区域初始分析误差对梅雨锋中尺度低压数值预报的影响

Impact of Regional Uncertainties of the Initial State upon Numerical Forecast of Mesoscale Low on Meiyu Front

以梅雨锋中尺度低压个例为研究对象,根据目标观测的思想,采用NCEP和T106再分析资料分析了区域初始分析误差对梅雨锋中尺度低压数值预报误差的影响。结果表明:区域初始分析误差对数值预报误差有重要影响,改善某些特定区域初始场质量有可能改善随后数值预报的效果。但是,区域初始分析误差对数值预报误差的影响较为复杂,它与天气类型、不同个例和区域间误差相互作用等因素密切相关。对梅雨锋中尺度低压短期数值预报有较大影响的初始分析误差与梅雨锋锋区及其附近地区的要素场关系密切,相比较而言,风场似乎更加重要一些。如果对梅雨锋带中低层风切变区及相伴低空急流区有更好的描述,这将对梅雨锋中尺度低压系统数值预报效果的改善有着积极的作用。在此基础上,就相关的目标观测设计问题作了简要讨论。

Present study is associated with the key idea underlying targeted observations of the initial state for nu merical forecast of mesoscale low on Meiyu front, which is called in China, Baiu in Japan and Changma in Korea and is the main synoptic system that brings rainfall to those countries during summer monsoon season every year. Mesoscale low on Meiyu front is one of the most important mesoscale systems associated with heavy rainfall. The effect of regional uncertainties of the initial state upon numerical forecast of mesoscale low on Meiyu front is concerned. The estimate of initial uncertainties is obtained by the differences between the NCEP and T106 reanalysis data. Con trol experiment is performed with NCEP data in whole model region. The impact of regional initial uncertainties is studied by a change of initial data from NCEP to T106 reanalysis first in whole model region, and then inside or outside the selected regions. Results show that regional uncertainties of the initial state have important impact on the numerical forecast error. Some improvement of numerical forecast may be obtained by improving the quality of initial state in certain region. However, this kind of effect is complex in that it is associated with weather pattern, individ- ual case and the interaction between uncertainties of different regions. The regional uncertainties of the initial state, which have important impact on numerical prediction of mesoscale low on Meiyu front, should locate on and in the vicinity of Meiyu front zone. Probably, the wind field plays an important role and the better depiction of low-level wind shear and jet could result in the improvement of numerical forecast of mesoseale low on Meiyu front.