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 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 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 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)