Effects of Parameterized Orographic Drag on Weather Forecasting and Simulated Climatology Over East Asia During Boreal Summer | CU Experts

AbstractThe impact of subgrid orographic drag on weather forecasting and simulated climatology over East Asia in boreal summer is examined using two parameterization schemes in a global forecast model. The schemes consider gravity wave drag (GWD) with and without lower‐level wave breaking drag (LLWD) and flow‐blocking drag (FBD). Simulation results from sensitivity experiments verify that the scheme with LLWD and FBD improves the intensity of a summertime continental high over the northern part of the Korean Peninsula, which is exaggerated with GWD only. This is because the enhanced lower tropospheric drag due to the effects of lower‐level wave breaking and flow blocking slows down the wind flowing out of the high‐pressure system in the lower troposphere. It is found that the decreased lower‐level divergence induces a compensating weakening of middle‐ to upper‐level convergence aloft. Extended experiments for medium‐range forecasts for July 2013 and seasonal simulations for June to August of 2013–2015 are also conducted. Statistical skill scores for medium‐range forecasting are improved not only in low‐level winds but also in surface pressure when both LLWD and FBD are considered. A simulated climatology of summertime monsoon circulation in East Asia is also realistically reproduced.

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