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

1. Impact of FORMOSAT-3 GPS Data Assimilation on WRF model during 2007 Mei-yu season in Taiwan Shyuan-Ru Miaw, Pay-Liam Lin Department of Atmospheric SciencesNational Central University, Taiwan Jing-San Hong, Bao-Jao Chen Central Weather Bureau, Taiwan 2008.7.1 UAW

2. Outline • Introduction • Methodology COSMIC data and model setup RAFS • Real time forecast validation • Real time forecast validation • Summary

3. Introduction • 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.

4. FORMOSAT-3/COSMIC provides ~2500 vertical profiles (green points) per day in near-real time • Ground based observation provides ~900 vertical profiles (red points)

5. What’s GPS Radio Occultation Data? • As the radio signals, transmitted by the GPS satellites, pass through the atmosphere, they are refracted 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.

6. Obtaining Temperature and Pressure from Refractivity Smith and Weintraub(1953) : Refractivity Dry air Water vapor P: Total atmospheric pressure (mb), T: Atmospheric temperature (K), Pv: Partial pressure of water vapor (mb).

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

8. Jul 1 2006 Aug 1 2006 Sep 1 2006 Oct 1 2006 GPS RO Soundings per day Jul. – Oct. in 2006 Realtime daily May and Jun. in 2007

9. Configuration of WRF model • 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

10. Configuration 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

11. Real-time Assimilating and Forecasting System

12. Real time forecast validation

13. domain2 Validation of q with sounding data RMS of q in domain2 July to October 2006

14. Validation In Grid point (May –Sep 2007) Profile of H Domain1 Domain2 Domain 2 have more significant result than Domain 1

15. Validation in Grid point (May –Sep 2007) Profile of H Profile of T RMS S_D RMS S_D M-error Abs_m M-error Abs_m

16. Validation in Grid point (May –Sep 2007) Profile of U Profile of V U 垂直剖面 RMS S_D RMS S_D M-error Abs_m M-error Abs_m

17. Validation in Grid point - timeseries (May-Sep) Height 850 hPa Typhoon 500 hPa 300 hPa Oct 1 May 1

18. Typhoon Wutip Model forecast rainfall accumulation in the past 3 hr at 72hr Init=Aug 6 00Z GPS run nonGPS run

19. Typhoon Wutip Model forecast rainfall accumulation in the past 3 hr at 48hr Init=Aug 7 00Z GPS run nonGPS run Aug. 9 00 UTC Radar

20. Validation in Grid point - timeseries (May-Sep) Temperature 850 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! 500 hPa 300 hPa

21. 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)

22. Mei-yu front heavy rainfall Model forecast rainfall accumulation in the past 3 hr at 57hr Init=Jun 5 00Z GPS run nonGPS run Jun 7 17 LST Radar

23. Number of GPS RO data during 2007 Mei-yu season • 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!

24. Validation of Update cycle run

25. Validation In Grid point (Update cycle run) H T RMS S_D RMS S_D M-error Abs_m M-error Abs_m

26. Validation In Grid point (Update cycle run) U V RMS S_D RMS S_D M-error Abs_m M-error Abs_m

27. Summary 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. • Preliminary results show that GPS RO data assimilation have positive impact on the WRF model forecast but not so much! • 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! • Cycling experiment show neutral impact during 2007 meiyu season.

28. ~Thank you~