Horizontal and vertical propagation and dissipation of gravity waves in the thermosphere from lower atmospheric and thermospheric sources

Abstract

[1] The dissipation of high-frequency gravity waves (GWs) in the thermosphere is primarily due to kinematic viscosity and thermal diffusivity. Recently, an anelastic GW dispersion relation was derived which includes the damping effects of kinematic viscosity and thermal diffusivity in the thermosphere and which is valid before and during dissipation. Using a ray trace model which incorporates this new dispersion relation, we explore many GW properties that result from this dispersion relation for a wide range of thermospheric temperatures. We calculate the dissipation altitudes, horizontal distances traveled, times taken, and maximum vertical wavelengths prior to dissipation in the thermosphere for a wide range of upward-propagating GWs that originate in the lower atmosphere and at several altitudes in the thermosphere. We show that the vertical wavelengths of dissipating GWs, l z (z diss ), increases exponentially with altitude, although with a smaller slope for z > 200 km. We also show how the horizontal wavelength, l H , and wave period spectra change with altitude for dissipating GWs. We find that a new dissipation condition can predict our results for l z (z diss ) very well up to altitudes of $500 km. We also find that a GW spectrum excited from convection shifts to increasingly larger l z and l H with altitude in the thermosphere that are not characteristic of the initial convective scales. Additionally, a lower thermospheric shear shifts this spectrum to even larger l z , consistent with observations. Finally, we show that our results agree well with observations.

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

“…Here, the indices i, j =1, 2, 3 indicate the components of the vector quantities x, V , k, and c g , and repeated indices imply a summation. The subscript "r" here denotes the real component of the frequency (Vadas andFritts, 2005, hereafter VF2005), not the relative frequency; the relative frequency (i.e., the frequency in the intrinsic frame of reference moving with the fluid) is denoted by the subscript "I ", where "I " stands for "intrinsic" (see Table 1 for definitions). We do not allow the ground-based frequency of a GW to vary in time in our model.…”

“…16 were also used to infer GW amplitudes at higher altitudes in the TI for this SpreadFEx campaign Fritts et al, 2008b). GWs with λ z > ∼ 100 km are those we expect to penetrate to the greatest altitudes, based on the viscous dispersion relation developed by VF2005 and the ray tracing studies by Vadas (2007) and Fritts and Vadas (2008). Fritts et al (2008b) employed the results of this study to infer maximum horizontal velocities near z∼80 km of ∼1−2 ms −1 for GWs with λ z ∼150 km and λ H ∼200−400 km arising from a single convective plume, with amplitudes ∼2 times larger in response to a small convective cluster.…”

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

“…Note that θ=90 o if the wave is propagating eastward. Although GWs with horizontal wavelengths greater than 100 km can penetrate above the turbopause, they must typically have intrinsic phase speeds greater than c I H >100 m/s to propagate to the bottomside of the F-region (Vadas, 2007). Using Eq.…”

“…Since kinematic viscosity and thermal diffusivity increase nearly exponentially with altitude, eventually every GW dissipates, although at differing altitudes depending on its characteristics (Vadas and Fritts, 2006;Vadas, 2007). As a GW begins to dissipate, its momentum flux decreases less rapidly with altitude.…”

Response of the equatorial ionosphere to the total solar eclipse of 22 July 2009 and annular eclipse of 15 January 2010 as observed from a network of stations situated in the Indian longitude sector

“…Singh et al (1989) from a detailed analysis of the data reported that TIDs were detected at distances more than 500 km away from the umbra region. Theoretical estimates show that the period and amplitude of gravity waves is dependent on the bearing of the source with respect to the observing point in the ionosphere (Chimonas, 1970;Vadas, 2007). First experimental signatures of the existence of gravity waves were observed with periodicity of 30-33 min in ionosphere.…”