Poleward Moisture Transport Associated with Subtropical Rossby Wave Breaking

Abstract:

Rossby wave activity propagating into low latitudes and associated wave-breaking events frequently lead to the onset of convection within the deep tropics through dynamical processes that are still incompletely understood. The orientation of these wave-breaking events also results in poleward transport of moisture from the tropics and subtropics on synoptic time scales. The time mean manifestation of this transport in the Southern Hemisphere results in “diagonal convergence zones” such as the South Pacific Convergence Zone (SPCZ) and South Atlantic Convergence Zone (SACZ). In the Northern Hemisphere, such geographically anchored convergence zones are much less evident, which presumably reflects a less zonally asymmetry in the distribution of the location of extratropical wave activity interacting with low latitudes. The relationship between extratropical Rossby wave activity, Rossby wave breaking events and poleward moisture transport is quantified on synoptic through interannual time scales in this study. While there are certainly preferred paths for moisture transport within both hemispheres, the lack of diagonal convergence zones within the Northern Hemisphere is shown to be a result of larger intraseasonal variability in the path of Rossby wave propagation. Nevertheless, the preferred path of this wave activity does lead to a local precipitation maximum in the eastern North Pacific ITCZ during northern winter.