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

forsythe@cira.colostate.edu

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