An upper-branch Brewer-Dobson circulation index for attribution of stratospheric variability and improved ozone and temperature trend analysis
We ﬁnd that wintertime temperature anomalies near 4hPa and 50◦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 60% of the total variability of temperature, peaking at ∼5hPa and dropping to 0 at ∼50 and ∼0.5hPa, respectively, and increasing again into the mesosphere. Ozone similarly sees up to an additional 50%ofvariabilityaccountedfor,withaslightlyhighermaximum and strong altitude dependence, with zero improvement found at 10hPa. Further, the uncertainty on all equatorial multiple-linear regression coefﬁcients can be reduced byupto35and20%intemperatureandozone,respectively, and so this index is an important tool for quantifying current and future ozone recovery.