The advection-condensation model and water-vapour probability density functions

Sukhatme, Jai and Young, William R (2011) The advection-condensation model and water-vapour probability density functions. In: Quarterly Journal of the Royal Meteorological Society, The, 137 (659, P). pp. 1561-1572.

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Abstract

The statistically steady humidity distribution resulting from an interaction of advection, modelled as an uncorrelated random walk of moist parcels on an isentropic surface, and a vapour sink, modelled as immediate condensation whenever the specific humidity exceeds a specified saturation humidity, is explored with theory and simulation. A source supplies moisture at the deep-tropical southern boundary of the domain and the saturation humidity is specified as a monotonically decreasing function of distance from the boundary. The boundary source balances the interior condensation sink, so that a stationary spatially inhomogeneous humidity distribution emerges. An exact solution of the Fokker-Planck equation delivers a simple expression for the resulting probability density function (PDF) of the wate-rvapour field and also the relative humidity. This solution agrees completely with a numerical simulation of the process, and the humidity PDF exhibits several features of interest, such as bimodality close to the source and unimodality further from the source. The PDFs of specific and relative humidity are broad and non-Gaussian. The domain-averaged relative humidity PDF is bimodal with distinct moist and dry peaks, a feature which we show agrees with middleworld isentropic PDFs derived from the ERA interim dataset. Copyright (C) 2011 Royal Meteorological Society

Item Type:	Journal Article
Publication:	Quarterly Journal of the Royal Meteorological Society, The
Publisher:	John Wiley and Sons
Additional Information:	Copyright of this article belongs to John Wiley and Sons.
Keywords:	diffusion;relative humidity;specific humidity;bimodal
Department/Centre:	Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited:	25 Oct 2011 10:02
Last Modified:	25 Oct 2011 11:55
URI:	http://eprints.iisc.ac.in/id/eprint/41668

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