Long-term analyses of surface shortwave irradiance, clouds and aerosols over China

T. Hayasaka1, K. Kawamoto1, and G.Y. Shi2

1.Research Institute for Humanity and Nature, Kyoto, Japan

2. Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

• Quality Control (QC) of CMA daily pyranometer data in China by three tests

• Comparison with satellite-derived data• Long-term trend of surface SW irradiance• Analyses of clouds and aerosols related t

o the surface SW irradiance trend

Contents

Evaluation of data (1)

• A set of quality control (QC) algorithm is used to test the qualities of daily solar global, direct and diffuse radiation data from 122 observatories in China during 1957 to 2000. The QC algorithms include three kinds of test.– Test of physical threshold (QC1): Global, direct, and diffuse solar

radiation data which fail to pass QC1 are 3.07%, 0.01%, and 2.52%, respectively.

– Sunshine duration test of global radiation (QC2): Global solar radiation data which fail to pass the QC2 are 0.77%.

– Standard deviation test of time series for averaged annual solar global radiation (QC3): Global solar radiation data which fail to pass the QC3 are 0.49%.

Shi et al., J.Climate, (submitted)

Evaluation of data (2)

• The ground-based routine irradiance data were compared with two satellite-derived datasets, i.e., ISCCP FD dataset and GEWEX SRB dataset.– The satellite-derived data overestimated surface shortwave

irradiance, particularly over large cities.– The positive biases can be attributed to aerosols with absorptive

properties.

Hayasaka et al., GRL(2006)

SW Radiation Averaged over China

110

120

130

140

150

160

170

180

190

200

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

SW

Rad

iati

on

(W

/m2

)

(W/m2)

80 90 100 110 120 130 140

20

30

40

50

-15 to -9-9 to -6-6 to -3-3 to 00 to 33 to 6

Global solar radiation trend (%/10yr)

80 90 100 110 120 130 140

20

30

40

50

80 90 100 110 120 130 140

20

30

40

50

-15 to -9-9 to -6-6 to -3-3 to 00 to 33 to 6

Global solar radiation trend (%/10yr)

1961-2000

80 90 100 110 120 130 140

20

30

40

50

-13 to -6-6 to -3-3 to 00 to 33 to 66 to 99 to 36

Global solar radiation trend (%/10yr)

80 90 100 110 120 130 140

20

30

40

50

80 90 100 110 120 130 140

20

30

40

50

-13 to -6-6 to -3-3 to 00 to 33 to 66 to 99 to 36

Global solar radiation trend (%/10yr)

Comparison with FD for 1991-2000

-2.5 -1.5 -0.5 0.5 1.5

Slope of the linear regression of FD for 1991 - 1999

(W/m2/Year)

The downward surface SW irradiance S for non-reflecting surface condition is formulated by following equation,

,

where S0 is incident solar irradiance at the top of atmosphere. Ac shows total cloud amount. Ta and Tc are transmittance of clear sky and cloudy sky atmospheres, respectively. Tc is the function of aerosol optical thickness a, cloud optical thickness c, and precipitable water vapor w, and Ta is the function of a and w,

,

.

S S0 1 Ac Ta AcTc

. wTT accc ,,

wTT aaa ,

From Qiu et al. (2000), Luo et al. (2001), Chu et al. (2003)

Kaiser (1998, GRL)

Total cloud amount trend for 1951 - 1994

45

50

55

60

65

70

75

2.5

3

3.5

4

4.5

5

5.5

6

6.5

84 86 88 90 92 94 96 98 100

tot-amt tot-tau

Tota

l clo

ud

am

ou

nt

Tota

l clou

d o

ptica

l de

pth

year

(%)

Averaged over China

0

100

200

300

400

0 5 10 15 20 25 30

a=1.0.ki=0.01.wv=2.0a=0.5.ki=0.03.wv=2.0a=0.5.ki=0.01.wv=4.0a=0.5.ki=0.01.wv=0.5a=0.5.ki=0.01.wv=2.0a=0.1.ki=0.01.wv=2.0

Cloud optical depth

(W/m2)

SW

irr

adia

nce

Beijing, Summer

CLOUD

AEROSOL

Sfc

20~105,

C

F

= 1~ 2

F = 10~40(W/m2)　 for Overcast condition

100

150

200

250

300

350

400

0 0.5 1 1.5 2

c=5.0.ki=0.01.wv=2.0c=5.0.ki=0.01.wv=4.0c=5.0.ki=0.03.wv=2.0c=10.ki=0.01.wv=2.0c=1.0.ki=0.01.wv=2.0c=5.0.ki=0.01.wv=0.5

Aerosol optical depth

SW

irr

adia

nce

(W/m2)

80~40

F

Beijing, Summer

CLOUD

AEROSOL

Sfc

~ 0.2

F ~ 16(W/m2)

SW in averaged tauc, taua and wv in Jul

(W/m2)

Total cloud amount in July

0 30 60 90(%)

Cloud optical depth in July (ISCCP D2)

RF due to 10% increase in cloud optical depth (ave. cld amt)

(W/m2)

Aerosol optical depth in July (MODIS)

RF due to 10% increase in aerosol optical depth (ave. cld amt)

(W/m2)

Summary

• There are clear decreasing trends of the surface SW irradiance in China during 1961 to 1989, and then changed to increase after 1990. “Global dimming and brightening”?

• ISCCP cloud data are not consistent with the SW irradiance trends in average over China.

• Cloud optical thickness change is more important than cloud amount change?

• Inter-annual variations of cloud optical thickness in each month are large.

• Aerosol direct effect is not negligible for the long-term-trend of surface SW irradiance.

150

200

250

300

350

400

450

0 1 2 3 4 5 6

c=10.a=0.5.ki=0.01c=5.0.a=1.0.ki=0.01c=5.0.a=0.5.ki=0.03c=5.0.a=0.5.ki=0.01c=5.0.a=0.1.ki=0.01c=1.0.a=0.5.ki=0.01

SW

irr

adia

nce

Water napor amount

(W/m2)

(g/cm2)

Beijing, Summer

CLOUD

AEROSOL

Sfc

)//(1~5.0 2 mmmWW

F

W(1970-1990) ~1mm

F ~ 1(W/m2)

(Zhai et al., 1997)

Total water vapor in July (ECMWF)

(cm)

RF due to 10% increase in total water vapor (+cld amt)

(W/m2)