Lightning Data Assimilation Scheme in a 4DVAR System and Its Impact on Very Short-Term Convective Forecasting
Lightning Data Assimilation Scheme in a 4DVAR System and Its Impact on Very Short-Term Convective Forecasting
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4DVAR系统中的闪电数据同化方案及其对极短期对流预报的影响
DOI：
10.1175/mwr-d-19-0396.1
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发表时间：
2020-11
影响因子：
3.2
通讯作者：
Zhang Lina
中科院分区：
文献类型：
--
作者：
Xiao Xian;Sun Juanzhen;Qie Xiushu;Ying Zhuming;Ji Lei;Chen Mingxuan;Zhang Lina
提出了一种在 4DVAR 框架中同化总闪电观测的概念验证方法，并将其应用到变分多普勒雷达分析系统 (VDRAS) 中。其性能针对中国东北地区局地对流事件的极短期降水预报进行评估。闪电 DA 方案同化了从观测到的总闪电率得出的垂直速度场的伪观测结果以及根据 VDRAS 分析数据统计计算出的垂直速度剖面。为了减少导出的垂直速度的代表性误差，在 DA 之前对输入数据应用距离加权水平插值。案例研究表明，尽管与 CTRL（无雷达或闪电）和 RAD（仅雷达）相比，单独同化闪电数据可以改善 0-2 小时降水临近预报，但当闪电数据与雷达数据同时同化时，可以获得更好的结果。两个数据源的同化可提高动力一致性，增强上升气流和潜热，并改善水分分布。进行了额外的实验来评估组合 DA 方案对不同垂直速度剖面、水平插值半径、分箱时间间隔以及用于根据闪电速率估计最大垂直速度的关系的敏感性。结果表明，该方案对于雷达和闪电同化数据的这些变化具有鲁棒性。
A proof-of-concept method for the assimilation of total lightning observations in the 4DVAR framework is proposed and implemented into the Variational Doppler Radar Analysis System (VDRAS). Its performance is evaluated for the very short-term precipitation forecasts of a localized convective event over northeastern China. The lightning DA scheme assimilated pseudo-observations for vertical velocity fields derived from observed total lightning rates and statistically computed vertical velocity profile from VDRAS analysis data. To reduce representative errors of the derived vertical velocity, a distance-weighted horizontal interpolation is applied to the input data prior to the DA. The case study reveals that although 0–2-h precipitation nowcasts are improved by assimilating lightning data alone compared to CTRL (no radar or lightning) and RAD (radar only), better results are obtained when the lightning data are assimilated with radar data simultaneously. The assimilation of both data sources results in improved dynamical consistency with enhanced updraft and latent heat as well as improved moisture distributions. Additional experiments are conducted to evaluate the sensitivity of the combined DA scheme to varied vertical velocity profiles, radii of horizontal interpolation, binning time intervals, and relationships used to estimate the maximum vertical velocity from lightning flash rates. It is shown that the scheme is robust to these variations with both radar and lightning assimilated data.