Comparison of ground-based measurements of solar UV radiation at four sites on the Tibetan Plateau

Abstract

We compare results for the UV index (UVI), the total ozone column (TOC), and the radiation modification factor (RMF, being 1 in the absence of clouds and aerosols) at four sites on the Tibetan Plateau. The results were obtained by analyzing ground measurements by multichannel moderate-bandwidth filter instruments for the period July 2008-September 2010, and radiative transfer modeling was used to aid the interpretation of the results. The highest UVI of 20.6 was measured in Tingri (28.7°N; 4335 m). For July, monthly mean UVI values were 14.5 and 12.9 in Tingri and Lhasa (29.7°N; 3683 m), respectively. Generally, the UVI levels in Tingri and Lhasa were higher than in Nagchu (31.5°N; 4510 m) and Linzhi (29.7°N; 2995 m), due to less cloud cover at the former two sites. In 2009, the annual mean UVI and RMF values were 6.8 and 0.7 for Linzhi, 8.8 and 0.92 for Lhasa, 10.5 and 0.92 for Tingri, and 6.7 and 0.7 for Nagchu. Radiative transfer simulations indicate that the latitude difference would correspond to an increase in the UVI of about 0.3 from Nagchu to Tingri; whereas, the altitude difference would correspond to a reduction of about 1.5%, implying that the observed difference is due to the difference in cloud cover. The annual mean TOC values were found to be 260-264 Dobson units (DU) in Lhasa, Linzhi, and Nagchu, and 252 DU in Tingri. TOC values in Lhasa were found to agree within 3% with those derived from Ozone Monitoring Instrument (OMI) measurements.

Validation of ozone monitoring instrument ultraviolet index against ground-based UV index in Kampala, Uganda

“…In similar studies conducted at several sites on the Tibetan Plateau, Norsang et al [10] found TOC values derived from NILU-UV measurements at all sites to have a mean relative difference of 0.6 3.1% compared with those derived from OMI measurements. Fan et al [11] developed a neural network-based method to infer TOC and cloud optical depth values directly from irradiances measured with multichannel, moderate bandwidth filter instruments.…”

Impact of particulate and dissolved material on light absorption properties in a High-Altitude Lake in Tibet, China

“…a Belzile et al (2004) b Davies-Colley et al (1984) c Tahoe Environmental Research Center (2015) d Rose et al (2009) e Hargreaves et al (2007) f Belzile et al (2002) g Liu et al (2009) h Mitamura et al (2003) above 4,000 m on the Yungui Plateau, China (Zhang et al, 2010) and Lake Puma Yumco, China , the latter being located on the TP. The low Chla concentrations in Lake Namtso water can be related to harsh environmental conditions with a short growing season [normally from mid-May until midSeptember (Dorji et al, 2013)], low temperatures [average annual temperature of À0.16 C (Kang et al, 2011)], and high UV exposure [UV index above 15 on TP (Norsang et al, 2014)]. The high Chl-a concentrations observed at the surface of St. 1 in late July 2013 compared to those observed at St. 2-St. 5 in the same period (see Fig.…”

“…On the TP, most lakes having an area larger than 1.0 km 2 are located at altitudes above 4,000 m (Jiang & Huang, 2004) and have a low content of biota because of harsh environmental conditions, such as a short growing season, low temperatures, and low nutrient inputs. Also, lakes on the TP are exposed to high fluxes of UV radiation (Norsang et al, 2009;Norsang et al, 2011;Norsang et al, 2014) due to the natural increase of UV radiation with altitude (Blumthaler et al, 1992;Alexandris et al, 1999) and the existence of a low total ozone column during summer (June-September) (Zhou et al, 2006). UV radiation has impact on both zooplankton and phytoplankton in aquatic ecosystems (Vinebrooke & Leavitt, 1996;Tartarotti et al, 1999;Helbling et al, 2001;Sommaruga, 2001).…”

Long-term comparisons of UV index values derived from a NILU-UV instrument, NWS, and OMI in the New York area

“…However, Norsang et al [14] pointed out that the largest deviation of the NILU-UV instrument from a perfect cosine response is less than 3% for clear-sky conditions. We ignored this small deviation from a perfect cosine response in this study because it is expected to lead to small errors.…”

“…They found that the differences between UVI values derived from data acquired by the two kinds of instruments lie between 38.1% and 60.7%. NILU-UV instruments have been used to carry out additional investigations of UV exposure in Tibet [12,13], including a very recent study involving NILU-UV measurements of solar UV radiation at four sites on the Tibetan plateau at altitudes ranging from 2995 to 4510 m with very high UVI values (monthly July average of 14.5 for Lhasa at 3683 m) [14].…”