Dry and moist atmospheric circulation with uniform sea-surface temperature

D. L. Suhas, Jai Sukhatme, Nili Harnik

Research output: Contribution to journalArticlepeer-review


The steady and transient response of “dynamically” dry and moist atmospheres to uniform sea-surface temperature (SST) is studied using an aquaplanet general circulation model (GCM). Specifically, the latent heat ((Formula presented.)) of water vapour is varied, so that for small (Formula presented.), water substance is essentially a passive tracer from a dynamical point of view. Despite the lack of SST gradients, Hadley and Ferrel cells in the same direction as that on present-day Earth are observed for relatively stronger moist coupling. Organized convergence by equatorial waves drives tropical overturning, and along with the equatorial deformation radius, the Hadley cell width increases with coupling strength. An abrupt switch to a much shallower tropical cell is noted when the system becomes completely passive. Moist static energy is transported equatorward in the tropics and a larger amount is directed poleward in the midlatitudes. As a whole, there is an almost invariant poleward transport of moist static energy for relatively strong coupling of water substance. Transient extratropical activity is seen in the form of intense warm-core vortices for strong coupling, and these systems become weaker and smaller as (Formula presented.) decreases. The drift of these moist vortices results in the observed poleward energy transport in the midlatitudes. In the tropics, intraseasonal variability is dominant and systematically shifts to longer time periods with stronger coupling. In fact, large-scale, low-frequency Kelvin waves and MJO-like modes disappear as water vapour becomes passive in nature. Further, the direction of tropical overturning reverses as (Formula presented.) decreases due to the off-equatorial convergence imposed by tropical Rossby waves. Finally, extreme rainfall events associated with cyclonic storms vanish as water vapour becomes dynamically inactive, however, moderate precipitation events increase leading to higher total precipitation for weaker coupling of water substance. Tropospheric heating due to a saturation of the outgoing longwave radiation results in an increase in the stability of the atmosphere for strong coupling, and provides a plausible physical mechanism for interpreting the behaviour of precipitation.

Original languageEnglish
Pages (from-to)35-56
Number of pages22
JournalQuarterly Journal of the Royal Meteorological Society
Issue number742
StatePublished - 1 Jan 2022


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