Applications of GPS Derived data to the Atmospheric Sciences

1. Applications of GPS Derived data to the Atmospheric Sciences Jaclyn Secora Trzaska

2. Overview • History of GPS • How GPS occultations work • 3 GPS campaigns • Applications of GPS • Characterizing the Atmosphere using GPS: Zonal Means and Arctic

3. Global Positioning System (GPS) • 24 Operational Satellites currently in orbit • 12 hour, 20,000km circular orbits • Inclination angle, i = 55˚ • Transmits at 2 frequencies, 1575MHz and 1227MHz (19 and 24.4 cm)

4. GPS Satellite

5. GPS Orbits

6. History of GPS • Originally called Navigation System with Timing And Ranging (NAVSTAR) • Developed by the US Department of Defense to provide all-weather round-the-clock navigation capabilities for military ground, sea, and air forces

7. Radio Occultations • Been used for over 30 years to characterize planetary atmospheres • Occultation occurs as satellite “rises or sets” on the horizon as viewed by receiver • Uses a microwave transmitter (GPS) to send a signal to a receiver (LEO) on the opposite side of some medium of interest (atmosphere) • Medium characterized by effect it has on radio signal

8. Features of GPS Occultations • No long term drift—ideal for global warming detection • Global coverage (~500 soundings/day) • All-weather remote sensing system • Measures profiles of refractivity, density, temperature and pressure from surface to 50 km • Measures water vapor profiles in the troposphere, with accuracy of 0.2 g/kg • 0.5K accuracy for individual profiles • 100 meters vertical resolution

9. Some Theory • Assume spherical symmetry (no horizontal variations in temperature or moisture) • Relationship formed between refractive index and bending angle • Assume dry atmosphere, pressure and temperature are found

11. Occultation Geometry a

12. Derivation of Geophysical Parameters

13. Occultation Movie http://genesis.jpl.nasa.gov/zope/GENESIS/Background/Movie

14. GPS/MET: The First Campaign • April 3, 1995 to March, 1997 • 100 to 150 occultations per day • 1 Low Earth Orbiting Receiver orbiting at ~775km

15. GPS/MET Coverage June 30, 1995 www.cosmic.ucar.edu/gpsmet

16. GPS/MET Coverage June 21, 1995 to July 4, 1995 www.cosmic.ucar.edu/gpsmet

17. GPS/MET Profiles genesis.jpl.nasa.gov/html/missions/gpsmet

18. Location of GPS Occultations 1 2 3 4 6 5

19. 1 2 3 4 5 6 4 5 6 --- GPS ---ECMWF

20. 2 3 1 5 4 4 5 6 6 --- GPS ---ECMWF

21. CHAMP • German satellite, launched in 2000 • Collecting data since February 2001 • Approximately 250 occultations per day • Scheduled to be in orbit for 5 years • Used for gravity field magnetic field and electric field recovery and atmospheric limb sounding

22. CHAMP Orbit http://op.gfz-potsdam.de/champ/index_CHAMP.html

23. CHAMP Temp Profile

24. SuomiNet • Network of GPS receivers located at or near universities • GPS receivers are ground based • provide realtime atmospheric precipitable water vapor measurements and other geodetic and meteorological information. • http://www.suominet.ucar.edu

27. SuomiNet Worlwide

28. SuomiNet US

29. Passage of Javier Remnants over Tucson http://www.gst.ucar.edu/gpsrg/realtime/

30. Hurricane Katrina • http://www.suominet.ucar.edu/katrina/katrina.mov

31. Applications of GPS • Temperature Measurement • Water Vapor Measurement • Planetary Boundary Layer • Ionosphere

32. Temperature Measurement October 2001

33. Water Vapor Measurements C. Minjuarez-Sosa

34. C. Minjuarez-Sosa

35. Planetary Boundary Layer F. Xie

36. F. Xie

38. F. Xie

39. PBL top F. Xie

40. Ionosphere max S. Syndergaard

41. max S. Syndergaard

42. Some Other Applications • Climate research • all weather viewing • Global dataset • Unaffected by aerosols • Long term accuracy • Assimilation into Weather Forecasts • Tropopause dynamics • Gravity field, magnetic field

43. An Investigation into Observed and Modeled Global Atmospheric Stability Jaci Secora, Rob Kursinski, Andrea Hahmann, Dan Hankins

44. Overview • Motivation of Study • GPS/MET Mission • ECMWF Analysis • NCAR Community Climate Model • GPS/ECMWF/CCM3 Comparisons • Conclusions

45. Motivation of Study • Sinha, 1995 showed that lapse rate feedback is important in determining the equilibrium surface temperature when the climate system is perturbed • 6% reduction in LR produces a 40% amplification in water vapor feedback, while a 12% increase extinguishes it • 2000 study by Gaffen et al. looked at the observed decadal change in lapse rate and determined that some climate models were not correctly depicting it

46. Purpose of Study • Study evaluates representation and variability of stability in climate models as well as characterizing the stability in the real atmosphere

47. Gaffen et al. (2000) • Examined 2 time periods: 1960 -1997 and 1979 - 1997 • 1960 - 1997: Overall stabilization of atmosphere • 1979 - 1997: Overall destabilization of atmosphere • 3 models showed no change in stability, over both time periods

48. Gaffen et al. Study

49. Data Sets Used in this Study • GPS: Observations • ECMWF: Analysis = Model + Observations (Not GPS Observations) • CCM3: Model

50. GPS/MET Data • GPS occultation data offers unique combination of high vertical resolution, accuracy and global coverage needed for this study • GPS/MET Mission from April 1995 - February 1997 • Current study focused on June 21 to July 4, 1995 - Anti - Spoofing encryption turned off - Over 800 occultations collected during period - Period falls during the northern summer/ southern winter near the solstice (24 hours of day/night in the poles)