Generation of large‐scale gravity waves and neutral winds in the thermosphere from the dissipation of convectively generated gravity waves

Abstract

We study the response of the thermosphere and ionosphere to the dissipation of gravity waves (GWs) excited by a deep convective plume on 1 October 2005 at 52.5°W, 15.0°S, and 2120 UT in Brazil. Those small‐ and medium‐scale GWs which reach the thermosphere dissipate at z ∼ 120–250 km in a direction opposite to the background wind ∼(1–2) density scale heights below. This localized momentum deposition creates horizontal thermospheric body forces that have large sizes and amplitudes and generates large‐scale secondary GWs and large‐scale traveling ionospheric disturbances (LSTIDs) that propagate globally away from the body force in all directions except that perpendicular to the force direction. For the convective plume at 2120 UT, the secondary GWs have horizontal wavelengths of λH ∼ 2100–2200 km, periods of τr ∼ 80 min, horizontal phase speeds of cH ∼ 480–510 m/s, density perturbations as large as ∣ρ′/∣ ∼ 3.6–5% at z = 400 km, relative [O] perturbations as large as ∼2–2.5% at z = 300 km, and total electron content perturbations as large as ∼8%. This transfer of momentum from local, relatively slow, small scales at the tropopause to global, fast, large scales in the thermosphere is independent of geomagnetic conditions. The various characteristics of these large‐scale waves may explain observations of LSTIDs at magnetically quiet times. We also find that this body force creates a localized “mean” horizontal wind in the direction of the body force. For the plume at 2120 UT, the wind is southward with an estimated maximum of vmax ∼ −400 m s−1 that is dissipated after ∼4 h. We also find that the induced body force direction varies throughout the day, depending on the winds in the lower thermosphere.

Simulation of non-hydrostatic gravity wave propagation in the upper atmosphere

“…The thermospheric body force created from the gravity wave dissipation has been calculated using the formula from Vadas and Liu (2009). Figure 3b than 1 m s −2 , and the vertical depth is ∼ 80 km, which are consistent with the results from the ray trace model (Vadas and Liu, 2009). The boundary conditions may strongly influence the variables close to the boundaries and cause something unrealistic.…”

“…The momentum flux decreases dramatically above 150 km and becomes almost negligible at 200 km and above. As discussed in Vadas and Liu (2009), the divergence of momentum flux is created by the dissipation of the smalland medium-scale gravity waves, which accelerates the background neutral wind. The thermospheric body force created from the gravity wave dissipation has been calculated using the formula from Vadas and Liu (2009).…”

“…As discussed in Vadas and Liu (2009), the divergence of momentum flux is created by the dissipation of the smalland medium-scale gravity waves, which accelerates the background neutral wind. The thermospheric body force created from the gravity wave dissipation has been calculated using the formula from Vadas and Liu (2009). Figure 3b than 1 m s −2 , and the vertical depth is ∼ 80 km, which are consistent with the results from the ray trace model (Vadas and Liu, 2009).…”

Determination of gravity wave parameters in the airglow combining photometer and imager data

“…(6). With the estimated intrinsic frequency, the horizontal wavelength was estimated using the dispersion relation of gravity waves (Vadas and Liu, 2009) and compared to the horizontal wavelength obtained from the keogram analysis of the simultaneously observed OH images. Both the analytical and numerical results of the horizontal wavelength agree reasonably, hence suggesting that the same wave was observed by the photometer and the all-sky imager.…”

“…Using the dispersion relation of gravity waves, the horizontal and vertical wavelengths are estimated for the observed short period oscillations (Vadas and Liu, 2009). The discussion will be focused on the similar periodicity observed within the three emission layers; the amplitude growth and the propagation direction.…”