1. GPS Radio Occultation Sounding Zhen Zeng (HAO&COSMIC)

2. Occultation is from the Latin word “Occult” meaning “to hide”. Conditions: both a transmitter and a receiver off the planet of interest; Value: many “conventional” measurements (comprehensive, continuous, synoptic); Cost: expansive or cheap? Establishment of GPS constellation

3. April, 1995 GPS/MET Early temperature profile from GPS/MET

4. CHAMP SAC-C GRACE Ørsted Sunsat IOX T. P. Yunck

5. Basic measurements: precise measurement of phase delay and amplitude of GPS signals. Principles of occultation technique

6. The velocity of GPS relative to LEO must be estimated to ~0.2 mm/sec (velocity of GPS is ~3 km/sec and velocity of LEO is ~7 km/sec) to determine precise temperature profiles The LEO tracks the GPS phase while the signal is occulted to determine the Doppler LEO v leo v GPS Tangent point Principles of occultation technique

7. Atmospheric refractive index where is the light velocity in a vacuum and is the light velocity in the atmosphere Refractivity Hydrostatic dry (1) and wet (2) terms dominate below 70 km Wet term (2) becomes important in the troposphere and can constitute up to 30% of refractivity at the surface in the tropics In the presence of water vapor, external information information is needed to obtain temperature and water vapor Liquid water and aerosols are generally ignored Ionospheric term (3) dominates above 70 km (1) (2) (3)

8. 6 Satellites was launched: 01:40 UTC 15 April 2006 Three instruments: GPS receiver, TIP, Tri-band beacon Weather + Space Weather data Global observations of: Pressure, Temperature, Humidity Refractivity Ionospheric Electron Density Ionospheric Scintillation Demonstrate quasi-operational GPS limb sounding with global coverage in near-real time Climate Monitoring COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate)

9. COSMIC launch picture provided by Orbital Sciences Corporation All six satellites stacked and launched on a Minotaur rocket Initial orbit altitude ~500 km; inclination ~72° Will be maneuvered into six different orbital planes for optimal global coverage (at ~800 km altitude) All satellites are in good health and providing initial data Launch on April 14, 2006 Vandenberg AFB, CA Chris Rocken

10. COSMIC Ionospheric Data GPS Receiver TECProfilesScintillation TIP UV Radiation TBB ScintillationTEC From presentation by Stig Syndergaard, UCAR/COSMIC

11. Absolute TEC Processing Pseudorange local multipath Phase cycle-slip & outliers (Blewitt, 1990) Phase-to-pseudorange leveling Differential code bias (DCB) calibration From presentation by Stig Syndergaard, UCAR/COSMIC

12. Pseudorange Local Multipath Calibration From presentation by Stig Syndergaard, UCAR/COSMIC

13. Pseudorange Local Multipath Calibration From presentation by Stig Syndergaard, UCAR/COSMIC

14. LEO Differential Code Bias Estimation From presentation by Stig Syndergaard, UCAR/COSMIC

15. LEO Differential Code Bias Estimation From presentation by Stig Syndergaard, UCAR/COSMIC

16. Electron Density Profile Processing Subtracting positive elevation angle data from negative elevation angle (Schreiner et al., 1999) Model independent estimate of upper boundary electron density (Syndergaard et al., 2006) Profile retrieval based on straight-line and spherical symmetry assumptions

17. First Collocated Ionospheric Profiles From presentation by Stig Syndergaard, UCAR/COSMIC

18. COSMIC Occultation Over South Atlantic: 1815 UTC Black: Cosmic Blue: IRI Red: IDA3D Horizontal Lines Representation Error From presentation by Gary S. Bust, Atmospheric & Space Technology Research Associates

19. COSMIC NmF2 - 1 week From presentation by Bill Kuo, UCAR/COSMIC

20. Quiet Storm COSMIC #2 GAIM Comparisons During Quiet and Disturbed Conditions From presentation by Ludger Scherliess, Utah State University

21. Comparison of NmF2 and HmF2 between COSMIC and GAIM during Apr. 21-28, 2006 Good agreement of NmF2 between COSMIC and GAIM; Higher peak heights from GAIM than those from COSMIC

22. Comparison of Ne(h) between COSMIC (red), Ionosondes (green)and TIEGCM (black) on Aug. 17 - 21nd COSMIC agree well with ionosonde obs, especially the HmF2; Vertical structures from COSMIC coincide well with TIEGCM in the mid- lat, but not in the tropics. TIEGCM shows a bit higher HmF2 compared with obs.

23. COSMIC agree well with ionosonde observations; Global map of NmF2 revealed from COSMIC is well represented by TIEGCM model, though TIEGCM shows higher peak density in the low latitude. Maps of NmF2 for: COSMIC (dots), Ionosondes (stars), TIEGCM (contour)

24. RED = COSMIC sat BLUE = GPS sat Formosat-3/COSMIC Observations of Scintillations From presentation by Chin S. Lin, AFRL

25. TIP 135.6-nm passes 14 Sep 2006 FM1 FM3 FM6 0-24 UT (2100 LT) From presentation by Clayton Coker, NRL

26. COSMIC Radiosondes COSMIC Soundings in 1 Day Chris Rocken About 90,000 soundings / month Or ~10 soundings / 2.5 x 2.5 pixel / month All local times sampled every day!

27. COSMIC Education Module A joint effort by COMET and COSMIC. It covers: - Basics of GPS radio occultation science - Applications to weather, climate, and ionosphere - COSMIC Mission description http://www.meted.ucar.edu/COSMIC/

28. http://www.cosmic.ucar.edu * Select the 'Sign Up ' link under COSMIC Accept data use agreement * Enter information: Name, Address, email, user_id, Password, planned use of data An email will be sent within 2-3 business days to indicate access has been granted. COSMIC Data Access More than 335 users have already registered

29. Applications Atmospheric science and weather forecasting Global change and Climate Ionospheric monitoring and space weather

30. Using GPS temperatures to study the extratropical tropopause 1) Observational characteristics of double tropopauses Occurs frequently, related to interaction between tropics and extratropics acd.ucar.edu/~randel (see also Schmidt et al., GRL, 2006) 2) The tropopause inversion layer W. Randel

31. Equatorial QBO -- T. Schmidt, Atmos. Chem. Phys., 2005 Diurnal tides

32. Some promising forecast scores in the stratosphere. EG, verification against radiosonde at 100 hPa. Red = COSMIC experiment. The results in the NH are new. We had not seen improvements in NH with CHAMP. Note that the improvements are generally statistically significant at the 5% level. NH TR SH Sean Healy

33. Shu-peng Ho Validation of Microwave Lower Stratosphere Temperatue using CHAMP RO data

34. Study ionospheric Irregularities Pavelyev, GPS solution, 2005 : Amplitude scintillations averaged in 40-80 km interval

35. Questions for the future Retrieval Problem -- Ionosphere residual -- Spherical symmetry assumption -- Orbits -- Multipath -- Cycle slips, qualtiy control … What is optimal assimilation variables? What is optimal processing strategy for climate records?