WMOD00416

• Title: Wintertime Cloud Systems Over the Rockies: Three Case Studies
• Date: 12/1/1980
• Weather Modification - Doc Type: Report

16

classified according to (a) absolutely stable: r. < r d
env~ronment saturate,
(b) conditionally unstable: r < r. < r
saturated env~ronment dry adiabatic,
or (c) absolutely unstable: r < r . The c1assi-
dry adiabatic environment'
fication (b) is conditional upon moisture, if the layer is saturated,

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then the layer is stable. Processes which bring a conditionally un-
I
I
stable layer to saturation or drive a saturated absolutely strb1e layer

to conditional instability will bring about convective motions through
I

the release of latent heat as water vapor condenses to liquid water and

liquid droplets freeze. Both of these processes may operature during

an orographic lift. Layers are lifted and cooled, so that condensation

takes place. On the other hand, vertical airmass stretching upon lift-

ing can drive the lapse rate of a saturated layer past the saturated

adiabatic so that conditional instability may be realized (Saucier,

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1955; Hess, 1959; Elliott and Hovind, 1964).

The second method, potential convective instability, can also be

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applied to an atmospheric layer. A layer is potentially unstable when

ae /az < 0 and non-saturated. If the layer is stable, lifted, and
e
cooled to saturation, it will become convective1y unstable. Wllen

ae /az > 0, non-saturated and stable, the layer is potentially stable.
e

After lifting to saturation, it will remain stable (Saucier, 1955; Hess,

1959). Because layer conditional instability is unable to account for

the vertical gradient of latent heat which may be present within the

layer, convective potential instability is a preferred analysis tech-

nique (see Appendix A).

Table II displays a summary of parcel and layer stability analysis

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performed upon the COSE I and COSE II sounding data sets.