Gravity WavesPhil EvansPaul Domm

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

Static Stability OverviewStably stratified atmosphere increases with height A parcel adiabatically displaced from its equilibrium height downward will become positively buoyant.Displaced upward, parcel will become negatively buoyant.d/dz > 0Statically stabled/dz = 0Statically neutrald/dz < 0Statically Unstable

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

Gravity Wave FormationStably Stratified AtmosphereTopographic flow e.g. Flow Over Mountains

Formation ContdDowndrafts hitting the ground Updrafts penetrating the tropopause

Transports & BalanceGW can provide moisture convergence which in turn drives the waveGeostrophic adjustment processesMass adjustment (carries momentum)

Propagation Achieve pressure equilibrium PGFCrests and troughs will travel outward in all directionsExample: throwing a stone into a pond.

Atmospheric preconditioningStably stratified Frontal inversion Strong wind shear aloft

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

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

Physical characteristics Amplitude: 1-15 mbWavelength: 50 500 km Period: 1 4 hours Range of wave speeds: 12 500 km/hr

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)

Considering g-waves in forecasting G-waves can trigger convective events G-waves can interact with existing dry lines

Example Jarrell, Texas tornado outbreak

Case StudyJarrel Supercell

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

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

earthobservatory.nasa.gov/ Newsroom/NewImages/

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