Poleward Shift of Subtropical Jets Inferred from Satellite-Observed Lower-Stratospheric Temperatures

One pronounced feature in observed latitudinal dependence of lower-stratospheric temperature trends is the enhanced cooling near 30 degrees latitude in both hemispheres. The observed phenomenon has not, to date, been explained in the literature. This study shows that the enhanced cooling is a direct response of the lower-stratospheric temperature to the poleward shift of subtropical jets. Furthermore, this enhanced lower-stratospheric cooling can be used to quantify the poleward shift of subtropical jets. Using the lower-stratospheric temperatures observed by satellite-borne microwave sounding units, it is shown that the subtropical jets have shifted poleward by 0.6 degrees +/- 0.1 degrees and 1.0 degrees +/- 0.3 degrees latitude in the Southern and Northern Hemispheres, respectively, in last 30 years since 1979, indicating a widening of tropical belt by 1.6 degrees +/- 0.4 degrees latitude.