@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{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{lu_liu_zhang_an_dodson_1999, title={Astronomical calibration of loess-paleosol deposits at Luochuan, central Chinese Loess Plateau}, volume={154}, ISSN={["0031-0182"]}, DOI={10.1016/S0031-0182(99)00113-3}, abstractNote={The 140 m loess–paleosol profile at Luochuan in the central Chinese Loess Plateau was sampled at 5-cm intervals in loess units and at 3 cm in paleosol units, in order to obtain a high resolution climatic record covering the past 2.5 million years. All samples were measured for magnetic susceptibility, which is regarded as a good proxy index of the East Asian summer monsoon strength. On the basis of the astronomical theory of Pleistocene climatic change, an age model of the Luochuan loess–paleosol sequence was developed by tuning the magnetic susceptibility record to time-series of insolation changes. The results show that the ages of the boundaries between the Malan and Lishi, and Lishi and Wucheng loess formations are 71 and 1320 kyr BP, respectively. The onset of loess accumulation is at 2470 kyr BP. Our age model was tested by comparing the orbitally derived ages with absolute age determinations of magnetic reversals, and cross-spectrum analyzing with solar radiation variations for summer at 65°N. These indicate that the calibration provides a reliable time scale for the Luochuan loess–paleosol deposit.}, number={3}, journal={PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY}, author={Lu, HU and Liu, XD and Zhang, FQ and An, ZS and Dodson, J}, year={1999}, month={Nov}, pages={237–246} }