Baroclinic instability with cumulus heating

• Published in: Journal of the atmospheric sciences 1985-01, Vol.42 (19), p.2007-2031
• Main Authors: SHRINIVAS MOORTHI, ARAKAWA, A
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; General circulation. Atmospheric waves; Meteorology
• ISSN: 0022-4928; 1520-0469
• DOI: 10.1175/1520-0469(1985)042<2007:BIWCH>2.0.CO;2

Baroclinic instability with cumulus heating has been investigated by using a vertically discrete, linearized, quasi-geostrophic model on a beta -plane. Two formulations of cumulus heating were used. The first formulation ( eta -model) rests on the assumption that heating at all levels is proportional to the vertical rho -velocity at the top of the lowest model layer. The second formulation (AS-model) follows the cumulus parameterization proposed by Arakawa and Schubert. The authors present results for basic states with a constant-temperature lapse rate and zonal flows linear in pressure. With both formulations, the Green modes for easterly shears are destabilized by cumulus heating. The mechanism of this destabilization and the vertical structure and energetics of the perturbations are discussed. The analyses for basic zonal flows similar to those observed during the Indian summer monsoon season are extended with the AS-model. The wavelength, phase speed, growth rate, and vertical structure corresponding to a peak growth rate are similar to some of the observed monsoon depressions. This similarity indicates that baroclinic instability with cumulus heating can be responsible for the development of monsoon depressions.