1. Vertical Air Motion

2. Air Parcels Ascend/Descend Adiabatically Expansional CoolingCompressional heating

3. Air parcel’s temperature changes according to the lapse rate Dry adiabatic lapse rate if it is unsaturated – 9.8  C/km (5.5  F/km) Wet adiabatic lapse rate if it is saturated – 6.0  C/km (3.3  F/km) Unsaturated air can become saturated as it cools because relative humidity increases

4. Atmospheric Stability Actual temperature profile (measured by sondings) of atmosphere may be different from these lapse rates Due to: – Radiational heating and cooling – Air mass advection – Large scale ascent or descent or air Difference between actual temperature profile and lapse rates determines stability

5. Stable Air Dry adiabat

6. Unstable Air Dry adiabat

7. Stability Regimes

8. Causes of Lifting Ascending branch of convection current Warm or cold fronts Topographical feature (orographic) Surface wind convergence