WMOD00289 ‎(2)‎

• Title: Observations and Numerical Simulations of Precipitation Mechanisms in Natural and Seeded Convective Clouds
• Prepared By: Lroen D. Nelson
• Date: 3/1/1979
• State: IL
• Weather Modification - Doc Type: Report

CHAPTER II

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THE NUMERICAL MODEL

The Numerical Framework

Any researcher beginning a numerical simulation of a fluid flow field must

first make a determination as to whether his model framework will be Lagrangian or

Eulerian. Since computers are discrete state devices, the fluid continium must be

approximated as a series of discrete states or locations. One can choose to define

one or more Lagrangian "parcelsll and then track these parcels through time IJnd

space as discrete entities within the cloud envrionment or define an Eulerian grid

of observation points and determine the flux of relevant quantities past each of

these points as functions of time.

Most early one-dimensional cumulus models as typified by the work of

Weinstein and Davis (1968) and Simpson (1969) were single parcel Lagrangian or
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"bubblell models. An imaginary "parcel" of air was given an impulse and allowedl

to rise buoyantly throughout an atmospheric sounding until its vertical motion

ceased at cloud top. More sophisticated versions of these models allowed the

parcel to dilute itself by mixing with its environment and to transfer such quantitiJs
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as temperature, pressure, water content, etc., between parcel and environment. I
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More recently, attempts have been made by Danielson (1972) and Young (1975) to!
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