阿克达拉大气本底站紫外辐射特征及影响因素分析

利用阿克达拉大气本底站基准辐射观测站紫外辐射UV-A和UV-B数据,分析阿克达拉大气本底站紫外辐射和UV-B在不同时间尺度、云量和降水过程的变化特征。结果表明：阿克达拉大气本底站全年紫外辐射年总量达到321.1 MJ/m2,年均日曝辐量为0.88 MJ/m2,UV-B年曝辐量为5.3 MJ/m2,紫外辐射年平均值占总辐射年平均值的比例为5.6%。紫外UV和紫外UV-B的辐射强度的季节变化表现为夏季>春季>秋季>冬季。夏季紫外辐射曝辐量是冬季的2.79倍;UV-B夏季平均日曝辐量是冬季的8.10倍。积雪导致紫外辐射及占总辐射比值增大,积雪期与非积雪期紫外辐射占总辐射比值均值分别为6.53%和5.83%,积雪使地面紫外辐射增加25.89%。在多云与阴雨时可能由于水汽作用大量吸收波长较大的红外辐射致使紫外辐射与总辐射的比值较大。     

Long-term variations of available solar radiation on seasonal timescales in 1955–2006 at Tartu-Tõravere Meteorological Station, Estonia

The time series of the daily sums of global and direct irradiance recorded at Tartu-Tõravere Meteorological Station site (58°16′N, 26°28′E, 70 m a.s.l.) in 1955–2006 have been analyzed in seasonal timescales. The average daily ratio G/G _clear of available global irradiance to its local climatic clear-sky value in the summer half-year corresponds to 65.5%, while that of the direct irradiance on the horizontal surface I′/I′ _clear was 41% of the climatic clear-sky value. In the case of dry Rayleigh atmosphere as a reference, these ratios are 53.5% and 28%, respectively. The time series of the summer season totals reveal a longer interval of reduced values in 1976–1993 as well as two periods of frequent sunny summers in 1967–1975 and since 1994. The probability density distribution of the summer season totals during the observed period is strongly asymmetric; in spring, however, it is close to the normal distribution. In winter, there is a moderate negative correlation between the G/G _clear and the North Atlantic Oscillation as well as the Arctic Oscillation indices.     

Changes to the Surface Level Solar Ultraviolet-B Radiation Due to Haze Perturbation

The South-East Asian region experienced a haze episode in 1994 which was widely believed to be due to widespread forest fires in Sumatra and Kalimantan (Indonesia). Broadband measurements of the surface level solar ultraviolet-B, UV-A and Global radiation at Penang (Malaysia) are used to study the effect of the 1994 haze on effective UV-B irradiance. We find that during the haze episode, there is enhanced absorption of surface level UV-B radiation. The effect of haze on UV-A and Global radiation is much less. The reduction in absolute noon time UV-B irradiance (mostly cloud free) during the 1994 haze period was 23% relative to the UV-B irradiance during thecorresponding haze-free period in 1995. Even though the noon time radiation data minimizes the cloud effect in the results presented some cloud effect is still present.     

A Possible Photochemical Link Between Stratospheric and Near-Surface Ozone on Swiss Mountain Sites in Late Winter

Record high near-surface ozone concentrations at two elevated sites (Chaumont, 1140 m asl, and Rigi, 1030 m asl) in Switzerland were observed simultaneously with extremely low total ozone during a fair weather period in mid-February 1993. An analysis of ozone, temperature, humidity, and wind profiles suggests that the surface ozone peaks were most possibly generated within the region in a layer between about 1000 and 1500 m asl. Mean diurnal cycles of ozone concentration during the period shows a strong increase from late morning to late afternoon at Chaumont and at the same time a decrease at the high alpine site Jungfraujoch (3580 m asl). The different diurnal ozone cycles can both be explained photochemically by taking into account the large difference in NOx concentrations (about two orders of magnitude) between the sites. Photochemical processes are also indicated by the diurnal cycles of NO2 and NO concentration. As a strong photochemical activity is not expected in mid-February at 47°N, we hypothesize that the extremely low total ozone played a role. Total ozone controls the amount of UV-B radiation reaching the troposphere and thus influences photochemical processes. Using a radiation model, we calculated an increase in ozone photolysis at Chaumont and Jungfraujoch of 73% and 83%, respectively, on the day with the lowest total ozone (243 DU) compared to average February conditions (335 DU). It is suggested that total ozone changes have the potential to stimulate photochemistry sufficiently to produce the observed surface ozone peaks at Chaumont and Rigi of 61 and 64 ppbv, respectively. A fog layer just below Chaumont during these days probably also influenced photochemistry, but on a smaller spatial scale. Our empirical results on the influence of changing UV radiation on tropospheric photochemistry are in close agreement with model studies of other groups. Although this case study represents unique conditions, a distinct anticorrelation between near-surface ozone at Chaumont and total ozone also appears in other years (1992–1997) when selecting fair weather days in mid-February. However, other influences cannot be excluded. The selected days provide evidence of a significant photochemical source of ozone in the mid-latitude lower troposphere in late winter.     

Analysis of 40 year records of solar radiation data in Shanghai,Nanjing and Hangzhou in Eastern China

Summary In this paper, we analyze global, direct and diffuse solar radiation data on a horizontal surface observed at stations in Shanghai, Nanjing and Hangzhou for the period of 1961 to 2000. The data include monthly averages of the daily clearness index (G/G₀: the ratio of global to extraterrestrial solar radiation) and the diffuse fraction (D/G: the ratio of diffuse to global solar radiation. The present study has processed and analyzed the data, including variables or statistics of mean, and annual monthly and daily total, the diurnal variation and the frequency of daily totals of global solar radiation. A correlation between daily values of clearness index and diffuse fraction is obtained and recommended correlation equations were calculated. The annual variations and trend of yearly series are analyzed for daily global, direct and diffuse radiation on a horizontal surface, as well as for daily clearness index and diffuse fraction in Shanghai, Nanjing and Hangzhou. The results show: 1) the east China is characterized by a decrease in global and direct radiation and a little increase in diffuse radiation and a negative linear relationship was obtained between clearness index and diffuse fraction. 2) The annual variations of global, direct and diffuse radiation for Shanghai, Nanjing and Hangzhou are similar with relative low values of global and direct radiation in June due to the Meiyu period. 3) The acceleration of air pollution and decrease of relative sunshine are the possible causes for the decrease of global and direct radiation.     

Effects of cloudiness on global and diffuse UV irradiance in a high-mountain area

Summary At the high-mountain station Jungfraujoch (3576 m a.s.l., Switzerland), measurements of the radiation fluxes were made during 16 periods of six to eight weeks by means of a Robertson—Berger sunburn meter (UVB data), an Eppley UVA radiometer and an Eppley pyranometer. Cloudiness, opacity and altitude of clouds were recorded at 30-minute intervals. A second set of instruments was employed for separate measurement of the diffuse radiation fluxes using shadow bands. The global and diffuse UVA- and UVB radiation fluxes change less with cloudiness than the corresponding total radiation fluxes. When the sun is covered by clouds, the global UVA- and UVB radiation fluxes are also affected less than the global total radiation flux. The roughly equal influence of cloudiness on the UVA- and UVB radiation fluxes suggests that the reduction is influenced more by scattering than by ozone. Also, the share of diffuse irradiance in global irradiance is considerably higher for UVA- and UVB irradiance than for total irradiance. At 50° solar elevation and 0/10 cloudiness, the share is 39% for UVB irradiance, 34% for UVA irradiance and 11% for total irradiance. The increased aerosol turbidity after the eruptions of El Chichon and Pinatubo has caused a significant increase in diffuse total irradiance but has not produced any significant changes in diffuse UVA- and UVB irradiances.With 7 Figures     

青藏高原冬季降雪对地面净辐射的影响

过去的研究结果指出，冬季青藏高原地面净辐射场是一个由地理因子决定的基本场叠加上一个降雪后地面积雪区造成的扰动场组成，为定量研究冬季青藏高原降对地面净辐射的扰动幅度，利用作者已经建立的冬季青藏高原后地面反射率与降雪降雪面无（有）积雪时计算地面净辐射的公式，计算了不同强度降雪后地面净辐射日总量及其变化。     

禹城地区光合有效辐射的计算方法

利用2005年7月-2006年10月在山东禹城对太阳辐射（包括光合有效辐射PAR、可见光辐射VIS、总辐射Q等）、气象要素等进行的4次综合观测资料,初步得到了朋R,VIS的日、季节变化特征并对其进行了分析,结果表明：各辐射的小时累计之比vIS／Q,PAR／Q,PAR／VIS相对稳定,其平均值分别为0．39,1．95（mol／MJ）,4．97（mol／MJ）,但它们均有明显的日、逐日、季节变化,并受水汽、气溶胶、云等因素的影响。同时建立了实际天气PAR,VIS的小时累计经验公式及其转换关系,计算值与观测值均比较接近。当考虑水汽和散射因子时,PAR,VIS的计算值与观测值的相对偏差分别为11．1％,10．6％。限于实际情况,可以只考虑水汽因子的作用来计算PAR和VIS的小时累计值,它们的相对偏差分别为13．3％,12．6％。水汽因子对于PAR,VIS的传输和计算具有重要作用。     

Investigation of the Planetary Boundary Layer in the Swiss Alps Using Remote Sensing and In Situ Measurements

The development of the planetary boundary layer (PBL) has been studied in a complex terrain using various remote sensing and in situ techniques. The high-altitude research station at Jungfraujoch (3,580 m a.s.l.) in the Swiss Alps lies for most of the time in the free troposphere except when it is influenced by the PBL reaching the station, especially during the summer season. A ceilometer and a wind profiler were installed at Kleine Scheidegg, a mountain pass close to Jungfraujoch, located at an altitude of 2,061 m a.s.l. Data from the ceilometer were analyzed using two different algorithms, while the signal-to-noise ratio of the wind profiler was studied to compare the retrieved PBL heights. The retrieved values from the ceilometer and wind profiler agreed well during daytime and cloud-free conditions. The results were additionally compared with the PBL height estimated by the numerical weather prediction model COSMO-2, which showed a clear underestimation of the PBL height for most of the cases but occasionally also a slight overestimation especially around noon, when the PBL showed its maximum extent. Air parcels were transported upwards by slope winds towards Jungfraujoch when the PBL was higher than 2,800 m a.s.l. during cloud-free cases. This was confirmed by the in situ aerosol measurements at Jungfraujoch with a significant increase in particle number concentration, particle light absorption and scattering coefficients when PBL-influenced air masses reached the station in the afternoon hours. The continuous aerosol in situ measurements at Jungfraujoch were clearly influenced by the local PBL development but also by long-range transport phenomena such as Saharan dust or pollution from the south.     

OBSERVATIONAL STUDY OF MERIDIONAL VARIATION OF UV-B RADIATION DURING VOYAGES TO THE ARCTIC AND ANTARCTIC REGIONS*

Based on 1999-2000 observations made by the first Arctic and sixteenth Antactic scientific voyages,a study is undertaken about the meridional surface UV-B (B band ultraviolet rays) variations in 75°N-70°S.It is mitigated as a function of latitudes and marked by lower radiation averaged over the Northern Hemisphere (NH) than over the Southern Hemisphere (SH),with its daily course basically similar to that of total radiation.Around polar summer noon hours (localtime) and where ice albedo is maximum,the strongest UV-B irradiance on the surface perpendicular to sun's beams as found at equatorial latitudes is measured sometimes.In the areas near Zhongshan Station the increase of surface UV-B radiation shows a close relation to the decrease of ozone in the higher atmosphere but it has a less intimate relation with its concentration at ground.     

UV-B辐射增强对不同品种花生结荚期生理特性日变化的影响

以3个花生品种（开农49号、64号和69号）为材料,通过大田模拟试验,研究UV-B辐射增强对花生结荚期叶片的净光合速率（P_n）、气孔导度（G_s）、胞间CO₂浓度（C_i）、蒸腾速率（T_r）和水分利用效率（E_wu）日变化的影响,为筛选高产、抗旱、抗UV-B辐射花生品种提供依据.UV-B辐射设2个水平即自然光（CK,1.5 kJ·m^-2）和UV-B增强20%（T,1.8 kJ·m^-2）.结果表明,UV-B辐射增强明显抑制花生的光合作用和蒸腾作用,与对照相比,UV-B增强条件下,开农49号、64号和69号P_n日均值分别降低19.4%、27.8%、24.7%;G_s日均值降低26.7%、42.9%、28.6%;C_i日均值降低27.2%、20.4%、23.1%;T_r日均值降低17.8%、23.3%、25.1%;E_wu日均值降低16.6%、23.2%、23.9%.UV-B辐射增强对3个品种生长都具有抑制效应,但品种间存在一定的敏感性差异,其中开农49号最不敏感,因此,开农49号在抗UV-B辐射方面比其他2个品种具有更大的优势.     

Effects of atmospheric river landfalls on the cold season precipitation in California

Effects of atmospheric river (AR) landfalls in the California coast on the cold-season precipitation in California are examined for the cold seasons of 10 water years (WYs) 2001–2010 using observed data and regional modeling in conjunction with AR-landfall inventory based on visual inspections of precipitable water vapor (PWV) from remote sensing and reanalysis. The PWV in the SSM/I and SSMIS retrievals and the ERA-Interim reanalysis shows 95 AR-landfall days in the California coast that are almost evenly split between the northern and southern coasts across 37.5N. The CPC/NCEP gridded daily precipitation analysis shows that 10–30% of the cold-season precipitation totals in California have occurred during these AR landfalls. The analysis also reveals that the percentage of precipitation and the precipitation intensity during AR landfalls in California are characterized by strong north-to-south gradient. This north–south contrast in the AR precipitation is reversed for the non-AR precipitation in the coastal range. The frequency of AR landfalls and the cold-season precipitation totals in the Sierra Nevada region are only marginally correlated. Instead, AR landfalls are closely related with the occurrence of heavy precipitation events. The freezing-level altitudes are systematically higher for AR wet days than non-AR wet days indicating warmer low-troposphere during AR storms. Cold season simulations for the 10 WYs 2001–2010 show that the Weather Research and Forecast (WRF) model can reasonably simulate important features in both the seasonal and AR precipitation totals. The daily pattern correlation coefficients between the simulated and ERA-Interim upper-air fields exceed 0.9 for most of the period. This suggests that the simulated temporal variations in the atmospheric circulation agree reasonably with the reanalysis over seasonal time scales, characteristics critical for reliable simulations of regional scale hydrologic cycle. The simulated seasonal and AR precipitation totals also agree reasonably with the CPC/NCEP precipitation analysis. The most notable model errors include the overestimation (underestimation) of the season-total and AR precipitation in the northern (southern) California region. The differences in the freezing-level altitudes during the AR- and non-AR wet days in the simulation agree with those from the ERA-Interim reanalysis. The freezing level altitudes are systematically overestimated in the simulations, suggesting warm biases in the low troposphere. Overall, WRF appears to perform reasonably in simulating the key features in the cold season precipitation related with AR landfalls, an important capability for assessing the impact of global climate variations and change on future hydrology in California.     

Surface albedo at a tower site in Lake Ontario

Measurements of incoming global, diffuse and reflected radiation at a tower site in Lake Ontario are used to evaluate components of surface albedo. Albedo for diffuse radiation lies between 0.074 and 0.082 and a coefficient for backscatter from sub-surface water layers shows little deviation from a mean of 0.017. Direct beam albedo for a calm surface follows the Fresnel law. Waves increase direct-beam albedo particularly at higher solar zenith angles. A pronounced dependence of albedo upon zenith angle for clear skies decreases with increasing cloud amount and becomes undetectable in overcast conditions. On a daily basis, albedo ranged between 0.07 in early July to 0.11 in mid-November. Day-to-day scatter is within ±1% of the mean seasonal trend.     

Analysis of cumulus solar irradiance reflectance (CSIR) events

Clouds are extremely important with regard to the transfer of solar radiation at Earth's surface. This study investigates Cumulus Solar Irradiance Reflection (CSIR) using ground-based pyranometers. CSIR events are short-term increases in solar radiation observed at the surface as a result of reflection off the sides of convective clouds. When Sun-cloud observer geometry is favorable, these occurrences produce characteristic spikes in the pyranometer traces and solar irradiance values may exceed expected clear-sky values. Ultraviolet CSIR events were investigated during the summer of 1995 using UVA and UVB pyranometers. Observed data were compared to clear-sky curves which were generated using a third degree polynomial best-fit line technique. Periods during which the observed data exceeded this clear-sky curve were identified as CSIR events. The magnitude of a CSIR event was determined by two different quantitative calculations. The MAC (magnitude above clear-sky) is an absolute measure of the difference between the observed and clear-sky irradiances. Maximum MAC values of 3.4 Win⁻² and 0.0169 Wm⁻² were observed at the UV-A and UV-B wavelengths, respectively. The second calculation determined the percentage above clear-sky (PAC) which indicated the relative magnitude of a CSIR event. Maximum UV-A and UV-B PAC magnitudes of 10.1% and 7.8%, respectively, were observed during the study. Also of interest was the duration of the CSIR events which is a function of Sun-cloud-sensor geometry and the speed of cloud propagation over the measuring site. In both the UV-A and UV-B wavelengths, significant CSIR durations of up to 30 minutes were observed. C 1997 Elsevier Science B.V.     

UV-B辐射增强对河南省夏直播花生产量及品质的影响

在大田条件下,研究了模拟地表UV-B辐射增强对花生（开农49号）的产量及品质的影响.UV-B辐射设3个水平,即对照、增强20%和增强40%.结果表明：UV-B辐射增强能显著降低花生产量,产量下降的原因主要是由单位面积产量、株荚果数、百仁重减少造成的;花生品质受UV-B影响较为复杂,UV-B增强20%时,花生脂肪质量分数为51.02%,蛋白质质量分数为22.34%,油酸/亚油酸质量比为1.19,较对照组提高了0.02;UV-B增强40%时,花生脂肪质量分数为51.82%,蛋白质质量分数为22.56%,油酸/亚油酸质量比为1.28,较对照组提高了0.11.研究认为,UV-B辐射增强,不足以对花生的品质产生显著影响,这可能与设定的UV-B辐射强度、试验设计方案及花生的品种有关.     

Spectral dependence on the correction factor of erythemal UV for cloud,aerosol, total ozone,and surface properties: A modeling study

Radiative transfer model simulations were used to investigate the erythemal ultraviolet(EUV) correction factors by separating the UV-A and UV-B spectral ranges. The correction factor was defined as the ratio of EUV caused by changing the amounts and characteristics of the extinction and scattering materials. The EUV correction factors(CFEUV) for UV-A[CFEUV(A)] and UV-B [CFEUV(B)] were affected by changes in the total ozone, optical depths of aerosol and cloud, and the solar zenith angle. The differences between CFEUV(A) and CFEUV(B) were also estimated as a function of solar zenith angle, the optical depths of aerosol and cloud, and total ozone. The differences between CFEUV(A) and CFEUV(B) ranged from-5.0% to 25.0% for aerosols, and from-9.5% to 2.0% for clouds in all simulations for different solar zenith angles and optical depths of aerosol and cloud. The rate of decline of CFEUV per unit optical depth between UV-A and UV-B differed by up to 20% for the same aerosol and cloud conditions. For total ozone, the variation in CFEUV(A) was negligible compared with that in CFEUV(B) because of the effective spectral range of the ozone absorption band. In addition, the sensitivity of the CFEUVs due to changes in surface conditions(i.e., surface albedo and surface altitude) was also estimated by using the model in this study. For changes in surface albedo, the sensitivity of the CFEUVs was 2.9%–4.1% per 0.1 albedo change,depending on the amount of aerosols or clouds. For changes in surface altitude, the sensitivity of CFEUV(B) was twice that of CFEUV(A), because the Rayleigh optical depth increased significantly at shorter wavelengths.     

南极长城站和中山站辐射特征的研究

对南极长城站和中山站1993～1994年辐射资料的分析表明:两站辐射分量的季节变化特征基本相似。但由于气候状况的差异,长城站到达地面的总辐射和吸收辐射分别为中山站的51%和42%。极昼期间（11～1月）中山站总辐射和紫外辐射总量均超过了青藏高原夏季（6～8月）的总量,两站净辐射夏半年为正,冬半年为负,显示出南极绿洲的辐射气候特点。     

Impact of UV-A radiation on erythemal UV and UV-index estimation over Korea

Because total UV(TUV) in the UV-A region is 100 times higher than in the UV-B region,UV-A is a considerable component when calculating erythemal UV(EUV) and UV-index.The ratio of EUV to TUV in the UV-A value [EUV(A)/TUV(A)]is investigated to convert the EUV(A) from TUV(A) for broadband observation. The representative value of EUV(A)/TUV(A),from the simulation study,is 6.9 × 10-4,changing from 6.1 × 10-4to 7.0 × 10-4as aerosol optical depth,total ozone and solar zenith angle change. By adopting the observational data of EUV(B) and TUV(A) from UV-biometer measurements at Yonsei University [(37.57?N,126.95?E),84 m above sea level],the EUV irradiance increases to 15% of EUV(B) due to the consideration of EUV(A) from the data of TUV(A) observation. Compared to the total EUV observed from the Brewer spectrophotometer at the same site,the EUV(B) from the UV-biometer observes only 95% of total EUV,and its underestimation is caused by neglecting the effect of UV-A. However,the sum of EUV(B) and EUV(A) [EUV(A+B)] from two UV-biometers is 10% larger than the EUV from the Brewer spectrophotometer because of the spectral overlap effect in the range 320–340nm. The correction factor for the overlap effect adjusts 8% of total EUV.