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Use of GPS RO in Operations at NCEP

Use of GPS RO in Operations at NCEP. Lidia Cucurull NOAA Joint Center for Satellite Data Assimilation. Outline. Introduction to COSMIC mission and GPS RO technique. Status of the assimilation of GPS RO data into the NCEP’s Global Data Assimilation System.

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Use of GPS RO in Operations at NCEP

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  1. Use of GPS RO in Operations at NCEP Lidia Cucurull NOAA Joint Center for Satellite Data Assimilation

  2. Outline • Introduction to COSMIC mission and GPS RO technique. • Status of the assimilation of GPS RO data into the NCEP’s Global Data Assimilation System. • Pre-implementation impact studies with COSMIC. • Summary and future plans.

  3. COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) • 6 Satellites launched in April 15 2006 • Three instruments: • GPS receiver, TIP, Tri-band beacon • Demonstrate quasi-operational • GPS limb sounding with global • coverage in near-real time • Climate Monitoring • web page: www.cosmic.ucar.edu

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

  5. Characteristics of GPS RO Data • Limb sounding geometry complementary to ground and space nadir viewing instruments • High vertical resolution (0.1 km surface - 1km tropopause) • Lower horizontal resolution (~300 km) • High accuracy (equivalent to < 1 deg K from 5-25 km) • All weather-minimally affected by aerosols, clouds or precipitation • Independent of radiosonde calibration • No instrument drift • No satellite-to-satellite observational bias

  6. 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

  7. Forward Models: Refractivity: Bending angle:

  8. Milestones accomplished • The JCSDA developed, tested and incorporated into the new generation of NCEP’s Global Data Assimilation System (GSI/GFS) the necessary components to assimilate two different type of GPS RO observations (refractivity and bending angle). These components include: • complex forward models to simulate the observations (refractivity and bending angles) from analysis variables and associated tangent linear and adjoint models • Quality control algorithms • Error characterization models • Data handling and decoding procedures • Verification and impact evaluation procedures

  9. Milestones accomplished (cont) • COSMIC became operationally assimilated at NCEP on May 1st 2007, along with the implementation of the new NCEP’s Global Data Assimilation System (GSI/GFS). • Profiles of refractivity were selected for implementation in operations, while the tuning of the assimilation of bending angles is currently being analyzed at NCEP. • Several impact studies for selected periods show a positive impact in model skill when COSMIC profiles are assimilated on top of the conventional/satellite observations.

  10. GSI/GFS Impact study with COSMIC • Anomaly correlation (the higher the better) as a function of forecast day for two different experiments: • PRYnc (assimilation of operational obs ), • PRYc (PRYnc + COSMIC refractivity) • We assimilated around 1,000 COSMIC profiles per day • In general, the impact of the COSMIC data will depend on the meteorological situation, model performance, location of the observations, etc.

  11. November 2006

  12. Fit to rawinsonde (November 2006) • Dashed lines: PRYnc • Solid lines: PRYc (with COSMIC) • Red: 6-hour forecast • Black: analysis

  13. Summary • COSMIC became operationally assimilated at NCEP on May 1st 2007, along with the implementation of the new NCEP’s Global Data Assimilation System (GSI/GFS). • Profiles of refractivity were selected for implementation in operations, while the tuning of the assimilation of bending angles is currently being analyzed at NCEP. • Several impact studies for selected periods show a positive impact in model skill when COSMIC profiles are assimilated on top of the conventional/satellite observations. We have recently improved the assimilation of GPSRO profiles over complex topography.

  14. What’s next? • More evaluation of the assimilation of GPSRO profiles operationally. • Update QC checks and obs error for refractivity. • Improve the performance of the assimilation of observations of bending angle (switch to BA in operations?). • Testing, tuning and assimilation of GSPRO from CHAMP/GRACE (in pre-operational mode) and MetOp/A GRAS (when available). • Assimilation of GPSRO observations into the regional model. • Explore more complex FO to take into account horizontal gradients of refractivity.

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