Gravity Waves
CPI is developing gravity-wave models for basic and applied research, such as the simulation of long-wave / short-wave
interactions in the ocean shown to the left. The aims include understanding gravity-wave dynamics in
the middle atmosphere, interpreting satellite observations and numerical model simulations, forecasting mountain waves and
associated turbulence on Earth and Mars, and determining gravity-wave influences on infrasound propagation. Related models
for the ocean predict the internal gravity wavefield generated by a submarine and its wake. These models are based on a
computationally fast Fourier synthesis of ray solutions. They are run in combination with mesoscale circulation models for the
atmosphere, and submarine hydrodynamic codes for the ocean. The work is in collaboration with teams at the Naval Research
Laboratory (NRL) and at Science Applications International Corporation (SAIC). Some example projects are described below.
Ray Methods for Atmospheric Gravity Waves
The aim is to develop computationally fast ray formulations for atmospheric gravity waves that account for full three-dimensional geometrical spreading from localized sources and that can be practically corrected for caustics and focal regions in three dimensions. The devised method uses a combination of Fourier and ray methods, and involves a new treatment of trapped waves. Typically 50,000 rays are traced simultaneously, with a computation time of 5-10 minutes on a standard processor. Shown below is a comparison of satellite observations (upper panel) and model simulations (lower panel) of gravity waves over Jan Mayen Island.
Gravity waves over Jan Mayen Island on Jan 25, 2000, 1635-1643 UTD: a) AVHRR image, b) Fourier-ray image reconstruction with radiosonde profiles.
This project is sponsored by the National Science Foundation (NSF) and NRL.
Gravity Wave Scattering of Infrasound in the Atmosphere
Infrasound from sources at or near the Earth's surface can propagate high into the atmosphere, reaching the thermosphere above 100km altitude. The propagation paths are influenced by wind and temperature fields, including small-scale fluctuations induced by gravity waves. CPI has developed a new specification of the gravity wavefield for infrasound modeling. The resulting infrasound simulations give improved comparisons with measurements. Shown below is a sample infrasound simulation that includes the CPI specification of gravity waves.
Infrasound simulation from Ruffle Cyprus propogation analysis. The color bar shows the transmission loss in decibels. (Courtesy of Doug Drob, NRL.)
This project is sponsored by the Office of Naval Research (ONR) and is a collaboration between CPI and NRL.
Internal waves generated by a submarine
Submarines generate internal waves in two ways: by flow over the body of the submarine and by turbulent motions in the wake of the submarine. CPI is developing computationally fast models of internal-wave production for body and wake generated internal waves, which also follow internal-wave propagation through a realistic ocean, from the submarine to the sea surface.
Submarine generated internal waves in a thermocline. The colorbar shows a non-dimensional vertical velocity that corresponds to a peak value of a few cm/sec under realistic coastal-ocean conditions.
This project is sponsored by ONR and is a collaboration between CPI and SAIC.
Selected Publications
Broutman, D., S. D. Eckermann, and J. W. Rottman, 2009: Practical application of two turning point theory to mountain-wave transmission through a wind jet. J. Atmos. Sci. , 66, 481-494
Broutman, D., J. Ma, S. D. Eckermann, and J. Lindeman, 2006. Fourier-ray modeling of transient trapped lee waves. Mon. Wea. Rev. 134, 2849-2956.
Broutman, D., and J. W. Rottman, 2004: A simplified Fourier method for computing the internal wavefield generated by an oscillating source in a horizontally moving, depth-dependent background. Phys. Fluids, 16, 3682-3689.
Broutman, D., J.W. Rottman, and S. Eckermann, 2003: A simplified Fourier method for non-hydrostatic mountain waves. J. Atmos. Sci., 60, 2686-2696.
Broutman, D., C. Macaskill, M.E. McIntyre, and J. Rottman, 1997: On Doppler spreading models of internal waves. Geophys. Res. Lett., 224, 2813-2816.
Broutman, D., and R. Grimshaw, 1988: The energetics of the interaction of short small-amplitude internal waves with inertial waves. J. Fluid Mech., 196, 93-106.
Broutman, D., and W. R. Young, 1986: On the interaction of small-scale internal waves with near-inertial waves. J. Fluid Mech., 166, 341-358.
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