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The Effect Of An Equatorial Continent On The Tropical Rain Belt. Part 2: Summer Monsoons
  • Michela Biasutti,
  • Spencer Hill,
  • Aiko Voigt
Michela Biasutti
Lamont-Doherty Earth Observatory, Columbia University, Lamont-Doherty Earth Observatory, Columbia University

Corresponding Author:[email protected]

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Spencer Hill
Lamont-Doherty Earth Observatory, Lamont-Doherty Earth Observatory
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Aiko Voigt
Department of Meteorology and Geophysics, Universität Vienna, Department of Meteorology and Geophysics, Universität Vienna
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The TRACMIP ensemble includes slab-ocean aquaplanet control simulations and experiments with a highly idealized narrow tropical continent (0-45ºW; 30ºS - 30ºN). We compare the two setups to contrast the characteristics of oceanic and continental rain bands and investigate monsoon development in GCMs with CMIP5-class dynamics and physics. Over land, the rainy season occurs close to the time of maximum insolation. Other than in its timing, the continental rain band remains in an ITCZ-like regime akin deep-tropical monsoons, with a smooth latitudinal transition, a poleward reach only slightly farther than the oceanic ITCZ’s (about 10º), and a constant width throughout the year. This confinement of the monsoon to the deep tropics is the result of a tight coupling between regional rainfall and circulation anomalies: ventilation of the lower troposphere by the anomalous meridional circulation is the main limiting mechanism, while ventilation by the mean westerly jet aloft is secondary. Comparison of two sub-sets of TRACMIP simulations indicates that a low heat capacity determines, to a first degree, both the timing and the strength of the regional solsticial circulation; this lends support to the choice of idealizing land as a thin slab ocean in much theoretical literature on monsoon dynamics. Yet, the timing and strength of the monsoon are modulated by the treatment of evaporation over land, especially when moisture and radiation can interact. This points to the need for a fuller exploration of land characteristics in the hierarchical modeling of the tropical rain bands.