4:15 PM - 4:30 PM
[AAS08-10] Influence of the cumulus parameterization scheme on June precipitation over the land in East Asia
Keywords:East Asian monsoon, Dynamical downscaling, Precipitation bias
Precipitation increases in East Asia during the summer monsoon season, and it is particularly intensified forming a quasi-stationary rainband during the Meiyu/Baiu season between the end of May and mid-July. Therefore, it is important to verify a simulation skill for precipitation along the Meiyu/Baiu rainband for the climate study using dynamical-downscaling product covering this region. In this study, numerical experiments with 20-km horizontal resolution were conducted using the Weather forecasting and Research (WRF) model version 3.9.1.1 during May−August from 1991 through 2015 over East Asia as a product for the LS4P/TPEMIP program (Xue et al. 2021, GMD; https://ls4p.geog.ucla.edu/). The precipitation bias over the land areas in June was intensively investigated.
In the model experiment, simulated June precipitation underestimated the observation along the Meiyu/Baiu rainband, while the overestimation was found over north and south of the rainband. The precipitation along and south of the Meiy/Baiu rain band was mainly produced by the cumulus parameterization scheme, and the microphysics precipitation was dominant over north of the rainband. Focusing over the land, the dry and wet biases in June precipitation were mainly located over south and north of the Yangtze River, respectively, which tended to be intensified in the years when spatial correlation of June precipitation was low (LCC years).
Comparing to the reanalysis dataset, simulated moisture supply to the Meiyu/Baiu rainband was weak at 850 hPa associated with more active convection over the western North Pacific. Meanwhile, the anticyclonic circulation bias developed over the northern China was slightly intensified corresponding to the low-level moisture convergence there, which would be related with the bias in the atmospheric circulation pattern at 200 hPa. In the LCC years, the moisture transport was further suppressed at 850 and 500 hPa in the reanalysis dataset because of a pair of the higher geopotential height anomaly over the northern China and the lower height anomaly over the western North Pacific. This weakening of moisture transport was also captured in the model, suggesting the influence of the lateral boundary condition (reanalysis dataset) on the simulated precipitation. In addition, positive feedback between the suppression of convection and the reduction of the horizontal moisture supply was found over the southern and southeastern China, which induced the anticyclonic circulation in the lower troposphere. This anticyclonic circulation anomaly substantially weakened the moisture transport to the southeastern China while it was intensified the moisture supply to the central and northern China in the LCC years. As a result, the dry and wet biases over south and north of the Yangtze River, respectively, were emphasized in the LCC years which enhanced the bias found in climatological precipitation. When other cumulus parameterization scheme was used, the simulated atmospheric circulation pattern was modified in East Asia, which was resulted from the disappearance of the feedback between the reduction of the moisture supply and the suppression of convection, and then the dry bias over south of the Yangtze River was reduced.
Reference: Xue, Y., et al. 2021: Impact of initialized land surface temperature and snowpack on subseasonal to seasonal prediction project, Phase I (LS4P-I): organization and experimental design. Geosci. Model. Dev., 14, 4465–4494. https://doi.org/10.5194/gmd-14-4465-2021
In the model experiment, simulated June precipitation underestimated the observation along the Meiyu/Baiu rainband, while the overestimation was found over north and south of the rainband. The precipitation along and south of the Meiy/Baiu rain band was mainly produced by the cumulus parameterization scheme, and the microphysics precipitation was dominant over north of the rainband. Focusing over the land, the dry and wet biases in June precipitation were mainly located over south and north of the Yangtze River, respectively, which tended to be intensified in the years when spatial correlation of June precipitation was low (LCC years).
Comparing to the reanalysis dataset, simulated moisture supply to the Meiyu/Baiu rainband was weak at 850 hPa associated with more active convection over the western North Pacific. Meanwhile, the anticyclonic circulation bias developed over the northern China was slightly intensified corresponding to the low-level moisture convergence there, which would be related with the bias in the atmospheric circulation pattern at 200 hPa. In the LCC years, the moisture transport was further suppressed at 850 and 500 hPa in the reanalysis dataset because of a pair of the higher geopotential height anomaly over the northern China and the lower height anomaly over the western North Pacific. This weakening of moisture transport was also captured in the model, suggesting the influence of the lateral boundary condition (reanalysis dataset) on the simulated precipitation. In addition, positive feedback between the suppression of convection and the reduction of the horizontal moisture supply was found over the southern and southeastern China, which induced the anticyclonic circulation in the lower troposphere. This anticyclonic circulation anomaly substantially weakened the moisture transport to the southeastern China while it was intensified the moisture supply to the central and northern China in the LCC years. As a result, the dry and wet biases over south and north of the Yangtze River, respectively, were emphasized in the LCC years which enhanced the bias found in climatological precipitation. When other cumulus parameterization scheme was used, the simulated atmospheric circulation pattern was modified in East Asia, which was resulted from the disappearance of the feedback between the reduction of the moisture supply and the suppression of convection, and then the dry bias over south of the Yangtze River was reduced.
Reference: Xue, Y., et al. 2021: Impact of initialized land surface temperature and snowpack on subseasonal to seasonal prediction project, Phase I (LS4P-I): organization and experimental design. Geosci. Model. Dev., 14, 4465–4494. https://doi.org/10.5194/gmd-14-4465-2021