The effect of ENSO activity on lower stratospheric water vapor

Abstract

Using the ECMWF/NCEP reanalysis data, satellite observations from AURA MLS and UARS HALOE, and Oceanic NiñoNi˜Niño Index (ONI) data, the effects of El NiñoNi˜Niño and La NiñaNi˜Niña events on the stratospheric water vapor changes are investigated. Overall, El NiñoNi˜Niño events tend to moisten the lower stratosphere but dry the middle stratosphere. La NiñaNi˜Niña 5 events are likely to dry the lower stratosphere over a narrow band of tropics (5 • S-5 • N) but have a moistening effect on the whole stratosphere when averaged over a broader region of tropics between 25 • S-25 • N. The moistening effect of La NiñaNi˜Niña events mainly occurs in lower stratosphere in the Southern Hemisphere tropics where a significant 20% increase in the tropical upwelling is caused by La NiñaNi˜Niña events. El NiñoNi˜Niño events 10 have a more significant effect on the tropical upwelling in the Northern Hemisphere ex-tratropics than in Southern Hemisphere extratropics. The net effect of ENSO activities on the lower stratospheric water vapor is stronger in the Southern Hemisphere tropics than in the Northern Hemisphere tropics.