loading page

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:biasutti@ldeo.columbia.edu

Author Profile
Spencer Hill
Lamont-Doherty Earth Observatory, Lamont-Doherty Earth Observatory
Author Profile
Aiko Voigt
Department of Meteorology and Geophysics, Universität Vienna, Department of Meteorology and Geophysics, Universität Vienna
Author Profile


The Tropical Rain belts with an Annual cycle and Continent Model Intercomparison Project (TRACMIP) ensemble includes slab-ocean aquaplanet control simulations and experiments with a highly idealized tropical continent. We compare the two set-ups to investigate monsoon development and contrast the characteristics of oceanic and continental rain bands 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, consistent with expectations for deep-tropical monsoons: a smooth latitudinal transition, a poleward reach only slightly farther than the oceanic ITCZ’s, and a constant width throughout the year. This monsoon confinement 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 westerlies is only 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, both the timing and strength of the monsoon are strongly modulated by the treatment of evaporation over land and by the interaction of moisture and radiation. This points to the need for a fuller exploration of land characteristics in the hierarchical modeling of the tropical rain bands.