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Cloud cover and water vapor observed at Oma site,Tibet
W ang Hong-shuai (National Astronomical Observatories of China) Kislovodsk 8.10.2010


Wang Hongshuai ­Kislovodsk ­ Oct.2010

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2008.11 Oma Site

40 m CT 2 tow er

4.5 m antenna Satellite communication w eather station 10m tow er
SBIG seeing m onitor

DIMM seeing dome
MIR cloud m onitor

R en ew al p o w er supply

Wang Hongshuai ­Kislovodsk ­ Oct.2010

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Cloud cov er Cloud surv ey equipement
Day time NIKON COOLPIX 8800 camera with Fish-eye camera (2005.11-now) Night time SBIG A340 all-sky camera(2009.11now)

Wang Hongshuai ­Kislovodsk ­ Oct.2010

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Day time all sky picture

Wang Hongshuai ­Kislovodsk ­ Oct.2010

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daytime cloud cov er data processing
The best threshold of blue and red component is 1.3 to distinguish the cloud The threshold is obtained by a libradtran simulation(huo juan et al)

30 ° 60 ° 75°

Red circle correspond to different zenith angle

Comparison of cloudiness between computation and observation by naked eye
Wang Hongshuai ­Kislovodsk ­ Oct.2010

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Night time all sky picture

Wang Hongshuai ­Kislovodsk ­ Oct.2010

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nighttime cloud cov er data processing

30 °

60 °

We try to develope an method to get the cloud information,use an adaptive Threshold in the different area of the picture,but the precision need to be improved 8 Wang Hongshuai ­Kislovodsk ­ Oct.2010


Oma daytime cloudiness results
Period 2005.10-2006.12 2008.11-2010.03 to ta l
Clear day c<1 Partly cloudy c<3 Usable day c<7 Num. days

4 0 .3 % 4 5 .1 %
4 2 .8 %

5 4 .0 % 5 7 .2 %
5 5 .7 %

7 1 .6 % 7 2 .4 %
7 2 .0 %

425 481
906

daily variation

Wang Hongshuai ­Kislovodsk ­ Oct.2010

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Daytime cloudiness monthly v ariation
10

9 8 7 6 5
4 3
2005
2006

c loudine s s

2008
2009

2 1 0 1 2 3 4 5 6 7 8 9 10 11 12

2010

month

sep to mar : April may,july and august :

more clear sky cloudy 10

Wang Hongshuai ­Kislovodsk ­ Oct.2010


Oma: night time cloudiness results
(based on observation by naked eye)
Period 2005-2006 2008-2010 average Clear night c<1 4 2 .7 % 4 7 .8 % 4 5 .8 % Partly c 69 66 67 c loudy <3 .0 % .5 % .5 % Usable night c<7 7 5 .4 % 7 5 .4 % 7 5 .4 % Num. nights 310 480 790

daily variation

Wang Hongshuai ­Kislovodsk ­ Oct.2010

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Night time monthly v ariation
10 9 8
7 c loudine s s

6 5 4 3
2

1 0 1 2 3 4 5 6 month 7 8 9 10 11 12

sep to mar : April may,july and august : The same as daytime

more clear sky cloudy 12

Wang Hongshuai ­Kislovodsk ­ Oct.2010


Precipitable W ater Vapor instrument
DTF-5 , Sun- Photometer ,made by Anhui Institute of Optics & Fine Mechanics( Chinese Academy of Sciences) Use 8 filter of different wavelength(before 2009.12,pwv only) wavelength(nm) 400 520 610 670 780 860 940 1050 bandwidth(nm) 7.60 8.70 10.00 9.50 10.40 12.60 10.60 10.00 Measure the intensity of solar radiation ,retrieve atmospheric aerosol optical depth and atmospheric precipitable water vapor

DTF-5 at Oma site

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Comparison to PGS-100
Bef ore our observati on at Oma, DTF-5 had compared to a japanese Sun-photometer(PGS-100) at same wavelen gth ,the PGS-100 was used in AERONET

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the relative error

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Precipitable Water Vapor Result at Oma
Period 200508-200612 200811-201003
average

M e dia n (mm) 2 .2 1 .3
1 .6

Percent. PWV<0.5 5 .0 % 1 0 .1 %
8 .1 %

Percent. PWV<1.0 2 3 .1 % 3 7 .4 %
3 1 .8 %

Percent. PWV<1.5 3 9 .2 % 6 1 .8 %
5 3 .0 %

Percent. PWV<2.0 4 6 .5 % 7 5 .1 %
6 3 .9 %

Num. days 260 406
790

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Atmospheric aerosol Optical Depth Results at Oma
Period

Media n

Avera ge

Percent . AOD<0. 05 8.3%

Percent . AOD<0. 1 68.1%

Percent . AOD<0. 2

Num. d ays

2009.112010.03

0.08

0.11

91.7%

144

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Thank you for your question

Wang Hongshuai ­Kislovodsk ­ Oct.2010

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