Impact of Parameterized Topographic Drag on a Simulated Northeast China Cold Vortex

Abstract

Northeast China cold vortex (NECV) is the major influencing weather system in northern China. Yet the impacts of complex terrain on the evolution of NECV remains poorly understood. This work studies the influence of subgrid orographic drag (SOD) on a heavy‐rain‐producing NECV occurred in July 2011 using the Weather Research and Forecasting model. A series of numerical experiments are conducted with different parameterizations of SOD including turbulent orographic form drag (TOFD), flow blocking drag (FBD), and mountain wave drag (MWD). Results show that the NECV intensity is overestimated in the absence of SOD parameterization, accompanied with too‐low geopotential height (GPH) and too‐strong horizontal winds. The parameterization of TOFD can significantly decelerate the 10‐m winds, whereas the FBD and MWD play a minor role. However, the influence of TOFD is overwhelmed by FBD and MWD in the troposphere, especially the latter. This implies that the breaking of mountain waves play a more important role in weakening the NECV than the low‐level flow blocking. The lower‐tropospheric MWD directly weakens the convergence and ascent motion of the NECV, producing an anti‐cyclonic circulation that uplifts the GPH under the constraint of quasi‐geostrophic vertical vorticity. This MWD‐induced circulation indirectly weakens the NECV in the mid‐upper troposphere by producing a warm advection that counters the low‐level cold advection to the southwest of the NECV. The findings provide useful insights into the impacts of complex terrain on the NECV and highlight the importance of topographic drag parameterization in the simulation and short‐range forecast of NECV.

Reducing Winter Precipitation Biases Over the Western Tibetan Plateau in the Model for Prediction Across Scales (MPAS) With a Revised Parameterization of Orographic Gravity Wave Drag

“…The formation of this cyclonic circulation difference can be readily understood from the equation of quasi‐geostrophic vertical vorticity including the OGWD (see Equation 5 in Xu et al. (2023)), that is, $$$\frac{\partial {\zeta }_{g}}{\partial t}=-{\mathbf{V}}_{\mathbf{g}}\cdot \nabla \left({\zeta }_{g}+f\right)+{f}_{0}\frac{\partial \omega }{\partial p}+\left(\frac{\partial {G}_{y}}{\partial x}-\frac{\partial {G}_{x}}{\partial y}\right),$$$ where ζ g is the geostrophic vertical vorticity, V g is the geostrophic wind, f = f 0 + βy is the Coriolis parameter, ω is the vertical velocity in pressure coordinate, and G x and G y represent the parameterized OGWD in the zonal and meridional directions, respectively.…”

“…An alternative and efficient way is to improve the parameterization of orographic drag caused by unresolved complex terrain in coarse‐resolution models (i.e., subgrid‐scale orography, SSO), which greatly affects the atmospheric circulation and WVT over the TP. Depending on the atmospheric conditions (e.g., wind speed and stratification) and the topographic features (e.g., height and width), complex terrain can produce three types of orographic drag including orographic gravity wave drag (OGWD), flow‐blocking drag and turbulent orographic form drag that are caused by the breaking of orographic gravity waves (OGWs), blocking of low‐level flow, and terrain‐induced boundary layer turbulence, respectively (Beljaars et al., 2004; Choi & Hong, 2015; Kim et al., 2003; Koo et al., 2018; Sandu et al., 2019; Teixeira & Yu, 2014; Xu et al., 2023; Xue et al., 2021; Zhang et al., 2020). X. Zhou et al.…”

Effects of Precipitation Latent Heating on Structure and Evolution of Northeast China Cold Vortex: A PV Perspective

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Cold vortex is a closed cyclonic circulation with a cold core, usually found in the middle to upper troposphere at middle to high latitudes (Hsieh, 1949;Palmén & Newton, 1969). On the middle-to-upper level weather charts, cold vortices usually exhibit themselves as cut-off lows (e.g., Porcù et al, 2007;Xu et al, 2023). Northeastern China extending into the Siberia region is one of the preferred areas for cold vortices in the Northern Hemisphere (Bell & Bosart, 1989;Hu et al, 2010;Nieto et al, 2005).

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