1. Long-term analyses of surface shortwave irradiance, clouds and aerosols over China T. Hayasaka 1, K. Kawamoto 1, and G.Y. Shi 2 1.Research Institute for Humanity and Nature, Kyoto, Japan 2. Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

2. 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 to the surface SW irradiance trend Contents

3. 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)

4. 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)

5. (W/m2)

6. 1961-2000

7. Comparison with FD for 1991-2000

8. The downward surface SW irradiance S for non-reflecting surface condition is formulated by following equation,, where S 0 is incident solar irradiance at the top of atmosphere. A c shows total cloud amount. T a and T c are transmittance of clear sky and cloudy sky atmospheres, respectively. T c is the function of aerosol optical thickness  a, cloud optical thickness  c, and precipitable water vapor w, and T a is the function of  a and w,,..

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

10. Kaiser (1998, GRL) Total cloud amount trend for 1951 - 1994

11. Averaged over China

17. Beijing, Summer CLOUD AEROSOL Sfc  = 1~ 2  F = 10~40(W/m 2 ) for Overcast condition

18. Beijing, Summer CLOUD AEROSOL Sfc  ~ 0.2  F ~ 16(W/m 2 )

19. SW in averaged tauc, taua and wv in Jul (W/m 2 )

20. Total cloud amount in July 0 30 60 90(%)

21. Cloud optical depth in July (ISCCP D2)

22. RF due to 10% increase in cloud optical depth (ave. cld amt) (W/m 2 )

23. Aerosol optical depth in July (MODIS)

24. RF due to 10% increase in aerosol optical depth (ave. cld amt) (W/m 2 )

25. 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.

26. Beijing, Summer CLOUD AEROSOL Sfc  W  (1970-1990) ~1mm  F ~ 1(W/m 2 )

27. (Zhai et al., 1997)

28. Total water vapor in July (ECMWF) (cm)

29. RF due to 10% increase in total water vapor (+cld amt) (W/m 2 )