An upper-branch Brewer-Dobson circulation index for attribution of stratospheric variability and improved ozone and temperature trend analysis

Abstract

We find that wintertime temperature anomalies near 4g hPa and 50°g N/S are related, through dynamics, to anomalies in ozone and temperature, particularly in the tropical stratosphere but also throughout the upper stratosphere and mesosphere. These mid-latitude anomalies occur on timescales of up to a month, and are related to changes in wave forcing. A change in the meridional Brewer-Dobson circulation extends from the middle stratosphere into the mesosphere and forms a temperature-change quadrupole from Equator to pole. We develop a dynamical index based on detrended, deseasonalised mid-latitude temperature. When employed in multiple linear regression, this index can account for up to 60g % of the total variability of temperature, peaking at g1/4 g 5g hPa and dropping to 0 at g1/4 g 50 and g1/4 g 0.5g hPa, respectively, and increasing again into the mesosphere. Ozone similarly sees up to an additional 50g % of variability accounted for, with a slightly higher maximum and strong altitude dependence, with zero improvement found at 10g hPa. Further, the uncertainty on all equatorial multiple-linear regression coefficients can be reduced by up to 35 and 20g % in temperature and ozone, respectively, and so this index is an important tool for quantifying current and future ozone recovery.