Study On Quality Control Of Doppler Velocity Data For GRAPES 3DVAR

Doppler weather radars provide data with high spatial and temporal resolution capable of sampling the structure of individual convective cells in a convective system. Doppler radars data assimilation has the potential to improve the initial field with meso-microscale information and short-time numerical weather prediction. One of the long-standing issues in the use of radar radial velocity is velocity ambiguity. A Doppler velocity dealiasing algorithm is developed for the quality control of CINRAD Doppler radar velocity, based on VDRAS velocity dealiasing technique. Then, the assimilation and prediction experiments are conducted for the initialization of a squall line on June 3,2009. Radar radial velocity and reflectivity observations from three CINRADs are assimilated into GRAPES-Meso model with GRAPES 3DVAR system. The major conclusions are summarized as follows:(1)The velocity dealiasing algorithm was tested by using reference wind obtained from GRAPES RUC analysis. The results showed that the algorithm was effective in dealiasing aliased velocities, removing noises and improving the quality of radar observations. From a statistical perspective, the standard deviation of dealiased velocities is decreased, and the distribution of observation errors is closer to normal distribution. It can serve as an operational algorithm for CINRAD Doppler velocity quality control.(2)The results of the assimilation experiments with raw radial velocity and dealiased radial velocity demonstrate that the velocity dealiasing algorithm used in this paper is practicable in correcting the aliased velocities which could lead to false and overlarge wind innovation. A more accurate wind analysis is obtained by the assimilation of dealiased radial velocities.(3)The radar data assimilation can adjust the dynamical fields, the thermodynamics fields and moisture field. The radial velocity assimilation can bring more mesoscale information into initial wind fields and increase the wind shear of the squall line. The initial temperature field is also improved by the radial velocity assimilation. The assimilation of vertical velocity and rain mixing ratio retrieved from the reflectivity can rationalize the distribution of vertical velocity and water vapor, and thus accelerate convections.(4)The precipitation prediction with assimilation of vertical velocity and rain mixing ratio retrieved from the reflectivity is better than assimilation of radial velocity. The experiment with assimilation of radial velocity, vertical velocity and rain mixing ratio simultaneously has the most positive impact on the precipitation prediction.