Status of the assimilation of GPS RO observations: the COSMIC Mission

1. Status of the assimilation of GPS RO observations: the COSMIC Mission L. Cucurull JCSDA/UCAR J.C. Derber, R. Treadon, and R.J. Purser

4. Status • COSMIC successful launch, 14 April, 9:40pm Eastern time. • USAF Minotaur rocket • 6 Spacecraft deployed • Initial Orbit 500 km - final orbit 800 km, 71 degrees inclination, 6 separate planes. • All 6 satellites are healthy and functioning normally - preparing for orbit raising. • 6 GPS Radio Occultation Payloads in checkout phase • Payload hardware performing well - no problems noted- • Producing reasonable occultations • Payloads are being operated with the GPS payload on half time and TIP on full time. TBB is still going through its checkout process, operating occasionally. • A new version of GPS payload software is in the process of being loaded to all 6 satellites • Expect 2,000-3,000 occultations per day from constellation at final orbit

5. COSMIC (and CHAMP) data flow to JCSDA Input Data NESDIS CDAAC JCSDA BUFR Files file / sounding OSDPD

6. GPS Radio Occultation Basic measurement principle: Deduce atmospheric properties based on precise measurement of phase delay and amplitude.

7. GPS radio occultation measurements & processing Raw measurements of phase and amplitude of L1 and L2 s1, s2, a1, a2 Radio holographic method, Multi path Bending angles of L1 and L2 Spherical symmetry & Satellites orbits. a1, a2 Bending angle Single path a s1, s2 Refractivity Ionospheric effect cancellation N climatology Raw measurements of phase of L1 and L2 T, e, P Auxiliary meteorological data

8. Milestones accomplished (I) • GSI/GFS code - forward operators: • Local Refractivity: • Tested three different versions • Non linear forward operator • Linear forward operator • Improved linear forward operator • Implementation and testing completed of the forward, TL and Adjoint codes for the improved linear forward operator • Local Bending Angle: • Tested two different versions • Using approximations to solve the integral (ECMWF approach) • Solving the integral with less approximations and making use of the smoothed Lagrange-polynomial interpolators (NCEP approach) - easy upgrade to 2D • Implementation and testing completed for the forward TL and Adjoint codes for the NCEP forward operator.

9. Milestones accomplished (II) • QC, processing, data format • Superob vertical levels appropriate to model vertical resolution • Implementation of QC checks in the code (i.e. after UCAR QC) based on one month comparison (July 2005) of CHAMP observations of RO and model simulations (refractivity & bending angle). • Provide feed-back to UCAR on the comparison of observations and model simulations of profiles of refractivity & bending angle in order to improve their QC flags • Develop the model capability to read BUFR files for radio occultation observations. Conversion from WMO BUFR to NCEP BUFR formats. • Errors • Analysis of the RO errors in BUFR format and provide feed back to UCAR • Tune for representativeness of the model

10. An analysis case: 45 RO soundings (no other data) Refractivity 1st 2nd 3rd Bending angle O-FG (%) O-A (%)

11. Milestones accomplished (III) • Data Analysis (refractivity and bending angle) • Assimilation of a single observation of refractivity/bending (CHAMP) • Assimilation of a single profile of refractivity/bending (CHAMP) • Assimilation of all profiles available at a given analysis time • Observations of refractivity/bending alone • Observations of current (conventional and satellite) available observations alone • Both refractivity/bending and current observations together • Comparison between the analysis of soundings of refractivity and bending angle (CHAMP) • Impact no neutral • Different impact depending on the type of GPS RO observation being assimilated. • Data Assimilation impact studies (CHAMP): 2-month cycling with/without GPS refractivity/bending angle.

12. GSI/GFS Impact studies: Preliminary Results2-month cycling at T62L64 • JCSDA has implemented and tested the capability of assimilating profiles of Refractivity (N) and soundings of Bending Angles (BA) in the GSI/GFS DA system. • There are some encouraging preliminary results. Before being able to assimilate the RO data in operations we need to: • Understand the differences between the assimilation of N and BA. Why in some cases the assimilation of N results in a larger improvement than the assimilation of BA and visa versa? • Understand the strengths and weaknesses of the GPS RO data and the model in weather analyses and forecasts. Why does the assimilation of N or BA degrade the forecasts in some cases?

13. Current and future work • Finalize the ongoing experiments with CHAMP data in order to understand the differences between the assimilation of refractivity and bending angle. • QC • Superobs • Representativeness error • Correlated errors • Make sure that COSMIC RO files are providing what they are supposed to. • Preliminary analyses/assimilation of COSMIC observations for more tuning of GSI/GFS. • Keep providing feed back to UCAR/CDAAC on the quality of the GPS RO profiles. • Parallel runs with COSMIC data to select a Forward Operator (refractivity or bending angle) for operations. In addition, this will require some updates of the GSI code: • Sigma to hybrid vertical coordinate • Log(surface pressure) to surface pressure • Transition to operations. • Evaluate more sophisticated forward operators (2D).