The Brewer–Dobson circulation in the stratosphere and mesosphere – Is there a trend?

The Brewer–Dobson circulation brings tropospheric air, accompanied by CFCs and greenhouse gases, into the stratosphere. Many models predict an increased circulation associated with an increase in greenhouse gases, such as that since the 1960s. A recent observation supports this: the rate at which total ozone increases in Antarctica during early winter is consistent with the descent and convergence that are part of the Brewer–Dobson circulation; at 65°S the rate doubled between the 1960s and 1990s. Another recent observation may also support this: the decrease in temperature since 1960 in the Antarctic mid-winter lower stratosphere is much less than the decrease calculated from the greenhouse effect of increased H2O, suggesting less CH4 oxidation in the 1970s; this could be caused by an increase in Brewer–Dobson circulation during the 1970s. An important paradox may be resolved by an increase in Brewer–Dobson circulation: the decrease in tropical cold-point temperature since the 1960s conflicts with the increase in mid-latitude H2O in the lower stratosphere, if it represents an increase at tropical entry of H2O; the conflict could be resolved if dehydration during stratospheric entry is incomplete and the circulation has increased.