Abstract：The terrestrial solar spectrums record the imprints and information of sunlight passing through the atmosphere, it provides practical information for the study of atmospheric environment and ecological protection. Tibet is one of the world’s best-known areas with strongest solar radiation. Observation of solar radiation on the ground in Tibet can provide field data for solar energy utilization and research on atmospheric environment etc.. A systematic field observation was conducted to observe the surface solar spectrums, solar global irradiance and solar UV irradiance in Tibet by using the German RAMSES hyperspectral Irradiance Sensors, the Dutch CMP6 Pyranometers and the Norwegian NILU-UV Multi-filter Radiometers. The monthly spectral characteristics of Lhasa, Tibet, for 2017 were observed. The results of solar spectral observations at the local noons (13:55BJ) of Lhasa for the two equinoxes and the two solstices were reported. The ground spectra of Tibet were compared with the standard spectra of AM1.5 and AM0. The characteristics of global solar irradiance and solar ultraviolet intensity in Lhasa and Naqu of Tibet were observed and studied. It is found that the spectral intensities for visible and infrared lights in summer even exceed the corresponding wavelength spectral intensities of the AM0 spectra in Lhasa. In other words, the spectral intensities for visible and infrared lights on the surface of Lhasa occasionally exceed the spectral intensities of the corresponding radiation at the top of the atmosphere. The maximum spectral value of Lhasa usually occurs at wavelengths of about 476.6 nm, and the maximum observed in summer solstice in 2017 is about 2.331 W·m-2·nm-1. However, the observation of solar UV radiation (280～400 nm) spectrum shows that the spectral intensity of the ground solar UV region is always significantly lower than that of the corresponding intensity of the AM0 spectrum. Although Lhasa is located at about 3 680 meters above sea level, the ground measurements of the local noon solar UV spectrums indicate that the wavelengths less than 300 nanometers of UV irradiances are almost zeroes in Lhasa, which means that the solar UV irradiance with wavelengths less than 300 nm is absorbed by the atmosphere and does not reach the ground. It indicates that the short-wave solar UV radiations are absorbed effectively by atmospheric ozone. At the same time, the characteristics of the solar spectra at the high altitude of Tibet and lower places in Beijing and Chengdu are observed and studied, and the information on atmospheric composition and content in various places are revealed. The results of the solar global irradiance in Tibet during July of 2010—December of 2013 are reported. The results show that about 18% of the global irradiances in Lhasa exceed the solar constant (1 367 W·m-2). It is found that the instantaneous maximum value of the global irradiance in Lhasa reaches 1 756.09 W·m-2 (June 24, 2011). The observation results of solar UV radiation in Tibet during July of 2008—December of 2013 are also reported. The results show that the averaged daily maximum value of UVA for both Lhasa and Naqu is about 67 W·m-2, and the maximum value of UVB for the same places is about 5.1 W·m-2. The daily maximum values of UVA and UVB for both Lhasa and Naqu are maintained a good consistency. During the observation period of more than 5 years, there was no obvious enhancement or weakening trend for the UV intensities.
Key words：Tibet; Solar spectrum; Global irradiance; Solar UV irradiance
