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Teleconnection between the South Atlantic convergence zone and the southern Indian Ocean: Implications for tropical cyclone activity
Author(s) -
DeBlander Evan,
Shaman Jeffrey
Publication year - 2017
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2016jd025373
Subject(s) - convergence zone , rossby wave , climatology , geology , tropical cyclone , teleconnection , indian ocean dipole , convection , wind shear , tropical atlantic , equatorial waves , oceanography , tropical wave , intertropical convergence zone , precipitation , sea surface temperature , latitude , geography , wind speed , meteorology , el niño southern oscillation , equator , geodesy
A link between anomalous austral summer convection over the South Atlantic convergence zone (SACZ) and atmospheric conditions over the South Indian Ocean is investigated. Interannual north‐south shifts in the SACZ produce a dipole of anomalous convection and precipitation over South America. The South Atlantic convergence zone index (SACZI) capturing this variability is presented and associated with a midlatitude Rossby wave train that propagates from South America eastward and south of Africa before curving north into the tropical Indian Ocean. This wave train is reproduced using Rossby wave ray tracing and simulations with a linearized barotropic vorticity equation model forced with divergence and convergence consistent with the observed dipole of anomalous convection. The wave train acts to excite anomalies in wind shear and relative humidity over the tropical south Indian Ocean, which in turn impact tropical cyclone (TC) genesis and distribution over this region. We find that changes in the wind shear and relative humidity associated with the SACZI effect changes in TC genesis, which result in a change in observed TC days over portions of the South Indian Ocean.