GERB STM, Exeter, Oct. 2006 1

SW Diurnal Errors in ERB

monthly means: some studies from

CERES and GERB

LMD/IPSLM. Viollier and A. Ben Rehouma

Ecole Polytechnique, Palaiseau, France

GERB STM, Exeter, Oct. 2006 2

Comparison between the SW monthly means over two regions

Reg#1the whole area(45°S-45°N/60°W-60°E)

Reg#2(35°-10°S/10°W-10°E) with systematic diurnal cyclesharp diurnal errors

SW standard deviationMonth: August

GERB STM, Exeter, Oct. 2006 3

SW Mean over Reg#1

Monthly Anomalydefined /all available years

Scanners

Nonscanner

ISCCP-FD

Negative trendSee also, Wong et al(2006) Zhang et al(2004), for the tropicalmean

GERB STM, Exeter, Oct. 2006 4

Regional Anomaly (Reg#2 – Reg#1)

Nonscanner

ISCCP-FD+1.5 ± 3.0

+3.0 ± 0.8

Slope Wm-2/decade

± taking autocorrelation intoaccount, according to Weatherhead et al JGR (1998)

More on our Friday presentation

GERB STM, Exeter, Oct. 2006 5

Scanner Serie (Reg#2 – Reg#1) with Terra

with Averageof Terra andAqua

+5.0 ±1.5

+1.1 ± 2.0

GERB STM, Exeter, Oct. 2006 6

Diurnal corrections for CERES-Terra,several approaches

• SRBAVG geo products ( about 2 years, 2000/032004/05)

• Combination (or average) of Terra and Aqua (ES4, about 4 years, 2002/07 2005/12)

• Examination of GERB ARG Ed1 products 5 months: 2006, 04 to 08)

GERB STM, Exeter, Oct. 2006 7

Diurnal error, January 2003

Computed from differences betweenCERES SRBAVG GEO – NON GEO1 x 1°

Computed from differences between (Aqua+Terra) and Terra alone2.5 x 2.5 °

GERB STM, Exeter, Oct. 2006 8

Diurnal error, October 2003

GERB STM, Exeter, Oct. 2006 9

Terra-Terra_Aqua, reg 1

-2

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9 10 11 12

month

Flu

x (W

/m-2

) 2000

2001

2002

2003

2004

2005

SRBAVG nongeo-geo, reg 1

-2

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9 10 11 12

month

Flu

x (W

/m-2

) 2000

2001

2002

2003

2004

2005

SW Diurnal Errors, reg 2 (up) , reg 1 (down)

SRBAVG nongeo-geo, reg 2

-2

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9 10 11 12

month

Flu

x (W

/m-2

) 2000

2001

2002

2003

2004

2005

Terra-Terra_Aqua, reg 2

-2

0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8 9 10 11 12

month

Flu

x (

W/m

-2)

2000

2001

2002

2003

2004

2005

REG2

REG1

GERB STM, Exeter, Oct. 2006 10

Comparisons between contemporary T-(TA) and nonGeo-Geo / 2003

SW Diurnal Errors, reg 2-reg1 2003

0

2

4

6

8

10

12

14

1 2 3 4 5 6 7 8 9 10 11 12

MONTH

Flu

x (W

/m-2

)

reg2-reg1 T-TA

reg2-reg1SRBAVG

Agreement at least for these areas and their differences; the variations are higher for SRBAVG

GERB STM, Exeter, Oct. 2006 11

Same for Albedo , 2003 SRBAVG nongeo-geo, reg2-reg1

0,0000

0,0050

0,0100

0,0150

0,0200

0,0250

0,0300

1 2 3 4 5 6 7 8 9 10 11 12

month

Alb

ed

o

reg2-reg1

GERB STM, Exeter, Oct. 2006 12

GERB, 2006 July, 17-18LW flux SW flux

GERB STM, Exeter, Oct. 2006 13

Diurnal Cycle – August 2006

Area: 2.5x2.5°

X 1

00

GERB STM, Exeter, Oct. 2006 14

Albedo Diurnal Cycle – hourly means- off Angola Area: 2.5x2.5°

May 2006April 2006

July 2006 Aug 2006

GERB STM, Exeter, Oct. 2006 15

Albedo Diurnal Cycle – hourly means- Sahara Area: 2.5x2.5°

May 2006April 2006

July 2006 Aug 2006

GERB STM, Exeter, Oct. 2006 16

SW Monthly Means Computations with GERB

• Average the fluxes (2.5°x2.5°) and fill the 24x31 day-hour table

• Use ‘ERBE-type’ code, with Terra flux estimates (ES9- Ed1 - CV ) to compute monthly means

• Repeat using the GERB observed diurnal albedo variation shape in place of the ERBE modeled albedo

GERB STM, Exeter, Oct. 2006 17

GERB April 2006

GERB2006

GERB STM, Exeter, Oct. 2006 18

SRBAVG, TA and GERB April

GERB2006

SRBAVG2003

SRBAVG2002

TA2003

GERB STM, Exeter, Oct. 2006 19

SRBAVG, TA and GERB August

SRBAVG 2001 GERB2006

SRBAVG2003TA2003

GERB STM, Exeter, Oct. 2006 20

Summary of Diurnal Errors Wm-2

Reg2 – Reg1 JJA NDJ Year

SRBAVGnonGeo-Geo

4.6 10.4 6.5

Terra- Ave(Terra,Aqua)

4.2 9.4 6.6

GERB correction applied to Terra

4.9 - -

Caution: Not the same years for each case

GERB STM, Exeter, Oct. 2006 21

Conclusion• We have looked for inter-regional differences in the

evolution of the SW reflected flux (Reg1, Reg2)• Reg 2 (South East Atlantic): diurnal errors are critical

when using ES4-Terra (morning observation)• Significant agreement between 3 independent

evaluations of the relative diurnal errors (SRBAVG, Aqua, GERB); waiting for overlapping periods

• This is shown only for the studied regions and for their differences

• The 1985-2005 SW positive change (relatively to the average Reg1) observed with Terra seems slightly greater than the diurnal error

GERB STM, Exeter, Oct. 2006 22

Indo-French Megha-Tropiquessatellite project - 2009

Saphir : microwave sounder for water vapour sounding : 6 channels in the WV absoption band at 183.31 GHz. (cross track, 10 km)

MADRAS : microwave imager for precipitation : channels at 18, 23, 37, 89 and 157 GHz, H and V polarisations. (conical swath, <10 km to 40 km)

ScaRaB

GERB STM, Exeter, Oct. 2006 23

The three instruments of Megha-Tropiques

•ScaRaB : wide band instrument for inferring longwave and shortwage outgoing fluxes at the top of the atmosphere (cross track scanning, 40 km resolution at nadir)

•Saphir : microwave sounder for water vapour sounding : 6 channels in the WV absoption band at 183.31 GHz. (cross track, 10 km)

•MADRAS : microwave imager for precipitation : channels at 18, 23, 37, 89 and 157 GHz, H and V polarisations. (conical swath, <10 km to 40 km)