Definition of the Day
The point where a suddden break in the river's gradient occurs. See Knickpoints

Stability and Instabilty


Atmospheric stability occurs when the ELR is lower than the DALR.In other words the the parcel of air is cooling fast(cold) than the Atmospheric air(warm).eg ELR is 5oC whilst the the DALR is 10oC,this means for every 1000m rise in height the DALR temperature is dropping faster than the ELRThe parcel of air will not rise as far because of its weight therefore sinks back to lower levels.Stability is associated with calm weather,clear skies and occasional drizzles.
Simple diagram of Atmospheric Stability


This occurs when the DALR is warmer than the ELR(cold).eg ELR is dropping at 10oC/1000m whilst the DALR is dropping at 5oC/1000m thus DALR is warmer than ELR.Because the parcel is cooling slowly it is warm,thus its bouyant (light) and continue to rise and eventually condenses. Instability is associated with bad weather.Cumulonimbus clouds may form resulting in heavy thunderstorms with frequent lightning.High wind speeds may result and tornadoes may even form.
Simple diagram of Atmospheric Instability

Conditional Instability

This occurs when the ELR is lower (warm) than the DALR(stability) but higher than the SALR. The dense cold air must sink downwards but instead may continue to rise given a constant uplift mechanism.The air will eventually condense releasing latent heat in the process which is used to warm the SALR. Now, because the saturated air parcel is warm (light) it will continue to rise even if the uplift mechanism is removed. The parcel is unstable because it has risen in the first place instead of sinking.
Conditional instability
Simple Conditional instability
.The weather associated with conditional stability is usually fine at areas below condensation level.

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