Initialization of midlatitude convective storms by assimilation of single Doppler radar observations

Based on single Doppler radar observations, the McGill data assimilation system is used to initialize the convective storms at high resolution (1km). Particular attention is given to the background term in the assimilation system. By assuming the error covariance of control variables to be isotropic and homogeneous, the background error covariance matrix is modeled by a recursive filter. In addition, a high-resolution model forecasts at three-hour prior to the assimilation cycle is used as the background field in the background term. The analysis fields from the assimilation system successfully trigger the convective storms in radar observed regions. Without data assimilation, modeled convection did not occur at the right time and the right place.

To account for the rapid evolution of the convective storms and to correct the forecast errors with time, multiple-cycles assimilation is applied for a very short term forecast. When the spatial correlation coefficients between observed and simulated reflectivity are compared, it was found that the first cycle can maintain the high correlation up to 40 minutes in the forecast. The second cycle helps to maintain the intensity of the storms. However, the environment flow caused the forecasting system to drift away from the radar observations.