The Ed Lorenz Symposium


A simple 2-dimensional chaotic rain gush model

Stanley David Gedzelman, The City College of New York, New York, NY

A simple, 2-dimensional Lagrangian model of convection that produces chaotic rain gushes is developed. The model contains only 130 lines of code. Ambient lapse rates are specified for an unstably stratified troposphere and stably stratified stratosphere. Air particles enter the grid at lower left with constant horizontal velocity towards the right and an initial vertical velocity. Rising particles cool dry adiabatically below the condensation level and moist adiabatically above it. Individual raindrops and/or snowflakes form above the condensation level and fall at prescribed terminal velocities. At every time step the vertical velocity and temperature of the air particles in each grid box are separately averaged, the total mass of hydrometeors calculated, Newton’s Second Law with buoyancy is solved and all particles in each box are given their respective averaged new vertical velocities. Averaging mimics fluid behavior and so, bypasses the need for partial differential equations. Particles that leave the grid at right are recycled as new particles at lower left. Despite the model’s simplicity, it exhibits relatively complex behavior with several features often observed in thunderstorms. It has an overshooting top and an anvil extending downwind at the tropopause with stable buoyancy oscillations. It produces a narrow region of heavy convective rain and a wide region of light stratiform rain. The convective rain is episodic and chaotic in that it contains irregularly sized and spaced rain gushes caused by air that has been dragged down by large local concentrations of particles. Animations of the model are shown.

Poster Session 1, Lorenz Symposium Posters
Thursday, 13 January 2005, 9:45 AM-9:45 AM

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