Estimating net surface longwave radiation from net surface shortwave radiation for cloudy skies

Abstract

This work addresses the estimation of net surface longwave radiation (NSLR) from net surface shortwave radiation (NSSR) by analysing the Surface Radiation Budget Network (SURFRAD) radiation data under cloudy conditions. A general model is developed to estimate NSLR from the NSSR for cloudy skies with a root mean square error (RMSE) of 23.16 W m⁻² compared with in situ data. The model is applied to AmeriFlux data. The results show that the mean error and RMSE are –2.31 W m⁻² and 29.25 W m⁻², respectively, compared with the measurement of AmeriFlux. To examine the significance of the influence of seasons on the estimated NSLR, the model is proposed as a function of seasonal variation. The results show a slight improvement for winter and spring, whereas a larger error is found for autumn compared with the results obtained by the general model. The influences of land cover and elevation on the model are also investigated. The results show that the model is slightly sensitive to the normalized difference vegetation index (NDVI) and the elevation. The RMSE of the model decreases from 23.16 W m⁻² to 21.04 W m⁻² when the NDVI and the elevation are considered in the model.

Acknowledgements

This work was jointly supported by Excellent Young Talent Funds for Kezhen Distinguished Young Scholar in IGSNRR,CAS under grant 2012RC101, the Special Foundation of excellent doctoral dissertations of the Chinese Academy of Sciences and the National Nature Science Foundation of China under grant nos. 41171287 and 40801140. The authors would like to thank NOAA SURFRAD for providing the radiation data and the cloud fraction information data (ftp://ftp.srrb.noaa.gov/pub/data/surfrad/), the AmeriFlux network (http://public.ornl.gov/ameriflux/data-get.cfm) for the radiation data, and the Land Processes Distributed Active Archive Centre (LP DAAC) for providing the MODIS NDVI data products.