Impact of ENSO events on the interannual variability of Hadley circulation extents in boreal winter

摘要

The interannual variability of the boreal winter Hadley circulation extents during the period of 1979e2014 and its links to El Ni^no-Southern Oscillation(ENSO) were investigated by using reanalysis datasets. Results showed that the El Ni^no(La Ni^na) events can induce the shrinking(expansion) of Hadley circulation extent in the Southern Hemisphere. For the Northern Hemisphere, El Ni^no(La Ni^na) mainly leads to shrinking(expansion) of the Hadley circulation extent in the middle and lower troposphere and expansion(shrinking) of the Hadley circulation extent in the upper troposphere. The ENSO associated meridional temperature gradients have close relationship with the Hadley circulation extents in both Hemispheres. But in the Northern Hemisphere, the ENSO associated eddy momentum flux divergence plays more important role in affecting the Hadley circulation extent than the meridional temperature gradient because of the small local Rossby number. In the Southern Hemisphere, as the ENSO induced eddy momentum flux divergence is small, the meridional temperature gradient dominates the change of the Hadley circulation extent.