uncertainties, especially in the vertical structure. This makes it

difficult to produce accurate forecasts of tropical cyclones.

Radio occultation observations from the COSMIC satellites provide

soundings of atmospheric refractivity globally including over

tropical oceans. The measurements are not contaminated by clouds or

precipitation and have high vertical resolution in the middle and

lower troposphere.

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 cyclones. The RO

refractivity observations are assimilated along with many of the

conventional observations using the WRF model. Results are presented for

typhoon Shanshan of 2006. The RO observations significantly improve

the ensemble analyses and forecasts of the position and intensity of

the tropical storm.