WMOD00455

• Contract/Permit #: 14-06-D-6842
• Title: Research and Development Technique for Estimating Airflow and Diffussion Parameters Related to the Atmospheric Water Resources Program
• Date: 9/1/1969
• Country: United States
• Weather Modification - Doc Type: Report

be found in various publications and books such as McVehil, et al.,
(Ref. 25), Nemoto (Refs. 28 and 29), Bernstein (Ref. 4) and Cermak
et al., (Ref. 5). The Appendix gives a review of the present status
on obtaining similarity criteria for planetary and surface boundary-
layer studies.

*

Laboratory Airflow Models
The physical limitations of the present laboratory experimental
facilities requires the relaxation of certain similitude requirements
as listed under the section on laboratory restrictions. Thus, complete
similitude between field and model cannot be totally satisfied. How-
ever, past studies have indicated that partial similarity* may be
adequate for obtaining reasonable results.
The following statements summarizes the principal similarity
aspects of the two airflow models that have been used to obtain
diffusion results in this study:
1. Neutral airflow model
a. Thermal similarity
The atmospheric stability is assumed to be in a
neutral state or adiabatic equilibrium. Under these conditions
an air parcel displaced adiabatically will continue to possess
the same temperature and pressure as its surroundings, so
that no restoring force acts on a parcel displaced vertically.
The state of adiabatic equilibrium is approached in a layer
of air in which there is strong vertical mixing, e.g., when
the sky is thickly covered with cloud and there is a moderate
or high wind velocity.
In a neutral state the environmental lapse rate of
temperature is equal to the dry-adiabatic lapse rate or the
saturation-adiabatic lapse rate. When expressed in terms of
the potential temperature and air density one can write the
approximation,

l ~ - 0]
e az F

1 a p
- - paz

O]M

2.3

~

The main limitation in this approximation is that it
must be possible to treat the atmosphere like an incompressible
fluid. Generally, this limitation (Ref. 10) has been accepted
but the full consequences of such an assumption have not been
fully explored for modeling flow over irregular terrain.
b. Airflow and dispersion similarity
In this type of airflow the concentration at any
location downstream from a source is assumed a function of the
following variables,

- -?- 7 -?- -?-
C(r) = f(Q,L.,H,U(z) ,U ,K. ,t ,T)
g 1 s

2-4

Now according to similarity or dimensional analysis (Appendix)
one can write the relevant nondimensional variables which are
important in the neutral airflow model as,

* See Appendix

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