- no heat is added or removed from air
- rising air >> lower pressure >> expands >> temperature decreases
- sinking air >> higher pressure >> compresses >> temperature increases
Lapse Rates
- Dry Adiabatic Lapse Rate (DALR): 3 C / 1000 ft
- Saturated Adiabatic Lapse Rate (SALR): 1.5 C / 1000 ft
- Average: 2 C / 1000 ft
- Environmental Lapse Rate (ELR): indicates the temperature of the surrounding air; comparison to lapse rate of air parcel determines if it is stable or unstable
- shallow lapse rate compared to SALR: absolute stability
- lapse rate between DALR and SALR: conditional instability
- steeper lapse rate than DALR: absolute instability
Characteristics of Stable Air
- sustained low visibility (i.e. haze layers, drizzle, fog)
- continuous precipitation
- strato-form clouds (layers)
- steady winds
Characteristics of Unstable Air
- good visibility
- showery precipitation
- cumulo-form clouds (vertical development)
- gusty winds
DO YOU KNOW... why rising saturated air cool less rapidly than rising unsaturated air?
- heat is released during the condensation of water vapour
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