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

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numerically simulate cumulus convection as a series of discrete but interacting

Lagrangian "parcels. II While such a scheme retains the past "history" of each

parcel, great difficulties arise in allowing realistic interactions between parcels.

Unless all state parameters in a parcel vary together during a parcel-parcel

interaction,a new and discrete parcel will be formed to continue further inter-

action and parcel multiplication. Unless drastic simplifications are made, soon

there are too many "parcels" for cost-effective numerical simulation to continue.

This lack of realism in continued inter-parcel interactions is the basic fault of the

Lagrangian system.

Virtually all multi-space-dimensional convection flow field models (Ogura

[1971], Orville [1970], etc.) use the Eulerian approach, sacrificing knowledge of

the past time history of a particular cloud entity in return for knowing the in-

stantaneous values and fluxes of relevant parameters at a large number of regularly

spaced points within the cloud.

Detailed one-space-dimensional microphysical models of cloud structure

are also overwhelmingly Eulerian. This has occurred predominantly due to the in-

clusion of stochastic coalescence in such detailed microphysics. Were the frame-

work anything but Eulerian, then each 2-particle collision would create a previously

nonexistent particle ("parcel") leading to almost immediate numerical breakdown.

The Eulerian method has been carried over from the coalescence terms

and applied to spatial transport terms as well, resulting in a much more realistic

simulation of interactions and transport between and among the different regions

..,;

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