern East Sea at a later time. The mesoscale cyclone forms in the lower troposphere with strong baroclinicity and cyclonic circulation under the influence of an upper-level synoptic-scale cold vortex. Numerical simulation has captured major features of the observed cyclogenesis very well. The cyclogenesis occurs in a progressive manner. Basically, four distinctive stages of the cyclogenesis are identified. 1) First, a surface pressure trough forms on the lee side of the KMC under a northwesterly synoptic-scale flow that is deflected anticyclonically over the KMC. 2) Second, the lee trough deepens further into a strong convergence zone and a meso-β-scale vortex. 3) Next, the meso-β-scale vortex develops into a meso-α-scale vortex as the vortex and the trough begin to move southeastward from the lee of the KMC. 4) Finally, the surface trough deepens into a closed low and the meso-α-scale vortex becomes collocated with this deepening surface low to form a meso-α-scale cyclone over the southeastern East Sea. Several sensitivity experiments are performed to isolate the effects of a topography, warmer sea surface, diurnal thermal forcing, and latent heat release. During stages 1 and 2, it is found that the KMC and low-level baroclinicity are responsible for generating the strong lee trough and vortex. During stage 3, the development of the meso-α-scale vortex is brought on by the tilting of horizontal vorticity and vertical stretching in a synoptic-scale cyclonic circulation. In the final stage, the condensational heating plays the key role for the development of the meso-α-scale cyclone under the influence of an upper-level synoptic-scale cold vortex. The presence of the warm sea surface is found to be a necessary condition for the development of a polar air convergence zone and the mesoscale cyclone. It is also found that the low-level baroclinicity is essential for the present case of mesoscale cyclogenesis.}, number={9}, journal={MONTHLY WEATHER REVIEW}, author={Lee, TY and Park, YY and Lin, YL}, year={1998}, month={Sep}, pages={2305–2329} }
 @article{hamilton_lin_weglarz_kaplan_1998, title={Jetlet formation from diabatic forcing with applications to the 1994 Palm Sunday tornado outbreak}, volume={126}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(1998)126<2061:JFFDFW>2.0.CO;2}, abstractNote={Abstract The three-dimensional responses of simple stably stratified barotropic and baroclinic flows to prescribed diabatic forcing are investigated using a dry, hydrostatic, primitive equation numerical model (the North Carolina State University Geophysical Fluid Dynamics Model). A time-dependent diabatic forcing is utilized to isolate the effects of latent heat release in a midlatitude convective system. Examination of the mass-momentum adjustments to the diabatic forcing is performed with a focus on the development of an isolated midlevel wind maximum. The results of both cases suggest the formation of a midlevel wind maximum in the form of a perturbation meso-β-scale cyclone, which later propagates downstream as the heating is decreased. The scale of the perturbation cyclone remains at a sub-Rossby radius of deformation length scale. Therefore, the mass perturbations adjust to the wind perturbations as the mesocyclone propagates downstream. Transverse vertical circulations, which favor ascent on the r...}, number={8}, journal={MONTHLY WEATHER REVIEW}, author={Hamilton, DW and Lin, YL and Weglarz, RP and Kaplan, ML}, year={1998}, month={Aug}, pages={2061–2089} }
 @article{lin_deal_kulie_1998, title={Mechanisms of cell regeneration, development, and propagation within a two-dimensional multicell storm}, volume={55}, ISSN={["0022-4928"]}, DOI={10.1175/1520-0469(1998)055<1867:MOCRDA>2.0.CO;2}, abstractNote={In this study, mechanisms of cell regeneration, development, and propagation within a two-dimensional multicell storm are investigated using a numerical cloud model. The cell regeneration is explained by the advection mechanism. The following processes occur periodically during cell regeneration: (i) Near the edge of the gust front, the gust front updraft is formed by low-level convergence ahead of the gust front near the surface. (ii) The upper portion of the gust front updraft grows by midlevel inflow since the gust front propagates faster than the basic wind. (iii) The growing cell tends to produce and is flanked by strong compensating downdrafts. The upstream downdraft tends to cut off the growing cell from the gust front updraft. It is found that the period of cell regeneration is inversely proportional to the midlevel, strong relative wind speed. This advection mechanism is different from that proposed by Yang and Houze, which views the rearward propagating cell as gravity waves generated by the quasi-steady updraft moving through the ambient flow. Cell development and propagation within a two-dimensional multicell storm may be described in terms of two distinctive modes: (i) a growing mode and (ii) a propagating mode. When a growing cell reaches its maximum intensity, it splits and then propagates downstream without amplification. The dynamics of cell development and propagation is explained here by critical level argument. For the growing mode there is growth because of a conditionally unstable environment leading to steering level propagation, while for the propagating mode there is no growth because of a more stable environment leading to propagation relative to the flow (i.e., absence of critical level). It is found that the phase relationship between w′ and θ′ (w′ and u′) in the growing mode is different from that in the propagating mode and can be explained by the dominance of latent heating in the thermodynamic equation. The propagating mode is dominated by horizontal advection. The propagating mode exhibits gravity wave properties and propagates faster than the growing mode.}, number={10}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Lin, YL and Deal, RL and Kulie, MS}, year={1998}, month={May}, pages={1867–1886} }
 @article{weglarz_lin_1998, title={Nonlinear adjustment of a rotating homogeneous atmosphere to zonal momentum forcing}, volume={50}, ISSN={["0280-6495"]}, DOI={10.1034/j.1600-0870.1998.t01-4-00004.x}, number={5}, journal={TELLUS SERIES A-DYNAMIC METEOROLOGY AND OCEANOGRAPHY}, author={Weglarz, RP and Lin, YL}, year={1998}, month={Oct}, pages={616–636} }
 @article{kaplan_lin_hamilton_rozumalski_1998, title={The numerical simulation of an unbalanced jetlet and its role in the Palm Sunday 1994 tornado outbreak in Alabama and Georgia}, volume={126}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(1998)126<2133:TNSOAU>2.0.CO;2}, abstractNote={Abstract Meso-beta-scale numerical model simulations and observational data are synthesized in an effort to develop a multistage paradigm for use in forecasting tornadic convection in the southeastern United States. The case study to be utilized as an example of the multistage sequence of events is the Palm Sunday 1994 outbreak, which culminates with the development of an unbalanced mesoscale jet streak or jetlet that focuses a given region for significant values of low-level vertical wind shear, low-level confluence and vertical vorticity, midtropospheric cooling, and storm-relative helicity. The five-stage paradigm includes 1) the existence of a jet exit region accompanying a deep balanced thermally indirect circulation south of the outbreak and a return branch ageostrophic low-level southerly jet, both typically accompanying the subtropical jet stream and the leading edge of hot continental air; 2) the existence of a jet entrance region accompanying a deep balanced thermally direct circulation north of...}, number={8}, journal={MONTHLY WEATHER REVIEW}, author={Kaplan, ML and Lin, YL and Hamilton, DW and Rozumalski, RA}, year={1998}, month={Aug}, pages={2133–2165} }
 @article{kulie_lin_1998, title={The structure and evolution of a numerically simulated high-precipitation supercell thunderstorm}, volume={126}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(1998)126<2090:TSAEOA>2.0.CO;2}, abstractNote={The structure and evolution of a high-precipitation (HP) supercell thunderstorm is investigated using a threedimensional, nonhydrostatic, cloud-scale numerical model (TASS). The model is initialized with a sounding taken from a mesoscale modeling study of the environment that produced the 28 November 1988 Raleigh tornadic thunderstorm. TASS produces a long-lived convective system that compares favorably with the observed Raleigh tornadic thunderstorm. The simulated storm evolves from a multicell-type storm to a multiple-updraft supercell storm. The storm complex resembles a hybrid multicell-supercell thunderstorm and is consistent with the conceptual model of cool season strong dynamic HP supercells that are characterized by shallow mesocyclones. The origin of rotation in this type of storm is often in the lowest levels. Interactions between various cells in the simulated convective system are responsible for the transition to a supercellular structure. An intense low-level updraft core forms on the southwest flank of the simulated storm and moves over a region that is rich in vertical vorticity. The stretching of this preexisting vertical vorticity in the storm’s lowest levels is the most important vertical vorticity production mechanism during the initial stages of the main updraft’s development. Interactions with an extensive cold pool created by the storm complex are also important in producing vertical vorticity as the main updraft grows. Overall, the development of vorticity associated with the main updraft appears similar to nonsupercellular tornadic storms. However, classic supercell signatures are seen early in the simulation associated with other updrafts (e.g., formation of vortex couplet due to tilting of ambient horizontal vorticity, storm splitting, etc.) and are deemed important. In the storm’s supercell stage, rotation is sustained in the lowest levels of the storm despite large amounts of precipitation located near and within the main mesocyclone. Pulsating downdrafts periodically invigorate the storm and the gust front never occludes, thus allowing the main updraft to persist for a prolonged period of time. The storm’s intensity is also maintained by frequent updraft mergers.}, number={8}, journal={MONTHLY WEATHER REVIEW}, author={Kulie, MS and Lin, YL}, year={1998}, month={Aug}, pages={2090–2116} }
 @article{weglarz_lin_1997, title={A linear theory for jet streak formation due to zonal momentum forcing in a stably stratified atmosphere}, volume={54}, ISSN={["0022-4928"]}, DOI={10.1175/1520-0469(1997)054<0908:ALTFJS>2.0.CO;2}, abstractNote={Abstract A perturbation potential vorticity (PV) theory is developed to investigate the three-dimensional, time-dependent, linear geostrophic adjustment of a stably stratified, Boussinesq atmosphere that is disturbed from (i) quiescent equilibrium due to a localized, unbalanced, zonal wind anomaly and (ii) geostrophic equilibrium of the uniform zonal flow due to an isolated couplet of acceleration–deceleration forcing. This prescribed zonal momentum forcing propagates downstream at a speed c that is less than the basic-state zonal flow speed U and physically represents the parameterized effects of nonlinear inertial advection. Transient, dispersive inertia–gravity waves in all fields are essentially removed during the early stage of the response associated with the initial value problem. The steady-state equilibrium that conserves the initial perturbation PV is a localized, geostrophic zonal jet with meridionally confluent (diffluent) flow in its entrance (exit) region. This jet is supported by a couplet ...}, number={7}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Weglarz, RP and Lin, YL}, year={1997}, month={Apr}, pages={908–932} }
 @article{decroix_lin_schowalter_1997, title={Cellular convection embedded in the convective planetary boundary layer surface layer}, volume={67-68}, number={1997 Apr./June}, journal={Journal of Wind Engineering and Industrial Aerodynamics}, author={DeCroix, D. S. and Lin, Y. L. and Schowalter, D. G.}, year={1997}, pages={387–401} }
 @article{kaplan_koch_lin_weglarz_rozumalski_1997, title={Numerical simulations of a gravity wave event over CCOPE .1. The role of geostrophic adjustment in mesoscale jetlet formation}, volume={125}, ISSN={["1520-0493"]}, DOI={10.1175/1520-0493(1997)125<1185:NSOAGW>2.0.CO;2}, abstractNote={Mesoscale model simulations are performed in order to provide insight into the complex role of jet streak adjustments in establishing an environment favorable to the generation of gravity waves on 11–12 July 1981. This wave event was observed in unprecedented detail downstream of the Rocky Mountains in Montana during the Cooperative Convective Precipitation Experiment. The high-resolution model simulations employ a variety of terrain treatments in the absence of the complicating effects of precipitation physics in order to examine the complex interactions between orography and adiabatic geostrophic adjustment processes. Results indicate that prior to gravity wave formation, a four-stage geostrophic adjustment process modified the structure of the mid- to upper-tropospheric jet streak by creating secondary mesoscale jet streaks (jetlets) to the southeast of the polar jet streak in proximity to the gravity wave generation region (WGR). During stage I, a strong rightward-directed ageostrophic flow in the right exit region of the polar jet streak (J1) developed over west-central Montana. This thermally indirect transverse secondary circulation resulted from inertial-advective adjustments wherein momentum was transported downstream and to the right of J1 as air parcels decelerated through the exit region. During stage II, a highly unbalanced jetlet (J2) formed just northwest of the WGR in response to the inertial-advective forcing accompanying the ageostrophic circulation associated with J1. The mass field adjusted to this ageostrophic wind field. An adiabatic cooling and warming dipole resulting from this thermally indirect secondary circulation was the cause for frontogenesis and a rightward shift in the midtropospheric pressure gradients. Since this secondary circulation associated with J2 occurred above a dramatic vertical variation in the thermal wind, the vertical transport of potentially colder air from below was larger ahead of and to the right of J1, thus shifting the new jetlet (J2) well away from J1 as the mass field adjusted to the new wind field. Stage III was established when the new mass field, which developed in association with J2 during stage II, set up a dynamically unbalanced circulation oriented primarily across the stream, and directly over the WGR. This new leftward-directed ageostrophic cross-stream flow (A) formed between jetlet J2 and the original exit region of the polar jet streak J1. Finally, a midlevel mesoscale jetlet (J3) is simulated to have developed in stage IV over the WGR in response to the integrated mass flux divergence associated with both the stage II and III adjustment processes. This lower-level return branch circulation to jetlet J2 was further enhanced by velocity divergence accompanying the localized cross-stream ageostrophic wind maximum (A), which develops during stage III. The entire multistage geostrophic adjustment process required about 12 h to complete over a region encompassing approximately 400 km × 400 km.}, number={6}, journal={MONTHLY WEATHER REVIEW}, author={Kaplan, ML and Koch, SE and Lin, YL and Weglarz, RP and Rozumalski, RA}, year={1997}, month={Jun}, pages={1185–1211} }