Abstract：Accurate measurement of solar spectra on the ground can provide field data for the inversion of the atmospheric environment, utilization of solar energy resources, and protection of plant ecology, etc. . According to current satellite and ground-based observations, Tibet is one of the regions with the strongest instantaneous solar irradiance on the earth due to factors such as high altitude and thin air. Observing the characteristics of solar spectral changes in Tibet is of unique significance for studying various fields such as human health, ecological changes, and solar energy utilization under strong radiation environments. From 2020 to 2021, we use the German RAMSES-ACC-VIS spectrometers and the Canadian SolarSIM-G high-precision spectrometers to study the solar spectra of five high-altitude areas in Tibet (Lhasa, Nyingchi, Nacqu, Shigaze and Tingri) for a whole year. For the first time, obtain one-year solar spectral field data from many places in Tibet, and record the daily averaged spectral irradiance of solar ultraviolet, photosynthetically active radiation and infrared radiation for every minute. The annual daily averaged solar spectral characteristics in Tibet are analyzed and studied. It is found that the highest daily averaged spectral peak of 1.12 W·m-2·nm-1 appeared at the wavelength of 477.30 nm. The seasonal variation characteristics of the solar spectra in Lhasa, a typical plateau region in Tibet, are studied, and the range of spectral irradiance between the solstices. It is found that the daily averaged spectral irradiance at the summer solstice in Lhasa is more than twice as high as that at the winter solstice. The peak value of the spectral irradiance at the summer solstice is about 1.13 W·m-2·nm-1, and that at the winter solstice is 0.43 W·m-2·nm-1. The fluctuation change of the annual solar spectra in Shigaze, Tibet is smaller than that in Lhasa. Its spectral change of each solar term is relatively concentrated. The difference between the summer and winter solstice's peak spectral values is smaller than in Lhasa. The characteristics of annually averaged solar spectral irradiance over Tibet are studied. It is found that the annually averaged solar spectral irradiance of Shigaze and Mt. Everest is very close, and the peak value of the two places is about 0.83 W·m-2·nm-1; The annually averaged spectrum of Lhasa is slightly lower than that of Shigaze and Tingri, with a peak value of about 0.73 W·m-2·nm-1; The annually averaged spectral curve of Nacqu is the lowest, with a peak value of only 0.53 W·m-2·nm-1. The annual mean value of the solar spectrum and the distribution characteristics of solar energy resources in different regions have important application value for developing and utilizing solar energy resources on the Tibetan Plateau. In order to compare the solar spectral characteristics of the Tibetan Plateau and the mainland plain, clear sky solar spectra of high altitude Lhasa (3 693 m) and low altitude Beijing (32 m) are observed and studied simultaneously. On June 3, 2021, both places are clear sky days; analyzing the local noon solar spectral characteristics in both places, it is found that the full band spectral integral value of Lhasa at noon is about 20% higher than that of Beijing, and only about 5% lower than that of Air Mass AM0. the peak of the local noon spectrum of Lhasa reaches 1.80 W·m-2·nm-1, and that of Beijing is about 1.40 W·m-2·nm-1; The solar UV spectral integral value of local noon in Lhasa was about 15% higher than that of in Beijing.
Key words：Tibet;Solar spectral;Observation;Solar energy
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