Prediction of Convective Initiation and Precipitation for the 12 June Squall Line Case during IHOP and Impact of Simulated GPS Slant-path Water Vapor Data

The accurate low-level water vapor characterization is very important for convective initiation (CI) and quantitative precipitation forecasting (QPF). Global Positioning System (GPS) is capable of providing slant water vapor (SWV) observations with high temporal and spatial resolutions. Recently, we developed a three-dimensional variational (3DVAR) system that uses anisotropic recursive filter to model the background error covariances and applied the scheme to the analysis of simulated GPS SWV data. Our OSSE results show that, with the help of surface moisture observation, the moisture in the boundary layer can be analyzed well from the SWV data.

In this study, the initiation of convection at and near the intersecting point of a north-south trough and a cold outflow boundary at around 2100 UTC, 12 June 2002 during IHOP_2002 is first simulated. This rather successful simulation is used as the truth for Observation System Simulation Experiments (OSSEs) that examine the impact of simulated GPS SWV data on the analysis and precipitation forecast. The 3DVAR system described above is used for the analysis. The ability of GPS data in improving the timing and location of the predicted convective initiation will also be examined.