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GNSS Radio Occultation: progress report

GNSS Radio Occultation: progress report . Lidia Cucurull and John Derber. Maryland, 24-25 May 2011. Outline. Status of current and future GNSS RO sensors Assimilation algorithms development Outlook. GPS RO sensors.

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GNSS Radio Occultation: progress report

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  1. GNSS Radio Occultation:progress report Lidia Cucurull and John Derber Maryland, 24-25 May 2011

  2. Outline • Status of current and future GNSS RO sensors • Assimilation algorithms development • Outlook

  3. GPS RO sensors • NCEP Global Data Assimilation System (GDAS) assimilates operationally the following RO instruments for total daily soundings of ~ 2,000: • COSMIC 1-6 (US and Taiwan) – since May 2007 • Metop/GRAS (Eumetsat) - since February 2010 • GRACE-A (Germany) - since February 2010 • SAC-C (Argentina) – since May 2011 • C/NOFS (US Air Force) – since May 2011 • TerraSAR-X (Germany) - since May 2011 • Near-operational monitoring of the systems above can be found in: http://www.emc.ncep.noaa.gov/gmb/gdas/ under “GPSRO Monitoring”

  4. Number of profiles 8 May 2011

  5. Quality control • We assimilate 95-96 % of the observations that we “can” assimilate. These numbers do not consider observations: • outside the model vertical grid • above 30 km (maximum height being assimilated)

  6. GPS RO sensors (cont’d) • NCEP is getting ready for the assimilation of: • Oceansat2/ROSA (Italian instrument) - already operational, data should be • available to NWP centers soon. • KOMPSAT-5 (Korea) – to be launched late 2011. • PAZ (Spain) – to be launched late 2012. • COSMIC-2 (US NOAA and Taiwan) – on track. Moving forward on the design. Total of 12 satellites with two launches. First launch planned by 2015 (equatorial orbit), second launch by 2017 (polar orbit).

  7. Assimilation code • Operational GDAS assimilates refractivity observations up to 30 km. • A forward operator to assimilate bending angle observations (a rawer product than refractivity) has been developed, implemented and tested at NCEP. Quality control procedures and observation error characterization have been tuned accordingly. • An earlier version of this forward operator was available at NCEP in 2006. The updated bending angle code has many improvements over the earlier version. • The bending angle code enables the assimilation of GPS RO observations up to 50 km – QC procedures and observation error structures have been tuned up to this height.

  8. Assimilation code (cont’d) • Algorithms to include the compressibility factors in the computation of the geopotential heights have been implemented in GSI to compute a more accurate forward operator for GPS RO. • Both refractivity and bending angle codes have the option to use the compressibility factors. • When the compressibility factors are used, the GPS RO forward operators use a more accurate set of refractive indices. • The use of compressibility factors will affect the assimilation of GPS RO observations as well as all the observations that use geopotential heights. In fact, any subroutine within GSI that makes use of the geopotential heights will be affected by the changes.

  9. Experiments to test bending angle • Period: 2 February 2011 – 22 March 2011 • PRREF: current operational model – assimilation of refractivities up to 30 km. • PRBNDZ: experiment – assimilation of bending angles up to 50 km & use of compressibility factors & updated refractive indices. • Both experiments use the current GFS model

  10. AC - 500 mb

  11. AC - 700 mb

  12. AC - 250 mb

  13. Tropical winds - rmse

  14. Assimilation code (cont’d) • The assimilation of GPS RO into NCEP’s regional system is planned to be implemented operationally in July 2011. • However, the use of GPS RO observations in the global model already provides feedback to the regional – through boundary and initial conditions. • COSMIC-derived PBL heights do not provide the necessary coverage to be used into RTMA. Future COSMIC-2 should fit the needs much better due to very large increase in daily sounding density. Technique to retrieve PBL heights tends to be more accurate over oceans and flat areas over land than over mountainous areas.

  15. Outlook • Monitor current GPS RO observations (maintain operational effectiveness). • Evaluate future RO sensors (as early as possible) to enable operational assimilation of the new data as soon as possible. • Transitioning from refractivity to bending angle in operational GDAS - code under final parallel testing for FY12 GSI implementation. • Document the results from NCEP’s bending angle forward operator – Cucurull Bending Angle Method (CBAM) ….. • Evaluate the impact of the assimilation of RO observations on the use of satellite radiances – work done by Ling-Ling Tsao, visitor from Central Weather Bureau in Taiwan. • Improve the assimilation of GPS RO observations (more accurate forward operators, quality control, etc).

  16. Outlook (cont’d) • Operational assimilation of ground-based GPS (precipitable water, zenith total delays) into GDAS - in collaboration with NOAA OAR/ESRL/GSD • Support NCEP/SWPC on the assimilation of GPS RO observations in space weather models. • Explore other uses of GPS RO technology – eg. reflections over sea – for future assimilation into GDAS.

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