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GEOG 2110L (50)


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GEOG 2110L
David Stanley

ATMOSPHERIC STABILITY *** STABILITY: refers to the tendency of an air parcel, with its water vapor, either to remain in place or to change vertical position be ascending (rising) or descending (falling). * a stable parcel of air resists displacement upward or, when disturbed, tends to return to its starting place * an unstable parcel of air continues to rise until it reaches an altitude where the surrounding air has a density & T° similar to its own Rules of Stability 1) When an air parcel is warmer & less dense than the surrounding air, the parcel will rise: UNSTABLE air or condition 2) When an air parcel is colder & denser than the surrounding air, it will tend to stay at the same level or sink: STABLE air 3) the Environmental Lapse Rate (ELR) is the T° profile of the atmosphere (air surrounding a parcel of air). The actual (T°) lapse rate in the lower atmosphere at any particular time under local weather conditions. Whether a particular parcel of air will rise (unstable) or not rise (stable) is afunction of the T° inside the parcel of air as compared to the T° outside the parcel of air, thus the ELR determines air stability. Types of Stability Stable: the condition of the air when ELR < DAR; Absolutely Stable Conditions or Absolute Stability * usually results in NO UPLIFT of air, but subsidence or sinking of air * clear skies, maybe a few stratus clouds * associated with High pressure cells * most severe example is a T° inversion: when the air T° is increasing with increasing altitude in the troposphere Unstable: the condition of the air when ELR > DAR Absolutely Unstable Conditions or Absolute Instability * usually results in UPLIFT of air * often leads to cloudy skies, cumulus clouds and precipitation * associated with Low pressure cells * often occurs during the warmest months & on clear days Conditionally Unstable: the condition of the air when the ELR is between the DAR & the SAR SAR < ELR < DAR * atmosphere will vary between Stable & Unstable * usually if air is saturated then upper portion of the atmosphere is Unstable * usually if air is unsaturated th
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