Publication Date:
2013-11-01
Description:
This study investigates the potential contribution of observed changes in lower stratospheric water vapour to stratospheric temperature variations over the past three decades using a comprehensive global climate model (GCM). Three case studies are considered. In the first case study, the long-term positive stratospheric water vapour (SWV) trend from 1980-2010 (derived from the Boulder frost-point hygrometer record using the gross assumption that this is globally representative) is estimated to have cooled the lower stratosphere by up to ∼ 0.2 K decade − 1 in the global and annual mean; this is ∼ 40% of the observed cooling trend over this period. In the Arctic winter stratosphere, there is a dynamical response to the increase in SWV, with enhanced polar cooling of 0.6 K decade − 1 at 50 hPa, and a warming of 0.5 K decade − 1 at 1 hPa. In the second case study, the observed decrease in tropical lower stratospheric water vapour after the year 2000 (imposed in the GCM as a simplified representation of the observed changes derived from satellite data) is estimated to have caused a relative increase in tropical lower stratospheric temperatures by ∼ 0.3 K at 50 hPa. In the third case study, the wintertime dehydration in the Antarctic stratospheric polar vortex (again using a simplified representation of the changes seen in a satellite dataset) is estimated to cause a relative warming of the Southern hemisphere polar stratosphere by up to 1 K at 100 hPa from July to October. This is accompanied by a weakening of the westerly winds on the poleward flank of the stratospheric jet by up to 1.5 m s − 1 in the GCM. The results show that if the measurements are representative of how SWV has varied globally, it should be considered as important as increases in long-lived greenhouse gases and stratospheric ozone depletion as a driver of transient and long-term variations in lower stratospheric temperatures over the past 30 years.
Print ISSN:
0035-9009
Electronic ISSN:
1477-870X
Topics:
Geography
,
Physics
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