Atmospheric stability refers to the tendency of a parcel of air to either remain
ID: 116877 • Letter: A
Question
Atmospheric stability refers to the tendency of a parcel of air to either remain in place or change position by ascending (rising) or descending (sinking): 1. An air parcel is stable if it resists displacement upward. 2. An air parcel is unstable when it continues to rise until it reaches an altitude where the surrounding air has a temperature similar to its own Stability can be determined by comparing the temperature of an air parcel (which may be cooling at either the dry adiabatic rate, DAR, or the moist adiabatic rate, MAR) Note that a rising air parcel can cool at two rates (DAR-rate of cooling before saturation, and MAR-rate of cooling after saturation) depending on whether it has reached dew point temperature or not. On the other hand, the ELR-which is the rate at which the surrounding air through which a parcel of air is rising changes-is only one rate. If the ELR is greater than both the DAR and the MAR (i.e., ELR> 10 °C/1000 m), the rising air parcel will be warmer than the surrounding air, and wil continue to rise. If the ELR is less than both the DAR and the MAR (i.e., ELR :-6 / 1000 m), the rising parcel of air will be cooler than the surrounding air, and will resist further displacement. . In the circumstance that the ELR is between the MAR and DAR (MARExplanation / Answer
1. Stable when ELR = 5 degree/ km
2. Atmospheric temp at 2000m is (40-9*2)= 22 degree and at 4000m = (40- 9*4)=4degree
Parcel temp at 2000m is 20 degree and at 4000m is 8 degree
3. At all height, the air parcel will be stable since at each point it's temperature is less than lapse rate ( surrounding air) so air always tried to sink or move down to ground surface which is the sign of the Stable condition.
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