On downward shortwave and longwave radiations over high altitude regions: Observation and modeling in the Tibetan Plateau

Abstract

The downward solar or shortwave radiation (SWD) and atmospheric longwave radiation (LWD) play essential roles in controlling alpine environment and ecosystem. Meanwhile, utilization of solar energy has a growing demand by local residents, due to high energy cost in high altitude regions. However, it is always costly for acquiring the radiation data and there are few studies on the radiation modeling in these regions. This paper presented the major characteristics of SWD and LWD over the Tibetan Plateau (TP), which were measured at 11 stations built in the region. The results showed that LWD received by TP is much lower than that of its surrounding areas and their monthly-mean differences can be up to 100 W m −2. On the contrary, SWD over TP is significantly higher than that over its surrounding areas, due to low extinction rate of airmass, water vapor, and aerosol occurred in TP. The recorded maximum value (∼0.9) of daily-mean transmittances much exceeds the upper bound (∼0.75) implied in most of the Angström–Prescott models; therefore, these models may under-estimate SWD over TP. One set of surface data-based estimate by a non-Angström–Prescott model and two sets of satellite estimates were also evaluated against the measurements. It is found that the surface data-based estimate, though not calibrated locally, shows a good agreement with the measurements and has an advantage of producing less root-mean-square errors and higher correlation coefficients than the satellite estimates. Under this condition, it is suggested to combine both the surface data-based estimate together with the satellite estimates in order to improve the accuracy of the SWD and LWD data.