Gravity Waves Phil Evans Paul Domm. Gravity Waves Buoyancy oscillations –Should be called...

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Transcript of Gravity Waves Phil Evans Paul Domm. Gravity Waves Buoyancy oscillations –Should be called...

  • Gravity WavesPhil EvansPaul Domm

  • Gravity Waves Buoyancy oscillations Should be called buoyancy waves Only exist in stably stratified atmosphere Dynamical Process

  • 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

  • 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



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