选用每天12 :00 UTC时次的逐日ERA-Interim再分析资料,根据transformed Eulerian-mean (TEM)方程通过积分剩余速度v~(*-),研究了1979-2011年间Brewer-Dobson ( BD)环流的时空演变规律.并将其与downward control (DC)原理研究的结果进行比较,同时还探讨了平流层温度与BD环流之间的相互联系.结果表明,由TEM方程通过积分剩余速度v~(*-)估算的BD环流与利用DC原理估算的环流相比较,在热带地区的形势更加明显.环流在热带对流层中上层上升至平流层中下层,最高可达1 hPa等压面附近.然后在热带外向极向下运动,最后在中高纬度下沉回到对流层.BD环流的上升中心及质量通量均随季节的变化产生变动,环流在冬半球的形势显著地强于夏半球.在春季和秋季期间,环流呈现出南北两半球的对称形势.从全球尺度物质输送的角度来看,在过去的33a间平流层BD环流的长期变化趋势是减弱的,且在平流层中下层减弱是明显的.环流的减弱趋势与纬向平均温度的长期变化趋势相匹配.
英文摘要:
The spatial-temporal distribution characters of trace gases in the stratosphere and troposphere are affected by the Brewer-Dobson (BD) circulation. Understanding the distribution characters of BD circulation is very important to further study the influence of stratosphere and troposphere exchange and forecast the global climate change. The BD circulation is described as the Lagrangian-mean circulation, it is difficult to diagnose directly from meteorological observations. The methods of the transformed Eulerian-mean (TEM) equations,and integrating residual meridional velocity in the vertical were used to analyze the spatial-temporal distribution characters of BD circulation, by using the ERA-Interim reanalysis data for 1979-2011 at 12:00 UTC. We further compared the distribution characters of BD circulation with the result calculated by the method of DC (downward control) principle and studied the relationship between the stratospheric zonal mean temperature and BD circulation. The BD circulation was calculated from ERA-Interim reanalysis data for 1979-2011 by integrating residual meridional velocity in the vertical. The results showed that : (1) The ascending cencers of BD circulation were varied with seasons. It ascended at 30° S in the stratosphere for December to February (DJF),for June to August (JJA) it ascended between 25°N and 30° N,the circulation pattern in the winter hemisphere is stronger than the summer hemisphere. I:i March to May (MAM) and September to November (SON),the ascending center were between equator to 5°N, and circulation were relatively symmetrically for two hemispheres. (2) The maximum mass flux in the tropical and extratropical northern hemisphere appeared during DJF, the minimum appeared during JJA. The mass flux in extratropical southern hemisphere was just the opposite. Mass flux across the 100 hPa and 50 hPa pressure surface in tropical and extratropical trended to decreasing, and also had obviously seasonal variation. (3) The long-term trend of stratospheric zonal mean temperature was consistent with the long-term weakening trend of BD circulation, this indicated that the global BD circulation has been weakened. Meanwhile, the zonal mean temperature in different altitude and latitude bands varied with seasons. From the perspective of the global mass transportation, the stratospheric BD circulation has been weakened in the past 33 years, especially in the middle and lower stratosphere, and was consistent with the long-term trend of temperature. This weakened trend was consistent with the observation study in the age of stratospheric air and other model results. But the method of DC principle, GCMs model and other studies showed that the stratospheric BD circulation has been enhanced in the past years. Using different methods and data would lead the trend estimation of BD circulation were unreliable. Therefore,further research will be required to improve the reliability of ED circulation.