青藏高原中东部地表感热趋势转折特征的季节差异

Seasonal Differences in the Trend Turning Characteristics of Surface Sensible Heat over the Central and Eastern Tibetan Plateau

本文利用气候变化趋势转折判别模型(PLFIM),分析了1982~2018年青藏高原中东部70个气象站点地表感热趋势演变特征的季节差异,并利用线性倾向估计和方差分析方法定量评估了影响不同季节地表感热变化的关键气象要素。结果显示:(1)高原中东部四季平均地表感热通量均存在显著趋势转折特征,整体来看,秋、冬季转折时间较早(1999年),春、夏季稍晚(2000年);分区来看,高原Ⅱ区(东部)的转折时间最早,然后向Ⅳ区(东南部)和Ⅰ区(北部)扩展,高原Ⅲ区(西南部)转折时间最晚。在地表感热趋势转折之前,以夏季的感热减弱最突出,其次为春季和秋季,冬季最弱;在地表感热趋势转折之后,冬季的地表感热的增强最强,其他季节增强趋势相当。冬季和春季高原地表感热趋势转折的关键区分别在高原的东部和南部,夏、秋季的关键区主要为高原的Ⅱ区(东部)和Ⅲ区(西南部)。(2)在地表感热趋势转折之前,地面风速的减小对高原四季地表感热的减弱趋势均有重要贡献;但地表感热趋势转折之后,影响其趋势变化的关键气象要素在四季存在显著差异,夏季仍以地面风速的变化为主导,秋、冬季受地气温差和地面风速变化的共同影响,而春季地气温差的增大成为其趋势增强的主因。同时,在地表感热的年际变化中,地气温差的影响比地面风速更加突出,特别是在秋、冬季,转折前后地气温差始终是决定其年际变化的主导因子,春季高原东部也主要受地气温差变化所影响,夏季在地表感热趋势转折之前,受地气温差和地面风速的共同影响,而转折后,地气温差对其的影响更加突出。

This paper employed the piecewise linear fitting model(PLFIM)to analyze the seasonal differences of Surface Sensible Heat(SSH)trend evolution characteristics at 70 meteorological stations on the central and eastern part of Tibetan Plateau(TP)during 1982–2018.The key meteorological factors influencing the changes of SSH in different seasons were quantitatively evaluated using the linear tendency estimation and variance method analysis.Results show that:(1)the seasonal average SSH fluxes on the central and eastern TP have a trend turning feature in all four seasons.As a whole,the trend turning time of autumn and winter is earlier(1999)and that of spring and summer is later(2000).In terms of region,the turning time is earliest in Zone Ⅱ(Eastern part of TP)and then expands to Zone Ⅳ(Southeastern part of TP)and Zone I(Northern part of TP),while the turning time is latest in Zone Ⅲ(Southwestern part of TP).Before the trend turning time,the weakening of the SSH is most prominent in summer,followed by spring and autumn,and weakest in winter.After the trend turning time,the enhancement of SSH is strongest in winter and the enhancement trend is similar in other seasons.In winter and spring,the key areas for the trend turning of SSH are in the eastern and southern part of TP,respectively,while the key areas are mainly in Zone Ⅱ and Ⅲ in summer and autumn.(2)Before the trend turning time,the decrease in the surface wind speed has an important contribution to the decreasing trend of the SSH in four seasons;however,after the trend turning time,the key meteorological factors affecting the trend of SSH have significant differences in the four seasons,i.e.,the change of surface wind speed is still dominant in summer,whereas winter and autumn are affected by both the variations of the ground-air temperature difference and surface wind speed.The increase of ground-air temperature difference in spring is the main reason for the trend strengthening of SSH.Additionally,in the interannual variability of SSH,the effect of the ground-air temperature difference is more prominent than that of the surface wind speed,particularly in autumn and winter.The ground-air temperature difference is always the dominant factor affecting its interannual variation.The eastern part of TP is primarily affected by the ground-air temperature difference in spring.Before the trend turning time,the interannual variability of the SSH in summer is affected by both the variations of ground-air temperature difference and surface wind speed.After the trend turning time,the influence of ground-air temperature difference on the SSH is more prominent.