<span style="white-space:normal;">Observing and studying the solar radiation during solar eclipses is important in knowing the changes that occur to the environmental elements during this event. The ma...<span style="white-space:normal;">Observing and studying the solar radiation during solar eclipses is important in knowing the changes that occur to the environmental elements during this event. The main objective of this paper is the performance of the incoming variation of solar radiation components, global, direct and diffuse and their fractions during the partial annular solar eclipse on June 21</span><sup style="white-space:normal;">st</sup><span style="white-space:normal;">, 2020 in Helwan, Egypt (Lat. 29.866</span>°<span style="white-space:normal;">N and Long. 31.20</span>°<span style="white-space:normal;">E) has been made. A pyrheliometer for measuring the direct solar radiation, in three different bands;direct yellow (</span><em style="white-space:normal;">Y</em><span style="white-space:normal;">), direct red (</span><em style="white-space:normal;">R</em><span style="white-space:normal;">), direct infrared (</span><em style="white-space:normal;">IR</em><span style="white-space:normal;">), and also the total direct band (</span><em style="white-space:normal;">I</em><span style="white-space:normal;">);A pyranometers for measuring the different components of global solar radiation (</span><em style="white-space:normal;">G</em><span style="white-space:normal;">), global ultraviolet (</span><em style="white-space:normal;">G<sub>UV</sub></em><span style="white-space:normal;">), global infrared (</span><em style="white-space:normal;">G<sub>IR</sub></em><span style="white-space:normal;">) and a meteorological station to measure the different meteorological parameters. The duration of the solar eclipse was 01 h:59 m, and the maximum magnitude of the eclipse in this region was 0.449. The depression is clear at the solar radiation of all components due to the annular solar eclipse, while the depressions of the diffuse and global infrared solar radiation are lower. In all direct radiation compounds (</span><em style="white-space:normal;">I</em><span style="white-space:normal;">, </span><em style="white-space:normal;">Y</em><span style="white-space:normal;">, </span><em style="white-space:normal;">R</em><span style="white-space:normal;"> and </span><em style="white-space:normal;">IR</em><span style="white-space:normal;">) are greatly affected by the eclipse. The diffuse fraction </span><em style="white-space:normal;">K<sub>d</sub></em><span style="white-space:normal;"> is higher in the early time, before the partial eclipse, but during the partial annular eclipse time </span><em style="white-space:normal;">K<sub>d</sub></em><span style="white-space:normal;"> values are suffers variation and through the day, where the values of </span><em style="white-space:normal;">K<sub>d</sub></em><span style="white-space:normal;"> lies between </span><em style="white-space:normal;">K<sub>t</sub></em><span style="white-space:normal;"> and</span><em style="white-space:normal;"> K<sub>UV</sub></em><span style="white-space:normal;">. The values of direct infrared solar radiation are dominant before and after the partial annular solar eclipse. The intensity of color bands (W<span style="white-space:nowrap;">∙</span>m</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>2</sup><span style="white-space:normal;"><span style="white-space:nowrap;">∙</span>nm</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;">) are </span><em style="white-space:normal;">DIB</em><span style="white-space:normal;">3 ></span><em style="white-space:normal;"> DIB</em><span style="white-space:normal;">2 > </span><em style="white-space:normal;">DIB</em><span style="white-space:normal;">4, and </span><em style="white-space:normal;">DIB</em><span style="white-space:normal;">1 is opposite direction with </span><em style="white-space:normal;">DIB</em><span style="white-space:normal;">3 and </span><em style="white-space:normal;">DIB</em><span style="white-space:normal;">2, the highest intensity is direct red and the lowest intensity is the direct infrared. The highest values of extinction coefficient in (</span><em style="white-space:normal;">G<sub>IR</sub></em><span style="white-space:normal;">) solar radiation and the lowest values occur in (</span><em style="white-space:normal;">G<sub>UV</sub></em><span style="white-space:normal;">) solar radiation, while the values of (</span><em style="white-space:normal;">G</em><span style="white-space:normal;">) solar radiation occur between them. In general trend, the values of extinction coefficient during the partial eclipse are increasing, while the minimum values of extinction coefficient occur at noon time due to the air mass is less value in the noon.</span>展开更多
In this paper,land surface observation data at semi-arid climate and environmental observation station（ SACOL station） of Lanzhou University during 2006- 2012 and the data of Yuzhong meteorological station were used...In this paper,land surface observation data at semi-arid climate and environmental observation station（ SACOL station） of Lanzhou University during 2006- 2012 and the data of Yuzhong meteorological station were used to analyze the responses of land surface radiation budget components to climate fluctuation,study the interannual variability of surface albedo,and discuss the feedback of various land surface process parameters on the interannual fluctuations of temperature and precipitation in Loess Plateau. According to the type of precipitation in Loess Plateau,the year was divided into winter and summer in order to get more significant interannual variability and correlation. The results showed that the trends of temperature and precipitation during 2006- 2012 were consistent with the warming and drying total trend in recent years in Loess Plateau. Shallow surface soil moisture and temperature showed a good response to temperature and precipitation,and the annual variation of summer half year had greater impact on the trend in the whole year. Incident solar radiation increase was major reason for climate warming in the Loess Plateau region.The combined effect of climatic factors was the reason for the change of surface albedo. Through the distinguish inquiry by winter and summer data,it was obtained that most correlations between summer radiation components and climatic factors have been improved,and partial correlations between winter radiation components and climatic factors have been increased.展开更多
The power generation of bifacial photovoltaic modules is greatly related to the diffuse solar radiation component received by the rear side,but radiation component data are scarce in China,where bifacial solar market ...The power generation of bifacial photovoltaic modules is greatly related to the diffuse solar radiation component received by the rear side,but radiation component data are scarce in China,where bifacial solar market is large.Radiation components can be estimated from satellite data,but sufficient ground truth data are needed for calibrating empirical methods or training machine learning methods.In this work,a data-augmented machine learning method was proposed to estimate radiation components.Instead of using observed ground truth,far more abundant radiation component data derived from sunshine duration measured at 2,453 routine weather stations in China were used to augment samples for training a machine-learning-based model.The inputs of the model include solar radiation(either from ground observation or satellite remote sensing)and surface meteorological data.Independent validation of the model at Chinese stations and globally distributed stations demonstrates its effectiveness and generality.Using a state-of-the-art satellite product of solar radiation as input,the model is applied to construct a satellite-based radiation component dataset over China.The new dataset not only outperforms mainstream radiation component datasets,but also has significantly higher accuracy than satellite-based datasets derived from other machine learning methods trained with limited observations,indicating the superiority of our data-augmented method.In principle,this model can be applied on the global scale without additional training with local data.展开更多
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 sc...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.展开更多
Utilizing commercial off-the-shelf(COTS) components in satellites has received much attention due to the low cost. However, commercial memories suffer severe reliability problems in radiation environments. This paper ...Utilizing commercial off-the-shelf(COTS) components in satellites has received much attention due to the low cost. However, commercial memories suffer severe reliability problems in radiation environments. This paper studies the low-density parity-check(LDPC) coding scheme for improving the reliability of multi-level-cell(MLC) NAND Flash memory in radiation environments. Firstly, based on existing physical experiment works, we introduce a new error model for heavyion irradiations; secondly, we explore the optimization of writing voltage allocation to maximize the capacity of the storage channel; thirdly, we design the degree distribution of LDPC codes that is specially suitable for the proposed model; finally, we propose a joint detection-decoding scheme based on LDPC codes, which estimates the storage channel state and executes an adaptive log-likelihood ratio(LLR) calculation to achieve better performance. Simulation results show that, compared with the conventional LDPC coding scheme, the proposed scheme may almost double the lifetime of the MLC NAND Flash memory in radiation environments.展开更多
A comprehensive understanding of energy and water cycle characteristics in different regions is crucial for studying local land-atmosphere interactions and predicting regional weather and climate change.To explore sim...A comprehensive understanding of energy and water cycle characteristics in different regions is crucial for studying local land-atmosphere interactions and predicting regional weather and climate change.To explore similarities and differences in land-atmosphere energy and water exchanges between two regions-the Tibetan Plateau(TP),characterized by higher elevation and a drier climate,and the Yangtze River Region(YRR),with lower elevation and a wetter climate-this study analyzed and compared the radiation components and the turbulent heat fluxes at eight sites covering various land-cover types,including alpine desert and alpine grassland on the TP,as well as urban and grassland on the YRR.The following results were obtained:(1)Over the TP,the annual mean incoming and outgoing shortwave radiation are 251.3 and 59.6 W m^(-2),which are 1.70 and 2.87 times the values in the YRR,respectively.The incoming and outgoing longwave radiation are 231.5 and 338.0 W m^(-2),which are 0.64 and 0.83 times those in the YRR,respectively.However,the difference in net radiation is relatively small.(2)In grassland over both the TP and YRR,the latent heat fluxes have higher values of 35.0 and 38.8 W m^(-2),respectively,leading to a higher heating efficiency.Alpine desert has the highest sensible heat flux(SH)value of 42.1 W m^(-2),due to sparse vegetation and lower soil moisture,followed closely by urban land cover with an average SH value of 38.2 W m^(-2).These results highlight the different characteristics of land-atmosphere interaction across different land covers in different climatic contexts,laying the groundwork for future investigations of additional land-atmosphere coupling processes.展开更多
Data on instantaneous atmospheric Linke turbidity factor TL (m) are reported for clear days at Qena/Egypt in the period from June 1992 to May 1993.TL(m) is determined using the values of irradiance of direct solar rad...Data on instantaneous atmospheric Linke turbidity factor TL (m) are reported for clear days at Qena/Egypt in the period from June 1992 to May 1993.TL(m) is determined using the values of irradiance of direct solar radiation (I),which are calculated from global (G) and diffuse (D) - solar radiation measurements.Monthly and seasonally variations of both diurnal and daily average values of TL (m) increases steadily in the direction of sunset in the months from June to December 1992 as well as Summer and Autumn seasons,while it falls generally in this direction for the months from January to March and Winter season.In April and May,TL (m) fluctuates obviously through the day hours,it is also shown that the average values of TL(m) are particularly large during Summer months compared to other months of the year.This behavior of TL(m) is discussed in view of the variations of some weather elements,which affect the content of water vapor and dust particle in the atmosphere of the study region.It seems t be of similar trends to that of other locations inside and outside Egypt.The virtual variation of TL(m) is eliminated by reducing its value to relative optical air mass m=2,according to Kasten formula.The resulting TL (2) is more representative for the content of dust particles and water vapor in the atmosphere.展开更多
By using the climatological calculating method for each component of slope surface net radiation proposed by the authors,calculations and analyses are done of the distribution features of slope net radiation in China ...By using the climatological calculating method for each component of slope surface net radiation proposed by the authors,calculations and analyses are done of the distribution features of slope net radiation in China with emphasis on the discussion of variations of slope net radiation in typical stations and sites with slope direc- tion,slope,latitude and season.The distribution features of net radiation on the north and south slopes are, for the first time,mapped and discussed,revealing the great difference on the national basis,and thus acquiring a new interesting result that the negative-value area of winter net radiation on the north slope(20°)can reach Yunnan and Guizhou Provinces and middle and upper reaches of the Changjiang River.展开更多
Plant photosynthesis is the fundamental driver of all the biospheric functions. Alpine meadow on the Tibetan Plateau is sensitive to rapid climate change, and thus can be considered an indicator for the response of te...Plant photosynthesis is the fundamental driver of all the biospheric functions. Alpine meadow on the Tibetan Plateau is sensitive to rapid climate change, and thus can be considered an indicator for the response of terrestrial ecosystems to climate change. However, seasonal variations in photosynthetic parameters, including the fraction of photosynthetically active radiation by canopy(FPAR), the light extinction coefficient(k) through canopy, and the leaf area index(LAI) of plant communities, are not known for alpine meadows on the Tibetan Plateau. In this study, we used field measurements of radiation components and canopy structure from 2009 to 2011 at a typical alpine meadow on the northern Tibetan Plateau to calculate these three photosynthetic parameters. We developed a satellite-based(NDVI and EVI) method derived from the Beer-Lambert law to estimate the seasonal dynamics of FPAR, k,and LAI, and we compared these estimates with the Moderate Resolution Imaging Spectroradiometer(MODIS) FPAR(FPAR_MOD) and LAI product(LAI_MOD). The results showed that the average daily FPAR was 0.33, 0.37 and 0.35, respectively, from 2009 to 2011, and that the temporal variations could be explained by all four satellite-based FPAR estimations, including FPAR_MOD, an FPAR estimation derived from the Beer-Lambert law with a constant k(FPAR_LAI), and two FPAR estimations from the nonlinear functions between the ground measurements of FPAR(FAPRg) and NDVI/EVI(FPAR_NDVI and FPAR_EVI). We found that FPAR_MOD seriously undervalued FPARg by over 40%. Tower-based FPAR_LAI also significantly underestimated FPARg by approximately 20% due to the constant k(0.5) throughout the whole growing seasons. This indicated that using FPAR_LAI to validate the FPAR_MOD was not an appropriate method in this alpine meadow because the seasonal variation of k ranged from 0.19 to 2.95 in this alpine meadow. Thus, if the seasonal variation of k was taken into consideration, both FPAR_NDVI and FPAR_EVI provided better descriptions, with negligible overestimates of less than 5% of FAPRg(RMSE=0.05), in FPARg estimations than FPAR_MOD and FPAR_LAI. Combining the satellite-based(NDVI and EVI) estimations of seasonal FPAR and k, LAI_NDVI and LAI_EVI derived from the Beer-Lambert law also provided better LAIg estimations than LAI_MOD(less than 30% of LAIg). Therefore, this study concluded that satellite-based models derived from the Beer-Lambert law were a simple and efficient method for estimating the seasonal dynamics of FPAR, k and LAI in this alpine meadow.展开更多
Signal processing in phase space based on nonlinear dynamics theory is a new method for underwater acoustic signal processing. One key problem when analyzing actual acoustic signal in phase space is how to reduce the ...Signal processing in phase space based on nonlinear dynamics theory is a new method for underwater acoustic signal processing. One key problem when analyzing actual acoustic signal in phase space is how to reduce the noise and lower the embedding dimen- sion. In this paper, local-geometric-projection method is applied to obtain fow dimensional element from various target radiating noise and the derived phase portraits show obviously low dimensional attractors. Furthermore, attractor dimension and cross prediction error are used for classification. It concludes that combining these features representing the geometric and dynamical properties respectively shows effects in target classification.展开更多
文摘<span style="white-space:normal;">Observing and studying the solar radiation during solar eclipses is important in knowing the changes that occur to the environmental elements during this event. The main objective of this paper is the performance of the incoming variation of solar radiation components, global, direct and diffuse and their fractions during the partial annular solar eclipse on June 21</span><sup style="white-space:normal;">st</sup><span style="white-space:normal;">, 2020 in Helwan, Egypt (Lat. 29.866</span>°<span style="white-space:normal;">N and Long. 31.20</span>°<span style="white-space:normal;">E) has been made. A pyrheliometer for measuring the direct solar radiation, in three different bands;direct yellow (</span><em style="white-space:normal;">Y</em><span style="white-space:normal;">), direct red (</span><em style="white-space:normal;">R</em><span style="white-space:normal;">), direct infrared (</span><em style="white-space:normal;">IR</em><span style="white-space:normal;">), and also the total direct band (</span><em style="white-space:normal;">I</em><span style="white-space:normal;">);A pyranometers for measuring the different components of global solar radiation (</span><em style="white-space:normal;">G</em><span style="white-space:normal;">), global ultraviolet (</span><em style="white-space:normal;">G<sub>UV</sub></em><span style="white-space:normal;">), global infrared (</span><em style="white-space:normal;">G<sub>IR</sub></em><span style="white-space:normal;">) and a meteorological station to measure the different meteorological parameters. The duration of the solar eclipse was 01 h:59 m, and the maximum magnitude of the eclipse in this region was 0.449. The depression is clear at the solar radiation of all components due to the annular solar eclipse, while the depressions of the diffuse and global infrared solar radiation are lower. In all direct radiation compounds (</span><em style="white-space:normal;">I</em><span style="white-space:normal;">, </span><em style="white-space:normal;">Y</em><span style="white-space:normal;">, </span><em style="white-space:normal;">R</em><span style="white-space:normal;"> and </span><em style="white-space:normal;">IR</em><span style="white-space:normal;">) are greatly affected by the eclipse. The diffuse fraction </span><em style="white-space:normal;">K<sub>d</sub></em><span style="white-space:normal;"> is higher in the early time, before the partial eclipse, but during the partial annular eclipse time </span><em style="white-space:normal;">K<sub>d</sub></em><span style="white-space:normal;"> values are suffers variation and through the day, where the values of </span><em style="white-space:normal;">K<sub>d</sub></em><span style="white-space:normal;"> lies between </span><em style="white-space:normal;">K<sub>t</sub></em><span style="white-space:normal;"> and</span><em style="white-space:normal;"> K<sub>UV</sub></em><span style="white-space:normal;">. The values of direct infrared solar radiation are dominant before and after the partial annular solar eclipse. The intensity of color bands (W<span style="white-space:nowrap;">∙</span>m</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>2</sup><span style="white-space:normal;"><span style="white-space:nowrap;">∙</span>nm</span><sup style="white-space:normal;"><span style="white-space:nowrap;">−</span>1</sup><span style="white-space:normal;">) are </span><em style="white-space:normal;">DIB</em><span style="white-space:normal;">3 ></span><em style="white-space:normal;"> DIB</em><span style="white-space:normal;">2 > </span><em style="white-space:normal;">DIB</em><span style="white-space:normal;">4, and </span><em style="white-space:normal;">DIB</em><span style="white-space:normal;">1 is opposite direction with </span><em style="white-space:normal;">DIB</em><span style="white-space:normal;">3 and </span><em style="white-space:normal;">DIB</em><span style="white-space:normal;">2, the highest intensity is direct red and the lowest intensity is the direct infrared. The highest values of extinction coefficient in (</span><em style="white-space:normal;">G<sub>IR</sub></em><span style="white-space:normal;">) solar radiation and the lowest values occur in (</span><em style="white-space:normal;">G<sub>UV</sub></em><span style="white-space:normal;">) solar radiation, while the values of (</span><em style="white-space:normal;">G</em><span style="white-space:normal;">) solar radiation occur between them. In general trend, the values of extinction coefficient during the partial eclipse are increasing, while the minimum values of extinction coefficient occur at noon time due to the air mass is less value in the noon.</span>
基金Supported by National Natural Science Foundation of China(31300376)Natural Science Foundation of Gansu Province(1208RJYA025)
文摘In this paper,land surface observation data at semi-arid climate and environmental observation station（ SACOL station） of Lanzhou University during 2006- 2012 and the data of Yuzhong meteorological station were used to analyze the responses of land surface radiation budget components to climate fluctuation,study the interannual variability of surface albedo,and discuss the feedback of various land surface process parameters on the interannual fluctuations of temperature and precipitation in Loess Plateau. According to the type of precipitation in Loess Plateau,the year was divided into winter and summer in order to get more significant interannual variability and correlation. The results showed that the trends of temperature and precipitation during 2006- 2012 were consistent with the warming and drying total trend in recent years in Loess Plateau. Shallow surface soil moisture and temperature showed a good response to temperature and precipitation,and the annual variation of summer half year had greater impact on the trend in the whole year. Incident solar radiation increase was major reason for climate warming in the Loess Plateau region.The combined effect of climatic factors was the reason for the change of surface albedo. Through the distinguish inquiry by winter and summer data,it was obtained that most correlations between summer radiation components and climatic factors have been improved,and partial correlations between winter radiation components and climatic factors have been increased.
基金supported by the Sustainable Development International Cooperation Program of National Science Found-ation of China(Grant No.42361144875)the National Natural Science Foundation of China(Grant No.42171360).
文摘The power generation of bifacial photovoltaic modules is greatly related to the diffuse solar radiation component received by the rear side,but radiation component data are scarce in China,where bifacial solar market is large.Radiation components can be estimated from satellite data,but sufficient ground truth data are needed for calibrating empirical methods or training machine learning methods.In this work,a data-augmented machine learning method was proposed to estimate radiation components.Instead of using observed ground truth,far more abundant radiation component data derived from sunshine duration measured at 2,453 routine weather stations in China were used to augment samples for training a machine-learning-based model.The inputs of the model include solar radiation(either from ground observation or satellite remote sensing)and surface meteorological data.Independent validation of the model at Chinese stations and globally distributed stations demonstrates its effectiveness and generality.Using a state-of-the-art satellite product of solar radiation as input,the model is applied to construct a satellite-based radiation component dataset over China.The new dataset not only outperforms mainstream radiation component datasets,but also has significantly higher accuracy than satellite-based datasets derived from other machine learning methods trained with limited observations,indicating the superiority of our data-augmented method.In principle,this model can be applied on the global scale without additional training with local data.
基金supported by the "Strategic Priority Research Program" of the Chinese Academy of Sciences (Grant No.XDA05040201)the National Science and Technology Support Program of China (Grant No.2013CB430104)the Meteorology Project GYHY200906025
文摘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.
基金supported by the National Basic Research Project of China(973)(2013CB329006)National Natural Science Foundation of China(NSFC,91538203)the new strategic industries development projects of Shenzhen City(JCYJ20150403155812833)
文摘Utilizing commercial off-the-shelf(COTS) components in satellites has received much attention due to the low cost. However, commercial memories suffer severe reliability problems in radiation environments. This paper studies the low-density parity-check(LDPC) coding scheme for improving the reliability of multi-level-cell(MLC) NAND Flash memory in radiation environments. Firstly, based on existing physical experiment works, we introduce a new error model for heavyion irradiations; secondly, we explore the optimization of writing voltage allocation to maximize the capacity of the storage channel; thirdly, we design the degree distribution of LDPC codes that is specially suitable for the proposed model; finally, we propose a joint detection-decoding scheme based on LDPC codes, which estimates the storage channel state and executes an adaptive log-likelihood ratio(LLR) calculation to achieve better performance. Simulation results show that, compared with the conventional LDPC coding scheme, the proposed scheme may almost double the lifetime of the MLC NAND Flash memory in radiation environments.
基金supported by the National Natural Science Foundation of China,under the project entitled“The study of land-atmosphere water and heat flux interaction over the complex terrain of the north and south slopes of the Qomolangma region"[grant number 42230610]a Ministry of Science and Technology of China project called“Landatmosphere interaction and its climate effect of the Second Tibetan Plateau Scientific Expedition and Research Program"[grant number 2019QzKK0103]the Youth Innovation Promotion Association of the Chinese Academy of Sciences[2022069].
文摘A comprehensive understanding of energy and water cycle characteristics in different regions is crucial for studying local land-atmosphere interactions and predicting regional weather and climate change.To explore similarities and differences in land-atmosphere energy and water exchanges between two regions-the Tibetan Plateau(TP),characterized by higher elevation and a drier climate,and the Yangtze River Region(YRR),with lower elevation and a wetter climate-this study analyzed and compared the radiation components and the turbulent heat fluxes at eight sites covering various land-cover types,including alpine desert and alpine grassland on the TP,as well as urban and grassland on the YRR.The following results were obtained:(1)Over the TP,the annual mean incoming and outgoing shortwave radiation are 251.3 and 59.6 W m^(-2),which are 1.70 and 2.87 times the values in the YRR,respectively.The incoming and outgoing longwave radiation are 231.5 and 338.0 W m^(-2),which are 0.64 and 0.83 times those in the YRR,respectively.However,the difference in net radiation is relatively small.(2)In grassland over both the TP and YRR,the latent heat fluxes have higher values of 35.0 and 38.8 W m^(-2),respectively,leading to a higher heating efficiency.Alpine desert has the highest sensible heat flux(SH)value of 42.1 W m^(-2),due to sparse vegetation and lower soil moisture,followed closely by urban land cover with an average SH value of 38.2 W m^(-2).These results highlight the different characteristics of land-atmosphere interaction across different land covers in different climatic contexts,laying the groundwork for future investigations of additional land-atmosphere coupling processes.
文摘Data on instantaneous atmospheric Linke turbidity factor TL (m) are reported for clear days at Qena/Egypt in the period from June 1992 to May 1993.TL(m) is determined using the values of irradiance of direct solar radiation (I),which are calculated from global (G) and diffuse (D) - solar radiation measurements.Monthly and seasonally variations of both diurnal and daily average values of TL (m) increases steadily in the direction of sunset in the months from June to December 1992 as well as Summer and Autumn seasons,while it falls generally in this direction for the months from January to March and Winter season.In April and May,TL (m) fluctuates obviously through the day hours,it is also shown that the average values of TL(m) are particularly large during Summer months compared to other months of the year.This behavior of TL(m) is discussed in view of the variations of some weather elements,which affect the content of water vapor and dust particle in the atmosphere of the study region.It seems t be of similar trends to that of other locations inside and outside Egypt.The virtual variation of TL(m) is eliminated by reducing its value to relative optical air mass m=2,according to Kasten formula.The resulting TL (2) is more representative for the content of dust particles and water vapor in the atmosphere.
基金the State Meteorological Administration through the Meteorological Science Funds
文摘By using the climatological calculating method for each component of slope surface net radiation proposed by the authors,calculations and analyses are done of the distribution features of slope net radiation in China with emphasis on the discussion of variations of slope net radiation in typical stations and sites with slope direc- tion,slope,latitude and season.The distribution features of net radiation on the north and south slopes are, for the first time,mapped and discussed,revealing the great difference on the national basis,and thus acquiring a new interesting result that the negative-value area of winter net radiation on the north slope(20°)can reach Yunnan and Guizhou Provinces and middle and upper reaches of the Changjiang River.
基金The National Key Research and Development Program of China(2016YFC0502001)The National Natural Science Foundation of China(41807331)The West Light Foundation of the Chinese Academy of Sciences(2018)。
文摘Plant photosynthesis is the fundamental driver of all the biospheric functions. Alpine meadow on the Tibetan Plateau is sensitive to rapid climate change, and thus can be considered an indicator for the response of terrestrial ecosystems to climate change. However, seasonal variations in photosynthetic parameters, including the fraction of photosynthetically active radiation by canopy(FPAR), the light extinction coefficient(k) through canopy, and the leaf area index(LAI) of plant communities, are not known for alpine meadows on the Tibetan Plateau. In this study, we used field measurements of radiation components and canopy structure from 2009 to 2011 at a typical alpine meadow on the northern Tibetan Plateau to calculate these three photosynthetic parameters. We developed a satellite-based(NDVI and EVI) method derived from the Beer-Lambert law to estimate the seasonal dynamics of FPAR, k,and LAI, and we compared these estimates with the Moderate Resolution Imaging Spectroradiometer(MODIS) FPAR(FPAR_MOD) and LAI product(LAI_MOD). The results showed that the average daily FPAR was 0.33, 0.37 and 0.35, respectively, from 2009 to 2011, and that the temporal variations could be explained by all four satellite-based FPAR estimations, including FPAR_MOD, an FPAR estimation derived from the Beer-Lambert law with a constant k(FPAR_LAI), and two FPAR estimations from the nonlinear functions between the ground measurements of FPAR(FAPRg) and NDVI/EVI(FPAR_NDVI and FPAR_EVI). We found that FPAR_MOD seriously undervalued FPARg by over 40%. Tower-based FPAR_LAI also significantly underestimated FPARg by approximately 20% due to the constant k(0.5) throughout the whole growing seasons. This indicated that using FPAR_LAI to validate the FPAR_MOD was not an appropriate method in this alpine meadow because the seasonal variation of k ranged from 0.19 to 2.95 in this alpine meadow. Thus, if the seasonal variation of k was taken into consideration, both FPAR_NDVI and FPAR_EVI provided better descriptions, with negligible overestimates of less than 5% of FAPRg(RMSE=0.05), in FPARg estimations than FPAR_MOD and FPAR_LAI. Combining the satellite-based(NDVI and EVI) estimations of seasonal FPAR and k, LAI_NDVI and LAI_EVI derived from the Beer-Lambert law also provided better LAIg estimations than LAI_MOD(less than 30% of LAIg). Therefore, this study concluded that satellite-based models derived from the Beer-Lambert law were a simple and efficient method for estimating the seasonal dynamics of FPAR, k and LAI in this alpine meadow.
文摘Signal processing in phase space based on nonlinear dynamics theory is a new method for underwater acoustic signal processing. One key problem when analyzing actual acoustic signal in phase space is how to reduce the noise and lower the embedding dimen- sion. In this paper, local-geometric-projection method is applied to obtain fow dimensional element from various target radiating noise and the derived phase portraits show obviously low dimensional attractors. Furthermore, attractor dimension and cross prediction error are used for classification. It concludes that combining these features representing the geometric and dynamical properties respectively shows effects in target classification.
