Experimental Research On Doppler Radar Data Assimilation With WRF 3DVAR

Doppler radars provide measurements of the radar radial wind and reflectivity at high temporal and spatial resolution. The mesoscale information in numerical weather prediction models will be improved by fully utilized the radar data. The experiments of direct assimilation radar radial velocity or reflectivity are researched with the mesoscale numerical weather prediction model WRFV2.1 and 3DVAR system WRF-VAR2.1.they are tested with a heavy rainfall process in the mei-yu front occurred at Yangtze river during 4-5 july 2003 . The first guess was NCEP reanalysis data and the observations is Next-Generation Weather Radar data of heifei. The results are as followes:(1) Radar preprocessing and quality control which incloud removing anomalous propagation , ground clutter, isolated point, velocity dealiasing, data filling, data smoothing and thinning play an important role in the radar data assimilation.(2) The experiments of direct assimilation radial velocity can improve convergence zone and enhance low level jet. The increment field have cyclone vortex in the low levels. The improvement of vertical velocity in favor of the triggering and development of convection . The experiment of direct assimilation reflectivity can change the microphysical variables, dynamical variables and temperature in the model. The experiments of direct assimilation radial velocity and reflectivity have the advantage of the former experiments. The precipitation and simulation reflectivity is closer to observation and better than the control experiment(3) The experiments of choosing the different kinds of control variables and background error covariances have the different impact on the simulation of heavy rainfall. Their reasonable configuration can improve the prediction of the precipitation. The observation are assimilated every 10min is better than the every 30min.(4) The high resolution of the model can improve the mesosclae system heavy rainfall duiring the prediction. The six hour accumulate precipitation of the resolution of 2.5km is better than that of the resolution of 5km .(5) The small/meso scale information in first state is improved by direct assimilation radial velocity and reflectivity. The results incidate that the mesoscale convective vortex(MCV) and the convection impact each other by wave-CISK. There are vortexes and asymmetric convergence and divergence in the shear line at 850hPa when the rainfall occurred. The low level vortex on the north of the meiyu-front transports the cold air to the front and trigger the convection. The combine of wave-CISK and anticyclone before the low pressure results in the development of MCV in the low level. Then the MCV continually induce the development of the shear line at 850hPa and the convection which results in the intensity rainfall.