Assimilation of GPS RO Refractivity Data and Its Impact on Simulations of Trade Wind Inversion and a Winter Cold Front

Chunhua Zhou,Yi-Leng Chen

doi:10.4236/ns.2014.68060

Abstract

Assimilation of Global Positioning System (GPS) Radio Occultation (RO) refractivity based on WRF-3DVAR is applied to numerical weather predictions (NWP) in Hawaii, where limited conventional observations and poor representation of local circulations in global analysis constrain the quality of numerical weather predictions. For a summer trade wind case, with GPS RO refractivity assimilated, the trade wind inversion is better predicted. For a winter cold front case, the propagation of the cold front is also better simulated when GPS RO refractivity is assimilated. Furthermore, the moist tongue associated with the cold front is better defined and the vertical profiles of temperature and moisture are largely improved when compared to the model run without GPS RO assimilation.

Highlights

Located in the mid-Pacific Ocean, with limited conventional in situ observations, the Hawaiian Island chain is an excellent place to test the impact of remotely sensed satellite data on high-resolution weather modeling
As the assimilation of Global Positioning System (GPS) Radio Occultation (RO) is performed at 00UTC 29 January 2010, we examine the forecast field 24 hours or longer after the assimilation, which includes the 36-hour, 48-hour, and 60-hour forecasts
The 48-hour forecasts of total precipitable water (TPW) valid at 1200 UTC January 2010 are compared with satellite image and the Consistent with the results shown in Figure 5 and Figure 6, the simulated TPW with GPS RO assimilation at 0000 UTC January, 2010 is more realistic whereas the no-GPS RO run tends to produce large values of TPW further to the east

Summary

Introduction

Located in the mid-Pacific Ocean, with limited conventional in situ observations, the Hawaiian Island chain is an excellent place to test the impact of remotely sensed satellite data on high-resolution weather modeling. The Global Position System (GPS) radio occultation (RO) measurements provide a new data source to determine global trade wind inversion height in high vertical resolution (~200 m) (Ao et al 2012 [10]; Guo et al 2011 [11]; Xie et al 2012 [12]; and others) These data can be used to obtain vertical profiles of bending angle, atmospheric refractivity (Kuo et al 2004 [13]) and atmospheric soundings in all weather conditions, even under the presence of cloud cover (Kirsinski et al 1997 [14]; Kuo et al 2005 [15]; Ho et al 2007 [16]). Would assimilating GPS RO refractivity data during the 12-h model spin-up period affect the subsequent simulation of trade wind inversion height? In addition, we conducted data assimilation of GPS RO refractivity data during the first 12-h of the model run for a winter-time cold front case to investigate the impact of data assimilation on the simulated inversion height and the propagation and spatial distribution of the moist tongue associated with the cold front

Data and Experimental Design

Assimilating GPS RO Data for a Trade Wind Case

Impact of Assimilating GPS RO for a Cold Front Event

Conclusions