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1.
Analysis of solar radiation over Egypt 总被引：1，自引：0，他引：1
M. A. Omran 《Theoretical and Applied Climatology》2000,67(3-4):225-240
Summary The database utilized in this analysis consisted of daily sunshine duration and hourly global and diffuse radiation on a
horizontal surface (for Matruh Cairo, and Aswan), and normal incidence beam radiation (for Cairo and Aswan only). Monthly-average
hourly and daily values are reported for each of these three types of measured radiation, together with the calculated monthly-average
daily values for the components of global radiation, horizontal beam and diffuse radiation. The monthly-average hourly and
daily clearsky index values have also been calculated and analyzed. Monthly-average daily frequency distributions of the clearsky
index values are reported for each month.
The annual-average daily global irradiation values are 19.4, 18.67, and 21.78 MJ/m2 and for diffuse irradiation they are 6.34, 6.65 and 6.23 MJ/m2 for Matruh, Cairo and Aswan, respectively. For the normal incidence beam irradiation the annual-average daily values are
16.94 and 24.46 MJ/m2 for Cairo and Aswan, respectively. The annual-average daily fractions of the direct component of horizontal global radiation
are 0.70, 0.61 and 0.72 for the three stations, respectively. The annual-average daily values for the clearsky index are 0.585,
0.566, and 0.648, and the average frequency of clear days annually are 67.3, 42.3 and 77.6% respectively.
The annual variations and trend analysis were analyzed for daily global, direct, and diffuse radiation on a horizontal surface,
daily sunshine duration, and for the daily ratios G/G0, and D/G for the stations Matruh, Cairo and Aswan. The distribution of these components of radiation and their ratios over
the study stations in Egypt is also discussed.
The results show that Egypt is characterized by relatively high average-daily radiation rates, both global and direct, and
a relatively high frequency of clear days. Cairo, due to its urbanization and high pollution, has relatively low average-daily
radiation rates, particularly in direct radiation, and the frequency of clear days.
Received February 26, 1998 Revised February 4, 1999 相似文献
2.
Summary Previous estimates of average annual evaporation from the lake formed by the High Dam at Aswan, Egypt, fall in the range from 4.65 mm d–1 to 7.95 mm d–1. The difference between these limits, more than 7 billion m3 yr–1 at the highest storage level, is nearly one-eighth the share by treaty of Egypt, and more than one-third of the share of the Sudan. It is also more than the estimated increase of the annual water need for Egypt between 1990 and 2000. This state of affairs renders proper management of the river flow for the sake of Egypt and the Sudan quite difficult. This paper compares the relevant methods of estimating evaporation from the limited data available.These methods are:water-balance, energy budget, bulk aerodynamic (Dalton),combination (Penman) andComplementary Relations Lake Evaporation (CRLE) model (Morton). The new estimates have a much narrower range, from 5.70 mm d–1 to 7.05 mm d–1, or only a bit more than 4% of the annual Nile flow below the High Aswan Dam. The average of these annual estimates of evaporation, after excluding the bulk aerodynamic method because of its severe limitations, is 6.0 ± 0.3 mm d–1 or 20% less than the 7.5 mm d–1 adopted by the irrigation authorities in Egypt and the Sudan. This difference corresponds to 3 billion m3 yr–1 at the highest storage level or more than 5% of the annual outflow from the reservoir. Even when the higher estimates from the bulk aerodynamic method and from the Penman method with its usual wind function are included, the new average is still 15% less than the figure of 7.5 mm d–1. The monthly distribution of the annual evaporation varies more widely with the method applied. Similar comparative studies in future, aiming at obtaining improved estimates of evaporation, require all the data relevant to all the methods to be collected properly for a common period of several years at relatively stable lake level.With 1 Figure 相似文献
3.
Evaporation estimates from Nasser Lake, Egypt, based on three floating station data and Bowen ratio energy budget 总被引：2，自引：1，他引：1
Mohamed Elsawwaf Patrick Willems Andrea Pagano Jean Berlamont 《Theoretical and Applied Climatology》2010,100(3-4):439-465
Nasser Lake is located in a hyper-arid region in the south of Egypt. Evaporation is by far the most important factor in explaining the water losses from the lake. To obtain better management scenarios for Nasser Lake, an accurate estimation of the lake evaporation losses thus is essential. This paper presents an update of previous evaporation estimates, making use of local meteorological and hydrological data collected from instrumented platforms (floating weather stations) at three locations on the lake: at Raft, Allaqi, and Abusembel (respectively at 2, 75, and 280 km upstream of the Aswan High Dam). Results from six conventional evaporation quantification methods were compared with the values obtained by the Bowen ratio energy budget method (BREB). The results of the BREB method showed that there is no significant difference between the evaporation rates at Allaqi and Abusembel. At Raft, higher evaporation rates were obtained, which were assumed to be overestimated due to the high uncertainty of the Bowen ratio (BR) parameter. The average BR value at Allaqi and Abusembel was used to eliminate this overestimates evaporation. Variance-based sensitivity and uncertainty analyses on the BREB results were conducted based on quasi-Monte Carlo sequences (Latin Hypercube sampling). The standard deviation of the total uncertainty on the BREB evaporation rate was found to be 0.62 mm day?1. The parameter controlling the change in stored energy, followed by the BR parameter, was found to be the most sensitive parameters. Several of the six conventional methods showed substantial bias when compared with the BREB method. These were modified to eliminate the bias. When compared to the BREB-based values, the Penman method showed most favorably for the daily time scale, while for the monthly scale, the Priestley–Taylor and the deBruin–Keijman methods showed best agreement. Differences in mean evaporation estimates of these methods (against the BREB method) were found to be in the range 0.14 and 0.36 mm day?1. All estimates were based calculations at the daily time scale covering a 10-year period (1995–2004). 相似文献
4.
Joseph L. Awange Laban Ogalo Kwang-Ho Bae Paul Were Philip Omondi Paul Omute Monica Omullo 《Climatic change》2008,89(3-4):281-297
Recently, and perhaps most threatening, Lake Victoria water level has been receding at an alarming rate. A recent study suggested the possibility of the expanded hydroelectric power station in Uganda. However, since the lake receives 80% of its refill through direct rainfall and only 20% from the basin discharge, climatic contributions cannot be ignored, since the 80% water is directly dependant on it. It is therefore necessary to investigate climatic contribution to the declining Lake Victoria water level observed over a long period, i.e., 30 years. This contribution uses 30 years period anomalies for rainfall, river discharge and lake level changes of stations within Lake Victoria basin to analyse linear and cyclic trends of climate indicators in relation to Lake levels. Linear trend analysis using the Student’s t test indicate a decreasing pattern in rainfall anomalies, with the slope being statistically similar to those of water levels at both Kisumu, Maziba and Jinja stations for the same period of time (1976–1999), thus showing a strong correlation. On the other hand, cyclic trend analysis using Discrete Fourier Transform (DFT) shows cyclic period of water level to coincide with those of droughts and rainfall. The strong relationship between climatic indicators of drought and rainfall on one-hand and lake levels on the other hand signifies the need to incorporate climate information in predicting, monitoring and managing lake level changes. 相似文献
5.
雾是一种严重的天气灾害,极大地影响了交通和日常生活,并可能带来巨大的经济损失。利用1958～2007年678个中国地面观测站点的雾日数资料,采用相关系数分析、合成分析等方法分析了冬季雾日数的时空特征,发现冬季多雾地区和年际变率较强地区集中在西南、华北和华南等地区。根据冬季雾日分布特征,将中国划分为3个较为独立的雾区,从水汽条件、大气稳定度及大气环流背景等方面讨论了区域气候条件差异对局地雾形成机制的影响,发现不同区域冬季雾日产生的气候条件有着明显的差异性。结论如下:西南区冬季雾的形成受水汽输送影响较小,受大气稳定度影响较大,且巴尔喀什湖东侧高压脊加强,冷空气南下,西南较易发生雾;华北冬季雾日的形成受水汽输送影响较大,伴随长江中下游水汽异常推进偏北,水汽异常大值中心偏北,且西伯利亚高压、东亚大槽以及东北低压减弱,冷空气活动较弱,华北较易发生雾。华南冬季雾日的形成受水汽输送影响较大,伴随长江中下游水汽异常推进偏弱,水汽异常大值中心偏南,且东亚大槽减弱,华南较易发生雾。 相似文献
6.
Hydrologic impacts of climate change on the Nile River Basin: implications of the 2007 IPCC scenarios 总被引：2，自引：1，他引：1
We assess the potential impacts of climate change on the hydrology and water resources of the Nile River basin using a macroscale hydrology model. Model inputs are bias corrected and spatially downscaled 21st Century simulations from 11 General Circulation Models (GCMs) and two global emissions scenarios (A2 and B1) archived from the 2007 IPCC Fourth Assessment Report (AR4). While all GCMs agree with respect to the direction of 21st Century temperature changes, there is considerable variability in the magnitude, direction, and seasonality of projected precipitation changes. Our simulations show that, averaged over all 11 GCMs, the Nile River is expected to experience increase in streamflow early in the study period (2010–2039), due to generally increased precipitation. Streamflow is expected to decline during mid- (2040–2069) and late (2070–2099) century as a result of both precipitation declines and increased evaporative demand. The predicted multimodel average streamflow at High Aswan Dam (HAD) as a percentage of historical (1950–1999) annual average are 111 (114), 92 (93) and 84 (87) for A2 (B1) global emissions scenarios. Implications of these streamflow changes on the water resources of the Nile River basin were analyzed by quantifying the annual hydropower production and irrigation water release at HAD. The long-term HAD release for irrigation increases early in the century to 106 (109)% of historical, and then decreases to 87 (89) and 86 (84)% of historical in Periods II and III, respectively, for the A2 (B1) global emissions scenarios. Egypt’s hydropower production from HAD will be above the mean annual average historical value of about 10,000 GWH for the early part of 21st century, and thereafter will generally follow the streamflow trend, however with large variability among GCMs. Agricultural water supplies will be negatively impacted, especially in the second half of the century. 相似文献
7.
利用欧洲中期天气预报中心 (ECMWF) 提供的ERA-interim高分辨率资料,借助经验正交函数 (EOF) 分解、距平合成和相关分析等方法,讨论1979—2014年我国西南地区夏季大气水汽含量的时空变化特征及其与南亚高压的关系。研究结果表明:我国西南地区夏季大气水汽含量空间分布形态主要有全区一致型、南北振荡型和东西振荡型。全区一致型 (EOF1) 能够反映西南地区夏季水汽含量的主要特征,西南地区夏季大气水汽含量具有明显的年际变化特征;西南地区夏季大气水汽含量与南亚高压强度指数、面积指数及东伸指数均存在非常显著的正相关关系;南亚高压的异常偏强,有利于南海地区水汽向西南地区输送,且在西南地区气流由低层向高层的上升运动显著增强,引起西南地区大气水汽含量的异常偏多。 相似文献
8.
Abstract We have made a preliminary study of cloud‐to‐ground lightning over southern Ontario and the adjoining Great Lakes region. The lightning data set, using magnetic direction finding, is sufficiently accurate to study lightning climatology. Cloud‐to‐ground flash totals have been found for the three warm seasons 1989–91. A large variation in flash total, lightning‐day frequency and number of high flash density storms occurs over the area, with the maximum in southwestern Ontario. The area of the maximum also has a strong diurnal cycle and relatively few positive flashes. Several physical causes may contribute to this. Lake areas usually have slightly fewer flashes than nearby land areas and warm water usually has more flashes than cold water. The Great Lakes do produce more lightning than ocean areas. Convergence lines of lake breezes and other lake circulations can, however, be sites for storms with intense lightning. High surface temperature and moisture leads to an increase in lightning generation. Over land, upslope flow increases lightning‐producing storms and downslope flow decreases them. High flash density storms may be favoured by smooth rather than rough ground, and by open farmland rather than forest. On the other hand, there does not seem to be a clear urban effect increasing lightning in the Great Lakes 相似文献
9.
一个新的湖—气热传输模型及其模拟能力评估 总被引：3，自引：0，他引：3
基于原有模型,采用温度为预报变量,改进了数值计算方法,并为模型中的浅湖部分加入了底部沉积层模块,建立了一个新的湖泊一维涡扩散水热传输模型。利用德国Kossenblatter 湖的观测资料（2003 年5～10 月）对模型进行了验证,并与其他四个湖泊模式的模拟结果进行了对比。进一步应用本模型和洱海水上观测站的资料（2012 年1～12 月）详细分析了湖泊水热状态的季节变化和日变化。模拟结果表明:模型可以很好地模拟出洱海水温的季节变化以及日变化,湖泊表面温度和剖面温度的模拟值与观测值吻合很好,最大误差均在2℃ 范围内;湖泊表面通量的模拟效果比温度略差,尤其对感热通量有明显低估,差值约为实测值的33%。这部分偏差可能是由观测误差、缺测数据的填补与订正方法以及模型表面参数化过于简单所共同导致。 相似文献
10.
11.
1982—83年的厄尼诺和南方涛动是本世纪最强的一次ENSO(El-Nino/Southern Oscill-ation)事件。本文分析对比了El-Ni(?)o当年(1982)夏季(6—8月)和El-Nino次年(1983)夏季的西北太平洋低纬度环流特征发现有明显的差异,在1982年夏季,西北太平洋副热带高压明显偏弱;850hPa低纬度西风较强;200hPa上低纬度东风较强,在赤道海洋上已建立了沃克反环流,根据1982年和1983年夏季向外的长波辐射差异图可发现菲律宾以东洋面上ITCZ活跃。而在1983年夏季的低纬度环流几乎与1982年夏季的相反。这两年上述的差异是与赤道太平洋中部或东部的海温异常增暖有关的。 相似文献
12.
Zhengfang Wu Haibo Du Dongsheng Zhao Ming Li Xiangjun Meng Shengwei Zong 《Theoretical and Applied Climatology》2012,108(3-4):495-503
Daily global solar radiation is an important input required in most crop models. In the present study, a sunshine-based model, the ?ngstr?m–Prescott model, is employed to estimate daily global solar radiation on a horizontal surface during the growing season in Northeast China. Data from six control groups are used. The controls include the entire sequence, precipitation days, and non-precipitation days both during the growing season and year-round. Estimations are validated by comparing the calculated values with the corresponding measured values. The results indicate that estimating daily global solar radiation during the growing season using data only from the growing season is better than using year-round data. Classifying days with respect to precipitation and non-precipitation is also unnecessary. The performance on estimating daily global solar radiation during the growing season using the entire data in growing season performs best. A sunshine-based equation is obtained using our method to estimate growing season daily radiation for all meteorological stations in Northeast China. The approved approach is expected to be beneficial to crop models and other agricultural purposes. 相似文献
13.
湖面降水是影响湖泊水量和水质的重要因素之一,对湖面降水的研究有利于湖泊水环境的研究和治理。本文利用洱海周边11个气象站降水观测数据,对洱海周边站点的降水进行分析,并基于自然邻点插值法对洱海湖面降水进行分辨率为0.01°的网格插值,分析洱海湖面降水的分布特征。结果表明:洱海湖面降水分布时空差异显著,时间上具有季节性特征,夏季最多,秋季次之,冬季最少;空间上存在显著分布不均,降水高值中心位于洱海中部靠西岸湖湾区域,低值中心位于东南部湖区,最大格点降水量是最小格点的1.9倍;湖面降水存在明显的季节性空间振荡特征,降水的高值中心夏季略有北移向外呈发散性递减。洱海湖面降水时空分布特征的研究为大气湿沉降敏感区域和时段的划分提供数据支持,同时为湖泊水环境研究治理提供科学的技术支持。 相似文献
14.
Net radiation — soil heat flux relations as influenced by soil water content variations 总被引：1，自引：0，他引：1
Net radiation, soil heat flux, incoming and reflected solar radiation, and soil water content were measured during several clear day periods following approximate 10-cm applications of water to loam soils at Phoenix, Arizona, and at Sidney, Montana. The regression of soil heat flux on net radiation changed significantly as the soil dried, with the difference between them being a linear function of the volumetric soil water content of the uppermost 2 to 4 cm of soil. The net radiation-soil heat flux difference for soil in an air-dry state was only about one-half of what it was on the day after irrigation. Techniques discussed allow evaluation of what the net radiation-soil heat flux difference would be under conditions of no surface saturation deficit at any time of year from measurements of net solar radiation, soil water content, and air temperature, thereby improving the utility of many evaporation models. The data also indicate that water content measurements may be replaced by more easily measured soil albedo. 相似文献
15.
全球变暖减缓背景下欧亚秋冬温度变化特征和原因 总被引：3，自引：2，他引：1
采用气候序列变化趋势诊断和一元线性回归等分析法,研究和讨论了2000-2012年和1976-1999年两种年代际背景下全球陆地不同区域的年平均地表温度的变化特征。发现欧亚大陆中高纬度地区是对全球变暖减缓贡献最大的区域。且该地区在2000年以来秋季年代际增温,而冬季年代际降温。从同期大气环流的配置来看,在对流层低层,秋季西伯利亚高气压年代际减弱,而冬季西伯利亚高气压年代际增强。在对流层中高层,秋季从西欧至东北亚为"高-低-高"的高度场异常分布,纬向环流加强,经向环流减弱,而冬季极地与贝加尔湖地区的高度场呈偶极型分布,东亚大槽加深,经向环流加强。进一步研究发现,超前一个季节的喀拉海附近的海冰与欧亚中高纬度秋冬两季温度的年代际变率有着密切的联系。一方面,夏季(秋季)海冰减少影响秋季(冬季)中高纬度大气环流;另一方面,夏季(秋季)海冰减少,使得秋季(冬季)从北极至中高纬度大陆的对流层低层水汽含量增加(减少),大气逆辐射增强(减弱)导致秋季(冬季)增温(降温)。 相似文献
16.
S. M. El shazly 《大气科学进展》1996,13(3):349-358
The performance of two models,Jam and Baig,based on the modified version of Gaussian distribution function in estimating the daily total of global solar radiation and its distribution through the hours of the day from sunrise to sunset al any clear day is evaluated with our own measured data in the period from June 1992 to May 1993 in Qena Egypt The results show a high relative deviation of calculated values from measured ones,especially for Jain model,in the most hours of the day,except for those near to local noon.This misfit behavior is quite obvious in the early morning and late afternoon A new approach has been proposed in this paper to estimate the daily and hourly global solar radiation This model performs with very high accuracy on the recorded data in our region.The validity of this approach was verified with new measurements in some clear days in June and August 1994.The resultant very low relative deviation of the calculated values of global solar radiation from the measured ones confirms the 相似文献
17.
Diurnal and Seasonal Variations of Thermal Stratification and Vertical Mixing in a Shallow Fresh Water Lake 总被引：1，自引：0，他引：1
Yichen Yang Yongwei Wang Zhen Zhang Wei Wang Xia Ren Yaqi Gao Shoudong Liu Xuhui Lee 《Acta Meteorologica Sinica》2018,32(2):219-232
Among several influential factors, the geographical position and depth of a lake determine its thermal structure. In temperate zones, shallow lakes show significant differences in thermal stratification compared to deep lakes. Here, the variation in thermal stratification in Lake Taihu, a shallow fresh water lake, is studied systematically. Lake Taihu is a warm polymictic lake whose thermal stratification varies in short cycles of one day to a few days. The thermal stratification in Lake Taihu has shallow depths in the upper region and a large amplitude in the temperature gradient, the maximum of which exceeds 5°C m–1. The water temperature in the entire layer changes in a relatively consistent manner. Therefore, compared to a deep lake at similar latitude, the thermal stratification in Lake Taihu exhibits small seasonal differences, but the wide variation in the short term becomes important. Shallow polymictic lakes share the characteristic of diurnal mixing. Prominent differences on the duration and frequency of long-lasting thermal stratification are found in these lakes, which may result from the differences of local climate, lake depth, and fetch. A prominent response of thermal stratification to weather conditions is found, being controlled by the stratifying effect of solar radiation and the mixing effect of wind disturbance. Other than the diurnal stratification and convection, the representative responses of thermal stratification to these two factors with contrary effects are also discussed. When solar radiation increases, stronger wind is required to prevent the lake from becoming stratified. A daily average wind speed greater than 6 m s–1 can maintain the mixed state in Lake Taihu. Moreover, wind-induced convection is detected during thermal stratification. Due to lack of solar radiation, convection occurs more easily in nighttime than in daytime. Convection occurs frequently in fall and winter, whereas long-lasting and stable stratification causes less convection in summer. 相似文献
18.
In situ measured data of broadband solar radiation （Rs） and ultraviolet （Uv） radiation were used to investigate the spa- tiotemporal variation properties of Uv radiation and the ratio of Uv radiation to Rs over the North China Plain （NCP）. Based on the analysis, an empirical model for estimating Uv radiation under all weather conditions in this region was developed. The results showed that the annual Uv radiation over the NCP ranges from 0.38-0.52 MJ m^-2 d^-1. The highest value during the study period was recorded at the Changwu site, which is located near the margin of the Loess Plateau, while the lowest value appeared at the station in Beijing. The seasonal variation pattern of the ratio of Uv radiation to Rs is similar to that of Uv radiation; namely, the highest value appears in August and then decreases gradually until the lowest value appears in November. A small increasing trend in the Uv radiation levels and the ratio of Uv radiation to Rs was observed over the NCP. The evaluation results showed that the empirical estimation model can be widely used to estimate Uv radiation under all atmospheric conditions. The relative error between the modeled and measured daily values were within ± 15%. 相似文献
19.
H. P. Schmid H. A. Cleugh C. S. B. Grimmond T. R. Oke 《Boundary-Layer Meteorology》1991,54(3):249-276
Energy fluxes over an area of homogeneous suburban residential land-use in Vancouver, B.C., Canada are shown to vary by up to 25–40% within horizontal scales on the order of 102–103 m. Previously, variability of this magnitude has been expected to occur only at larger scales, between land-use zones or as urban-rural differences. In view of these findings, it is recognized that microadvective interaction between surface types at small scales may be important and can affect the energy balance even at larger scales. The present study discusses the small-scale spatial variability of energy fluxes and shows that it varies greatly for each term in the surface energy balance.Net radiation shows a relatively conservative behaviour (via albedo-surface temperature feedback) with little spatial variability. The turbulent fluxes (measured by eddy correlation at 28 m height), on the other hand, show a link between their temporal and spatial variability as the result of a temporally shifting source area which contains varying combinations of surface cover (using the dynamical source area concept of Schmid and Oke, 1990). As a result, part of the measured temporal variation is attributable to spatial differences in surface cover. Anthropogenic heat flux and storage heat flux (both modelled using a high resolution surface data-base) exhibit temporally varying spatial distributions. Their spatial pattern, however, is governed by nested scales of urban morphology (blocks, streets, properties, etc.). These differences in the source of variability between each component flux suggest a difficulty in the interpretation of the energy balance over urban areas, unless each term is spatially-averaged over the principal morphological units occurring in the area. 相似文献
20.
U. Feister 《Journal of Atmospheric Chemistry》1994,19(3):289-315
Solar ultraviolet radiation at the surface has been measured at Potsdam on cloudless days by spectrometer OL 752/10. The measurements are compared with broad-band filter measurements and with model calculations using a modified version of Green's model, which is independent of the measurements. Input data to the model such as atmospheric ozone and aerosol optical thicknesses were measured by a Dobson and Brewer spectrophotometer as well as a Linke Feussner pyrheliometer, respectively. Differences between the model and the measurements are discussed in terms of uncertainties in the calibration and errors of instruments as well as uncertainties in the model calculations including the errors of input data. It is demonstrated that different chemically and biologically effective radiances can be determined from only one set of measured spectral irradiance components, i.e. global radiation and diffuse downward and upward directed radiation. Examples of diurnal variations of the photochemical production of ozone and hydroxyl radicals as determined from spectral irradiance measurements and measured concentrations of relevant trace gases are given.It is shown from the measured irradiance that relations between different effects of radiation to the biosphere depend on solar zenith angle, and to a certain extent also on atmospheric ozone. This has to be taken into account when adverse effects of changing UV radiation are evaluated. Radiation Amplification Factors derived from measurements correspond to those determined from model calculations. 相似文献