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

Abstract

Abstract One pronounced feature in observed latitudinal dependence of lower-stratospheric temperature trends is the enhanced cooling near 30° 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° ± 0.1° and 1.0° ± 0.3° latitude in the Southern and Northern Hemispheres, respectively, in last 30 years since 1979, indicating a widening of tropical belt by 1.6° ± 0.4° latitude.