AREM初值敏感性试验及误差分析

本文基于区域暴雨数值预报模式AREM,对2008年7月四川地区的整月天气过程进行数值模拟试验,分别采用台站常规报文资料、T213预报场资料和以T213资料为背景场,融合常规报文资料3种初值,发现得到的模拟结果差异很大,其中以台站常规资料为初值模拟的降水最接近实况。和台站资料相比,T213预报场资料在四川盆地中西部中低层大气的湿度偏大,温度偏高,风场偏强,而位势高度偏低,直接导致了模拟的降水偏强。这些初值的差异随着积分时间逐渐变小,通过对比逐时降水发生发展过程,发现降水的差异与湿度的调整最为吻合,初值中各个量场对模拟结果都有一定的影响,其中水汽场的影响最为显著,位势高度场的影响最弱。通过比较不同时次初值的模拟结果还发现,0000UTC时刻大气系统相对稳定,故以此为初值模拟的降水比从1200UTC时刻开始模拟的降水更合理。模式模拟的前24h降水比后24h降水的效果更好,一方面说明临近预报的准确度更可靠,另一方面也反映积分前期模式对初值的响应相当敏感。 

Sensitivity Test for Initial Values and Error Analysis in AREM Model

Numerical simulation tests are conducted for the whole weather processes in July 2008 in Sichuan Basin using AREM model. The simulating results are much different based on three different initial values (conventional observation data (station data), 3213 forecasting field and objective analysis station data with T213 forecast data as background field respectively). Precipitation simulated by using station data as initial values is the most similar to the real value, while the humidity is too big, the temperature is too high, the wind field is too strong and the potential height is too low in the lower-middle layer atmosphere in the middle and west of Sichuan Basin, thus directly causing the simulating precipitation too big by using T213 forecast field as initial values. These differences of initial values gradually become smaller with the integral time cumulating. There is a high coherence between precipitation and humidity by comparing the occurring and developing process of hourly precipitation. Every element in initial values plays a certain part in the simulating results, and the influence of vapor field is the most marked and the weakest of potential height. In addition, it is much more reasonable to simulate the precipitation beginning from 0000UTC than from 1200UTC because the atmospheric system is relatively stable at 0000UTC. The simulating precipitation in pre-24-hour is better than that in post-24-hour. It indicates that the accuracy of short-term weather forecast is much reliable and the model is very sensitive to initial values in the early stage of integral.