Study On A Lightning Data Assimilation Technique And Its Application

Severe convective weather forecasting has been especially difficult for meteorological services. The improvement of numerical model depends on the accuracy of initial field information to a certain extent. Lightning activity serves as a good indicator of severe convective weather. Furthermore, lightning detection has the advantages of all-weather, high-precision, high-resolution, long-range coverage, and less influence by terrain. Therefore, the method of lightning data assimilation in mesoscale numerical prediction models has drawn great attention of the international academia. Based on the empirical relationship between flash frequency and the content of ice particles, a lightning data assimilation method is presented, which can effectively improve the simulation and forecast of numerical model for mesoscale convective precipitation systems. Moreover, this lightning data assimilation method has been evalusted by using two case studies of synoptic process simulations in northern China. The main results are as follows:(1) Because of the close relationship between ice particles with lightning activity, the content of ice particles (i.e. snows, crystals and graupels) was used as the assimilation parameter in lightning data assimilations. An empirical formula has been established by using the simulation result of several typical thunderstorms in northern China from WRF (Weather Research and Forecasting Model) model and the total lightning data from SAFIR3000lightning locating system of Beijing Meteorological Bureau. It shows in this formula that under the condition of low lightning frequency, the content of ice particles rapidly increases with the increasing lightning frequency, while this increase rate decreases gradually, and the content of ice particles remains stable when lightning frequency is up to5fl/lOsec. WRF Single-Moment6-Class Microphysics Scheme (WSM6) has been modified, so that the empirical formula between total lightning frequency and the content of ice particles is written into WRF model to adjust the matter field of WRF model by using lightning data.(3) Two case studies of mesoscale convective weather systems in northern China (13June2010and1August2009) have been tested. The results show that6-hour cumulative rainfall intensity, the central location and range of precipitation, the location and intensity of convective activities in sensitive experiments have been apparently improved, compared with control experiments. At the same time, near-ground10m wind field and6km vertical momentum field have been adjusted to some extent, which suggests that the lightning assimilation method presented here is effective and feasible.