利用同化资料改进WRF-Chem对华北秋季PM2.5预报的研究

Improvement of WRF-Chem for PM2.5 forecasting using assimilated data in North China Plain in autumn

中文关键词:  WRF-Chem, WRFDA-Chem, 气象-气溶胶联合资料同化, 耦合预报

英文关键词:WRF-Chem, WRFDA-Chem, Meteorology-aerosol joint data assimilation, Coupled forecast

中文摘要:

      气溶胶初始场同化能够提高WRF-Chem气象-气溶胶耦合预报的准确性。为了讨论气溶胶同化在不同时刻对耦合模式预报的影响,针对2015年10月一次重度霾污染过程,进行了一天四个不同时刻的气象-气溶胶联合同化及短时预报试验研究。结果表明,在同化气象资料的基础上同化气溶胶观测资料能够改善不确定性较大的排放源清单带来的模拟高估问题,减小初始场PM2.5的正偏差；随着初始场PM2.5浓度的减少,气溶胶导致的地面辐射的降低减弱,使得日间时刻6小时预报场的向下短波辐射量增加；日间近地面温度和湿度对辐射量变化的响应(增温减湿)呈现为在空间大面积上的吻合性和时间上的同步性,这种响应在循环滚动预报的影响下即使在夜间也得到了延续；近地面增温减湿的结构有助于边界层的向上发展,从而促进了气溶胶的向上传输,最终进一步减弱了预报场对地表PM2.5的高估。因此,气溶胶同化带来的初始场PM2.5信息的改善,使得6 小时耦合预报的结果更加准确。

英文摘要:

      Assimilation of the initial aerosol field can improve the accuracy of coupled meteorology-aerosol forecasts in WRF-Chem. To discuss the influence of the aerosol assimilation on forecasts of coupled model at different time, for a heavy haze pollution process in October 2015, the experimental study of joint meteorology-aerosol assimilation and short-term forecast at four different time of a day was conducted. The results show that, assimilating aerosol observations on the basis of assimilated meteorological data can improve the overestimation of simulation caused by the emission source inventory with large uncertainty, and reduce the positive bias of PM2.5 in the initial field; with the decrease of PM2.5 concentration in the initial field, the reduction of surface radiation caussed by aerosol is weakened, which makes the downward shortwave radiation in the 6-hour forecast field increase in the daytime. The response of near-surface temperature and humidity to radiation changes (warming and humidity reduction) during the daytime is spatially coincident over a large area and temporally synchronized, which is continued even at night under the influence of the circular rolling forecast; the structure of the near-surface warming and humidity reduction contributes to the upward development of the boundary layer, which in turn promotes the upward transport of aerosols, and ultimately further attenuates the overestimation of surface PM2.5 by the forecast field. Consequently, the improvement of the initial PM2.5 information due to aerosol assimilation makes the 6-hour coupled forecasts more accurate.