Long-chain alkenones (LCAs) can potentially be used as indicators to understand past variations in lacustrine environments.Previous research has suggested that the relationship between the temperature and the unsatura...Long-chain alkenones (LCAs) can potentially be used as indicators to understand past variations in lacustrine environments.Previous research has suggested that the relationship between the temperature and the unsaturation index of LCAs should be calibrated individually,because of the possible variations in the alkenone-producing algal species in the lacustrine environment.In this work,we have calibrated U37K' of water filter samples against the in-situ water temperature in Lake Qinghai,Tibetan Plateau.There are significant relationships between U37K' and the water temperature,a non-linear relationship was derived.Because the U37K' values did not respond sensitively at lower temperatures,we suggested that a quadratic regression (U37K' =0.0011×T2-0.0201×T+0.1959,n=15,r2=0.74) was appropriate than linear regression to represent the relationship between the in-situ temperatures and U37K'.Meanwhile,the U37K correlation relationship was not more significant than U37K' index in our study.Because of the C37:4 effects by salinity change,we suggest U37K is not as robust as the U37K' index as a temperature proxy,at least for the salt lake in the Tibetan Plateau.The calibration of the U37K' index in this work has provided a new understanding of historic climatic changes in the Tibetan Plateau.展开更多
The exploitation of systems using solar energy as a source of energy is not fluctuations free because of short passage of clouds on solar radiation. The amplitude, the persistence and the frequency of these fluctuatio...The exploitation of systems using solar energy as a source of energy is not fluctuations free because of short passage of clouds on solar radiation. The amplitude, the persistence and the frequency of these fluctuations should be analyzed with appropriate tools, instead of focusing on their location over time. The analysis of these fluctuations should use the instantaneous clearness index whose distribution is given as a first approximation which is independent not only of the season but also of the site. It is important to evaluate the potential solar energy in a region. Indeed such evaluation helps the decision-makers in their reflections on agricultural or photovoltaic solar projects. Then this study was conducted for a predictive purpose. The method used in our work combines the classification method which is the hierarchical ascending classification and two partitioning methods, the principal component?analysis and the K-means method. The partitioning method enabled to?achieve a number of well-known situations (in advance) that are representative of the day. The study was based on the data of a climatic weather station in the district of Yamoussoukro located in the center region of Côte d’Ivoire during the 2017 year. Using the clearness index, the study allowed the classification of the solar radiation in the region. Thus, it showed that only 346 days of the 365 days in 2017 were classified (95%). We identified three clusters of days, the cloudy sky (29%), the partly cloudy sky?(32%) and the clear sky (39%). The statistical tests used for the characterization?of these clusters will be detailed in a future study.展开更多
基金supported by the National Natural Science Foundation of China(41002059)the West Light Foundation of the Chinese Academy of Sciences
文摘Long-chain alkenones (LCAs) can potentially be used as indicators to understand past variations in lacustrine environments.Previous research has suggested that the relationship between the temperature and the unsaturation index of LCAs should be calibrated individually,because of the possible variations in the alkenone-producing algal species in the lacustrine environment.In this work,we have calibrated U37K' of water filter samples against the in-situ water temperature in Lake Qinghai,Tibetan Plateau.There are significant relationships between U37K' and the water temperature,a non-linear relationship was derived.Because the U37K' values did not respond sensitively at lower temperatures,we suggested that a quadratic regression (U37K' =0.0011×T2-0.0201×T+0.1959,n=15,r2=0.74) was appropriate than linear regression to represent the relationship between the in-situ temperatures and U37K'.Meanwhile,the U37K correlation relationship was not more significant than U37K' index in our study.Because of the C37:4 effects by salinity change,we suggest U37K is not as robust as the U37K' index as a temperature proxy,at least for the salt lake in the Tibetan Plateau.The calibration of the U37K' index in this work has provided a new understanding of historic climatic changes in the Tibetan Plateau.
文摘The exploitation of systems using solar energy as a source of energy is not fluctuations free because of short passage of clouds on solar radiation. The amplitude, the persistence and the frequency of these fluctuations should be analyzed with appropriate tools, instead of focusing on their location over time. The analysis of these fluctuations should use the instantaneous clearness index whose distribution is given as a first approximation which is independent not only of the season but also of the site. It is important to evaluate the potential solar energy in a region. Indeed such evaluation helps the decision-makers in their reflections on agricultural or photovoltaic solar projects. Then this study was conducted for a predictive purpose. The method used in our work combines the classification method which is the hierarchical ascending classification and two partitioning methods, the principal component?analysis and the K-means method. The partitioning method enabled to?achieve a number of well-known situations (in advance) that are representative of the day. The study was based on the data of a climatic weather station in the district of Yamoussoukro located in the center region of Côte d’Ivoire during the 2017 year. Using the clearness index, the study allowed the classification of the solar radiation in the region. Thus, it showed that only 346 days of the 365 days in 2017 were classified (95%). We identified three clusters of days, the cloudy sky (29%), the partly cloudy sky?(32%) and the clear sky (39%). The statistical tests used for the characterization?of these clusters will be detailed in a future study.
