Design of a Satellite-Based Observing System for the Analysis and Prediction of Multi-Scale Weather and Convectively-Coupled Tropical Waves using EnKF

This study assesses the potential improvement of using a satellite-based observing system over the Indian Ocean for prediction of multiscale weather and convectively-coupled tropical waves during the active phase of the October 2011 MJO event. The observing system consists of temperature and moisture profiles from Advanced TIROS Operational Vertical Sounder (ATOVS) retrieval products, Atmospheric Motion Vector (AMV), surface wind speed derived from the Cyclone Global Navigation Satellite System (CYGNSS), and IR brightness temperature from Meteosat7 water vapor channel. The Weather Research and Forecasting (WRF) model is employed to conduct regional convection-permitting simulation and a previous simulation from Wang et al. is used as the verifying truth. Synthetic observations are generated from the truth, and a 60-member EnKF is used to assimilate the observations every 3 h for a 15-day period. In a perfect model scenario, a series of Observing System Simulation Experiments show that the filter is skillful in reducing the realistic initial condition errors for horizontal wind, temperature, and moisture. A spectral analysis shows that the reduction in error is mostly at large scale (>200 km). Assimilating AMV and CYGNSS reduce the wind error, with AMV improving mid- to upper-level wind and CYGNSS improving wind near the surface. The temperature and moisture are consistently improved by the ATOVS profiles. For vertical motion and precipitation, as most of their variability is in the small scale, the error grows very rapidly for these variables and therefore improvement is small due to intrinsic predictability limits. We show that directly assimilating IR brightness temperature is the primary means to improve hydrometeor distribution in the model domain, although the analysis increment is not optimal due to nonlinearity in observation operator. Another challenge is the fast error saturation at small scales for the hydrometeors that quickly removes the impact from assimilation.