absolute instability

absolute instability

[′ab·sə‚lüt ‚in·stə′bil·ə·dē]
(meteorology)
The state of a column of air in the atmosphere when it has a superadiabatic lapse rate of temperature, that is, greater than the dry-adiabatic lapse rate. Also known as autoconvective instability; mechanical instability.

absolute instability

absolute instabilityclick for a larger image
As it relates to meteorology, the state of a layer of air within the atmosphere in which a parcel of air, if given an upward push, will move away from its initial level without further outside force being applied. It is that condition in which the observed lapse rate is more than the dry and saturated adiabatic lapse rates. A mass of dry air in this case will rise until it becomes saturated and will still continue to rise, as the observed lapse rate is still greater. See also dry adiabatic lapse rate and saturated adiabatic lapse rate.
References in periodicals archive ?
The aim of this paper is to track the transition between the absolute instability and convective instability in a compressible shear layer.
This study focuses on the transition between absolute instability (AI) and convective instability (CI) for a compressible inviscid shear layer, which are dominated by modes with zero group velocity.
The effect of velocity ratio [LAMBDA] on the absolute instability of an inviscid shear layer is illustrated in Figure 3.
Hence the strategy for suppressing absolute instability is to increase temperature ratio.
However, the temperature effects do not always tend to depress the absolute instability. When the temperature ratio is relatively small ([S.sub.T] < 1), the absolute growth rates shows minor increase with increase of [S.sub.T] for every case.
Now, we check the effect of obliquity of the disturbance wave on the absolute instability by varying the oblique angle, [phi].
The parameter M is naturally supposed to be parameter influencing the absolute instability behavior of flow.
Figure 7 shows the critical value of [LAMBDA] at which the flow transits into absolute instability at different M and [S.sub.T].
In this work, we explore the transition of absolute instability and convective instability in a compressible inviscid shear layer, through a linear spatial-temporal instability analysis.
There are classes of instability like conditional and absolute instability, but in aviation this distinction is not important.
Absolute instability [DELTA][[theta].sub.v,dry] = 0 [??] [chi]* = [[chi].sub.c].
Also note that the absolute instability regime is marked by isolines of [delta][[theta].sub.v,m,min] = 0.