# The effect of coherent stirring on the advection-condensation of water vapour

## TL;DR

This paper investigates how large-scale advection, turbulence, and condensation interact to shape atmospheric water vapor distribution using simplified kinematic models that incorporate flow and turbulence effects.

## Contribution

It introduces a novel combination of a single circulating flow with Brownian motion to model moisture dynamics and analyzes steady states resembling atmospheric circulation patterns.

## Key findings

- Identified boundary layers and precipitation regions in the model
- Characterized humidity minima in steady states
- Provided explicit results for strong flow regimes

## Abstract

Atmospheric water vapour is an essential ingredient of weather and climate. Key features of its distribution can be represented by kinematic models which treat it as a passive scalar advected by a prescribed flow and reacting through condensation. Condensation acts as a sink that maintains specific humidity below a prescribed, space-dependent saturation value. In order to investigate how the interplay between large-scale advection, small-scale turbulence and condensation controls the moisture distribution, we develop simple kinematic models which combine a single circulating flow with a Brownian-motion representation of turbulence. We first study the drying mechanism of a water-vapour anomaly released inside a vortex at an initial time. Next, we consider a cellular flow with a moisture source at a boundary. The statistically steady state attained shows features reminiscent of the Hadley cell such as boundary layers, a region of intense precipitation and a relative humidity minimum. Explicit results provide a detailed characterisation of these features in the limit of strong flow.