Abstract
Time series of daily UV radiation measured by the ground-based Brewer spectrophotometer #115 in Hong Kong during 1995-2005 were studied through statistics analysis, with focus on the variability and long term changes in relation to total ozone, clouds and AOD (Aerosol Optical Depth). The 11-year mean UV daily dose is 2644±262 J/m2, with maxima(3311 J/m2) in 2000 and minima (2415 J/m2) in 2002. The data were compared with that from TOMS (Total Ozone Mapping Spectrometer) Version 8 and show general agreement between the two. However, the Brewer UV measurement is about 10% lower compared to TOMS data. Apart from the common-known strong seasonal cycle, 26 month periodical was resolved by use of wavelet analysis, which was believed to be associated with quasi-biennial oscillation (QBO) of general circulation. In cloudy days, the annual mean UV daily dose decrease 3.5% to 44.5% compared to clear days. It was also found that surface UV irradiance has close relation to air pollution. Under clear sky condition, 1% AOD increase will lead to 0.2% UV decrease. While global UV radiation increase due to the worldwide observed ozone depletion, investigations indicate that this trend is not significant in Hong Kong during the last 11 years. The possible causes can be attributed to the compensative effect from two aspects. One is the increase of UV resulting from the reduction of clouds with rate of 0.56/10 yr. The other is the decrease of UV due to the enhancement of total ozone and AOD with a rate of 4.23 DU/10 yr and 0.33/10 yr, respectively.
Highlights
The ultraviolet (UV) radiation refers to solar radiation in the spectral band of 280nm to 400 nm, consisting of UV-A (315 to 400 nm), UV-B (280 to 315 nm) and UV-C, of which UV-B is the most dangerous portion of UV radiation that can reach the ground level
Time series of daily UV radiation measured by the ground-based Brewer spectrophotometer #115 in Hong Kong during 1995-2005 were studied through statistics analysis, with focus on the variability and long term changes in relation to total ozone, clouds and AOD (Aerosol Optical Depth)
The Brewer UV measurement is about 10% lower compared to total ozone measured by satellite (TOMS) data
Summary
The ultraviolet (UV) radiation refers to solar radiation in the spectral band of 280nm to 400 nm, consisting of UV-A (315 to 400 nm), UV-B (280 to 315 nm) and UV-C (less than 280 nm), of which UV-B is the most dangerous portion of UV radiation that can reach the ground level. The ground-based UV observations have been available in the world to measure the long term variability of UV radiation. Such monitoring sites are very scarce in Asia. The Hong Kong Polytechnic University first set up a YES broadband UVB-1 pyranometer and 1 spectral Brewer MKIV Ozone Spectrophotometer (spectral range: 290-325 nm) in 1994 and 1995, respectively to measure UV irradiance at the regional air monitoring station at Cape D’Aguilar. In 1999, the Hong Kong Observatory installed two Yankee Environmental System broadband UVB-1 pyranometers with a spectral range of 280-320 nm to measure the erythemal UV radiation at King’s Park meteorological station. In 1999, the Hong Kong Observatory installed two Yankee Environmental System broadband UVB-1 pyranometers with a spectral range of 280-320 nm to measure the erythemal UV radiation at King’s Park meteorological station. [3] reported that the UV Index often rises above 10 in a summer day from
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