Transport Changes Inferred from HALOE Water and Methane Measurements

Abstract

Changes in water vapor and methane covering the period 1992 through April 2001 are discussed. Global increases in 2 × CH₄ + H₂O are evident, however there is significant spatial structure at levels between 10 and 100 hPa. Anti-correlated decreases in methane and increases in water vapor are noted in the upper stratosphere; these are associated with a slowing of the mass flux into the upper stratosphere and a concomitant increase in residence time above 10 hPa. Increases greater than those due to the surface increase in methane are more difficult to explain. One possibility is changes in the water vapor flux into the middle and upper stratosphere associated with a widening of the tropical upwelling. Another possible cause is a change in the ratio of summer/winter net upwelling. Additionally, the first 3 years of the period considered appear anomalous at many levels simultaneously. It is postulated that this is due to enhanced vertical mixing at the start of the data record.