1. Gravity Waves Phil Evans Paul Domm

2. Gravity Waves  Buoyancy oscillations –Should be called buoyancy waves  Only exist in stably stratified atmosphere  Dynamical Process http://sprg.ssl.berkeley.edu/atmos/gj_science.html

3. Static Stability Overview  Stably stratified atmosphere –θ increases with height –A parcel adiabatically displaced from its equilibrium height downward will become positively buoyant. –Displaced upward, parcel will become negatively buoyant.  dθ/dz > 0Statically stable  dθ/dz = 0Statically neutral  dθ/dz < 0Statically Unstable

4. Buoyancy Oscillations  Adiabatic oscillations of a fluid parcel about its equilibrium level.  Period of oscillation –τ = 2π/N –N – buoyancy frequency  Average values of N = 1.2 x 10 -1 s -1  Period buoyancy oscillation is about 8 min

5. Gravity Wave Formation  Stably Stratified Atmosphere  Topographic flow e.g. Flow Over Mountains

6. Formation Cont’d  Downdrafts hitting the ground  Updrafts penetrating the tropopause

7. Transports & Balance  GW can provide moisture convergence which in turn drives the wave  Geostrophic adjustment processes  Mass adjustment (carries momentum)

8. Propagation  Achieve pressure equilibrium  PGF  Crests and troughs will travel outward in all directions –Example: throwing a stone into a pond.

9. Atmospheric preconditioning  Stably stratified  Frontal inversion  Strong wind shear aloft http://www.mcwar.org/articles/cafe/gw/gravwaves.html

10. Convection  Amplitude of wave can force parcel above LCL, LFC  Can force/hinder condensation and convection  Clear air turbulence (CAT) –If air is too dry or upward forcing is not strong enough.

11. Physical characteristics  Amplitude: 1-15 mb  Wavelength: 50 – 500 km  Period: 1 – 4 hours  Range of wave speeds: 12 – 500 km/hr

12. Detecting g-waves  Microbarographs –Can detect pressure fluctuations with 0.001mb precision. –Useful when no visible signs are present.  Visible Satellite –Only useful when g-wave forces parcel above LCL or LFC (produces condensation)

13. Considering g-waves in forecasting  G-waves can trigger convective events  G-waves can interact with existing dry lines  Example –Jarrell, Texas tornado outbreak

14. Case Study  Jarrel Supercell

15. http://www.vvm.com/%7Ecurtis/Jarrell/Jarrell.htm

16. http://www.mcwar.org/articles/cafe/gw/gravwaves.html

17. earthobservatory.nasa.gov/ Newsroom/NewImages/

18. http://www.gesource.ac.uk/worldguide/html/image_84.html