11.2 Improving Analyses and Forecasts of the Asian Monsoon with GPS Radio Occultation Refractivity Observations (2008

11.2

Improving Analyses and Forecasts of the Asian Monsoon with GPS Radio Occultation Refractivity Observations

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

Over the Western Pacific ocean, radiosonde observations are sparse

and analyses and forecasts of temperature and moisture rely heavily on

satellite microwave (MW) and infrared radiance (IR) measurements. The

radiances have relatively low vertical resolution in the troposphere.

Operational analyses and forecasts of the subtropical anti-cyclone

and its associated water vapor flux toward Asia may have relatively

large uncertainties. Improving analyses of these aspects of the

monsoon is important for producing better forecasts of high impact

events like heavy rainfall.

The new COSMIC GPS radio occultation measurements provide atmospheric

refractivity soundings globally including over the Western Pacific ocean.

The measurements have relatively high vertical resolution in the lower

troposphere and are not contaminated by clouds or precipitation.

This study explores the impact of using GPS

refractivity observations in the WRF/DART ensemble data assimilation

system to improve analyses and forecasts of the anti-cyclone and

associated water vapor flux.

During June 2007, there were several heavy rainfall events over Taiwan and

southern China that caused significant loss of life and property damage.

RO refractivity, radiosondes, AIRS retrieved temperature, and satellite cloud

drift winds are assimilated using a 36 km resolution WRF configuration for

the period of June 1-14, 2007. A heavy rainfall event occurred in the middle

of this period on June 8-9, 2007. Assimilating the RO data

significantly reduces the RMS error of the RO refractivity analyses over the

Western Pacific Ocean and the bias of the water vapor analyses over Asia.

Analyses of the anti-cyclone position and forecasts of the

heavy monsoon rainfall are improved.