WMOD00400

• Contract/Permit #: 14-06-D-6801
• Title: Structure and Seedability of San Juan Storms
• Date: 11/1/1976
• Weather Modification - Doc Type: Report

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C. Transport and Diffusion Studies

Field experience has sho,vn that the transport and diffusion* of seeding

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material into and through orographic clouds is a complex problem. The prob-

lem is unique for each mountain range. In addition to having tracers such

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as SF6, AgI and chaff t~ study the transport and diffusion of seeding

materials, it is now possible to fly well-instrumented research aircraft

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upwind and over the orographic barrier and directly measure the transport

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and diffusive properties of the air. Specifically, what is measured is the

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longitudinal, lateral and vertical components of the wind vector above wave-

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lengths of 10 m at accuracies of + 0.1 m s

These measurements are made

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with an inertial navigation system (INS) and an air sensing C'gust") probe

(Lenschow, 1970). The INS also presents continuous positioning of the air-

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craft in realtime for navigation and records that data for later analysis.

Since all atmospheric research aircraft sense and record static pressure,

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free air temperature and dew. point, it is possible to derive a variety of

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state parameters such as equ~valent potential temperature, potential tempera-

ture and specific humidity. These parameters are conservative under non-

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mixing and other conditions. \ihen there is a vertical gradient of one of

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.the derived state parameters, then it is also possible to infer the mean

vertical displacement of air parcels.

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The Department of Atmospheric Science at the University of Wyoming, was

one of the first users of the NCAR Queen Air when the INS and air sensing

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probe was first installed in February 1975. As such, we participated and

suffered in many of the "childhood diseases" associated with any ne,v system.

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*Transport is the movement of air by the mean flow, whether it be by dis-
placement by the orography or by convection. Diffusion is the three-
dimensional mixing by turbulence.

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