Assimilating GPM hydrometeor retrievals in HWRF: choice of observation operators

Abstract

AbstractA recent study investigated the capability to assimilate hydrometeor retrievals in the National Oceanic and Atmospheric Administration (NOAA) Hurricane Weather Research and Forecasting (HWRF) system. Hydrometeor retrievals were obtained from a hurricane‐specific retrieval that utilizes data from the Global Measurement Mission Microwave Imager. Data assimilation system used in HWRF is the hybrid ensemble‐variational Gridpoint Statistical Interpolation (GSI). As a first attempt to assimilate hydrometeor retrievals in HWRF, observation operators for solid and liquid integrated water content were developed using the GSI standard control variables, such as temperature, pressure, and specific humidity, under the assumption that all water vapor in excess of saturation is condensed out. To improve the usefulness of assimilating hydrometeor retrievals in HWRF, this study extends this previous work by introducing new observation operators that (1) directly use hydrometeor species estimated from HWRF microphysics and (2) include total cloud condensate as a control variable. Hurricane Gonzalo (2014) was used to examine the performance of the old and new observation operators on HWRF analysis and subsequent forecasts with three pairs of experiments. Results suggest that when new observation operators are used the analysis is an improved fit to observations and realistic adjustments to control variables are evident as seen in analysis increment. In addition, the forecasts also indicate some improvements in hurricane intensity.