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## Section 5.4 Gravity Waves

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**Gravity Waves**• Gravity acts as the restoring force on parcels displaced from hydrostatic equilibrium. • Pure gravity exists when the fluid is stably stratified. • Two types of gravity waves: • external gravity waves: static stability is due to the density discontinuity at the interface between two fluids • internal gravity waves: static stability arises from the stable stratification, buoyancy force acts as the restoring force**External Gravity Waves: Density Discontinuity**Air: Small Density h’ h’ Water: Large Density**Transverse Waves:**Waves are oscillations (in field variables, such as velocity or pressure) that propagate in space.**Gravity Waves**• Gravity acts as the restoring force on parcels displaced from hydrostatic equilibrium. • Pure gravity exists when the fluid is stably stratified. • Two types of gravity waves: • external gravity waves: static stability is due to the density discontinuity at the interface between two fluids • internal gravity waves: static stability arises from the stable stratification, buoyancy force acts as the restoring force**Internal Gravity Waves: Stable Stratification**Colder than the env.; Downward acc. Warmer than the env.; Upward acc.**Vertical Velocity (w) Field During a Model Initial**Adjustment Periods**Internal Gravity Waves Generated by Rapidly Rising Deep**Convection