Air temperature is a key index reflecting climate change. Air temperature extremes are very important because they strongly influence the natural environment and societal activities. The Arctic air temperature extreme...Air temperature is a key index reflecting climate change. Air temperature extremes are very important because they strongly influence the natural environment and societal activities. The Arctic air temperature extremes north of 60°N are investigated in the winter. Daily data from 238 stations at north of 60°N from the global summary of the day for the period 1979–2015 are used to study the trends of cold days, cold nights, warm days and warm nights during the wintertime. The results show a decreasing trend of cold days and nights(rate of –0.2 to –0.3 d/a) and an increasing trend of warm days and nights(rate of +0.2 to +0.3 d/a) in the Arctic. The mean temperature increases,which contributes to the increasing(decreasing) occurrence of warm(cold) days and nights. On the other hand,the variance at most stations decreased, leading to a reduced number of cold events. A positive AO(Arctic Oscillation) index leads to an increased(decreased) number of warm(cold) days and nights over northern Europe and western Russia and an increased(decreased) number of cold(warm) days and nights over the Bering Strait and Greenland. The lower extent of Arctic autumn sea ice leads to a decreased number of cold days and nights.The occurrences of abrupt changes are detected using the Mann-Kendall method for cold nights occurring in Canada in 1998 and for warm nights occurring in northwestern Eurasia in 1988. This abrupt change mainly resulted from the mean warming induced by south winds and an increased North Atlantic sea surface temperature.展开更多
Extreme temperature events can influence the natural environment and societal activities more so than mean temperature events. This study used daily data from 238 stations north of 60°N, obtained from the Global ...Extreme temperature events can influence the natural environment and societal activities more so than mean temperature events. This study used daily data from 238 stations north of 60°N, obtained from the Global Summary of the Day dataset for the period 1979~015, to investigate the trends of summertime extreme temperature. The results revealed most stations north of 60°N with trends of decrease in the number of cold days (nights) and increase in the number of warm clays (nights). The regional average results showed trends of consistent decline (rise) of cold days and nights (warm days and nights) in Eurasia and Greenland. Similarly, the trends of the seasonal maximum and minimum values were most significant in these regions. In summer, of three indices considered (i.e., Arctic Oscillation, Arctic dipole, and E1 Nifi^Southem Oscillation), the largest contributor to the trends of extreme temperature events was the Arctic dipole. Prevailing southerly winds in summer brought warm moist air across northern Eurasia and Greenland, conducive to increased numbers of warm days (nights) and decreased numbers of cold day (nights). Moreover, we defined extreme events using different thresholds and found the spatial distributions of the trends were similar.展开更多
Based on a monthly dataset of precipitation time series (1961-2010) from 12 me- teorological stations across the Three-River Headwater Region (THRHR) of Qinghai Province China, the spatio-temporal variation and ab...Based on a monthly dataset of precipitation time series (1961-2010) from 12 me- teorological stations across the Three-River Headwater Region (THRHR) of Qinghai Province China, the spatio-temporal variation and abrupt change analysis of precipitation were exam- ined by using moving average, linear regression, spline interpolation, the Mann-Kendall test and so on. Major conclusions were as follows. (1) The long-term annual and seasonal pre- cipitation in the study area indicated an increasing trend with some oscillations during 1961-2010; however, the summer precipitation in the Lantsang (Lancang) River Headwater Region (LARHR), and the autumn precipitation in the Yangtze River Headwater Region (YERHR) of the THRHR decreased in the same period. (2) The amount of annual precipita- tion in the THRHR and its three sub-headwater regions was greater in the 1980s and 2000s. The springs were fairly wet after the 1970s, while the summers were relatively wet in the 1960s, 1980s and 2000s. In addition, the amount of precipitation in the autumn was greater in the 1970s and 1980s, but it was relatively less for the winter precipitation, except in the 1990s (3) The normal values of spring, summer, winter and annual precipitation in the THRHR and its three sub-headwater regions all increased, but the normal value of summer precipitation in the LARHR had a negative trend and the normal value of winter precipitation declined in general. (4) The spring and winter precipitation increased in most of the THRHR. The summer autumn and annual precipitation increased mainly in the marginal area of the west and north and decreased in the regions of Yushu, Zaduo, Jiuzhi and Banma. (5) The spring and winter precipitation in the THRHR and its three sub-headwater regions showed an abrupt change, except for the spring precipitation in the YARHR. The abrupt changes of spring precipitation were mainly in the late 1980s and early 1990s, while the abrupt changes of winter precipita- tion were primary in the mid- to late 1970s. This research would be helpful for further under- standing the trends and periodicity of precipitation and for watershed-based water resource management in the THRHR.展开更多
基金The Chinese Polar Environment Comprehensive Investigation and Evaluation Program under contract No.CHINARE2016-04-04the Public Science and Technology Research Funds Project of Ocean under contract No.201505013the National Natural Science Foundation of China under contract No.41576029
文摘Air temperature is a key index reflecting climate change. Air temperature extremes are very important because they strongly influence the natural environment and societal activities. The Arctic air temperature extremes north of 60°N are investigated in the winter. Daily data from 238 stations at north of 60°N from the global summary of the day for the period 1979–2015 are used to study the trends of cold days, cold nights, warm days and warm nights during the wintertime. The results show a decreasing trend of cold days and nights(rate of –0.2 to –0.3 d/a) and an increasing trend of warm days and nights(rate of +0.2 to +0.3 d/a) in the Arctic. The mean temperature increases,which contributes to the increasing(decreasing) occurrence of warm(cold) days and nights. On the other hand,the variance at most stations decreased, leading to a reduced number of cold events. A positive AO(Arctic Oscillation) index leads to an increased(decreased) number of warm(cold) days and nights over northern Europe and western Russia and an increased(decreased) number of cold(warm) days and nights over the Bering Strait and Greenland. The lower extent of Arctic autumn sea ice leads to a decreased number of cold days and nights.The occurrences of abrupt changes are detected using the Mann-Kendall method for cold nights occurring in Canada in 1998 and for warm nights occurring in northwestern Eurasia in 1988. This abrupt change mainly resulted from the mean warming induced by south winds and an increased North Atlantic sea surface temperature.
基金supported by National Key R&D Program of China (Grant no.2017YFE0111700)Beijing Municipal Natural Science Foundation (Grant no.8182023)
文摘Extreme temperature events can influence the natural environment and societal activities more so than mean temperature events. This study used daily data from 238 stations north of 60°N, obtained from the Global Summary of the Day dataset for the period 1979~015, to investigate the trends of summertime extreme temperature. The results revealed most stations north of 60°N with trends of decrease in the number of cold days (nights) and increase in the number of warm clays (nights). The regional average results showed trends of consistent decline (rise) of cold days and nights (warm days and nights) in Eurasia and Greenland. Similarly, the trends of the seasonal maximum and minimum values were most significant in these regions. In summer, of three indices considered (i.e., Arctic Oscillation, Arctic dipole, and E1 Nifi^Southem Oscillation), the largest contributor to the trends of extreme temperature events was the Arctic dipole. Prevailing southerly winds in summer brought warm moist air across northern Eurasia and Greenland, conducive to increased numbers of warm days (nights) and decreased numbers of cold day (nights). Moreover, we defined extreme events using different thresholds and found the spatial distributions of the trends were similar.
基金The National Science and Technology Support Plan, No.2009BAC61B01
文摘Based on a monthly dataset of precipitation time series (1961-2010) from 12 me- teorological stations across the Three-River Headwater Region (THRHR) of Qinghai Province China, the spatio-temporal variation and abrupt change analysis of precipitation were exam- ined by using moving average, linear regression, spline interpolation, the Mann-Kendall test and so on. Major conclusions were as follows. (1) The long-term annual and seasonal pre- cipitation in the study area indicated an increasing trend with some oscillations during 1961-2010; however, the summer precipitation in the Lantsang (Lancang) River Headwater Region (LARHR), and the autumn precipitation in the Yangtze River Headwater Region (YERHR) of the THRHR decreased in the same period. (2) The amount of annual precipita- tion in the THRHR and its three sub-headwater regions was greater in the 1980s and 2000s. The springs were fairly wet after the 1970s, while the summers were relatively wet in the 1960s, 1980s and 2000s. In addition, the amount of precipitation in the autumn was greater in the 1970s and 1980s, but it was relatively less for the winter precipitation, except in the 1990s (3) The normal values of spring, summer, winter and annual precipitation in the THRHR and its three sub-headwater regions all increased, but the normal value of summer precipitation in the LARHR had a negative trend and the normal value of winter precipitation declined in general. (4) The spring and winter precipitation increased in most of the THRHR. The summer autumn and annual precipitation increased mainly in the marginal area of the west and north and decreased in the regions of Yushu, Zaduo, Jiuzhi and Banma. (5) The spring and winter precipitation in the THRHR and its three sub-headwater regions showed an abrupt change, except for the spring precipitation in the YARHR. The abrupt changes of spring precipitation were mainly in the late 1980s and early 1990s, while the abrupt changes of winter precipita- tion were primary in the mid- to late 1970s. This research would be helpful for further under- standing the trends and periodicity of precipitation and for watershed-based water resource management in the THRHR.