青藏高原新增探空资料同化对南疆夏季降水预报的影响

Impact of Assimilating the New Radiosonde Data on Qinghai-Tibetan Plateau on Summer Rainfall Forecast over Southern Xinjiang

利用第三次青藏高原大气科学试验中青藏高原西部新增3个探空站(狮泉河、申扎、改则)的探空资料,基于中尺度数值(WRF)模式和GSI同化系统,选取2015年夏季南疆两次不同类型(南亚高压双体型和单体型)的强降水过程进行同化敏感试验,以初步评估新增3个站探空资料同化对南疆夏季降水预报的影响。从初始场物理量的增量场来看,同化高原3个站探空资料对两次过程的初始场均有一定改进,对南亚双体型过程的改进较显著,这可能与其偏南气流及上下游效应较强有关。中、高层物理量的增量中心均出现在高原中、西部,分别对应申扎和狮泉河两站,并向周边地区逐渐减小,南疆地区表现为弱的正或负增量。虽然高原探空资料均在600 h Pa以上,通过动力调整对低层物理量也有一定影响。同化后低层的散度和湿度增量中心出现在高原西南侧,南疆地区变化较小。随着模式时间积分,各高度上的物理量和降水影响系统调整效果逐渐显著,总体使得200 h Pa副热带长波槽有所加深、南疆上空的偏南急流得到加强,500 h Pa低值系统强度有所减弱,850 h Pa的散度和湿度在南疆地区均有显著调整,但低层散度和湿度在南疆西部强降水中心调整相对较小。从降水预报结果来看,同化高原3个站探空资料后,对两次过程的小量级降水评分显著提高,即对降水落区预报能力有所提高;但对强降水中心结果影响不大,即对局地性强降水的预报能力仍有所欠缺。

Using the radiosonde data of the three newly-built stations （ Shiquanhe, Shenzha and Gaize） on the Qinghai-Tibetan Plateau （QTP） in the third Tibetan Plateau Experiment of Atmospheric Sciences （TIPEX）, em- ploying the Weather Research and Forecasting （WRF） model and the Gridpoint Statistical Interpolation （GSI） system, two summer rainfall processes occurred in Southern Xinjiang in 2015, in the background of double-body （Process I ） and one-body （Process II ） of the South Asia High （ SAH）, respectively, were selected to con- duct the data assimilation sensitive experiments, in order to assess the impacts of assimilating the new radiosonde data on the QTP upon summer rainfall forecasts over Southern Xinjiang preliminary. In the terms of the analysis increments, the initial fields of the two processes were improved after assimilating the new radiosonde data, and the Process 11 was more significant, which might be related to stronger southerly airflow and the effect of upper and lower courses. The centers of increment on the high and middle levels occurred in the middle and west of the QTP, corresponding to the Shenzha and Shiquanhe, respectively. Then the increments decreased to the surround- ing regions, and showed weak positive or negative increments over the Southern Xinjiang. Although the new ra- diosonde data on the QTP are above 600 hPa, the meteorological fields in the low levels were also affected through dynamic readjustment. The increment centers of the divergence and humidity presented in the southwest of the QTP, while it changed little over the Southern Xinjiang. The adjustments of the meteorological fields and main effect systems became remarkable gradually with the model integrating. As a result, the subtropical long wave trough got deepened, the south jet over the Southern Xinjiang strengthened, the low pressure systems on the 500 hPa weakened, and the divergence and humidity changed obviously over the Southen Xinjiang. Howev- er, over the precipitation centers in the west of the Southen Xinjiang, the divergence and humidity varied little relatively. The precipitation forecasts showed that the Threat Score of the small thresholds increased remarkably, which meant the forecast capacity of the rainfall area were improved to some extent. Moreover, the result of heavy rainfall were affected little, which also agreed with the variation of the meteorological fields.