利用WRF-3DVAR同化常规观测资料对近地层风速预报的改进试验

Experiment of Surface-Layer Wind Forecast Improvement by Assimilating Conventional Data with WRF-3DVAR

利用WRF 3DVAR同化系统和Evenson提出的方法在分析时刻添加扰动形成扰动型初始场,并在此基础上同化常规观测资料(包括固定站点的探空观测和常规地面观测),通过比较WRF3DVAR系统对整层大气的初始(分析)场及预报场的改进,检验了同化常规观测资料后WRF模式对研究区域内近地层风速的预报效果。结果表明,同化常规观测资料对初始场有改进,且对低层大气风场和温度场的改进较FNL资料明显;GFS同化常规观测资料后生成的初始场和FNL资料提供的初始场对风速和温度的预报在不同气压层存在不同的预报时效,低层(1000 hPa)风速和温度预报在前36 h改善明显,而在较高的500 hPa和200 hPa上风速预报在前36 h改进明显,温度预报则只在前12 h得到了改善;无论是采用FNL资料还是同化常规观测资料作为初始场,对近地层风速预报均在前36 h有改进,表明对于近地面风速这种短时间内变化较大的变量,同化与之时间和空间上较为接近的资料可能改善其预报效果。

Using WRF 3DVAR assimilation system,add the perturbations with the method advanced by Evenson at initial time to generate disturbance type initial fields and assimilate conventional observation data( including radiosonde observation and conventional ground observation),comparing the improvement effects of the whole atmosphere for initial and forecast fields with WRF 3DVAR system,the forecast effects of the local atmosphere for near-surface wind was also verified. The results show that: Compared to the GFS forecast directly,assimilation of conventional data improves initial fields,especially for wind and temperature fields in lower layer compared with the initial fields produced by FNL data; The initial fields produced by FNL data and assimilation of conventional data have the different valid forecast time at different pressure levels,the forecast effects of wind and temperature are improved within 36 h at lower pressure level( 1000 hPa),on 500 hPa and 200 hPa,the valid forecast time of wind and temperature is 36 h and 12 h respectively; No matter FNL data or assimilation of conventional data,the forecast improvements of near-surface layer wind are only within 36 h,this implies that the forecasting effects of variables as wind,which changes greatly in short time,may improve remarkably if assimilating data that close to variables itself in spatial and temporal.