Reconstruction of the gravity wave field from convective plumes via ray tracing

Abstract

Abstract. We implement gravity wave (GW) phases into our convective plume and anelastic ray trace models. This allows us to successfully reconstruct the GW velocity, temperature, and density perturbation amplitudes and phases in the Mesosphere-Lower-Thermosphere (MLT) via ray tracing (in real space) those GWs that are excited from a deep convective plume. We find that the ray trace solutions agree very well with the exact, isothermal, zero-wind, Fourier-Laplace solutions in the Boussinesq limit. This comparison also allows us to determine the normalization factor which converts the GW spectral amplitudes to real-space amplitudes in the ray trace model. This normalization factor can then be used for ray tracing GWs through varying temperature and wind profiles. We show that by adding GW reflection off the Earth's surface, the resulting GW spectrum has more power at larger vertical and horizontal wavelengths. We determine the form of the momentum flux and velocity spectra which allows for easy calculation of GW amplitudes in the MLT and thermosphere. Finally, we find that the reconstructed (ray traced) solution for a deep, convective plume with a duration much shorter than the buoyancy period does not equal the Fourier-Laplace Boussinesq solution; this is likely due to errors in the Boussinesq dispersion relation for very high frequency GWs.

Simultaneous observations of equatorial F-region plasma depletions over Brazil during the Spread-F Experiment (SpreadFEx)

“…As it is difficult to determine the exact cause of this longitudinal difference, the data are consistent with a more localized origin for the seeding/growth of the plasma bubbles observed on this night, possibly associated with tropospheric convection (McClure et al, 1998;Vadas et al, 2009b). Associated studies presenting analyses of the data gathered during the SpreadFEx campaign suggest a correlation between tropospheric convective activity, gravity wave propagation into the lower ionosphere, and the generation of the plasma bubbles Takahashi et al, 2009;Vadas and Fritts, 2009;Vadas et al, 2009a, b).…”

“…A primary goal of this campaign was to investigate the properties of gravity waves at ionospheric heights and their potential role in seeding Rayleigh-Taylor instabilities, strong equatorial spread-F and plasma bubble development. Detailed studies of the convective sources that may have generated gravity waves able to propagate up to the ionosphere to seed plasma irregularities are given by Taylor et al (2009);Vadas and Fritts (2009);and Vadas et al (2009a, b). The impact of such gravity waves on the spread-F generation and evolution has also been investigated by and .…”

Convection: the likely source of the medium-scale gravity waves observed in the OH airglow layer near Brasilia, Brazil, during the SpreadFEx campaign

“…This factor equals 1 if all of the air within the envelope is upward-moving at the tropopause at t, and equals 0.5 if only 1/2 of the volume of air within the convective plume envelope is upward-moving at the tropopause at t. Here, we choose =0.75, as this gives good agreement with observations of concentric rings in the OH layer . Figure 18a shows the GW horizontal wind amplitudes at z=87 km if the winds are zero, using the spectral form determined by Vadas and Fritts (2009). These amplitudes are the maximum amplitudes that a GW can have at that altitude; they therefore provide an upper bound.…”

“…A full description of this dissipative ray trace model is given in Vadas and Fritts (2009). Consider a GW observed in the OH airglow layer with ground-based frequency ω r and wavenumber vector k=(k, l, m).…”

Mesospheric gravity wave characteristics and identification of their sources around spring equinox over Indian low latitudes

“…Of these, one of the events (17 March 2012) was discussed earlier to be caused by the wind shears (Pramitha et al, 2015). Other sources may be mesospheric-thermospheric body forcing or secondary waves (e.g., Fritts and Alexander, 2003;Vadas and Fritts, 2009;Vadas and Liu, 2011), where convection may remain as the prime source (∼ 66 %) of gravity waves.…”