Monitoring Temperature Trends in Antarctica Using GPS RO

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Monitoring Temperature Trends in Antarctica Using
GPS RO

• Erick Adame
• Oneonta State College
• State University of New York
• adame_at_ucar.edu

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Outline

• GPS Introduction
• Summer Research Intro.
• Data Retrieval and Analysis
• Data Comparison
• Sampling Issues
• Future Work
• Comments / Questions

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EarthsLayers
Courtesy of IPCC (2001) Climate Change 2001
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GPS Radio Occultation

• GPS at a high Earth orbit on 6 planes.
• LEO satellites used to capture signals through
  Earths Atmosphere.
• Index of Refraction (N) calculated to create
  vertical sounding.

Courtesy of Aerospace Corporation
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GPS Radio Occultation
GPS Satellite
Radio Signal
LEO Orbit
LEO Satellite
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Characteristics of GPS RO Data

• Limb sounding geometry complementary to ground
  and space nadir viewing instruments
• High accuracy (equivalent to lt 1 deg K from 5-25
  km)
• High vertical resolution (0.1 km surface - 1km
  tropopause)
• No instrument drift

• All weather-minimally affected by aerosols,
  clouds or precipitation
• Independent height and pressure
• Requires no first guess sounding
• Independent of radiosonde calibration
• No satellite-to-satellite bias

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CHAMP

• Challenging Mini-Satellite Payload launched in
  2001.
• Similar to USA/Taiwan COSMIC mission to be
  launched in 2005.
• CHAMP is one satellite, COSMIC will have six.

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Summer Research
Objective 1 To determine if GPS data can more
precisely monitor global climate change.
Objective 2 To use GPS data to assess the
quality of global analyses used in climate
studies.
Courtesy of National Geographic
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Motivation
Anthes et al. 2003

• Lack of radiosonde stations over oceans and Polar
  Regions, difficult to monitor climate over Poles.
• Increasing demand for data in weather forecasting
  and climate models as their resolutions increases.

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Changing Globe

• CO2 gases increase globally, first major impact
  likely to occur at poles.
• Delicate to climate change contains ice sheets.
• Rising Sea Levels

Courtesy of NOAA
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Climate

• GPS sounding perhaps most accurate and stable
  global thermometer for estimating climate change
• GPS RO sounding is most accurate where
  model-predicted temperature changes are large
  upper troposphere and lower stratosphere

Meehl et al. 2000, J. Climate.
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6 Satellite COSMIC Microsat Constellation
Data Retrieval
S band
S band
28 GPS s/c
Taiwan OPS
S band
L band
R.O. RT Data E/S(Kiruna)
RT Fiducal Network
R.O. RT Data E/S(Fairbanks)

• Occultations occur between GPS and LEO Satellites
• Data is retrieved
• Data sent to CDAAC for Analysis and to be
  archived.
• Information distributed to many different users.

TTC
NSPO MOC, MCC, SCC, FDF
T1
T1
ISDN,Modem Internet
Frame Relay
Frame Relay
Payload Commands and All Real-Time Data Products
LAN
Real Time CDAAC (Boulder)
S/C Telemetry
C W B
T1
TACC
Frame Relay OR vBNSSTARTAPTanet, I2
Internet
Frame Relay
Internet
NESDIS
Other Users
U.S. Universities Mission Teams
University Science Centers
Other Customers
Operational Centers
All Frame Relay links backed up by Internet.
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Data Analysis Using CDAAC

• Monitor trends from 2001 to Present.
• Sample area 65ºS to 90ºS.
• Sample atmosphere from Surface up to 25 km.
• Divide atmosphere vertically.
• Compute average monthly temperatures for each
  layer.
• CHAMP, ECMWF, NCEP-RA, Radiosondes

Courtesy of www.siteatlas.com
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Data Analysis

• Plotting averages on one plot shall reveal
• Seasonal Trends
• Vertical Structure
• Antarctic Climate Trends
• Troposphere
• Stratosphere
• Compare trends detected by GPS data with global
  analyses and Radiosonde data

• Definition of Tropopause
• The lowest level at which the lapse rate
  decreases to 2 degrees C/km or less, provided
  also the average lapse rate between this level
  and all higher levels within 2 km does not exceed
  2 degrees C/km.
• - From WMO bulletin October 1957 (Vol. VI,
  number 4)

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CHAMP
Std. Dev.
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ECMWF
Std. Dev.
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NCPPRF
NCPPRF
NCEP-RA
Std. Dev.
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Radiosonde
Std. Dev.
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Data Comparison
CHAMP
ECMWF
NCEP-RA
Radiosondes
NCPPRF
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Data Comparison Tropopause Altitude
NCEP-RA
ECMWF
CHAMP
Radiosonde
Jan 02 June 02 Jan 03 June
03 Jan 04
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Data Comparison Tropopause Temperature
NCEP-RA
ECMWF
CHAMP
Radiosonde
Jan 02 June 02 Jan 03 June
03 Jan 04
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Sampling Issue
Grid Model Data

• CDAAC is occultation based.
• Comparisons are done based on occultation
  locations, not on location of other data source.

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Model domain / GPS RO
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Conventional observation network
Red dots are radiosonde stations Green dots are
surface stations
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Summary

• Advantages of GPS data are evident with CHAMP,
  will be even better with COSMIC in late 2005.
• Radiosonde does not provide uniform coverage,
  which poses a sampling problem.
• Global analyses hint at similar trends but unable
  to resolve with same detail.
• Further verification that ECMWF is closer to true
  values than NCEP-RA, even in climate studies.
• All data show a dramatic seasonal change in the
  stratosphere over Antarctica much cooler in 2003
  than 2002.

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Future Work

• -Address Two Issues
• SAMPLING ISSUE
• Compare CHAMP data with all model grid points.
• Compare CHAMP data with all Radiosondes at
  stations.
• RESOLUTION ISSUE
• How different are vertical structures with
  different data sources?

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Acknowledgements

• Bill Kuo, Bill Schreiner, Chris Rocken
• Mike Page
• Doug Hunt
• Karl Hudnut
• Kim Prinzi-Kimbro
• COSMIC Office
• SOARS Staff and Protégés

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Questions?
GPS Satellite
Radio Signal
LEO Orbit
LEO Satellite