Climate applications of a global, 2hourly atmospheric precipitable water dataset from IGS tropospher

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Climate applications of a global, 2-hourly
atmospheric precipitable water dataset from IGS
tropospheric products
Junhong (June) Wang Earth Observing
Laboratory National Center for Atmospheric
Research
Collaborators Liangying (Liz) Zhang (EOL), Aiguo
Dai (CGD), Teresa Van Hove and Ted Iwabuchi
(UCAR/COSMIC), and Joel Van Baelen (CNRS)
Thank Support from NOAA Climate Change Data and
Detection program
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Outline

• The analysis technique and GPS PW dataset
• Application 1 Quantifying systematic errors in
  global radiosonde humidity data
• Application 2 Diurnal variations
• Summary
• Future needs

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How does GPS estimate precipitable water?
ZPD ZHD ZWD
ZWD ZPD - ZHD
PW ? ZWD ? f (Tm)
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A global, 11-year, 2-hourly PW dataset from
ground-based GPS measurements(Wang et al. 2007,
JGR)
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Highlight of GPS-PW data
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Hurricane Ernesto (24 Aug 1 Sep. 2006)
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• Problems
• Errors and biases
• Spatial and temporal inhomogeneity
• Spatial sampling errors
• Diurnal sampling errors

Results The role of radiosonde observations in
climate studies is limited.
Solutions To quantify radiosonde errors and
correct them.
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Matched GPS and radiosonde data (lt 50 km in
distance, lt 100 m in elevation, lt 2 hours 14
types and 136 stations)

• Humidity sensors
• Capacitive
• Carbon hygristor
• Goldbeaters skin

Wang and Zhang (2008a)
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Systematic errors mean biases
Wang and Zhang (2008a)
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Impacts of the sensor boom cover on Vaisala RS80
dry bias
Wang and Zhang (2008a)
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Temporal inhomogeneity of radiosonde PW data
Miami, U.S.A
Suwon-Shi, Korea
Relative PW differences ( Radiosonde-GPS)
Beijing, China
Wang and Zhang (2008)
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Impacts of temporal inhomogeneity
Carbon hygristor
Capacitive
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PW diurnal variations in four regions
Europe
30-70S
Month
Month
LST
LST
mm
N.H. Mountains
Darwin region
Month
Month
LST
LST
Wang and Zhang (2008b)
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Seasonal variations of diurnal and sub-monthly
variability over Europe
GPS
NCEP/NCAR
JRA
ERA-40
mm
Wang and Zhang (2008c)
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Summary

• Dataset A global, 11-year, 2-hourly GPS-PW
  dataset is created from IGS tropospheric products
  for various scientific applications.
• Climate applications The dataset is used to
  quantify systematic errors in global radiosonde
  PW data, validate global reanalysis products and
  study diurnal variations.
• 3. More information
• Wang, J., and L. Zhang, 2008 Validation of
  Atmospheric Precipitable Water in Three
  Reanalysis Products using Ground-based GPS
  Measurements, extended abstract for Third WCRP
  International Conference on Reanalysis, Jan. 28
  Feb. 1, 2008, Tokyo, Japan.
• Wang, J., and L. Zhang, 2008 Climate
  applications of a global, 2-hourly atmospheric
  precipitable water dataset from IGS ground-based
  GPS measurements, J. of Geodesy, accepted.
• Wang, J., and L. Zhang, 2008 Systematic errors
  in global radiosonde precipitable water data from
  comparisons with ground-based GPS measurements.
  J. Climate, in press.
• Wang, J., L. Zhang, A. Dai, T. Van Hove and J.
  Van Baelen, 2007 A near-global, 8-year, 2-hourly
  atmospheric precipitable water dataset from
  ground-based GPS measurements, J. Geophys. Res.,
  112, D11107. doi10.1029/2006JD007529. .
• Wang, J., L. Zhang, and A. Dai, Global estimates
  of water-vapor-weighted mean temperature of the
  atmosphere for GPS applications. J. Geophys.
  Res., 110, D21101, doi10.1029/2005JD006215, 2005.

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Future Needs Recommendations on improving future
IGS products

• To continuously produce the ZTD product and
  maintain its long-term stability and high quality
  
• To reduce diurnal biases in the ZTD product
• To improve and increase sfc-met data
• To co-locate with radiosonde stations
• To increase the spatial and temporal coverage

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1. To maintain long-term stability and high
quality of the ZTD product
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4. To co-locate with radiosonde stations

• Provide long-term, high-quality climate records
• Constrain/calibrate data from more
  spatially-comprehensive global observing systems
• Measure large suite of co-related climate
  variables

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5. To increase the spatial and temporal coverage
13 stations with complete 10-year (1997-2006)
GPS-PW record
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5. To increase the spatial and temporal coverage
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Towards a GCOS Reference Upper Air Network
(GRUAN)

• Initiation
• 10/2004 GCOS Implementation Plan Key Action
  12 To establish a high quality reference network
  of about 30 precision radiosonde stations and
  other collocated observations (2005-2009)
• Motivation
• Problems for climate in accuracy, long-term
  stability
• Changes in measurement systems
• Objectives
• Provide long-term, high-quality climate records
• Constrain/calibrate data from more
  spatially-comprehensive global observing systems
  (including satellites)
• Measure large suite of co-related climate
  variables

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2. To reduce diurnal biases in the ZTD product
?PW/PW ?ZTD/ZWD ?PW/PW5 ZWD113mm ZTD2334
mm Requirement ?ZTD/ZTD0.24
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3. To improve and increase sfc-met data
Connections between water vapor and precipitation
(Foster et al. 2000, 2003 Champollion et al.
2004)
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3. To improve and increase sfc-met data
Change of P sensor on July 20, 2000
10/1999 7/2000
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Global PW diurnal anomaly

• The diurnal cycle is less than 5 of annual mean
  PW
• Larger magnitude in summer than in winter
• Peak around late afternoon to early evening
• An order of magnitude smaller than seasonal
  variation

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Diurnal sampling errors

• 2/3 of global stations launch sondes twice
  daily, 1/6 at 00 UTC and 1/6 at 12 UTC
• The sampling error is generally small (?2) for
  2-daily soundings
• The sampling error can be as much as 10-15 for
  1-daily sounding at some stations
• Suggesting that in order to get a unbiased
  monthly mean PW, at least twice daily soundings
  are required.

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Precipitable water (PW, TCWV, IWV, PWV)
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Goal 4Values for GRUAN NAME (Summer 2004)