东亚典型干旱、半干旱区夏季感热通量的年代际变化特征

Interdecadal Variation Characteristics of Summer Sensible Heat Flux in Typical Arid and Semi-Arid Areas of East Asia

基于1901—2010年ERA-20C地表感热通量和其他气象要素逐月资料,利用Lanczos低通滤波、多元逐步回归、Mann-Kendall检验和滑动t检验等方法,分析东亚典型极端干旱区、干旱区、半干旱区和湿润偏干区4个区域夏季感热通量的变化趋势及年代际变化特征。结果表明:(1)近110 a,东亚干旱、半干旱区4种类型区域的夏季感热通量变化趋势不尽相同,极端干旱区无明显变化趋势,而其他3个区域均呈显著上升趋势,且随着地表湿润度的增加上升趋势越大;半干旱区和湿润偏干区夏季感热通量在显著上升趋势上还叠加了明显的年代际特征,均在1960年代发生由偏低向偏高的突变,而干旱区夏季感热通量突变时间在1950年代中期。(2)各气象要素对夏季感热通量变化的贡献在东亚干旱、半干旱区不同区域有显著差异。极端干旱区和干旱区夏季感热通量的变化主要由地表净辐射和降水贡献,而半干旱区和湿润偏干区则主要由地气温差和10 m风速贡献,且突变后期的贡献均高于突变前期。(3)大气环流异常对东亚夏季感热通量变化有重要作用。突变前期,东亚干旱、半干旱区大部高空200 hPa为东风异常,低层850 hPa为东南风异常,配合500 hPa正涡度异常,导致辐合上升气流偏强,有利于维持夏季感热通量偏低;反之突变后期,200 hPa为西风异常,500 hPa为负涡度异常,低层850 hPa为西北风异常,导致辐合上升气流偏弱,有利于维持夏季感热通量偏高。

Based on the monthly surface sensible heat flux and meteorological elements of ERA-20C datasets during 1901-2010,the variation trends and interdecadal characteristics of summer sensible heat flux in different zones of arid and semi-arid areas of East Asia were analyzed by using Lanczos low-pass filters,stepwise multiple regression analysis,Mann-Kendall test and moving t test,firstly.Then,the contribution of climatic elements to summer sensible heat flux change and the relation of summer sensible heat flux with atmospheric circulation were discussed.The results are as follows:(1)In the past 110-year,the variation trends of summer sensible heat flux in hyper-arid,arid,semi-arid and dry-sub humid zones of East Asia were completely different,the summer sensible heat flux in hyper-arid area didn’t have an obvious change trend,while in other areas it had significant increasing trend,and the increasing rate increased with surface moisture index rising.The interdecadal signals of summer sensible heat flux in semi-arid and dry-sub humid areas were stronger,and the mutation happened in the 1960s,while in arid area it happened in the middle of the 1950s.(2)Relative contributions of meteorological elements to the variation of summer sensible heat flux in different zones of arid and semi-arid areas of East Asia were significantly different.The surface net radiation and precipitation were main drivers to the variations of summer sensible heat flux in hyper-arid and arid regions,while temperature difference between the surface and air and wind speed on 10-meter height were main drivers in semi-arid and dry-sub humid regions,and the contributions after the mutation were more than that before the mutation.(3)The anomalies of atmospheric circulation played an important role on the variations of summer sensible heat flux in arid and semi-arid areas of East Asia.Before the mutation,the circulation situation with the east wind anomalies on 200 hPa,positive vorticity anomalies on 500 hPa and southeast wind anomalies on 850 hPa was in favor of convergence and upward motion,which was easily to sustain lower sensible heat flux in summer,and after the mutation,the circulation situation with the west wind anomalies on 200 hPa,negative vorticity anomalies on 500 hPa and northwest wind anomalies on 850 hPa wasn’t conductive to convergence and upward motion,which was easily to sustain higher sensible heat flux.