JP1.10 Impact of GPS Radio Occultation Observations on Ensemble Analyses and Forecasts of Tropical Storms (2008

JP1.10

Impact of GPS Radio Occultation Observations on Ensemble Analyses and Forecasts of Tropical Storms

Hui Liu, NCAR, Boulder, CO; and J. Anderson, Y. H. Kuo, Y. Chen, and C. Snyder

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. In cloudy situations,

like hurricanes, the IR radiances are not yet routinely used and the MW

radiances have relatively low vertical resolutions in the troposphere. 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.

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 relatively high vertical resolutions in the 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 storms over the Atlantic

and Western Pacific Oceans. The RO refractivity observations are assimilated

along with 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.