Model simulations of an intense meso-ß scale cyclone The role of condensation parameterization

Jón Egill Kristjánsson

doi:10.3402/tellusa.v42i1.11861

Model simulations of an intense meso-ß scale cyclone The role of condensation parameterization

Tellus

Volume 42 (1990): Issue 1

By: Jón Egill Kristjánsson

Open Access

|Jan 1990

Abstract

On 23 July 1985, an unusual mesoscale storm struck the Baltic Sea coast of Sweden. Locally, more than 50 mm of precipitation fell in 12 h and mean winds exceeding 25 m s^-1 were recorded. The failure of operational models to predict this storm, as well as the damage it caused (2 people were killed), raised important questions. What physical process caused this rare event? Could it be predicted with existing data, and if so, how? Diagnostic studies reveal the following features. The development took place in a very humid air mass, which possessed weak conditional stability. The synoptic-scale environment provided large relative vorticity, which helped to spin up the mesoscale vortex. Calculations show significant adiabatic forcing initially, but then latent heat release takes over as the main driving mechanism. Numerical simulations of this storm show that it can be successfully simulated with a regional model, provided that condensation and latent heat release are treated in a consistent manner. This is demonstrated, e.g., by comparing latent heating distributions in 2 different condensation schemes. The simulations, furthermore, demonstrate the crucial role of good humidity data for this type of simulations.

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