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)