@article{brennan_lackmann_koch_2004, title={The impact of a split-front rainband on Appalachian cold-air damming erosion}, volume={85}, ISSN={["1520-0477"]}, DOI={10.1175/BAMS-85-7-935}, abstractNote={AFFILIATIONS: BRENNAN AND LACKMANN—Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina; KOCH—NOAA/Forecast Systems Laboratory, Boulder, Colorado CORRESPONDING AUTHOR: Michael J. Brennan, Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, 1125 Jordan Hall, Box 8208, Raleigh, NC 27695-8208 E-mail: mike_brennan@ncsu.edu}, number={7}, journal={BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY}, author={Brennan, MJ and Lackmann, GM and Koch, SE}, year={2004}, month={Jul}, pages={935–939} }
 @article{businger_adams_koch_kaplan_2001, title={Extraction of geopotential height and temperature structure from profiler and rawinsonde winds}, volume={129}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(2001)129<1729:EOGHAT>2.0.CO;2}, abstractNote={Mesoscale height and temperature fields can be extracted from the observed wind field by making use of the full divergence equation. Mass changes associated with irrotational ageostrophic motions are retained for a nearly complete description of the height field. Above the boundary layer, in the absence of friction, the divergence equation includes terms composed of the components of the wind and a Laplacian of the geopotential height field. Once the mass field is determined, the thermal structure is obtained through application of the hypsometric equation. In this paper an error analysis of this divergence method is undertaken to estimate the potential magnitude of errors associated with random errors in the wind data. Previous applications of the divergence method have been refined in the following ways. (i) The domain over which the method is applied is expanded to encompass the entire STORM-FEST domain. (ii) Wind data from 23 profiler and 38 rawinsonde sites are combined in the analysis. (iii) Observed profiler and rawinsonde data are interpolated to grid points through a modified objective analysis, and (iv) the variation in elevation of the profiler sites is taken into account. The results of the application of the divergence method to the combined wind data from profiler and rawinsonde sites show good agreement between the retrieved heights and temperatures and the observed values at rawinsonde sites. Standard deviations of the difference between the retrieved and observed data lie well within the precision of the rawinsonde instruments. The difference field shows features whose magnitude is significantly larger than the errors predicted by the error analysis, and these features are systematic rather than random in nature, suggesting that the retrieved fields are able to resolve mesoscale signatures not fully captured by the rawinsonde data alone. The divergence method is also applied solely to the profiler data to demonstrate the potential of the divergence method to provide mass and thermal fields on a routine basis at synoptic times when operational rawinsonde data are not available. A comparison of the heights derived from the profiler winds with those independently measured by rawinsondes indicates that valuable information on the evolution of atmospheric height and temperature fields can be retrieved between conventional rawinsonde release times through application of the divergence method. The implications of the results for applications of the method in weather analysis and in numerical weather prediction are discussed.}, number={7}, journal={MONTHLY WEATHER REVIEW}, author={Businger, S and Adams, ME and Koch, SE and Kaplan, ML}, year={2001}, pages={1729–1739} }
 @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={Abstract 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 move...}, 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{koch_2001, title={Real-time detection of split fronts using mesoscale models and WSR-88D radar products}, volume={16}, ISSN={["1520-0434"]}, DOI={10.1175/1520-0434(2001)016<0035:RTDOSF>2.0.CO;2}, abstractNote={Abstract A structured methodology for detecting the presence of split cold fronts in an operational forecast environment is developed and applied to a case in which a split front passed over a region of cold air damming in the southeastern United States. A real-time mesoscale model and various products from the WSR-88D—including the velocity–azimuth display wind profile (VWP) and hodograph products, plus a thermal advection retrieval scheme applied to the VWP data—are used to study this split front and an associated convective rainband that occurred on 19 December 1995. Wet-bulb temperature and vertical motion forecasts at 700 hPa from the model revealed the arc-shaped split front 300–500 km ahead of the surface cold front. As this midtropospheric front passed across the surface warm front and entered the cold air damming region, model vertical cross-section analyses showed that it created a deep elevated layer of potential instability. Furthermore, an ageostrophic transverse circulation associated with t...}, number={1}, journal={WEATHER AND FORECASTING}, author={Koch, SE}, year={2001}, month={Feb}, pages={35–55} }
 @article{zhang_koch_davis_kaplan_2001, title={Wavelet analysis and the governing dynamics of a large-amplitude mesoscale gravity-wave event along the East Coast of the United States}, volume={127}, DOI={10.1256/smsqj.57701}, abstractNote={Detailed diagnostic analyses are performed upon a mesoscale numerical simulation of a well-observed gravity-wave event that occurred on 4 January 1994 along the East Coast of the United States. The value of using wavelet analysis to investigate the evolving gravity-wave structure and of using potential vorticity (PV) inversion to study the nature of the flow imbalance in the wave generation region is demonstrated. The cross-stream Lagrangian Rossby number, the residual in the nonlinear balance equation, and the unbalanced geopotential-height field obtained from PV inversion are each evaluated for their usefulness in diagnosing the flow imbalance. All of these fields showed clear evidence of strong imbalance associated with a middle-to-upper tropospheric jet streak, and tropopause fold upstream of the large-amplitude gravity wave several hours before the wave became apparent at the surface. Analysis indicates that a train of gravity waves was continuously generated by geostrophic adjustment in the exit region of the unbalanced upper-level jet streak as it approached the inflection axis in the height field immediately downstream of the maximum imbalance associated with the tropopause fold. A split front in the middle troposphere, characterized by the advance of the dry conveyor belt above the warm front, was overtaken by one of these propagating waves. During this merger process, a resonant interaction resulted, which promoted the rapid amplification and scale contraction of both the incipient wave (nonlinear wave development) and the split front (frontogenesis). The gravity wave and front aloft became inseparable following this merger. The situation became even more complex within a few hours as the vertical motion enhanced by this front-wave interaction acted upon a saturated, potentially unstable layer to produce elevated moist convection. An analysis of the temporal changes in the vertical profile of wave energy flux suggests that moist convective downdraughts efficiently transported the wave energy from the midlevels downward beneath the warm-front surface, where the wave became ducted. However, pure ducting was not sufficient for maintaining and amplifying the waves; rather, wave-CISK (Conditional Instability of the Second Kind) was crucial. This complex sequence of nonlinear interactions produced a long-lived, large-amplitude gravity wave that created hazardous winter weather and disrupted society over a broad and highly populated area. Although gravity waves with similar appearance to this large-amplitude wave of depression occasionally have been seen in other strong cyclogenesis cases involving a jet streak ahead of the upper-level trough axis, it is unknown whether other such events share this same sequence of interactions.}, number={577}, journal={Quarterly Journal of the Royal Meteorological Society}, author={Zhang, F. Q. and Koch, S. E. and Davis, C. A. and Kaplan, M. L.}, year={2001}, pages={2209–2245} }
 @article{zhang_koch_davis_kaplan_2000, title={A survey of unbalanced flow diagnostics and their application}, volume={17}, ISSN={["0256-1530"]}, DOI={10.1007/s00376-000-0001-1}, number={2}, journal={ADVANCES IN ATMOSPHERIC SCIENCES}, author={Zhang, FQ and Koch, SE and Davis, CA and Kaplan, ML}, year={2000}, pages={165–183} }
 @article{zhang_koch_2000, title={Numerical simulations of a gravity wave event over CCOPE. Part II: Waves generated by an orographic density current}, volume={128}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(2000)128<2777:NSOAGW>2.0.CO;2}, abstractNote={A mesoscale numerical model and detailed observations are used to investigate the generation and maintenance of a mesoscale gravity wave event observed in eastern Montana on 11 July 1981 during the Cooperative Convective Precipitation Experiment (CCOPE). It is shown that the interaction between an orographic density current and a mountain barrier leads to the generation of the gravity waves. The simulation results suggest the following four-stage conceptual model. During stage I, shortly after sunset, the remnant up-branch of a thermally driven upslope flow east of the Rockies was driven back toward the mountain by the pressure gradient force associated with a cool pool over North Dakota. The nocturnal stable layer over eastern Montana was strengthened during passage of this density current. During the 1‐2-h transition period of stage II, the advancing density current became blocked as it encountered the higher terrain. An isentropic ridge developed above the original warm lee trough due to strong adiabatic cooling caused by the sustained upward motion in the presence of orographic blocking. During stage III, an even stronger upward motion center formed to the east of the density current head updraft in response to an eastward horizontal pressure gradient force produced by the isentropic ridge. In stage IV, as the density current head collapsed and downward motion developed to the west of the original updraft in quadrature phase with the isentropic perturbation, a gravity wave was generated. This wave propagated eastward with the mean wind (opposite to the motion of the earlier density current) and was maintained by the strong wave duct established earlier by the density current. Thus, the mountain‐plains circulation may at times generate mesoscale gravity waves (and deep convection) hours after diurnal heating has ended.}, number={8}, journal={MONTHLY WEATHER REVIEW}, author={Zhang, FQ and Koch, SE}, year={2000}, month={Aug}, pages={2777–2796} }
 @article{trexler_koch_2000, title={The life cycle of a mesoscale gravity wave as observed by a network of Doppler wind profilers}, volume={128}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(2000)128<2423:TLCOAM>2.0.CO;2}, abstractNote={Abstract For the first time, an analysis has been made of the evolving vertical structure of a long-lived mesoscale gravity wave that exerted a strong influence upon the precipitation distribution across a large area. This paper describes this gravity wave system on 14 February 1992, which was observed using a combination of a surface mesonetwork, digital satellite and radar imagery, and several Doppler wind profilers. The resulting vertical structures are compared to the predictions of linear stability theory. Since the signature of the gravity waves in the profiler vertical beam data was often complicated by the presence of precipitation, a kinematic method was developed for estimating the vertical air motions during these periods. The resultant time–height fields show vertical and horizontal winds that are consistent with a gravity wave conceptual model, the microbarograph traces, and the cloud and precipitation patterns. In the early stages of development, a strong vertically erect wave of depression ...}, number={7}, journal={MONTHLY WEATHER REVIEW}, author={Trexler, CM and Koch, SE}, year={2000}, month={Jul}, pages={2423–2446} }
 @article{koch_clark_1999, title={A nonclassical cold front observed during COPS-91: Frontal structure and the process of severe storm initiation}, volume={56}, ISSN={["0022-4928"]}, DOI={10.1175/1520-0469(1999)056<2862:ANCFOD>2.0.CO;2}, abstractNote={Abstract This case study addresses the issue of gravity current and bore development at surface cold fronts, and the role of these phenomena in the generation of severe frontal convection. The event investigated occurred on 27 April 1991 during the Cooperative Oklahoma Profiler Studies 1991 field project. The development of a bore from a gravity current–like structure along a cold front, the subsequent propagation of the bore ahead of the front on a low-level inversion, and the process of severe thunderstorm development along the front are revealed by a dense network of remote sensing and other special observations. Evidence for the gravity current and bore is strengthened by comparisons made between the synthesized observations and theory. The bore developed after a nocturnal inversion, which acted as a waveguide, had become established. The bore and gravity current were both evident as “fine lines” in the radar reflectivity displays. A microscale envelope of enhanced water vapor with an embedded roll cl...}, number={16}, journal={JOURNAL OF THE ATMOSPHERIC SCIENCES}, author={Koch, SE and Clark, WL}, year={1999}, month={Aug}, pages={2862–2890} }
 @misc{koch_1999, title={Comments on "Numerical simulations of an observed narrow cold-frontal rainband"}, volume={127}, ISSN={["1520-0493"]}, DOI={10.1175/1520-0493(1999)127<0252:consoa>2.0.co;2}, abstractNote={In a recent paper, Chen et al. (1997, hereafter C97) presented a detailed mesoscale model simulation of the intense cold front event of 28 December 1988 in Maryland studied by Koch and Kocin (1991, hereafter KK91). Although the findings of C97 are interesting, there are several issues that are of concern. In order to put these matters into proper perspective, it is first necessary to understand that the observational synthesis conducted by KK91 suggested that the frontal-scale contraction process culminating in the generation of this narrow cold-frontal rainband (NCFR) was the result of a complex series of interactions between phenomena on several scales. First of all, the NCFR developed following merger of an arctic front with a stalled cold front over the Appalachian Mountains. The merged frontal system displayed a pressure jump at its leading edge, which appeared to be dynamically linked to a deep tropopause fold. An ageostrophic momentum surge associated with this isallobaric feature appeared to have initiated rapid frontogenesis over the lee slopes of the Appalachians. KK91 hypothesized that the subsequent descent of the merged frontal system down the lee slopes and evaporative cooling of intense precipitation that developed within the NCFR led to the formation of a new microscale pressure jump of 8-mb amplitude and a gravity current–like microstructure at the leading edge of the front. They explained the intensity and maintenance of the NCFR on the basis of a balance between the solenoidally forced vorticity within the gravity current and the vorticity produced by strong vertical wind shear associated with a prefrontal low-level jet, in a manner described by Rotunno et al. (1988). The fundamental issue that was raised by the KK91}, number={2}, journal={MONTHLY WEATHER REVIEW}, author={Koch, SE}, year={1999}, month={Feb}, pages={252–257} }
 @article{koch_siedlarz_1999, title={Mesoscale gravity waves and their environment in the central United States during STORM-FEST}, volume={127}, ISSN={["0027-0644"]}, DOI={10.1175/1520-0493(1999)127<2854:MGWATE>2.0.CO;2}, abstractNote={Abstract In an effort to better understand mesoscale gravity waves in winter storms in the central United States—their frequency of occurrence, wave characteristics, the general conditions under which they occur, and their effects upon the weather—mesoscale surface and rawinsonde data as well as radar and satellite imagery collected during the Storm-scale Operational and Research Meteorology–Fronts and Experimental System Test are analyzed. In addition, factors affecting the ability of objective surface map analysis to properly represent the waves are investigated. Thirteen coherent pressure pulse events with amplitudes of 0.2–4.0 mb and periods of 1–6 h were identified in the surface pressure data during the 6 weeks of the project, involving 34% of the total hours investigated. A variety of wave types occurred, including wavelets, wave trains, and singular waves. The three largest amplitude events were analyzed in detail using autospectral analysis and a Barnes time-to-space conversion objective analysis...}, number={12}, journal={MONTHLY WEATHER REVIEW}, author={Koch, SE and Siedlarz, LM}, year={1999}, month={Dec}, pages={2854–2879} }
 @article{wetzel_dempsey_nilsson_ramamurthy_koch_moody_knight_murphy_fulker_marlino_et al._1998, title={Faculty workshop on using instructional technologies and satellite data for college-level education in the atmospheric and earth sciences}, volume={79}, ISSN={["0003-0007"]}, DOI={10.1175/1520-0477-79.10.2153}, abstractNote={An education-oriented workshop for college faculty in the atmospheric and related sciences was held in Boulder, Colorado, during June 1997 by three programs of the University Corporation for Atmospheric Research. The objective of this workshop was to provide faculty with hands-on training in the use of Web-based instructional methods for specific application to the teaching of satellite remote sensing in their subject areas. More than 150 faculty and associated scientists participated, and postworkshop evaluation showed it to have been a very successful integration of information and activities related to computer-based instruction, educational principles, and scientific lectures.}, number={10}, journal={BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY}, author={Wetzel, M and Dempsey, D and Nilsson, S and Ramamurthy, M and Koch, S and Moody, J and Knight, D and Murphy, C and Fulker, D and Marlino, M and et al.}, year={1998}, month={Oct}, pages={2153–2160} }
 @article{koch_hamilton_kramer_langmaid_1998, title={Mesoscale dynamics in the Palm Sunday tornado outbreak}, volume={126}, ISSN={["1520-0493"]}, DOI={10.1175/1520-0493(1998)126<2031:MDITPS>2.0.CO;2}, abstractNote={Abstract Radar and satellite imagery suggest that strong mesoscale forcing occurred in the Palm Sunday tornado outbreak on 27 March 1994. Parallel lines of severe thunderstorms within each of three mesoscale convective systems developed just ahead of a cold front in Mississippi and Alabama on this date. Analyses of routine meteorological observations, barograph data, and forecasts from the Eta and NGM models and a mesoscale research model (MASS) are used to examine the relative roles of large-scale dynamics and mesoscale processes in triggering and organizing the mesoscale convection. Quasigeostrophic forcing was absent in the outbreak region. Likewise, a thermally direct circulation system transverse to the upper-level jet that was present to the northwest of the outbreak region was decoupled from the strong low-level ascent occurring in northern Alabama and Mississippi at the time of the outbreak. Strong ageostrophic frontogenesis in the presence of conditional symmetric instability (CSI) was the chief ...}, number={8}, journal={MONTHLY WEATHER REVIEW}, author={Koch, SE and Hamilton, D and Kramer, D and Langmaid, A}, year={1998}, month={Aug}, pages={2031–2060} }
 @article{koch_ray_1997, title={Mesoanalysis of summertime convergence zones in central and eastern North Carolina}, volume={12}, ISSN={["0882-8156"]}, DOI={10.1175/1520-0434(1997)012<0056:MOSCZI>2.0.CO;2}, abstractNote={Abstract It is demonstrated that it is possible to perform informative mesoanalysis of summertime convergence boundaries in the southeastern United States by combining capabilities of the new WSR-88D Doppler radar with Geostationary Operational Environmental Satellite imagery and conventional surface data. Observed phenomena are identified as thunderstorm outflow boundaries, sea-breeze fronts, horizontal convective rolls, deep synoptic-scale fronts, prefrontal troughs, shallow fronts (airmass boundaries lacking upper-level support), stationary and propagating boundaries of unknown origin, and the “Piedmont trough,” which is apparently a new feature discovered in the course of this research. The transition zone between the Piedmont and the Coastal Plain was found to be a preferred location for convergence boundaries. An unexpectedly far inland advance of the sea breeze to central North Carolina occurred in some instances. The very sensitive “clear air mode” of the WSR-88D radar, when used in combination wi...}, number={1}, journal={WEATHER AND FORECASTING}, author={Koch, SE and Ray, CA}, year={1997}, month={Mar}, pages={56–77} }
 @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={Abstract 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 i...}, 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} }
 @article{koch_ohandley_1997, title={Operational forecasting and detection of mesoscale gravity waves}, volume={12}, ISSN={["0882-8156"]}, DOI={10.1175/1520-0434(1997)012<0253:OFADOM>2.0.CO;2}, abstractNote={Abstract Mesoscale gravity waves display periods of 1–4 h, have wavelengths of 50–500 km, and can have important effects upon the sensible weather. Real-time prediction, detection, and nowcasting of these mesoscale phenomena is shown to be feasible, due to recent major advances in operational observing and modeling systems. The ability to predict the likelihood of a gravity wave event rests upon recognizing the synoptic flow pattern in which such waves are consistently found to occur. The delineation of the most likely region for wave activity can be further refined by computing simple indicators of unbalanced flow and conducting a cursory search for a suitable wave “duct” with meso-Eta Model data. Particular emphasis should be placed on propagating unbalanced fields. Whenever and wherever a suitable gravity wave environment is found, the Automated Surface Observing System pressure data should be carefully monitored for evidence of gravity wave activity. An automated gravity wave detection system is devel...}, number={2}, journal={WEATHER AND FORECASTING}, author={Koch, SE and OHandley, C}, year={1997}, month={Jun}, pages={253–281} }
 @article{koch_aksakal_mcqueen_1997, title={The influence of mesoscale humidity and evapotranspiration fields on a model forecast of a cold-frontal squall line}, volume={125}, ISSN={["1520-0493"]}, DOI={10.1175/1520-0493(1997)125<0384:TIOMHA>2.0.CO;2}, abstractNote={Abstract Satellite imagery and rain gauge data are combined to create mesoscale detail in the initial states of relative humidity (RH) and surface moisture availability (M) for a mesoscale model simulation. The most profound impact of inserting the mesoscale initial fields was the development of a strong vertical circulation transverse to an intensifying cold front that triggered an intense frontal rainband similar to a severe squall line that was observed to develop explosively. This paper explores the causative factors leading to the formation of this intense circulation and the sensitivity of the model to the mesoscale initial fields. A substantial gradient in the initialized RH and M fields occurred across the cold front in the region where the observed frontal squall line formed. In contrast to the control run, the model simulations that incorporated the mesoscale initial analysis displayed considerable daytime warming just ahead of the front. This warming was due principally to a reduction in the RH...}, number={3}, journal={MONTHLY WEATHER REVIEW}, author={Koch, SE and Aksakal, A and McQueen, JT}, year={1997}, month={Mar}, pages={384–409} }