地球自转与北半球中纬度地面温度的年代际关系及其可能物理过程分析

摘要

利用地球日长(LOD)资料和美国环境预报中心/国家大气研究中心(NCEP/NCAR)的气象要素资料,统计分析发现1962-2010 年LOD的变化和北半球中纬度地面温度均存在明显的十年以上的波动周期.相关分析、合成分析等统计方法均检测到LOD与中纬度地面温度的显著负相关关系,当地球自转速率加快时,北半球中纬度地面增温;反之,中纬度地面降温.小波功率谱和交叉谱分析则确定二者的相互关系属于准20 年周期尺度上的年代际变化联系,并且LOD的变化超前于地面温度的变化大概3～4 年.平均而言,LOD的变化可带来中纬度地面温度0.2 ℃的降温(或增温).通过对大气相对角动量、纬向风场、海平面气压场的年代际合成分析,揭示了LOD与地面温度的年代际联系形成的具体物理过程.当地球自转加速时,北半球高低纬度经向温差梯度减弱,热带地区向极地扩展,造成北半球中纬度地区地面增温;地球自转减速时段相反,经向温差梯度增强,热带地区向赤道收缩,中纬度地区地面降温.%This study investigates the possible relationship between interdecadal variation of the Earth rotation and skin temperature in northern midlatitude via analyzing the length-of-day(LOD)data and the NCEP/NCAR reanalysis data during 1962-2010.It is found that there exists a significant out of phase connection between the interdecadal variation of Earth rotation and the skin temperature in northern midlatitude.In particular,the skin temperature over the northern midlatitude has a tendency to be warmer(cooler)when the earth rotates faster(slower).The wavelet power spectrum analysis and the cross wavelet transform technique show that there exists a quasi-20 year cycle in the connection between Earth rotation and skin temperature in the northern midlatitude,with the LOD leading the skin temperature variation by about 3～4 years.In average,the magnitude of 0.2 ℃ change of skin temperature may be attributed to the LOD interdecadal variability.We further examined atmospheric circulation anomalies during strong and weak LOD phases,respectively,to identify the possible physical process underlying the Earth rotation-skin temperature connection.In high LOD phase,the zero contour of the zonal mean U-wind and the subtropical westerly jet tend to shift towards the equator,the Ferrell circulation is strengthened,and the subtropical high belt in northern hemisphere is enhanced and moved southward.This leads to increase in the meridional temperature gradient,the contraction of tropical region,which favor the surface cooling in northern midlatitude.In low LOD phase,the atmospheric anomalies conditions are generally opposite to those in the high LOD phase,which favor surface warming in northern midlatitude.