Impact of FORMOSAT-3 GPS Data Assimilation on WRF model during 2007 Mei-yu season in Taiwan

Shyuan-Ru Miaw, Pay-Liam LinDepartment of Atmospheric SciencesNational Central University, Taiwan

Jing-San Hong, Bao-Jao ChenCentral Weather Bureau, Taiwan

2008.7.1 UAW

OutlineOutline

IntroductionMethodology COSMIC data and model setup RAFS

Real time forecast validationReal time forecast validationSummary

Radiosondes (weather sensors launched by balloon) have obtained vertical profiles since the 1930s. However, they are launched only twice a day in most spots, and few are deployed over the ocean.

The Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission was launched in April 2006. As part of its mission, COSMIC will provide approximately 2000-2500 global positioning system (GPS) radio occultation (RO) soundings per day distributed uniformly around the globe.

Introduction

FORMOSAT-3/COSMIC provides ~2500 vertical profiles (green points)

per day in near-real timeGround based observation provides ~900 vertical profiles (red points)

What’s GPS Radio Occultation Data?

•As the radio signals, transmitted by the GPS satellites, pass through the atmosphere, they are refractedrefracted due to the density gradients along the path. •As a LEO satellite sets or rises behind the earth’s limb relative to the GPS satellite, the onboard GPS receiver takes measurements of the phase and amplitude of the GPS signals.

Obtaining Temperature and Pressure from Refractivity

Refractivity

Dry air Water vapor

Smith and Weintraub(1953) :

P: Total atmospheric pressure (mb),

T: Atmospheric temperature (K),

Pv: Partial pressure of water vapor (mb).

The number of GPS RO soundings per day from 21,Apr, 2006 to 31,July,2007 (from TACC website)

GPS RO Soundings per dayGPS RO Soundings per day

Jul. – Oct. in 2006

2007 5 6 GPS-RO realtime年 月 月 接收數量

0

500

1000

1500

2000

2500TACC realtime

Jul 1 2006 Aug 1 2006 Sep 1 2006 Oct 1 2006

May and Jun. in 2007

GPS RO Soundings per dayGPS RO Soundings per day

Realtimedaily

Mp physics 　　　　　　　： WSM 5-class scheme Longwave radiation option ： rrtm scheme Shortwave radiation option ： Goddard short wave bl_pbl_ physics ： YSU scheme cu physics ： Kain-Fritsch （ new Eta ） scheme Resolution: 45 （ 222×128 ）、 15 （ 184×196 ）、 5 （ 94×124 ） Vertical: 41 simga levels

Configuration of WRF modelConfiguration of WRF model

Configuration of WRF modelConfiguration of WRF model

Control Run (NO GPS) 、 GPS Run(GPS)

IC & BC:CWB GFS WRF 3DVAR Assimilation data: ALL SYNOP 、 SHIPS 、 METAR 、 PILOT 、 SOUND 、 SATEM SATOB 、 AIREP 、 wind profiler 、 BUOY 。 GPS RO

Forecast :72 hours

RReal-time eal-time AAssimilating and ssimilating and FForecasting orecasting SSystemystem

Real time forecast validation

Validation of q with sounding dataValidation of q with sounding data

domain2

RMS of q in domain2 July to October 2006

Profile of HDomain1 Domain2

Validation In Grid point (May –Sep 2007)Validation In Grid point (May –Sep 2007)

Domain 2 have more significant result than Domain 1

RMS RMS

M-error M-errorAbs_m Abs_m

S_D S_D

Validation in Grid point (May –Sep 2007)Validation in Grid point (May –Sep 2007)Profile of H Profile of T

U 垂直剖面RMS RMS

M-error M-errorAbs_m Abs_m

S_D S_D

Profile of U Profile of V

Validation in Grid point (May –Sep 2007)Validation in Grid point (May –Sep 2007)

Validation in Grid point - timeseries (May-Sep)Validation in Grid point - timeseries (May-Sep)

850 hPa

500 hPa

300 hPaMay 1 Oct 1

Typhoon

Height

Typhoon WutipModel forecast rainfall accumulation in the past 3 hr at 72hr

GPS run nonGPS run Init=Aug 6 00Z

GPS run nonGPS run Aug. 9 00 UTC

Typhoon WutipModel forecast rainfall accumulation in the past 3 hr at 48hr

Init=Aug 7 00Z

Radar

Validation in Grid point - timeseries (May-Sep)Validation in Grid point - timeseries (May-Sep)

850 hPa

500 hPa

300 hPa

•When H have significant result, T maybe not have so much different result at the same time.

•The results of validation show that GPS RO data assimilation have positive impact on the WRF model forecast but not so much!

Temperature

Mei-yu front heavy rainfall

Accumulate precipitation on Jun 7, 2007 by CWB

The location of the GPS RO sounding on Jun 5 00Z, 2007(Time window is 3 hr)

GPS run nonGPS run Jun 7 17 LST

Mei-yu front heavy rainfall

Model forecast rainfall accumulation in the past 3 hr at 57hr

Radar

Init=Jun 5 00Z

time month 00Z 06Z 12Z 18Z

(May) RO sounding number in the domain/ all receive

10.87 / 173.19

21.47 / 302.65

15.90 / 185.35

27.58 / 257.48

(Jun) 16.23 / 227.53

24.17 / 332.27

20.13 / 252.07

22.17 / 357.5

• 00Z and 12Z has less RO soundings than 06Z and 18Z

• We need to proceed post run (ex. Update cycle) to optimize use GPS RO data and to assess the impacts!

Number of GPS RO data during 2007 Mei-yu season

Validation of Update cycle run

H T

RMS

M-error Abs_m

S_D RMS

M-error Abs_m

S_D

Validation In Grid point (Update cycle run)Validation In Grid point (Update cycle run)

U V

RMS

M-error Abs_m

S_D RMS

M-error Abs_m

S_D

Validation In Grid point (Update cycle run)Validation In Grid point (Update cycle run)

1. In order to assess the impact of COSMIC GPS RO data on the regional weather forecast we conduct near real time WRF 3dvar assimilation forecast and validation.

2. Preliminary results show that GPS RO data assimilation have positive impact on the WRF model forecast but not so much!

3. Cases studies show that GPS RO data assimilation have impact on typhoon track and precipitation system forecast when initial condition is not good, but not always have positive impact. We need more cases studies in the coming days!

4. Cycling experiment show neutral impact during 2007 meiyu season.

SummarySummary

~Thank you~