Steps Towards Ingesting Radar Retrieved Refractivity into Numerical Models

Low-level moisture plays a critical role in convective precipitation.  Obtaining accurate finer resolution initial conditions of the moisture field thus becomes important for storm-scale simulations.  Radar retrieved refractivity fields provide high temporal and spatial resolution maps of moisture, which might help to fill up the current observational data gap.  Here, two cases are presented to illustrate the variation of refractivity fields associated with the change in low-level moisture.  One case shows the propagation of the land-sea breeze front and the other demonstrates the diurnal moisture contrast between rural and urban areas during summertime.

To use or to assimilate the radar retrieved refractivity field, good knowledge of the characteristics of the data is required.  Three aspects are discussed here:  1) Quantifying the observational error based on the assumptions of the radar refractivity retrieval method and in comparison with surface stations.  2) Determining the representative height of the refractivity data.  A shallow refractivity profile is further estimated from radars and is validated with the in-situ tower to provide diurnal mixing conditions in the surface layer. This profile affects the propagation of information vertically.  3) Investigating the background error covariance of refractivity from numerical model.