Assimilation across multiple scales for simulated squall lines

The present network of Doppler radars in the US can observe individual convective cells as well as the organization of those cells into larger, mesoscale systems. Both ensemble-based and variational assimilation schemes have been demonstrated for one or a few cells and observations from a single radar over a short time period. We present experiments with an ensemble Kalman filter (EnKF) for the Weather Research and Forecasting (WRF) model using simulated observations from two squall-line cases, one over Illinois and that of 13 June 2002 observed during IHOP. The EnKF is well suited for this problem, as it is readily applied to the complete WRF model and can also provide analyses across the multiple, interactive, nested domains that ease simulation of explicit convective cells and squall-line organization. The EnKF analyses successfully capture the mesoscale features of the squall lines given only simulated observations of radial velocity and reflectivity from several (2-5) radars. It is crucial that the ensemble for the EnKF prior to assimilation of the first observations includes the uncertainty in both the convective-scale and mesoscale fields. We will present details of these results and of the scheme that allows the EnKF to update nested domains consistently.