By using the data set of light rain days and low cloud cover at 51 stations in South China(SC), and the method of linear regression and correlative analysis, we analyze the spatiotemporal characteristics of the light ...By using the data set of light rain days and low cloud cover at 51 stations in South China(SC), and the method of linear regression and correlative analysis, we analyze the spatiotemporal characteristics of the light rain days and low cloud cover including annual variation and long-term seasonal change. The results are as follows:(1) The trends of light rain days and low cloud cover over SC are opposite(light rain days tended to decrease and low cloud cover tended to increase in the past 46 years). The value distributed in east is higher than that in west, and coastal area higher than inland area.(2) The regression coefficients of light rain days and low cloud cover during 1960-2005 are4.88 d/10 years and 1.14%/10 years respectively, which had all passed the 0.001 significance level.(3) Variations of light rain days are relatively small in spring and summer, but their contributions are larger for annual value than that of autumn and winter.(4) There are two regions with large values of aerosol optical depth(AOD), which distribute in central and southern Guangxi and Pearl River Delta(PRD) of Guangdong, and the value of AOD in PRD is up to 0.7.The aerosol index distributed in coastal area is higher than in the inland area, which is similar to the light rain days and low cloud cover over SC. Aerosol indexes in SC kept increasing with fluctuation during the past 27 years. The GDP of the three provinces in SC increased obviously during the past 28 years, especially in Guangdong, which exhibited that there is simultaneous correlation between light rain days with the variables of low cloud cover and release of aerosols over SC during 1960 to 2005.展开更多
Total Cloud Cover （TCC） over China deter- mined from four climate datasets including the Interna- tional Satellite Cloud Climatology Project （ISCCP）, the 40-year Re-Analysis Project of the European Centre for Medi...Total Cloud Cover （TCC） over China deter- mined from four climate datasets including the Interna- tional Satellite Cloud Climatology Project （ISCCP）, the 40-year Re-Analysis Project of the European Centre for Medium-Range Weather Forecasts （ERA-40）, Climate Research Unit Time Series 3.0 （CRU3）, and ground sta- tion datasets are used to show spatial and temporal varia- tion of TCC and their differences. It is demonstrated that the four datasets show similar spatial pattern and seasonal variation. The maximum value is derived from ISCCE TCC value in North China derived from ERA-40 is 50% larger than that from the station dataset; however, the value is 50% less than that in South China. The annual TCC of ISCCP, ERA-40, and ground station datasets shows a decreasing trend during 1984-2002; however, an increasing trend is derived from CRU3. The results of this study imply remarkable differences of TCC derived from surface and satellite observations as well as model simu- lations. The potential effects of these differences on cloud climatology and associated climatic issues should be carefully considered.展开更多
Currently, the historical archive images of Landsat family sensors are probably the most effective data products for tracking global longitudinal changes since the 1970 s. However, the issue of the degree and extent o...Currently, the historical archive images of Landsat family sensors are probably the most effective data products for tracking global longitudinal changes since the 1970 s. However, the issue of the degree and extent of cloud coverage is always a challenge and varies distinctively worldwide. So far, acquisition probability（AP） analyses of cloud cover（CC） of Landsat observations have been conducted with different sensors at regional scale. To our knowledge, CC probability analysis for the newly-launched Landsat-8 Operational Land Imager（OLI） across China is not reported. In this paper, monthly, seasonal, and annual APs for Landsat OLI（44,228 in total） images over China acquired from April 2013 to October 2016 with various CC thresholds were analyzed. The results showed that： first, the cumulative average APs of all OLI data over China at the CC thresholds ≤30% was about 49.6% which illustrated the availability of OLI imagery across China. Second, the spatial patterns of 10%, 20%, and 30% CC thresholds of OLI observations, coincided well with the precipitation distributions separated by the respective 200 mm, 400 mm, and 800 mm isohyetal lines. Third, the APs of images with the 30% CC threshold are the highest in autumn and winter especially in October of 58.7%, while the corresponding lowest probability occurred in June of 41.0%. Finally, the spatial differences in APs of targeted images with ≤30% CC thresholds were quite significant. At regional scales, the arid and semi-arid areas, Inland River and Songliao River basins, and northwestern side of the Hu Huanyong population line had the larger probabilities of obtaining high-quality images. Our study suggested that OLI imagery satisfy the data requirements needed for land surface monitoring, although there existed obvious spatio-temporal differences in APs over China at the 30% CC threshold.展开更多
Satellite and human visual observation are two of the most important observation approaches for cloud cover. In this study, the total cloud cover （TCC） observed by MODIS onboard the Terra and Aqua satellites was com...Satellite and human visual observation are two of the most important observation approaches for cloud cover. In this study, the total cloud cover （TCC） observed by MODIS onboard the Terra and Aqua satellites was compared with Synop meteorological station observations over the North China Plain and its surrounding regions for 11 years during daytime and 7 years during nighttime. The Synop data were recorded eight times a day at 3-h intervals. Linear interpolation was used to interpolate the Synop data to the MODIS overpass time in order to reduce the temporal deviation between the satellite and Synop observations. Results showed that MODIS-derived TCC had good consistency with the Synop observations; the correlation coefficients ranged from 0.56 in winter to 0.73 in summer for Terra MODIS, and from 0.55 in winter to 0.71 in summer for Aqua MODIS. However, they also had certain differences. On average, the MODIS-derived TCC was 15.16% higher than the Synop data, and this value was higher at nighttime （15.58%-16.64%） than daytime （12.74%-14.14%）. The deviation between the MODIS and Synop TCC had large seasonal variation, being largest in winter （29.53%-31.07%） and smallest in summer （4.46%-6.07%）. Analysis indicated that cloud with low cloud-top height and small cloud optical thickness was more likely to cause observation bias. Besides, an increase in the satellite view zenith angle, aerosol optical depth, or snow cover could lead to positively biased MODIS results, and this affect differed among different cloud types.展开更多
Based on the data of cloud cover, precipitation, temperature, sunshine hours and relative humidity from nine ground meteorological stations in Heze region in the southwest of Shandong Province from 1961 to 2012, chang...Based on the data of cloud cover, precipitation, temperature, sunshine hours and relative humidity from nine ground meteorological stations in Heze region in the southwest of Shandong Province from 1961 to 2012, changes of total and low cloud cover and its relationship with climatic factors associated in the southwest of Shandong Province in recent 52 years were analyzed. The results showed that average total cloud cover in- creased by 0.89%/10 a, but average low cloud cover decreased by 1.1%/10 a in Heze region in recent 52 years. The positive correlation between the average total cloud cover and temperature in autumn and winter was obvious, that is, when cloud cover increased by 10%, the average temper- ature increased by 0.48 ~C in autumn and increased by 0.83~（3 in winter. The average low. cloud cover negatively correlated with the average tam- perature in each season, and the negative correlation was very significant in spring. When cloud cover increased by 10%, the average temperature decreased by 1.49 ~C. The positive correlation between the average cloud cover and average precipitation was significant. The annual precipitation increased by 148.1 mm when annual mean total cloud cover increased by 10%. When seasonal mean cloud cover increased by 10%, the precipita- tion increased by 48.4, 107.1,55.4 and 12.2 mm in spring, summer, autumn and winter respectively. The annual average total cloud cover and low cloud cover had significantly positive correlation with 〉~0.1, ~〉1.0, ~〉10 and ~〉25 mm precipitation days respectively. The sunshine hours were seriously influenced by cloud cover, and when cloud cover increased by 10%, the sunshine hours decreased by 54.5 h in spring, 134.2 h in sum- mer, 154.3 h in autumn and 60.6 h in winter. The total cloud cover significantly positively correlated with relative humidity in summer and autumn, and when cloud cover increased by 10%, the relative humidity increased by 3.3% in summer and 4.1% in autumn.展开更多
Water resources are one of the key factors restricting the development of arid areas,and cloud water resources is an important part of water resources.The arid region of central Asia is the core region of the current ...Water resources are one of the key factors restricting the development of arid areas,and cloud water resources is an important part of water resources.The arid region of central Asia is the core region of the current national green silk road construction,and is the largest arid region in the world.Based on cloud cover data of ECMWF,the current study analyzed temporal and spatial characteristics of cloud properties in arid regions of Central Asia between 1980 and 2019.Our findings show that:(1)From the point of view of spatial distribution,total cloudiness in arid regions of Central Asia was low in the south and high in the north.The distribution of high cloud frequency and medium cloud frequency was higher in the south and lower in the north,while low cloud frequency distribution was low in the south and high in the north.(2)In terms of time,the variation of cloud cover and cloud type frequency had obvious seasonal characteristics.From winter to spring,cloud cover increased,and the change of cloud type frequency increased.From spring to summer,cloud cover continued to increase and the change of cloud type frequency increased further.Cloud cover began to decrease from summer to autumn,and the change of cloud type frequency also decreased.(3)Generally,average total cloud cover decreased in most of central Asia,and high and medium cloud cover increased while low cloud cover decreased.This study provides a reference for the rational development of cloud resources in the region.展开更多
The energy of solar radiation absorbed by the Earth,as well as the thermal radiation of the Earth’s surface,which is released to the space through the atmospheric transparency window,depends on variations of the area...The energy of solar radiation absorbed by the Earth,as well as the thermal radiation of the Earth’s surface,which is released to the space through the atmospheric transparency window,depends on variations of the area of the cloud cover.Svensmark et al.suggest that the increase in the area of the cloud cover in the lower atmosphere,presumably caused by an increase in the flux of galactic cosmic rays during the quasi-bicentennial minimum of solar activity,results only in an increase in the fraction of the solar radiation reflected back to the space and weakens the flux of the solar radiation that reached the Earth surface.It is suggested,without any corresponding calculations of the variations of the average annual energy balance of the EarthЕ,that the consequences will include only a deficit of the solar energy absorbed by the Earth and a cooling of the climate up to the onset of the Little Ice Age.These suggestions ignore simultaneous impact of the opposite aspects of the increase in the area of the cloud cover on the climate warming.The latter will result from a decrease in the power of thermal radiation of the Earth’s surface released to the space,and also in the power of the solar radiation reflected from the Earth’s surface,due to the increase in their absorption and reflection back to the surface.A substantial strengthening in the greenhouse effect and the narrowing of the atmospheric transparency window will also occur.Here,we estimate the impact of all aspects of possible long-term 2%growth of the cloud cover area in the lower atmosphere byЕ.We found that an increase in the cloud cover area in the lower atmosphere will result simultaneously both in the decrease and in the increase in the temperature,which will virtually compensate each other,while the energy balance of the Earth E before and after the increase in the cloud cover area by 2%will stay essentially the same:E1-E0≈0.展开更多
As is well known,clouds impact the radiative budget,climate change,hydrological processes,and the global carbon,nitrogen and sulfur cycles.To understand the wide-ranging effects of clouds,it is necessary to assess cha...As is well known,clouds impact the radiative budget,climate change,hydrological processes,and the global carbon,nitrogen and sulfur cycles.To understand the wide-ranging effects of clouds,it is necessary to assess changes in cloud cover at high spatial and temporal resolution.In this study,we calculate global cloud cover during the day and at night using cloud products estimated from Moderate Resolution Imaging Spectroradiometer(MODIS)data.Results indicate that the global mean cloud cover from 2003 to 2012 was 66%.Moreover,global cloud cover increased over this recent decade.Specifically,cloud cover over land areas(especially North America,Antarctica,and Europe)decreased(slope=–0.001,R^2=0.5254),whereas cloud cover over ocean areas(especially the Indian and Pacific Oceans)increased(slope=0.0011,R^2=0.4955).Cloud cover is relatively high between the latitudes of 36°S and 68°S compared to other regions,and cloud cover is lowest over Oceania and Antarctica.The highest rates of increase occurred over Southeast Asia and Oceania,whereas the highest rates of decrease occurred over Antarctica and North America.The global distribution of cloud cover regulates global temperature change,and the trends of these two variables over the 10-year period examined in this study(2003–2012)oppose one another in some regions.These findings are very important for studies of global climate change.展开更多
Three kinds of the widely-used cloudiness parameterizations are compared with data produced from the cloud-resolving model(CRM) simulations of the tropical cloud system. The investigated schemes include those based on...Three kinds of the widely-used cloudiness parameterizations are compared with data produced from the cloud-resolving model(CRM) simulations of the tropical cloud system. The investigated schemes include those based on relative humidity(RH), the semi-empirical scheme using cloud condensate as a predictor, and the statistical scheme based on probability distribution functions(PDFs). Results show that all three schemes are successful in reproducing the timing of cloud generation, except for the RH-based scheme, in which low-level clouds are artificially simulated during cloudless days. In contrast, the low-level clouds are well simulated in the semi-empirical and PDF-based statistical schemes, both of which are close to the CRM explicit simulations. In addition to the Gaussian PDF, two alternative PDFs are also explored to investigate the impact of different PDFs on cloud parameterizations. All the PDF-based parameterizations are found to be inaccurate for high cloud simulations, in either the magnitude or the structure. The primary reason is that the investigated PDFs are symmetrically assumed, yet the skewness factors in deep convective cloud regimes are highly significant, indicating the symmetrical assumption is not well satisfied in those regimes. Results imply the need to seek a skewed PDF in statistical schemes so that it can yield better performance in high cloud simulations.展开更多
Because of similar reflective characteristics of snow and cloud, the weather status seriously affects snow monitoring using optical remote sensing data. Cloud amount analysis during 2010 to 2011 snow seasons shows tha...Because of similar reflective characteristics of snow and cloud, the weather status seriously affects snow monitoring using optical remote sensing data. Cloud amount analysis during 2010 to 2011 snow seasons shows that cloud cover is the major limitation for snow cover monitoring using MOD10A1 and MYD10A1. By use of MODIS daily snow cover products and AMSR-E snow wa- ter equivalent products （SWE）, several cloud elimination methods were integrated to produce a new daily cloud flee snow cover product, and information of snow depth from 85 climate stations in Tibetan Plateau area （TP） were used to validate the accuracy of the new composite snow cover product. The results indicate that snow classification accuracy of the new daily snow cover product reaches 91.7% when snow depth is over 3 cm. This suggests that the new daily snow cover mapping algorithm is suitable for monitoring snow cover dynamic changes in TP.展开更多
With excellent seeing conditions,ultra-low infrared background noise,high frequency of space debris transits,and continuous polar night coverage,Dome A in Antarctica has become an ideal platform for ground-based astro...With excellent seeing conditions,ultra-low infrared background noise,high frequency of space debris transits,and continuous polar night coverage,Dome A in Antarctica has become an ideal platform for ground-based astronomy and space situational monitoring.As a crucial observatory site for international deep space,deep Earth,deep sea,and polar exploration,it is very important to evaluate the suitability of Dome A as an observatory site.However,owing to extreme environmental constraints,the evaluation of site conditions is mainly based on single-point measurements,making it challenging to comprehensively evaluate the effective site range and uniformity.This study integrated satellite remote sensing data to develop a cross-comparison framework for diverse indicators across Dome A,to evaluate its spatial uniformity.We find that the area surrounding the Dome A site,defined within a roughly 1°×1°latitude and longitude range,possesses excellent astronomical observation conditions.展开更多
Variability of power generation due to the prevalence of cloud cover over solar photovoltaics(PV)power plants is a challenge faced by grid operators and independent system operators(ISOs)in the integration of solar en...Variability of power generation due to the prevalence of cloud cover over solar photovoltaics(PV)power plants is a challenge faced by grid operators and independent system operators(ISOs)in the integration of solar energy into the grid.Solar forecasts generated through ground⁃based sky imaging systems are useful for short⁃term cloud motion predictions.However,the cost of sky imaging systems currently available in industries is relatively high.Hence,a ground⁃based camera system utilizing a simple webcam is proposed in this study.The proposed method can produce predictions with high levels of accuracy.Forecasts were generated through video analysis using MATLAB for the computation of cloud motion predictions.The image processing involved in the implementation of the proposed system is based on the detection of cloud regions in the form of a cluster of white pixels within individual frames and tracking their motion through comparison of subsequent frames.This study describes the techniques and processes used in the development of the proposed method,along with the evaluation of performance through analysis of the results.The predictions were carried out over multiple time horizons.The time horizons selected include 5,10,15,20,25,and 30 s.The overall results computed showed promising accuracy levels above 94.60%,which makes it adequate for generating reliable forecasts.展开更多
During a research cruise over the Pacific Ocean in 1989, solar irradiance was measured with a broad-band pyranometer along the cruise track. Cloud cover was photographed with an all-sky time-lapse came ra. Cloud types...During a research cruise over the Pacific Ocean in 1989, solar irradiance was measured with a broad-band pyranometer along the cruise track. Cloud cover was photographed with an all-sky time-lapse came ra. Cloud types were observed and recorded. The data show that both the types and the amounts of clouds affect radiation fluxes on the sea surface. For low-level and middle-level clouds, the correlations (r) between measured irradiance (in Percent of calculated maximum irradiance) and cloud amount (in fraction of sky) were significant: r=-0. 79 and - 0. 66, respectively. For high-level clouds, the correlation was not significant: r=-0. 21. The results indicate that cloud shortwave forcing is a major modifier of the earth's surface insolation and change of cloud amount may affect global climate.展开更多
In this study,the decomposed fast and slow responses of clouds to an abruptly quadrupled CO_(2)concentration(approximately 1139 ppmv)in East Asia(EA)are obtained quantitatively by using a general circulation model,BCC...In this study,the decomposed fast and slow responses of clouds to an abruptly quadrupled CO_(2)concentration(approximately 1139 ppmv)in East Asia(EA)are obtained quantitatively by using a general circulation model,BCC–AGCM2.0.Our results show that in the total response,the total cloud cover(TCC),low cloud cover(LCC),and high cloud cover(HCC)all increased north of 40°N and decreased south of 40°N except in the Tibetan Plateau(TP).The mean changes of the TCC,LCC,and HCC in EA were–0.74%,0.38%,and–0.38%in the total response,respectively;1.05%,–0.03%,and 1.63%in the fast response,respectively;and–1.79%,0.41%,and–2.01%in the slow response,respectively.By comparison,we found that changes in cloud cover were dominated by the slow response in most areas in EA due to the changes in atmospheric temperature,circulation,and water vapor supply together.Overall,the changes in the cloud forcing over EA related to the fast and slow responses were opposite to each other,and the final cloud forcing was dominated by the slow response.The mean net cloud forcing(NCF)in the total response over EA was–1.80 W m^(–2),indicating a cooling effect which partially offset the warming effect caused by the quadrupled CO_(2).The total responses of NCF in the TP,south China(SC),and northeast China(NE)were–6.74 W m^(–2),6.11 W m^(–2),and–7.49 W m^(–2),respectively.Thus,the local effects of offsetting or amplifying warming were particularly obvious.展开更多
基金National Key Project of Research and Development Plan of China(2016YFA0602501)National Natural Science Foundation of China(4163053241275082)
文摘By using the data set of light rain days and low cloud cover at 51 stations in South China(SC), and the method of linear regression and correlative analysis, we analyze the spatiotemporal characteristics of the light rain days and low cloud cover including annual variation and long-term seasonal change. The results are as follows:(1) The trends of light rain days and low cloud cover over SC are opposite(light rain days tended to decrease and low cloud cover tended to increase in the past 46 years). The value distributed in east is higher than that in west, and coastal area higher than inland area.(2) The regression coefficients of light rain days and low cloud cover during 1960-2005 are4.88 d/10 years and 1.14%/10 years respectively, which had all passed the 0.001 significance level.(3) Variations of light rain days are relatively small in spring and summer, but their contributions are larger for annual value than that of autumn and winter.(4) There are two regions with large values of aerosol optical depth(AOD), which distribute in central and southern Guangxi and Pearl River Delta(PRD) of Guangdong, and the value of AOD in PRD is up to 0.7.The aerosol index distributed in coastal area is higher than in the inland area, which is similar to the light rain days and low cloud cover over SC. Aerosol indexes in SC kept increasing with fluctuation during the past 27 years. The GDP of the three provinces in SC increased obviously during the past 28 years, especially in Guangdong, which exhibited that there is simultaneous correlation between light rain days with the variables of low cloud cover and release of aerosols over SC during 1960 to 2005.
基金supported by the "Strategic Priority Research Program" of the Chinese Academy of Sciences(XDA05100300)the National Basic Research Program of China(2013CB955801)the National Natural Science Foundation of China(41175030)
文摘Total Cloud Cover （TCC） over China deter- mined from four climate datasets including the Interna- tional Satellite Cloud Climatology Project （ISCCP）, the 40-year Re-Analysis Project of the European Centre for Medium-Range Weather Forecasts （ERA-40）, Climate Research Unit Time Series 3.0 （CRU3）, and ground sta- tion datasets are used to show spatial and temporal varia- tion of TCC and their differences. It is demonstrated that the four datasets show similar spatial pattern and seasonal variation. The maximum value is derived from ISCCE TCC value in North China derived from ERA-40 is 50% larger than that from the station dataset; however, the value is 50% less than that in South China. The annual TCC of ISCCP, ERA-40, and ground station datasets shows a decreasing trend during 1984-2002; however, an increasing trend is derived from CRU3. The results of this study imply remarkable differences of TCC derived from surface and satellite observations as well as model simu- lations. The potential effects of these differences on cloud climatology and associated climatic issues should be carefully considered.
基金National Natural Science Foundation of China,No.41430861National Key Research and Development Program of China,No.2016YFC0503500Opening Fund of Key Laboratory of Poyang Lake Wetland and Watershed Research,Ministry of Education,Jiangxi Normal University,No.PK2016004
文摘Currently, the historical archive images of Landsat family sensors are probably the most effective data products for tracking global longitudinal changes since the 1970 s. However, the issue of the degree and extent of cloud coverage is always a challenge and varies distinctively worldwide. So far, acquisition probability（AP） analyses of cloud cover（CC） of Landsat observations have been conducted with different sensors at regional scale. To our knowledge, CC probability analysis for the newly-launched Landsat-8 Operational Land Imager（OLI） across China is not reported. In this paper, monthly, seasonal, and annual APs for Landsat OLI（44,228 in total） images over China acquired from April 2013 to October 2016 with various CC thresholds were analyzed. The results showed that： first, the cumulative average APs of all OLI data over China at the CC thresholds ≤30% was about 49.6% which illustrated the availability of OLI imagery across China. Second, the spatial patterns of 10%, 20%, and 30% CC thresholds of OLI observations, coincided well with the precipitation distributions separated by the respective 200 mm, 400 mm, and 800 mm isohyetal lines. Third, the APs of images with the 30% CC threshold are the highest in autumn and winter especially in October of 58.7%, while the corresponding lowest probability occurred in June of 41.0%. Finally, the spatial differences in APs of targeted images with ≤30% CC thresholds were quite significant. At regional scales, the arid and semi-arid areas, Inland River and Songliao River basins, and northwestern side of the Hu Huanyong population line had the larger probabilities of obtaining high-quality images. Our study suggested that OLI imagery satisfy the data requirements needed for land surface monitoring, although there existed obvious spatio-temporal differences in APs over China at the 30% CC threshold.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41590874 and 41590875)the Ministry of Science and Technology of China (Grant No. 2014CB953703)
文摘Satellite and human visual observation are two of the most important observation approaches for cloud cover. In this study, the total cloud cover （TCC） observed by MODIS onboard the Terra and Aqua satellites was compared with Synop meteorological station observations over the North China Plain and its surrounding regions for 11 years during daytime and 7 years during nighttime. The Synop data were recorded eight times a day at 3-h intervals. Linear interpolation was used to interpolate the Synop data to the MODIS overpass time in order to reduce the temporal deviation between the satellite and Synop observations. Results showed that MODIS-derived TCC had good consistency with the Synop observations; the correlation coefficients ranged from 0.56 in winter to 0.73 in summer for Terra MODIS, and from 0.55 in winter to 0.71 in summer for Aqua MODIS. However, they also had certain differences. On average, the MODIS-derived TCC was 15.16% higher than the Synop data, and this value was higher at nighttime （15.58%-16.64%） than daytime （12.74%-14.14%）. The deviation between the MODIS and Synop TCC had large seasonal variation, being largest in winter （29.53%-31.07%） and smallest in summer （4.46%-6.07%）. Analysis indicated that cloud with low cloud-top height and small cloud optical thickness was more likely to cause observation bias. Besides, an increase in the satellite view zenith angle, aerosol optical depth, or snow cover could lead to positively biased MODIS results, and this affect differed among different cloud types.
基金Supported by the Scientific Research Foundation for Young Scholars of Shandong Meteorological Bureau
文摘Based on the data of cloud cover, precipitation, temperature, sunshine hours and relative humidity from nine ground meteorological stations in Heze region in the southwest of Shandong Province from 1961 to 2012, changes of total and low cloud cover and its relationship with climatic factors associated in the southwest of Shandong Province in recent 52 years were analyzed. The results showed that average total cloud cover in- creased by 0.89%/10 a, but average low cloud cover decreased by 1.1%/10 a in Heze region in recent 52 years. The positive correlation between the average total cloud cover and temperature in autumn and winter was obvious, that is, when cloud cover increased by 10%, the average temper- ature increased by 0.48 ~C in autumn and increased by 0.83~（3 in winter. The average low. cloud cover negatively correlated with the average tam- perature in each season, and the negative correlation was very significant in spring. When cloud cover increased by 10%, the average temperature decreased by 1.49 ~C. The positive correlation between the average cloud cover and average precipitation was significant. The annual precipitation increased by 148.1 mm when annual mean total cloud cover increased by 10%. When seasonal mean cloud cover increased by 10%, the precipita- tion increased by 48.4, 107.1,55.4 and 12.2 mm in spring, summer, autumn and winter respectively. The annual average total cloud cover and low cloud cover had significantly positive correlation with 〉~0.1, ~〉1.0, ~〉10 and ~〉25 mm precipitation days respectively. The sunshine hours were seriously influenced by cloud cover, and when cloud cover increased by 10%, the sunshine hours decreased by 54.5 h in spring, 134.2 h in sum- mer, 154.3 h in autumn and 60.6 h in winter. The total cloud cover significantly positively correlated with relative humidity in summer and autumn, and when cloud cover increased by 10%, the relative humidity increased by 3.3% in summer and 4.1% in autumn.
基金financially supported by the National Natural Science Foundation of China (41867030, 41971036)the National Natural Science Foundation innovation research group science foundation of China (41421061)
文摘Water resources are one of the key factors restricting the development of arid areas,and cloud water resources is an important part of water resources.The arid region of central Asia is the core region of the current national green silk road construction,and is the largest arid region in the world.Based on cloud cover data of ECMWF,the current study analyzed temporal and spatial characteristics of cloud properties in arid regions of Central Asia between 1980 and 2019.Our findings show that:(1)From the point of view of spatial distribution,total cloudiness in arid regions of Central Asia was low in the south and high in the north.The distribution of high cloud frequency and medium cloud frequency was higher in the south and lower in the north,while low cloud frequency distribution was low in the south and high in the north.(2)In terms of time,the variation of cloud cover and cloud type frequency had obvious seasonal characteristics.From winter to spring,cloud cover increased,and the change of cloud type frequency increased.From spring to summer,cloud cover continued to increase and the change of cloud type frequency increased further.Cloud cover began to decrease from summer to autumn,and the change of cloud type frequency also decreased.(3)Generally,average total cloud cover decreased in most of central Asia,and high and medium cloud cover increased while low cloud cover decreased.This study provides a reference for the rational development of cloud resources in the region.
文摘The energy of solar radiation absorbed by the Earth,as well as the thermal radiation of the Earth’s surface,which is released to the space through the atmospheric transparency window,depends on variations of the area of the cloud cover.Svensmark et al.suggest that the increase in the area of the cloud cover in the lower atmosphere,presumably caused by an increase in the flux of galactic cosmic rays during the quasi-bicentennial minimum of solar activity,results only in an increase in the fraction of the solar radiation reflected back to the space and weakens the flux of the solar radiation that reached the Earth surface.It is suggested,without any corresponding calculations of the variations of the average annual energy balance of the EarthЕ,that the consequences will include only a deficit of the solar energy absorbed by the Earth and a cooling of the climate up to the onset of the Little Ice Age.These suggestions ignore simultaneous impact of the opposite aspects of the increase in the area of the cloud cover on the climate warming.The latter will result from a decrease in the power of thermal radiation of the Earth’s surface released to the space,and also in the power of the solar radiation reflected from the Earth’s surface,due to the increase in their absorption and reflection back to the surface.A substantial strengthening in the greenhouse effect and the narrowing of the atmospheric transparency window will also occur.Here,we estimate the impact of all aspects of possible long-term 2%growth of the cloud cover area in the lower atmosphere byЕ.We found that an increase in the cloud cover area in the lower atmosphere will result simultaneously both in the decrease and in the increase in the temperature,which will virtually compensate each other,while the energy balance of the Earth E before and after the increase in the cloud cover area by 2%will stay essentially the same:E1-E0≈0.
基金Under the auspices of the National Key Project of China(No.2018YFC1506602,2018YFC1506502)National Natural Science Foundation of China(No.41571427)+1 种基金the Anhui Natural Science Foundation(No.1808085MF195)Open Fund of State Key Laboratory of Remote Sensing Science(No.OFSLRSS201708)
文摘As is well known,clouds impact the radiative budget,climate change,hydrological processes,and the global carbon,nitrogen and sulfur cycles.To understand the wide-ranging effects of clouds,it is necessary to assess changes in cloud cover at high spatial and temporal resolution.In this study,we calculate global cloud cover during the day and at night using cloud products estimated from Moderate Resolution Imaging Spectroradiometer(MODIS)data.Results indicate that the global mean cloud cover from 2003 to 2012 was 66%.Moreover,global cloud cover increased over this recent decade.Specifically,cloud cover over land areas(especially North America,Antarctica,and Europe)decreased(slope=–0.001,R^2=0.5254),whereas cloud cover over ocean areas(especially the Indian and Pacific Oceans)increased(slope=0.0011,R^2=0.4955).Cloud cover is relatively high between the latitudes of 36°S and 68°S compared to other regions,and cloud cover is lowest over Oceania and Antarctica.The highest rates of increase occurred over Southeast Asia and Oceania,whereas the highest rates of decrease occurred over Antarctica and North America.The global distribution of cloud cover regulates global temperature change,and the trends of these two variables over the 10-year period examined in this study(2003–2012)oppose one another in some regions.These findings are very important for studies of global climate change.
基金supported by the National Basic Research Program of China(Grant Nos.2014CB441202,2013CB955803)the National Natural Science Foundation of China(Grant Nos.41305102,91337110)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA11010402)the Joint Center for Global Change Studies(Grant No.105019)
文摘Three kinds of the widely-used cloudiness parameterizations are compared with data produced from the cloud-resolving model(CRM) simulations of the tropical cloud system. The investigated schemes include those based on relative humidity(RH), the semi-empirical scheme using cloud condensate as a predictor, and the statistical scheme based on probability distribution functions(PDFs). Results show that all three schemes are successful in reproducing the timing of cloud generation, except for the RH-based scheme, in which low-level clouds are artificially simulated during cloudless days. In contrast, the low-level clouds are well simulated in the semi-empirical and PDF-based statistical schemes, both of which are close to the CRM explicit simulations. In addition to the Gaussian PDF, two alternative PDFs are also explored to investigate the impact of different PDFs on cloud parameterizations. All the PDF-based parameterizations are found to be inaccurate for high cloud simulations, in either the magnitude or the structure. The primary reason is that the investigated PDFs are symmetrically assumed, yet the skewness factors in deep convective cloud regimes are highly significant, indicating the symmetrical assumption is not well satisfied in those regimes. Results imply the need to seek a skewed PDF in statistical schemes so that it can yield better performance in high cloud simulations.
基金supported by the China State Kay Basic Research Project(2013CBA01802)Chinese National Natural Science Foundation(41101337+2 种基金41001197and 31228021)the Fundamental Research Funds for the Central Universities(lzujbky-2013-103)
文摘Because of similar reflective characteristics of snow and cloud, the weather status seriously affects snow monitoring using optical remote sensing data. Cloud amount analysis during 2010 to 2011 snow seasons shows that cloud cover is the major limitation for snow cover monitoring using MOD10A1 and MYD10A1. By use of MODIS daily snow cover products and AMSR-E snow wa- ter equivalent products （SWE）, several cloud elimination methods were integrated to produce a new daily cloud flee snow cover product, and information of snow depth from 85 climate stations in Tibetan Plateau area （TP） were used to validate the accuracy of the new composite snow cover product. The results indicate that snow classification accuracy of the new daily snow cover product reaches 91.7% when snow depth is over 3 cm. This suggests that the new daily snow cover mapping algorithm is suitable for monitoring snow cover dynamic changes in TP.
基金supported by the Space Debris Research Project,China(KJSP2020010102)the National Key R&D Program of China(2022YFC2807300).
文摘With excellent seeing conditions,ultra-low infrared background noise,high frequency of space debris transits,and continuous polar night coverage,Dome A in Antarctica has become an ideal platform for ground-based astronomy and space situational monitoring.As a crucial observatory site for international deep space,deep Earth,deep sea,and polar exploration,it is very important to evaluate the suitability of Dome A as an observatory site.However,owing to extreme environmental constraints,the evaluation of site conditions is mainly based on single-point measurements,making it challenging to comprehensively evaluate the effective site range and uniformity.This study integrated satellite remote sensing data to develop a cross-comparison framework for diverse indicators across Dome A,to evaluate its spatial uniformity.We find that the area surrounding the Dome A site,defined within a roughly 1°×1°latitude and longitude range,possesses excellent astronomical observation conditions.
文摘Variability of power generation due to the prevalence of cloud cover over solar photovoltaics(PV)power plants is a challenge faced by grid operators and independent system operators(ISOs)in the integration of solar energy into the grid.Solar forecasts generated through ground⁃based sky imaging systems are useful for short⁃term cloud motion predictions.However,the cost of sky imaging systems currently available in industries is relatively high.Hence,a ground⁃based camera system utilizing a simple webcam is proposed in this study.The proposed method can produce predictions with high levels of accuracy.Forecasts were generated through video analysis using MATLAB for the computation of cloud motion predictions.The image processing involved in the implementation of the proposed system is based on the detection of cloud regions in the form of a cluster of white pixels within individual frames and tracking their motion through comparison of subsequent frames.This study describes the techniques and processes used in the development of the proposed method,along with the evaluation of performance through analysis of the results.The predictions were carried out over multiple time horizons.The time horizons selected include 5,10,15,20,25,and 30 s.The overall results computed showed promising accuracy levels above 94.60%,which makes it adequate for generating reliable forecasts.
文摘During a research cruise over the Pacific Ocean in 1989, solar irradiance was measured with a broad-band pyranometer along the cruise track. Cloud cover was photographed with an all-sky time-lapse came ra. Cloud types were observed and recorded. The data show that both the types and the amounts of clouds affect radiation fluxes on the sea surface. For low-level and middle-level clouds, the correlations (r) between measured irradiance (in Percent of calculated maximum irradiance) and cloud amount (in fraction of sky) were significant: r=-0. 79 and - 0. 66, respectively. For high-level clouds, the correlation was not significant: r=-0. 21. The results indicate that cloud shortwave forcing is a major modifier of the earth's surface insolation and change of cloud amount may affect global climate.
基金supported by the National Key R&D Program of China(2017YFA0603502)the National Natural Science Foundation of China(Grant No.41905081)S&T Development Fund of CAMS(2021KJ004&2022KJ019).
文摘In this study,the decomposed fast and slow responses of clouds to an abruptly quadrupled CO_(2)concentration(approximately 1139 ppmv)in East Asia(EA)are obtained quantitatively by using a general circulation model,BCC–AGCM2.0.Our results show that in the total response,the total cloud cover(TCC),low cloud cover(LCC),and high cloud cover(HCC)all increased north of 40°N and decreased south of 40°N except in the Tibetan Plateau(TP).The mean changes of the TCC,LCC,and HCC in EA were–0.74%,0.38%,and–0.38%in the total response,respectively;1.05%,–0.03%,and 1.63%in the fast response,respectively;and–1.79%,0.41%,and–2.01%in the slow response,respectively.By comparison,we found that changes in cloud cover were dominated by the slow response in most areas in EA due to the changes in atmospheric temperature,circulation,and water vapor supply together.Overall,the changes in the cloud forcing over EA related to the fast and slow responses were opposite to each other,and the final cloud forcing was dominated by the slow response.The mean net cloud forcing(NCF)in the total response over EA was–1.80 W m^(–2),indicating a cooling effect which partially offset the warming effect caused by the quadrupled CO_(2).The total responses of NCF in the TP,south China(SC),and northeast China(NE)were–6.74 W m^(–2),6.11 W m^(–2),and–7.49 W m^(–2),respectively.Thus,the local effects of offsetting or amplifying warming were particularly obvious.
