Three-dimensional Analyses of Several Thunderstorms observed during VORTEX2 field operations

The assimilation of WSR-88D radar data into storm-scale weather prediction models represents a significant scientific and technological challenge. Several data assimilation methods are candidates for use, including ensemble Kalman filter methods and variational (3DVAR, or 4DVAR) assimilation methods. Much of the radar data assimilation research using the ensemble Kalman filter and 4DVAR is found to be computationally very expensive and it will be challenging to implement these two approaches in the next several years. In contrast, the 3DVAR approach is computationally very efficient and also produces reasonable results.

In this study, we will present results from assimilating WSR-88D observations of reflectivity and radial velocity for several thunderstorms targeted during VORTEX2 field operations using the ARPS 3DVAR system formulated in an incremental form. For every selected case, the 3DVAR analyses will begin with the first 30 dBZ radar echo associated with the eventual thunderstorm of interest and continue until the end of VORTEX2 data collection for this thunderstorm. Three-dimensional storm-scale analyses will be produced every 5 minutes using a cycling approach where the Advanced Regional Prediction System (ARPS) model is used to advance the 3DVAR analysis forward in time between data insertions.

The 3DVAR analyses can be compared against the high-resolution VORTEX2 observations to determine both analysis accuracy and whether or not the unobserved structures generated by the analyses agree with the special surface observations from mobile mesonets and stick-nets. The benefits and limitations of the 3dvar approach and the usefulness of the 3DVAR system will be assessed.