Impact of Assimilating Environmental Satellite Observations on Tropical Storm Position and Intensity Analyses and Forecasts

Accurate estimates of the position and intensity of tropical cyclones have been difficult to obtain, especially for weak vortices and during cyclogenesis. This is partly due to the lack of appropriate observations as well as effective data assimilation techniques for the latent heat driven tropical atmosphere. The recent emerging ensemble data assimilation techniques use a collection of short-range forecasts to estimate flow dependent multivariate forecast error covariances. Appropriate cross covariances of moisture with winds and temperature can improve analyses produced for the tropics when satellite observations of water vapor and temperature are assimilated. This study explores the impact of assimilating satellite sounding observations of the environment surrounding developing tropical cyclones with an ensemble filter.

As a first example, GPS radio occultation (RO) refractivity profiles are assimilated in NCAR's WRF/DART ensemble system. The first case is over the western Pacific Ocean during the TPARC period (August 11 - September 30, 2008). A second case covers the genesis period of Hurricane Ernesto (2008). The impact of the RO data on the analyses and forecasts of the storms' track and intensity are examined.

The impact of assimilating environmental satellite microwave and IR soundings of water vapor and temperature is also examined for the Ernesto case. It is found that the satellite observations improve the analyses and forecasts of the intensifying tropical cyclones.

The mechanisms of the positive impacts of the observations are explored.