临安与龙凤山辐射数据质量及初步结果比较

Quality Evaluations and Comparisons of Radiation Data at Lin'an and Longfengshan Stations

采用国际通用的辐射数据质量评估方法对2005—2011年浙江临安、黑龙江龙凤山两个区域大气本底站辐射观测资料进行质量评估与比较分析。结果表明:两站辐射数据通过物理可能限制检验与极端罕见限制检验的百分比均超过99.5%,但通过相关要素比较限制检验的百分比上,临安与龙凤山站分别降至97.9%与95.9%;双轴定位追踪太阳出现偏差是造成直接辐射与散射辐射数据精度降低的主要原因。CM21表的热偏移在-5W·m^(-2)以内,而其进行热偏移订正可以显著提高数据的通过率。对应同一太阳天顶角,临安站晴空总辐射与直接辐射均低于龙凤山站,散射辐射则相反,其原因是临安的大气透明系数较低,大气浑浊度较高。2006—2011年,临安站的大气向下长波辐射呈下降趋势,达到了0.01的显著性水平,且其多年平均值(363.7±59.3W·m^(-2))显著高于龙凤山站(274.9±77.6W·m^(-2));龙凤山站晴空太阳总辐射呈增加趋势,达到了0.1的显著性水平。

Solar radiation is widely used in the studies of climate change, evaluation of model simulations and as- sessment of solar radiation energy resources. Therefore, accurate observations of solar radiation data are absolutely needed. An international BSRN method of solar data quality assessment and quality control （QA-QC） is applied to investigate data quality of solar radiation and downward long-wave radiation （DLR） measured from 2005 to 2011 at Lin＇an and Longfengshan, two regional background stations in the main- land of China. The method includes 3 steps of testing. They are the sequential limits of physically possi- ble, extremely rare and relevant factor comparison. The results show that percentages of radiation data meeting requirements of the first two test steps of the quality test at both sites are more than 99.5 %, but in the third step, the percentage dropped to 97.90% at Lin＇an and 95.9% at Longfengshan. The error of the 2AP （2 axis position） in tracking sun-disk is the main cause for those direct and diffuse radiation data failing to meet the conditions of quality test, and the scenario is more frequent at the high SZA （solar zen- ith angle）. Compared to the rate evaluated by the prevalent limit of global radiation error, the BSRN third step makes the rate of validated solar radiation data be reduced by 0.9%0 and 1.6% at Lin＇an and Long- fengshan, respectively. The thermal offset of CM21 pyrometer is from --5 W · m- 2 to --2 W · m-2. With the compensation of thermal offset, the rate of radiation data meeting requirements of the BSRN quality test is obviously improved. It is well known that the most important factor affecting the surface solar radiation includes cloud, water va- por and aerosol. Therefore, variations of solar radiation with changes of SZA are analyzed with removal of cloud effect. It is identified that the global and direct radiation irradiances at Lin＇ an are obviously lower than those at Longfengshan with the same SZA, while the diffuse radiation is opposite. The cause for these phenomena is due to the lower atmospheric transparency and higher atmospheric turbidity at Lin^an. The annual averages of solar radiation and DLR at the sites are calculated. The annual averaged daily integrated global solar radiation and global solar radiation under clear condition at Lin＇ an are 12.4± 7.2, 16.5±5.0 MJ · m 2 while the coincident average radiations at Longfengshan are 13. 5±7. 2, 15.5± 6.2 MJ · m-2. Annual average DLR at Lin＇an is 363.7±59.3 W · m 2, obviously higher than that at Longfengshan （274.9±77.6 W · m -2）. There is an obvious decreasing trend of DLR at Lin＇an, and glob- al solar radiation takes on an increasing trend at Longfengshan under clear sky.