Impact of the Assimilation Frequency of Radar Data with the ARPS 3DVar and Cloud Analysis System on Forecasts of a Squall Line in Southern China

摘要

Assimilation configurations have significant impacts on analysis results and subsequent forecasts.A squall line system that occurred on 23 April 2007 over southern China was used to investigate the impacts of the data assimilation frequency of radar data on analyses and forecasts.A three-dimensional variational system was used to assimilate radial velocity data,and a cloud analysis system was used for reflectivity assimilation with a 2-h assimilation window covering the initial stage of the squall line.Two operators of radar reflectivity for cloud analyses corresponding to single-and double-moment schemes were used.In this study,we examined the sensitivity of assimilation frequency using 10-,20-,30-,and 60-min assimilation intervals.The results showed that analysis fields were not consistent with model dynamics and microphysics in general;thus,model states,including dynamic and microphysical variables,required approximately 20 min to reach a new balance after data assimilation in all experiments.Moreover,a 20-min data assimilation interval generally produced better forecasts for both single-and double-moment schemes in terms of equitable threat and bias scores.We conclude that a higher data assimilation frequency can produce a more intense cold pool and rear inflow jets but does not necessarily lead to a better forecast.