Taiping Zhang – Processing of the BSRN Data and its ... - GEWEX

Taiping Zhang 1 , Paul W. Stackhouse, Jr. 2 , Shashi K. Gupta 1 ,
Stephen J. Cox 1 , J. Colleen Mikovitz 1
1. SSAI / NASA Langley Research Center !
Hampton, Virginia, USA !
2. NASA Langley Research Center!
Hampton, Virginia, USA!
The 12 th Biennial BSRN Scientific Review and Workshop
01-03 August, 2012 Potsdam, Germany

Analysis of the original BSRN data before
and after quality check;
Processing of the data to generate
3-hourly, 3-hourly-monthly, daily and
monthly means;
Application of the processed data in
validating the GEWEX SRB(V3.0) data;
Trend analysis;
Conclusions.
2

Quality Flags for the BSRN Data:
01. Physically possible limit of G 1 (Global 1, or DIR+DIF);
02. Extremely rare limits of G 1 ;
03. Physically possible limit of I DIR (DIRECT SW) radiation;
04. Extremely rare limits of I DIR radiation;
05. Physically possible limit of I DIF (DIFFUSE) radiation;
06. Extremely rare limits of I DIF radiation;
07. Physically possible limit of I LW (DOWNWARD LW) radiation;
08. Extremely rare limits of I LW radiation;
09. Comparison of G 1 and G 2 (Global 2) ;
10. Comparison between I DIF and G 1 radiation;
11. I LW to AIR TEMPERATURE comparison.
The values and meanings of the Quality Flags are as
follows:
• 2: Suspected to be erroneous;
• 5: Cannot be performed;
• 9: Passed the procedure.

Logical Procedure to Reject “Bad” Values:
• If either Flag 01 or Flag 02 has value “2”, then G 1 is rejected;
• If either Flag 03 or Flag 04 has value “2”, then I DIR and G 1 are rejected;
• If either Flag 05 or Flag 06 has value “2”, then I DIF and G 1 are rejected;
• If either Flag 07 or Flag 08 or Flag 11 has value “2”, then I LW is rejected;
• If Flag 09 has value “2” and G 1 >0, then G 2 is rejected;
• If Flag 10 has value “2”, then I DIF and G 1 are rejected.
8

15-Minute Mean: requiring at least 1 x-minute value;
Hourly Mean: from 4 valid 15-minute means;
Hourly-Monthly Mean: requiring at least 1 day with
valid hourly mean for the corresponding hour;
3-Hourly Mean: from 3 valid hourly means;
3-Hourly-Monthly Mean: requiring at least 1 day with
valid 3-hourly mean for the corresponding time;
Daily Mean: from hourly means, with up to 5 or 12 hours
of either cosine or linear interpolations depending on the
variable and latitude;
Monthly Mean: i.) from daily means, requiring at least 1
daily mean in the month; ii.) from 24 valid hourly-monthly
means.
12

Daily Mean
14

Monthly Mean
15

Bias
(W m -2 )
RMS
(W m -2 )
σ
(Wm -2 )
ρ
N
G 1
-6.99 88.32 88.05 0.9475 597867
G 2
-4.39 88.13 88.02 0.9474 697862
Blended -4.96 88.38 88.24 0.9465 716742
17

SRB(V3.0)-BSRN SW Daily and Monthly Mean Comparisons
Daily
Monthly
22

SRB(V3.0)-BSRN LW Daily and Monthly Mean Comparisons
Daily
Monthly
23

GEWEX SRB(V3.0)-BSRN Comparison
Bias/(RMS) from 1992-01 to 2007-12!
BSRN SW G 1 Used with the Laxest Availability Control!
Model
3-Hourly
(W m -2 )
Daily
(W m -2 )
3-Hourly-
Monthly
(W m -2 )
Monthly
(W m -2 )
GEWEX SRB
GSW(V3.0)
-6.99
(88.32)
-3.58
(35.50)
-8.81
(47.43)
-5.22
(23.34)
GEWEX SRB
GLW(V3.0)
1.25
(30.50)
1.13
(22.16)
0.89
(13.75)
0.97
(11.18)
BSRN data from http://bsrn.awi.de/ as of 2011-08-22.

Dependence on Choice of Time Period
BSRN
SRB
References
• Weatherhead, E.C. et al., 1998. JGR, 103(D14), 17,149-17,161.
• Hinkelman, L.M., et al., 2009. JGR, 114, D00D20, doi:10.1029/2008JD011004.
• Liebmann, B., 2010. BAMS, November, 2010, 1485-1491.
27

Dependence on Choice of Time Period
Positive Trend
BSRN
SRB
28

Dependence on Choice of Time Period
Negative Trend
BSRN
SRB
29

As of August 2011, there are 5969 site-months of BSRN
data in archive from 48 of 52 BSRN sites, spanning a
period of 19 years and 7 months beginning from January,
1992;
Quality-flags are produced based on the methodology by
ETH and Long and Shi (2008). About 4% of the original
records are rejected through quality-check;
About 25% of the sites show G 2 -G 1 RMS errors above 25 up
to 54 Wm -2 . After quality check, all but one RMS errors
reduce to below 20 Wm -2 . The G 2 -G 1 bias error change is
not as dramatic except for ILO, FLO and DAA;
The site ILO has problems with G 1 , but its G 2 and longwave
values appear to be normal, as they agree with their
GEWEX SRB counterparts reasonably well;
30

SYO and GVN tend to be outliers in the SRB-BSRN shortwave
comparisons. This might be resulted from the questionable satellitebased
cloud identification over the snow-covered Antarctica;
The G 2 values at NYA, PAY, KWA, GVN and SPO are continuously
available for a 15-year period from 1993-01 to 2007-12. The
Weatherhead et al. (1998) method was used to determine the 95%
confidence intervals of trends of these sites and of their ensemble
average. The chosen time period for the trend detection ranges from
2 to 15 years. Over the 15-year period, the BSRN ensemble average
shows no significant positive or negative trend, but its SRB
counterpart shows a negative trend of very small magnitude.
Considering the uncertainties in the SRB data, no conclusions can
be made about these trends.
31

For More Information about GEWEX SRB:
http://gewex-srb.larc.nasa.gov
Taiping.Zhang@NASA.gov
The 12 th Biennial BSRN Scientific Review and Workshop!
01-03 August, 2012. Potsdam, Germany