干旱半干旱区太阳辐射特征

Climatic characteristics of broadband solar radiation （Rs） in Chinese arid and semi-arid areas are reported in this study. The annual average daily Rs in the arid and semi-arid areas is 16.3 ±5.77 and 15.3 ± 5.16 MJ m^-2 d^-1, respectively. The highest value （17.2 ± 5.84 MJ m^-2 d^-1） appears in an arid area at Linze. The lowest value appears in the semi-arid area of Ansai. Pronounced seasonal variation of Rs is observed with the highest value in summer and the lowest in winter. The clearness index showed similar seasonal pattern at most sites, with the minimum observed in the summer and the highest values in winter at both arid and semi-arid areas. The seasonal variation of the ratio of Rs to its extraterrestrial value Kt in the arid area is more significant than that observed in the semi-arid region, and it is caused by the different range of variation of water vapor between arid and semi-arid areas. The seasonal fluctuations in Rs and Kt are mainly controlled by the water vapor content in these areas. The aerosol particles have significant influence on Rs and Kt at stations with higher aerosol burden.     

A Field Experiment on Dust Emission by Wind Erosion in the Taklimakan Desert

Dust emission by wind erosion in surface is a serious problem in many arid regions around the world,and it is harmful to the ecological environment,human health,and social economy.To monitor the characteristics of saltation activity and to calculate the threshold wind velocity and sediment discharge under field conditions have significance on the research of dust emission by wind erosion.Therefore,a field experiment was conducted over the flat sand in the hinterland of the Taklimakan Desert.One sampling system was installed on the flat sand surface at Tazhong,consisting of a meteorological tower with a height of 2 m,a piezoelectric saltation sensor(Sensit),and a Big Spring Number Eight(BSNE) sampler station.Occurrence of saltation activity was recorded every second using the Sensit.Each BSNE station consisted of five BSNE samplers with the lowest sampler at 0.05 m and the highest sampler at 1.0 m above the soil surface.Sediment was collected from the samplers every 24 h.It is found that saltation activity was detected for only 21.5% of the hours measured,and the longest period of saltation activity occurring continuously was not longer than 5 min under the field conditions.The threshold wind velocity was variable,its minimum value was 4.9 m s 1,the maximum value was 9.2 m s 1,and the average value was 7.0 m s 1.The threshold wind velocity presented a positive linear increase during the measurement period.The observation site had a sediment discharge of 82.1 kg m 1 over a period of 24 h.Based on hourly saltation counts,hourly sediment discharge was estimated.Overall,there was no obvious linear or other functional relationship between the hourly sediment discharge and wind velocity.The results show that the changes of sediment discharge do not quite depend on wind velocity.     

Airborne Observations of Cloud Condensation Nuclei Spectra and Aerosols over East Inner Mongolia

A set of vertical profiles of aerosol number concentrations, size distributions and cloud condensation nuclei(CCN)spectra was observed using a passive cloud and aerosol spectrometer(PCASP) and cloud condensation nuclei counter, over the Tongliao area, East Inner Mongolia, China. The results showed that the average aerosol number concentration in this region was much lower than that in heavily polluted areas. Monthly average aerosol number concentrations within the boundary layer reached a maximum in May and a minimum in September, and the variations in CCN number concentrations at different supersaturations showed the same trend. The parameters c and k of the empirical function N = c S~kwere 539 and1.477 under clean conditions, and their counterparts under polluted conditions were 1615 and 1.42. Measurements from the airborne probe mounted on a Yun-12(Y12) aircraft, together with Hybrid Single-Particle Lagrangian Integrated Trajectory model backward trajectories indicated that the air mass from the south of Tongliao contained a high concentration of aerosol particles(1000–2500 cm~(-3)) in the middle and lower parts of the troposphere. Moreover, detailed intercomparison of data obtained on two days in 2010 indicated that the activation efficiency in terms of the ratio of NCCNto N_a(aerosols measured from PCASP) was 0.74(0.4 supersaturations) when the air mass mainly came from south of Tongliao, and this value increased to 0.83 on the relatively cleaner day. Thus, long-range transport of anthropogenic pollutants from heavily polluted mega cities,such as Beijing and Tianjin, may result in slightly decreasing activation efficiencies.     

The Seasonal Climatic Simulation of 9000 Years before Present by Using the IAP Atmospheric General Circulation Model

The seasonal cycle of the climate of 9000 years before present was simulated with the IAP two-level atmospheric general circulation model. The incoming solar radiation was specified from the orbital parameters for 9000 years ago. The boundary conditions of that time were prescribed to the present value because of the small differences between the two. The change in radiation makes temperature to be higher in summer and lower in winter over large areas of the land; and the increased temperature contrast between the land and the ocean strengthens the summer monsoon circulation and increases the precipitation over there. The asymmetry of temperature change between the Northern Hemisphere and the Southern Hemisphere and between summer and winter still exists, which agrees with that get from the previous perpetual experiments.     

Parameterizations of surface radiation in the semiarid grasslands of Inner Mongolia under clear-sky conditions using MODIS data

A set of improved and efficient radiation parameterization schemes for surface radiation balance components under clear- sky conditions was developed by using general surface measurements and MODIS data. The set of schemes was then adapted for regions similar to the present study sites under different grazing intensities and varying degrees of drought in the semiarid grasslands of Inner Mongolia. Specifically, we mainly improved two schemes for estimating downward shortwave and longwave radiation at the surface, which could be applied to regions with certain degrees of drought. The validation datasets were from ground-based observations at various grazing sites during the growing season （May to September） of different drought years, 2005 and 2006. Through comparisons of parameterized versus measured radiation values, the increased or modified factors in the original schemes demonstrated improved estimation accuracy, and the rationalities of input parameters and variables were analyzed. The regional instantaneous net radiation estimations had root-mean-square errors of less than 30 W m-2 compared with ground measurements at the sites during the study period. The statistical results showed the improved schemes are suitable for estimating surface net radiation in regional semiarid areas during the growing season. Analyses of the sensitivity of the schemes to corresponding variables were conducted to ascertain the major error sources of the schemes and potential variables for improving the performance of the schemes in agreement with observations.     

Integration of Multi-source Measurements to Monitor Dust over North China：A Case Study

The aerosol optical depth （AOD） data from the Moderate Resolution Imaging Spectroradiometer （MODIS） aboard Satellite Aqua, along with the altitude-resolved aerosol subtypes product from the Cloud-Aerosol LIdar with Orthogonal Polarization （CALIOP）, as well as surface PM 10 measurements, were utilized to investigate the dust activities common in springtime of northern China. Specifically, a dust storm episode that occurred over the North China Plain （NCP） during 17-21 March 2010 was identified. The PM 10 concentration at Beijing （39.8 °N, 116.47 °E） reached the peak value of 283 μgm -3 on 20 March 2010 from the background value of 15 μg m-3 measured on 17 March 2010, then dropped to 176 μgm-3 on 21 March 2010. Analysis of the CALIOP aerosol subtypes product showed that numerous large dust plumes floated over northern China, downwind of main desert source regions, and were lifted to altitudes as high as 3.5 km during this time period. The MODIS AOD data provided spatial distributions of dust load, broadly consistent with ground-level PM 10 , especially in cloud free areas. However, inconsistency between the MODIS AOD and surface PM 10 measurements under cloudy conditions did exist, further highlighting the unique capability of the CALIOP lidar. CALIOP can penetrate the cloud layer to give unambiguous and altitude-resolved dust measurements, albeit a relatively long revisit period （16 days） and narrower swath （90 m）. A back trajectory simulation using the Hybrid Single-Particle Lagrangian Integrated Trajectory （HYSPLIT） model was performed, and it was found that the sand-dust storm originated from the Gobi Desert on 18 March 2010 travelled approxi-mately 1200-1500 km day-1 eastward and passed over the NCP on 19 March 2010, in good agreement with previous findings. In addition, the multi-sensor measurements integrated with the HYSPLIT model output formed a three-dimensional view of the transport pathway for this dust episode, indicating that this episode was largely associated with the desert source regions to the northwest of the NCP. The results imply the importance of integration of multi-sensor measurements for clarifying the overall structure of dust events over northern China.     

NUMERICAL SIMULATION OF THE SEASONAL VARIATION OF TROPOSPHERIC OZONE OVER CHINA

An updated version of the Regional Acid Deposition Model(RADM)driven by meteorologicalfields derived from Chinese Regional Climate Model(CRegCM)is used to simulate seasonal variationof tropospheric ozone over the eastern China.The results show that:(1)Peak O_3 concentration moves from south China to north China responding to the changing ofsolar perpendicular incidence point from south to north.When solar perpendicular incidence pointmoves from north to south,so does the peak O_3 concentration.(2)In the eastern China.the highest O_3 month-average concentration appears in July.thelowest in January and the medium in April and October.The pattern mainly depends on the solarradiation,the concentration of O_3 precursors NO_x and NMHC and the ratio of NMHC/NO_x.(3)Daily variations of O_3 over the eastern China are clear.Namely,O_3 concentrations rise withthe sun rising and the maximums appear at noon.then O_3 concentrations decrease.The highest dailyvariation range of O_3 appears in summer(40×10~(-9) in volume fraction)and the lowest in winter(20×10~(-9) in volume fraction).(4)Daily variations of O_3 over the western China are not clear.The daily variation range of O_3 isless than 10×10~(-9) in volume fraction.     

Testing and Improving the Performance of the Common Land Model:A Case Study for the Gobi Landscape

Land surface processes take place on the interface between the earth and atmosphere, exerting significant influences on the weather and climate. Correct modeling of these processes is important to numerical weather forecast and climate prediction. In order to obtain a more thorough understanding of the land surface processes over the Gobi landscape, we evaluated the performance of the Common Land Model(Co LM) at Dunhuang station in Gansu Province of China to determine whether the model formulation, driven by observational data, is capable of simulating surface fluxes over the underlying desert surface. In comparison with the enhanced observation data collected at Dunhuang station over the period 22–28 August 2008, the results showed that the surface albedo simulated by Co LM was larger than that in the observation, and the simulated surface temperature was lower than the observed. After the measured values were used to correct the surface albedo, the solar radiation absorbed by the ground surface was more consistent with the measurements. A new empirical relationship of the surface thermal exchange coefficient rah was used to modify the thermal aerodynamic impedance. The simulated soil surface temperature became significantly closer to the observed value, and the simulated surface sensible heat as well as net radiative fluxes were also improved.     

Satellite-based estimation of daily average net radiation under clear-sky conditions

ABSTRACT Daily average net radiation （DANR） is an important variable for estimating evapotranspiration from satellite data at regional scales, and is used for atmospheric and hydrologic modeling, as well as ecosystem management. A scheme is proposed to estimate the DANR over large heterogeneous areas under clear-sky conditions using only remotely sensed data. The method was designed to overcome the dependence of DANR estimates on ground data, and to map spatially consistent and reasonably distributed DANR, by using various land and atmospheric data products retrieved from MODIS （Moderate Resolution Imaging Spectroradiometer） data. An improved sinusoidal model was used to retrieve the diurnal variations of downward shortwave radiation using a single instantaneous value from satellites. The downward shortwave component of DANR was directly obtained from this instantaneous value, and the upward shortwave component was estimated using satellite-derived albedo products. Four observations of air temperature from MOD07_L2 and MYD07_L2 data products were used to derive the downward longwave component of DANR, while the upward longwave component was estimated using the land surface temperature （LST） and the surface emissivity from MOD1 l_L2. Compared to in situ observations at the cropland and grassland sites located in Tongyu, northern China, the root mean square error （RMSE） of DANR estimated for both sites under clear-sky conditions was 37 W m-2 and 40 W m-2, respectively. The errors in estimation of DANR were comparable to those from previous satellite-based methods. Our estimates can be used for studying the surface radiation balance and evapotranspiration.     

Influences of the clearness index on UV solar radiation for two locations in the Tibetan Plateau-Lhasa and Haibei

Ultraviolet （UV） solar radiation has a significant influence on human health, the environment and climate. A series of measurements, including UV radiation （290 400 nm） and global solar radiation （Rs）, were continuously recorded from August 2004 at the Lhasa and Haibei sites on the Tibetan Plateau. Both observation sites＇ altitudes are above 3000 m and have similar meteorological conditions. The data from 2005 2006 was used to identify the varying characteristics of UV radiation. It＇s relation to the clearness index Ks, the relative optical mass mr, and Rs were established. The annual mean values of total daily UV radiation are 0.92 and 0.67 MJ m^-2 at Lhasa and Haibei, respectively. The UV radiation in Lhasa represented 4.6% of the global solar radiation while in Haibei this percentage was 4.2%. In the case of clear days （Ks 〉 0.8）, these percentages ranged between 4.0% and 4.5% in Lhasa and between 5.1% and 5.5% in Haibei. In the case of cloudy days （Ks 〈 0.4）, these percentages ranged from 4.4% to 6.8% in Lhasa and from 5.1% to 5.5% in Haibei. The maximum values of UV radiation for each relative optical mass diminished exponentially with mr. Thus, for Lhasa and Haibei, UV=46.25mr-129, and UV=51.76mr-142, respectively. The results of this study can be used to obtain more UV radiation data for the study of UV climate characteristics, the effects of UV on ecological processes and the feedback of the thinning of the stratospheric ozone, from more routine measurements Rs data.     

拉萨紫外辐射特征分析及估算公式的建立

本文利用2005~2010年的辐射观测资料对拉萨地区紫外辐射的时间变化特征及紫外辐射与总辐射比值的变化特征进行了分析,结果表明,紫外辐射与太阳总辐射的变化规律基本一致,日变化表现为正午大、早晚小;季变化特征是夏季6月最大,冬季1月最小.紫外辐射日累积值6年平均为0.87 MJ·m-2·d-1;紫外辐射有逐年递减的趋势.紫外辐射与总辐射比值也存在着明显日变化,表现为正午大、早晚小的规律;其季节变化也是夏季最大,冬季最小.紫外辐射与总辐射比值6年平均为0.0418;紫外辐射与总辐射比值也呈现逐年递减的趋势.利用2010年大气质量数和晴空指数,建立了适合于拉萨紫外辐射估量的公式,估算值的瞬时值与观测值的平均相对误差最大为8.66%,紫外辐射日累积重构值与观测值平均相对误差仅为5.5%.     

三江平原紫外辐射变化特征

利用2005~2011年共7年的太阳辐射观测资料对三江平原紫外辐射的时间变化规律及紫外辐射与总辐射比值的变化特征进行了分析,结果表明紫外辐射与总辐射的变化规律一致,日变化为正午大、早晚小;季节变化规律是夏季高、冬季低。紫外辐射日累积值的7年年平均值为0.53 MJ m–2 d–1。紫外辐射与总辐射比值存在着明显日、季节变化特征,日变化特征为正午大、早晚小,而季节变化与紫外辐射的季节变化一致也是夏季大、冬季小。紫外辐射与总辐射比值7年平均为0.0433。利用2011年观测的总辐射、紫外辐射数据,通过紫外辐射与总辐射比值和大气质量数与晴空指数的相互依赖关系,建立了适合于三江地区紫外辐射估算的方程。利用建立的估算方程估算的紫外辐射瞬时值和日累积值与观测值之间的平均相对误差最大分别为8.5%和6.1%。     

Ultraviolet radiation in the background region over Northeast China

Measurements of broadband global solar and ultraviolet radiation (UV-KZ) by a Kipp & Zonen radiometer from 2005 to 2011 at three sites in the background region over Northeast China were used to investigate the characteristics of the temporal variability of UV-KZ radiation in Northeast China. The highest annual mean daily values of UV-KZ (0.53 MJ m^?2 d^?1) were observed at Sanjiang and Changbai Mountain. The lowest value (0.49 MJ m^?2 d^?1) was measured at Hailun due to the high aerosol burden and the long path of solar radiation. The diurnal variation in UV-KZ radiation on four clear days near the equinoxes and solstices exhibited bell-shaped curves, with a maximum at approximately noon. There was little difference in UV-KZ radiation between representative spring and autumn days except that the amount of UV-KZ radiation during the spring was higher than that during the autumn. The relationship between the maximum values of UV-KZ radiation and clearness index can be accurately demonstrated with three polynomial equations. An empirical estimation model suited for all weather conditions was developed using measurements collected at Hailun. The slope of the linear regression between the measured and modeled UV-KZ radiation was approximately 1, the intercept of the linear regression equation was near zero, and the relative error of the equation was less than 8.5 %. These validation results suggest that this model can accurately estimate the UV-KZ radiation based on more conventional measured radiation data. The empirical estimation model can also serve as a valuable method for the study of ecological processes in other regions.     

山东禹城紫外辐射变化特征及其估测方程的建立

本文对2005～2011年山东禹城地区观测得到的紫外辐射的时间变化特征及紫外辐射与总辐射比值的变化特征进行了分析, 并结合气温、降水和露点温度资料建立了禹城地区的紫外辐射估测方程。结果表明:紫外辐射日累计值的变化范围为0.10～1.20 MJ m-2 d-1, 年平均值为0.468 MJ m-2 d-1;紫外辐射日、季节变化规律与总辐射一致, 季节变化都表现为冬季小夏季大, 最小值出现在1月, 最大值出现在6月, 日变化则呈现早晚小中午大的特征;紫外辐射与总辐射的比值范围为0.023～0.046, 其季节变化特征也是冬季小夏季大, 该比值随晴空指数的增大而减小, 而在晴空指数大于0.5时比较稳定。利用温度日较差(日最高气温与最低气温的差值)建立了紫外辐射估测方程, 决定系数R2达0.80, 平均相对误差为0.19, 估测紫外线等级与实测紫外线等级相差不大于1的数据占95%, 该方法可以较好地进行紫外辐射等级的估测。     

Analysis of photosynthetically active radiation and applied parameterization model for estimating of PAR in the North China Plain

As photosynthetically active radiation (PAR) variability and PAR estimating methods play an important role in climate change and ecological process research, PAR variation trends and broadband global solar radiation (R _s ) ratios (PAR/R _s ) in the North China Plain (NCP) are examined using in situ PAR and R _s observed data for 2005 to 2011. The annual average PAR value found in the NCP is 22.9 mol m^?2 d^?1. The highest and lowest values were recorded at Changwu and Luancheng sites, respectively. The highest PAR/R _s value was found in Jiaozhouwan due to large water vapor volumes present in this area. PAR/R _s levels have increased in the NCP due to a decrease in fine aerosols and increase in water vapor concentration. From these analysis results, a parameterization model that can be applied to all sky conditions was checked. Empirical estimation model comparisons for obtaining PAR values indicate that model was least accurate when R _s was used independently. When the model included R _s, the clearness index (K _s) and the solar zenith angle, the model estimated PAR values with acceptable accuracy. A parameterization model was constructed by considering K _s and attenuation factors of PAR under clear weather conditions (ρ _clear). The improved parameterization model more accurately predicts values for local sites and for various observation sites.     

银川城市道路路面温度变化特征及统计模型

采用人工定点观测路面温度资料,分析了不同天空状况和不同材质道路的路面温度日变化特征。结果表明：路面温度具有明显的日变化特征,晴空或少云时,日出和日落时段路面温度略高于气温,中午前后路面温度变幅最大,且明显高于气温;阴雨天时,路面温度略高于气温,变化相对平缓且与气温保持较好的相关性。由于水泥和沥青不同的物理特征,沥青路面对气温的反应灵敏,水泥路面反应平缓,即水泥路面最高温度多低于沥青路面,最低温度多高于沥青路面。在此基础上应用逐步回归方法建立逐时路面温度预报模型和最高道面温度预报模型,并应用模型模拟的结果与实测路面温度作对比分析,结果表明逐时道面温度预报模型的模拟效果较好,最高道面温度预报模型误差较大,需要进一步修正和改进。     

敦煌地区荒漠戈壁地表热量和辐射平衡特征的研究

利用2000年5月25日～6月17日"敦煌试验"在戈壁的微气象观测资料,分析了极端干旱地区晴天、阴天和降水等天气条件下的地表辐射平衡、热量平衡和土壤温度等微气象特征的日变化规律.发现在不同天气条件微气象特征有很大变化.但观测期间的平均微气象特征与晴天比较接近,天气过程的影响不是很大,平均的总辐射、净辐射和感热通量与晴天的比值在白天基本大于0.8.观测期间的平均Bowen比全天大于1,在白天都在10以上,最大超过100.     

The characteristics of ultraviolet radiation in arid and semi-arid regions of China

Measurements of the broadband global solar radiation (R _S) and total ultraviolet radiation (the sum of UV-A and UV-B) were conducted from 2005 to 2010 at 9 sites in arid and semi-arid regions of China. These data were used to determine the temporal variability of UV and UV/R _S and their dependence on the water vapor content and clearness index. The dependence of UV/R _S on aerosol optical depth (AOD) and water vapor content was also investigated. In addition, a simple and efficient empirically model suited for all-weather conditions was developed to estimate UV from R _s. The annual average daily UV level in arid and semi-arid areas is 0.61 and 0.59 MJ m^?2 d^?1, respectively. The highest value (0.66?±?0.25 MJ m^?2 d^?1) was recorded at an arid area at Linze. The lowest value (0.53?±?0.22 MJ m^?2 d^?1) was recorded at a semi-arid area at Ansai. The highest daily value of UV radiation was measured in May, whereas the lowest value was measured in December. The monthly variation of the UV/R _s ratio ranged from 0.41 in Aksu to 0.35 in Qira. The monthly mean value of UV/R _s gradually increased from November and then decreased in August. A small decreasing trend of UV/R _s was observed in the arid and semi-arid regions due to recently increasing amounts of fine aerosol. A simple and efficient empirically model suit for all-weather condition was developed to estimate UV from R _s. The slope a and intercept b of the regression line between the estimated and measured values were close to 1 and zero, respectively. The relative error between the estimated and measured values was less than 11.5%. Application of the model to data collected from different locations in this region also resulted in reasonable estimates of UV.     

东疆黑戈壁太阳紫外辐射变化特征

本文利用东疆红柳河黑戈壁下垫面陆气相互作用观测站2017年太阳紫外辐射、总辐射和气象站天气现象观测数据，对东疆黑戈壁不同时间尺度和不同天气背景下的太阳紫外辐射A波段(UVA)和B波段（UVB）的变化特征进行了分析。结果表明：1）紫外辐射UVA和UVB日变化呈正态分布，UVA、UVB最大瞬时辐照度为67.97W·m-2、2.15W·m-2，日均最大曝辐量为2.09MJ·m-2和0.05MJ·m-2，年曝辐量为400.31 MJ·m-2和8.63 MJ·m-2；季节变化呈现夏季高，冬季低、春季高于秋季的特点；年变化呈现倒“U”型，年变化幅度呈夏季大，冬季小的趋势。2）紫外辐射占总辐射的比例呈夏高冬低的特点。不同天气下，其比例变化幅度也不相同，晴天大于雨天。3）太阳紫外辐射的月和年平均量以及紫外辐射年均值占总辐射年均值的比例，东疆黑戈壁地区都明显高于其他地区。