Preliminary results of FORMOSAT-3/COSMIC data assimilation with WRF 3DVar

1. Preliminary results of FORMOSAT-3/COSMIC data assimilation with WRF 3DVar Y.-R. Guo, H.-C. Lin, W. Wang and Y.-H. Kuo National Center for Atmospheric Research (NCAR) 16 November 2006

2. Outline • COSMIC GPSRO data preparation for WRFVar • WRFVar (3DVar) system for GPSRO data assimilation • Experiments for Hurricane Florence • Summary and conclusions

3. COSMIC GPSRO data preparation • Download the bfrPrf (BUFR format) data from CDAAC • Decoder the bfrPrf to be LITTLE_R (ASCII) file 1, The BUFR format data downloaded is a binary file, and cannot be viewed and edited; 2, To be used by WRF 3DVar system, the observation data file must be in LITTLE_R ACSII format. • 3DVAR_OBSPROC Download the daily data: Use the unix command curl 1, download the filename curl -u {username}:“{password}" -L -O ${UTL} 2, download the files: curl -u {username}:“{password}" -L -O ${URL}/${file} The username and password should be obtained when you sign up.

4. 3DVAR Preprocessor: To get a clean OBS assimilated by WRF 3DVar, the 3DVAR_OBSPROC should be run first with OBS LITTLE_R file as input. Meanwhile, the observation errors are assigned to the specific type of the observations. For GPSRO refractivity, the observation errors vary with height and latitude (Chen and Kuo, 2005).

5. We have developed COSMIC GPSRO bfrPrf decoder and 3DVAR_OBSPROC for application of a variety of the observation operators: Local (Refractivity), Non-local (Excess phase), and bending angle. The 3DVAR_OBSPROC can also used to plot the data distribution of GPSRO soundings by using MAP_plot.

6. WRFVar (3DVar) system for GPSRO data assimilation When the first guess (from a large model analysis or a forecast initiated certain hours (6-h or 12-h) and the background error statistics files are available, the GPSRO refractivity data can be assimilated without or with other types of observations via WRFVar (3DVar). • Observation operator Currently, only the local refractivity operator is implemented in WRFVar: All of the procedure for GPSRO data processing here are for the refractivity, but it is not difficult to extend to other measurements, such as bending angle, excess phase, etc.

7. Other observation operators could be developed and implemented, such as: • bending angle based on the Abel inversion (Healy and Thepaut 2006): • Non-local excess phase (Sokolovskiy et al. 2005): and the new observable is where Nmod is calculated from NPW analysis or forecast, and Nar is the Abel Refractivity from GPSRO observation data. l is a straight line passing through the tangent point, TP, and symmetric with respect to that point.

8. Quality Control procedure for Refractivity N • Step 1. Background check: |(O-B)| > 5o • Step 2. Relative Error check: h =< 7 km, R.E. > 5.0% 7 km < h < 25 km, R.E > 4.0% h >= 25 km, R.E> 10.0% • Step 3. Low level check: if the data at certain level fails to pass relative error check, all the data below that level will be discarded.

9. Innovations (O-B) before the quality control COSMIC 2006 August (Saomai) 113 GPSRO soundings CHAMP 2003 August (Dujuan) 53 GPSRO soundings Innovations (O-B) after quality control for the different OBS error specifications

10. The number of the data points assimilated after quality Control procedure The percentages of the points relative to ingested points are shown in parenthesis COSMIC data from brfPrf with 200 m resolution for 113 GPSRO soundings (2 days) (The bad flag (or pccf < 100) was turned off for COSMIC data). CHAMP data from wetPrf with 100 m resolution for 53 GPSRO soundings (3 days)

11. The averaged (O-A) of the GPS Refractivity from 3D-Var experiments with 6-h time window assimilation for Typhoon Saomai (2006) and Dujuan (2003) COSMIC 2006 August (Saomai) CHAMP 2003 August (Dujuan)

12. The averaged (O-B) and (O-A) of the GPS Refractivityfrom 3D-Var experiments with 6-h time window assimilation The RMS reduction percentages (O-A)/(O-B) are shown in parenthesis COSMIC data from brfPrf with 200 m resolution for 113 GPSRO soundings (2 days) CHAMP data from wetPrf with 100 m resolution for 53 GPSRO soundings (3 days)

13. There are 4 steps for GPSRO data assimilation: • 1, to download the data from CDAAC or future from WMO GTS; • 2, to decode the data from BUFR/netCDF file to ASCII LITTLE_R file; • 3, to further process the data to be ASCII 3DVAR format with OBS errors assigned; • 4, to assimilate the GPSRO refractivity data by 3DVar. • From point of view in 3DVar, the quality of COSMIC GPSRO data is comparable to the CHAMP data. • Data problems: • 1) there is no optimized bending angle available in bfrPrf data; • 2) the pccf (percentage of confidence) is too conservative; • 3) the data available 4~5 hours after the observing time.

14. Experiments for Hurricane Florence • Real time WRF-ARW Hurricane forecast (Wei Wang) Initial condition and boundary condition from GFDL Hurricane analysis and forecast domain size: 502x301x35, grid size: 12-km • WRFVar (3DVar) assimilation COSMIC GPSRF data only First guess: the initial condition used in real-time WRF-ARW Hurricane forecast Background Error statistics: CV5 BE interpolated from a 12-km (460x351x51) CV5 BE over the north America and Atlantic (derived by Zhiquan Liu) Observations: FORMOSAT-3/COSMIC GPS Refractivity soundings. The experiments were conducted for three initial times: 2006090600Z, 2006090700Z and 2006090800Z, and the forecast length is 120h.

15. Hurricane FlorenceThe track from 2100 UTC 3 to 2100 UTC 12 September 2006 with 6h interval 090800Z 090700Z 090600Z

16. COSMIC GPSRO soundings distribution within 6h time window centered at 2006090600Z, 2006090700Z, and 2006090800Z 9 GOSRO soundings, 2006090600Z 5 GOSRO soundings, 2006090700Z 3 GOSRO soundings, 2006090800Z

17. Track forecast from Exp. RT and 3DVAR for the different initial times Init. At 2006090600Z Init. At 2006090700Z Init. At 2006090800Z

18. Track forecast errors at the different initial times Red numbers indicate the smaller errors between Exp.RT and 3DVAR.

19. Summary and conclusions • FORMOSAT-3/COSMIC GPSRO data can be successfully assimilated with the Local (Refractivity) observation operator in WRFVar (3DVar), including I) download the bfrPrf data from CDAAC; 2) decode the bfrPrf data to be a LITTLE_R ASCII file; c) preprocess (3DVAR_OBSPROC) the data to be a 3DVar obs file (obs_gts.3dvar); 4) WRFVar (3DVar). • The experiments with assimilation of GPSRO data for Hurricane Florence were conducted. In compared the results from 3DVar with those from the real-time WRF-ARW forecast, the COSMIC GPSRO data assimilation showed the positive impact on the track forecasts of Hurricane Florence although only few GPSRO soundings were available in this case.

20. END THANK YOU !