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On the Validation and Intercomparison of Global Water Vapor Climate Data Records (CDR’s) from Satellites John M. Forsythe and Thomas H. Vonder Haar Cooperative Institute for Research in the Atmosphere Colorado State University Fort Collins, CO USA [email protected]. - PowerPoint PPT Presentation
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12nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
On the Validation and Intercomparison of Global Water
Vapor Climate Data Records (CDR’s) from Satellites
John M. Forsythe and Thomas H. Vonder Haar
Cooperative Institute for Research in the Atmosphere
Colorado State UniversityFort Collins, CO USA
22nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
Satellites are Essential for Climate Monitoring
The NASA Water Vapor Project
(NVAP) dataset, was originated at CIRA
in the early 1990’s to employ satellites to study water vapor.
Now covering 1988-2001, NVAP is a blended satellite
dataset designed to provide daily, global views of layered and
total water vapor.
NVAP data available at http://eosweb.larc.nasa.gov/PRODOCS/nvap/table_nvap.html
32nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
Motivation
Global Total Atmospheric Water Vapor
from 2xCO2 Model Run (Garratt et al., 1996)
22
23
24
25
26
27
28
29
1 50 99 148
Years from 1900
(mm
)
CSIRO Model
NVAP Observations
1950 2000 2050Year
The NVAP (1988 – 1999) global average of TPW is 24.5 mm, with no significant trend
• Water vapor in the atmosphere is expected to increase with warming (~ 7 % / K; Trenberth et al). Water vapor is a key greenhouse gas.
• Trends have been reported in surface and radiosonde observations (IPCC, 2001) and SSM/I over oceans (Wentz et al, 2000).
• What is the error in our water vapor CDR’s? Can we detect trends? How can new sensors (Aqua, GPS) be used to refine the water vapor CDR?
Wentz and Schabel (2000):
+ 2.1 % (~0.5 mm) / decade in Tropical Oceans (SSM/I)
Ross and Elliott (2001) (radiosondes) :
~3 % / decade over N. America
42nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
AMSU
SSM/T2
ATOVS
TOVS
SSMI(3)
TMI
TPW 0 20 40 60 80mm
AMSUAMSU
SSM/T2SSM/T2
ATOVSATOVS
TOVSTOVS
SSMI(3)SSMI(3)
TMITMI
TPW 0 20 40 60 80mm
0 10 20 30 40 50 60 70mm0 10 20 30 40 50 60 70mm
Multiple satellite products are
blended to create the NVAP dataset.
January 1, 2000 Total Precipitable
Water (TPW) shown here.
NVAP covers 1988 - 2001
Blended satellite products are often
used to measure climate variables:
(e.g. ISCCP, GPCP, NVAP)
Each sensor has strengths and weaknesses
52nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
20
21
22
23
24
25
26
27
28
1 13 25 37 49 61 73 85 97 109 121 133
1988 1999Months from January, 1988
Time series of NVAP Global Mean TPW, 1988 - 1999(m
m)
Annual Cycle ~ 10 % of Global Mean
62nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
Comparison of the Total Column Water Vapor, Sea Surface Temperature, and Lower Tropospheric Temperature Anomalies
- Global Means
-1.50
-1.20
-0.90
-0.60
-0.30
0.00
0.30
0.60
0.90
1.20
1.50
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
(mm
)
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
oC
Total Column Water Vapor Anomalies - NVAP
Lower Tropospheric Temperature Anomalies -MSUSea Surface Temperature Anomalies - Reynolds
Mt. Pinatubo Eruption March 1991
Major El Nino begins May 1997
Three Independent Satellite Measurements – Highly Coupled
Multiple, unrelated CDR’s
can reinforce each other
72nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
Global TPW Anomalies
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00J
an
-88
Ja
n-9
0
Ja
n-9
2
Ja
n-9
4
Ja
n-9
6
Ja
n-9
8
(mm
)
NVAP TPW
8-Radiosondeonly
6-SSMI only
3-TOVS only
NOAA Operational TOVS seems to be biased low and to have larger amplitude than SSM/I or radiosondes
82nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 | | | | | | | | | | | | | | |
F8
F10
F11
F13
F14
F15
5/95
5/97
4/99 1/00, 2/00
11/15
NVAP SSM/I Instruments Usage
3/00
1988, 1989, 1990, 1991, 1992 All months- F8
1993, 1994 All months - F10, F11
1995 All months - F10, F11, F13 starts 5/95, except: Jul - F10, F11 only
1996 All months - F10, F11, F13
1997 F10 ends 11/15, F11, F13, F14 starts May, except: Feb - F10, F11 only, Dec - F11, F14 only
1998 All months - F11, F13, F14, except: Apr - F11, F14 only, Aug - F11, F14 only
1999 F11 ends Apr, F13, F14
2000 F11 Jan and Feb, F13, F14, F15 starts March
2001 All months – F13, F14, F15
Every transition in this record represents
a challenge for climate monitoring
92nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
8 = Radiosonde data only
7 = TOVS and SSM/I combination
6 = SSM/I only
5 = SSM/I interpolated / TOVS combination
4 = SSM/I interpolated
3 = TOVS only
2 = Space interpolated-filled
1 = Time interpolated-filled
0 = Missing data
NVAP Mode (Most Common) Data Source Changes Through Time
Dominated by SSM/I over ocean
1996
1992
More TOVS soundings produced by NESDIS
after 1992
1988 - 1999
A reanalysis of NVAP is needed to reduce time-dependent biases
102nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
Ten GCOS Satellite Climate Monitoring Principles (from Tom Karl, NCDC)
Minimize orbit drift
Ensure sufficient overlap
Replace prior to failure
Rigorous pre-launchcalibration
Adequate on-boardcalibration
Continue baselineinstrument observations on decommissioned satellites
Operational production ofpriority climate products
Facilitate access to products,metadata, and raw data
Need in situ baselineobservations
Real-time monitoring of observing system performance
Use of multiple observing systems and multiple analysis teams (for the same variable)
The Unwritten Principle
These have not been achieved for the water vapor CDR
112nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
Conclusions
• The blended NVAP global TPW anomalies have no significant trend from 1988 – 1999.
• The operational TOVS record is discontinuous and has a downward trend. SSM/I and radiosonde show upwards global trends in TPW.
• There are some significant regional trends. Whether these are real climate trends or instrument & algorithm effects requires further study and NVAP reanalysis.
A climate dataset must be initially inspected for time-dependent biases, then it can be reanalyzed
to sharpen it’s ability to detect trends.
122nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
Work in Progress at CIRA - “Science Stewardship of Thematic Climate Data Records:
A Pilot Study with Global Water Vapor”
Supported by NESDIS/ORA
•Problem: Aqua water vapor products became available in mid-2002, but NVAP only covers through 2001. Aqua is the most capable water vapor-sensing spacecraft flown. How does Aqua compare to NVAP? GPS?• Solution: Create ~ 6 months of NVAP from 2003-2004 using heritage data and algorithms and compare to Aqua (AIRS/HSB, AMSR) and GPS.Expect to submit a journal paper with these results in December
Goal: Demonstrate scientific stewardship (Bates, 2004, AMS Satellite Conf.) applied to the water vapor CDR.
132nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
Backup Slides
142nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
Wentz and Schabel, Nature, Jan. 27, 2000
1.9 % / decade
2.1 % / decade
1.0 % / decade
152nd NOAA/NESDIS Cooperative Research Program Symposium July 13-14 2005 Madison WI
Figure 2.26: Trends in annual mean surface water vapour pressure, 1975 to 1995, expressed as a percentage of the 1975 to 1995 mean. Areas without dots have no data. Blue shaded areas have nominally significant increasing trends and brown shaded areas have significant decreasing trends, both at the 5% significance level. Biases in these data have been little studied so the level of significance may be overstated. From New et al. (2000). [IPCC 2001].
A similar trend analysis of NVAP is in progress at CIRA