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. Uses of GPS Recreational Uses (boating,aircraft, hiking) Surveying Fleet tracking Roadside Assistance (OnStar) GeoCaching: people hunt for treasure with only coordinates as a clue

8. 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

9. 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

10. 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

12. Occultation Geometry 

13. Derivation of Geophysical Parameters

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

15. 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

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

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

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

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

20. 456 --- GPS --- ECMWF 123 4 56

21. 456 --- GPS --- ECMWF 1 23 4 5 6

22. 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

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

24. CHAMP Temp Profile

25. 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

28. SuomiNet Worlwide

29. SuomiNet US

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

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

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

33. Temperature Measurement October 2001

34. Water Vapor Measurements C. Minjuarez-Sosa

36. Planetary Boundary Layer F. Xie

40. PBL top

41. Ionosphere S. Syndergaard max

42. S. Syndergaard max

43. 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

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

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

46. 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

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

48. 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

49. Gaffen et al. Study

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

51. 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)

52. Coverage of Occultations June 21 – July 4, 1995

53. ECMWF Data Global 6 hour analyses (not reanalyses) 1º x 1º horizontal resolution 31 vertical levels (up to 30mb) High resolution and accuracy make it a good comparison to GPS Interpolated to GPS occultation locations in the JPL Processing System

54. NCAR Community Climate Model (CCM3) 18 vertical levels, ranging from the surface up to 2.9 mb horizontal resolution of 2.8° x 2.8° CCM3 data both horizontally and vertically interpolated to GPS occultation locations Uses Zhang and McFarlane deep convection scheme, Slingo expression for shortwave radiation Model forced by observed SST’s (NMC)

55. Temperature vs Heights 456 --- GPS --- ECMWF

56. GPS Zonal Mean Temperatures Latitude Pressure

57. Large displacement Least stability GPS Zonal Mean Temperature Gradients

58. ECMWF Zonal Mean Temperature Gradients Least stability oscillations

59. GPS - ECMWF Zonal Mean Gradient Differences

60. ECMWF - CCM3 Zonal Gradient Difference

61. -2K/km 0K/km

62. NH/SH Asymmetry

63. ECMWF Zonal Mean Gradient Standard Deviations

64. CCM3 Temperature Gradient Standard Deviation

65. GPS Temp. Gradient Frequency

66. Temperature Gradient Histograms from 40S to 50S GPS ECMWF CCM3 375 - 300300 - 250250 - 200200 - 150

67. GPS/ECMWF/CCM3 Histograms Width and shape of variability differs greatly between GPS/ECMWF and CCM3 300 - 250 mb level: CCM3 variability much smaller than GPS or ECMWF Observed transition between stratosphere and troposphere GPS and ECMWF have significantly different distributions 250 - 200 mb level: CCM3 peak is more negative than observations indication of too high tropopause in CCM3 CCM3 has no skew while GPS/ECMWF have negative skew 200 - 150 mb level: CCM3 transition between troposphere and stratosphere GPS and ECMWF have a positive skew, CCM3 has a slightly negative skew.

68. Conclusions GPS and ECMWF are quite similar though they are completely independent CCM3 tropical/subtropical upper troposphere temperature gradients are similar to the observed temperature gradients CCM3 Polar tropopause is much too high CCM3 has a smooth transition from the tropics to the poles in the SH while the observations show a very steep drop around 35S

69. Conclusions (con’t) GPS observations exhibit larger lapse rate variability than CCM3 in general * Peak std dev. ~4.5 K/km (GPS) much larger than 2.0 K/km (CCM3) *CCM3 shows almost no variability associated with the tropical tropopause whereas GPS observations indicate it is a local maximum *In SH high latitudes, CCM3 has a local maximum in std dev while the observational std dev is decreasing towards the poles

70. Acknowledgements Rob Kursinski Feiqin Xie Stig Syndergaard Carlos Minjuarez-Sosa

71. GPS in the Arctic

74. GPS ECMWF ARM