Impact of GPS Radio occultation observations on ensemble analyses and forecasts of tropical Storms

Over tropical oceans, high quality radiosonde observations are sparse and

analyses and forecast of temperature and moisture rely heavily on satellite

microwave (MW) and infrared radiance (IR) measurements. The resulting operational analyses and forecasts of water vapor and temperature have relatively large uncertainties. This is a significant challenge for producing good analyses and forecasts of tropical storms.

The new GPS radio occultation (RO) observations from the COSMIC satellites since 2006 provide soundings of atmospheric refractivity globally including over tropical oceans. The measurements are not contaminated by clouds or precipitation

and have relatively high vertical resolutions in the lower troposphere.

In this study, we examine the potential of the new RO data to improve the analyses and forecasts of tropical cyclones. Observations of RO refractivity are assimilated in the WRF/DART ensemble filtering system to evaluate the impact of these measurements on analyses and forecasts of tropical storms over the Atlantic

and Western Pacific Oceans. The RO refractivity observations are assimilated

along with radiosodes, satellite cloud drift winds, and AIRS retrieved temperatures using a 36 km resolution WRF model. Results are presented for

hurricane Ernesto and typhoon Shanshan of 2006. The RO observations

significantly reduce the bias of the water vapor analysis and improve the

analyses and forecasts of the intensity and position of the tropical storms.