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Applications of GPS Derived data to the Atmospheric Sciences

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Title: 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
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 driftideal 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

11
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12
Occultation Geometry
a

13
Derivation of Geophysical Parameters

14
Occultation Movie
http//genesis.jpl.nasa.gov/zope/GENESIS/Backgroun
d/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
6
5
20
1
2
3
4
5
6
4
5
6
--- GPS --- ECMWF
21
2
3
1
5
4
5
6
4
6
--- GPS --- ECMWF
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

26
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27
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28
SuomiNet Worlwide
29
SuomiNet US
30
Passage of Javier Remnants over Tucson
http//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
35
C. Minjuarez-Sosa
36
Planetary Boundary Layer
F. Xie
37
F. Xie
38
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39
F. Xie
40
PBL top
F. Xie
41
Ionosphere
max
S. Syndergaard
42
max
S. Syndergaard
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 SSTs (NMC)

55
Temperature vs Heights
4
5
6
--- GPS --- ECMWF
56
GPS Zonal Mean Temperatures
Pressure
Latitude

57
GPS Zonal Mean Temperature Gradients
Large displacement
Least stability
58
ECMWF Zonal Mean Temperature Gradients
oscillations
Least stability
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
375 - 300
300 - 250
250 - 200
200 - 150
GPS
ECMWF
CCM3
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 (cont)
  • 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
72
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73
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74
GPS ECMWF ARM
75
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