Impacts of Gravity Wave Drag Parameterizations on the Middle Atmosphere in Korea Institute of Atmospheric Prediction Systems-Global Model 

Thursday, 18 December 2014
Hyun-Joo Choi and Emilia Kyung Jin, KIAPS Korea Insititute of Atmospheric Prediction Systems, Seoul, South Korea
The initial version of Korea Institute of Atmospheric Prediction Systems-Global Model (KIAPS-GM) with a cubed sphere gird of ne30np4 resolution (~1ox1o) and 70 vertical levels up to about 85 km was developed late last year. For reasonable middle atmosphere simulations, the model uses parameterizations of orograhpic and nonorographic gravity wave drag (GWD). The orographic GWD parameterization is based on the McFarlane scheme, and the nonorographic GWD parameterization is based on the ultra-simple spectral parameterization (USSP) scheme. In order to obtain results in good agreement with observations, some tunable parameters included in the GWD parameterizations are adjusted in the range of physically reasonable values.

In this study, the impacts of GWD parameterizations on the middle atmosphere are investigated and their performances are evaluated against observations and reanalysis data. For this, a pair of simulations is performed: one initialized by ECMWF Interim Reanalysis data for 1 June 2008, the other one for 1 December 2008, respectively. The results during two weeks after a one month spin-up period are analyzed. In these simulations, model captures a cold summer polar mesopause and a warm winter polar stratopause reasonably, which means that model produce a realistic meridional circulation. The horizontal and vertical structure of zonal-mean zonal wind is also realistically simulated although summer easterlies and winter polar night jet are a little stronger and poleward and equatorward vertical inclinations of the easterly and westerly jets are underestimated compared with the observations. Recently, we also implemented source-based parameterizations schemes of nonorograhpic GWD (convective and frontal GWD) into the latest version of the KIAPS-GM for more physically based parameterizations of GWD. The impacts of the source-based GWD schemes are compared with those of the USSP scheme and their performances are also evaluated against the observations and reanalysis data. The detailed results will be shown at the conference.