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121.
气温日较差研究进展:变化趋势及其影响因素 总被引:6,自引:0,他引:6
从日较差的变化趋势、影响因素以及人类活动对气候变化影响的指示3个方面对日较差的研究进行了总结和概括。观测数据以及气候模式模拟的结果表明,全球气温日较差在近半个多世纪以来呈下降趋势,而这种下降趋势不仅仅是自然变化的结果,还受到人类活动的影响。辐射、云量、气溶胶、下垫面的变化、水汽、降水以及航迹云等因素都能对日较差的变化造成影响。日较差的"周末效应"以及城市化过程中日较差的变化相对于平均气温的变化,能够更有效地指示人类活动对气候变化的影响。 相似文献
123.
Qi Zhang Jiquan Zhang Denghua Yan Yongfang Wang 《Theoretical and Applied Climatology》2014,117(1-2):169-174
Extreme weather events include unusual, severe or unseasonal weather, and weather at the extremes of the historical distribution. They have become more frequent and intense under global warming, especially in mid-latitude areas. They bring about great agricultural and economic losses. It is important to define the threshold of extreme weather event because it is the starting point of extreme weather event research, though it has been of seldom concern. Taking extreme precipitation events in Anhui, China as an example, the detrended fluctuation analysis (DFA) method is introduced to define the threshold of extreme weather events. Based on it, the spatial and temporal distributions of extreme precipitation events are analyzed. Compared to the traditional percentile method, DFA is based on the long-term correlation of time series. Thresholds calculated by DFA are much higher than the 99th percentile and the values are higher in the south and lower in the north. This spatial pattern is similar to the annual precipitation spatial pattern. There is an obvious increasing trend in the number of days with extreme precipitation, especially after the 1980s. This observation supports the point that more extreme events happen under global warming. 相似文献
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Mass and energy fluxes between the atmosphere and vegetation are driven by meteorological variables, and controlled by plant
water status, which may change more markedly diurnally than soil water. We tested the hypothesis that integration of dynamic
changes in leaf water potential may improve the simulation of CO2 and water fluxes over a wheat canopy. Simulation of leaf water potential was integrated into a comprehensive model (the ChinaAgrosys)
of heat, water and CO2 fluxes and crop growth. Photosynthesis from individual leaves was integrated to the canopy by taking into consideration the
attenuation of radiation when penetrating the canopy. Transpiration was calculated with the Shuttleworth-Wallace model in
which canopy resistance was taken as a link between energy balance and physiological regulation. A revised version of the
Ball-Woodrow-Berry stomatal model was applied to produce a new canopy resistance model, which was validated against measured
CO2 and water vapour fluxes over winter wheat fields in Yucheng (36°57′ N, 116°36′ E, 28 m above sea level) in the North China
Plain during 1997, 2001 and 2004. Leaf water potential played an important role in causing stomatal conductance to fall at
midday, which caused diurnal changes in photosynthesis and transpiration. Changes in soil water potential were less important.
Inclusion of the dynamics of leaf water potential can improve the precision of the simulation of CO2 and water vapour fluxes, especially in the afternoon under water stress conditions. 相似文献
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Comparison of manual and automatic methods for measurement of methane emission from rice paddy fields 总被引:29,自引:0,他引:29
Zheng Xunhu Wang Mingxing Wang Yuesi Shen Renxing Li Jing J. Heyer M. Kogge Li Laotu Jin Jisheng 《大气科学进展》1998,15(4):569-579
The methane emission flux from rice paddies was simultaneously measured with automatic and manual methods in the suburban of Suzhou. Both methods were based on the static chamber/ GC-FID techniques. Detail analysis of the experimental results indicates: a) The data of methane emission measured with the automatic method is reliable. b) About 11 or 19 o’clock of local time is recommended as the optimum sampling time for the manual spot measurement of methane emission from rice paddies. The methane emission fluxes measured by manual sampling at local time other than the optimum time have to be corrected. The correction coefficient may be determined by automatic and continuous measurement. c) In order to get a more accurate result, an empirical correction factor, such as 18%, is recommended to correct the seasonally total amount of measured methane emission by enlarging the au-tomatically measured data or reducing the manually measured ones. 相似文献