The Distribution Characters of the Stratospheric Brewer‐Dobson Circulation Inferred from Era‐Interim

Abstract

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 the BD circulation is very important for further studying the influence of stratosphere and troposphere exchange and forecasting the global climate change. The BD circulation is described as the Lagrangian-mean circulation, which 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 the BD circulation based on the ERA-Interim reanalysis data at 12:00 UTC for 1979–2011. 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 using ERA-Interim reanalysis data for 1979–2011 by integrating residual meridional velocity in the vertical direction. The results show that the ascending centers of BD circulation varied with seasons. It ascended at 30°S in the stratosphere from December to February (DJF), while from June to August (JJA) it ascended between 25°N and 30°N. The circulation pattern in the winter hemisphere was stronger than the summer hemisphere. In March to May (MAM) and September to November (SON), the ascending centers were between equator to 5°N, and circulation were relatively symmetric between the two hemispheres. The maximum mass flux in the tropical and extratropical northern hemisphere appeared during DJF, and the minimum appeared during JJA. The mass flux in the extratropical southern hemisphere was just the opposite. Mass flux across the 100 hPa and 50 hPa pressure surface in the tropical and extratropical areas tended to decrease, and also varied obviously with the changing of season. The long-term trend of stratospheric zonal mean temperature was consistent with the long-term weakening trend of BD circulation, which indicates that the global BD circulation has been weakened. Meanwhile, the zonal mean temperature at different altitudes and latitudes 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, which was consistent with the long-term trend of temperature. This weakened trend was consistent with the observations of stratospheric air and other model results. But the method of DC principle, GCMs model and other studies show that the stratospheric BD circulation has been enhanced in the past years. Using different methods and data would make the trend estimation of BD circulation unreliable. Therefore, further research is required to improve this estimation.