phase speeds of cH � 480–510 m/s, density perturbations as large as jr 0 /r j� 3.6–5% at z = 400 km, relative [O] perturbations as large as � 2–2.5% atz = 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 � 4h . We also find that the induced body force direction varies throughout the day, depending on the winds in the lower thermosphere.

https://www.cora.nwra.com/~vasha/VadasLiu2009.pdf

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

The Earth's thermosphere and ionosphere (TI) are characterized by perpetual variability as integral parts of the atmosphere system, with intermittent disturbances from solar and geomagnetic forcing. This review examines how the TI variability is affected by processes originating from the lower atmosphere and implications for quantifying and forecasting the TI. This aspect of the TI variability has been increasingly appreciated in recent years from both observational and numerical studies, especially during the last extended solar minimum. This review focuses on the role of atmospheric waves, including tides, planetary waves, gravity waves, and acoustic waves, which become increasingly significant as they propagate from their source region to the upper atmosphere. Recent studies have led to better understanding of how these waves directly or indirectly affect TI wind, temperature, and compositional structures; the circulation pattern; neutral and ion species transport; and ionospheric wind dynamo. The variability of these waves on daily to interannual scales has been found to significantly impact the TI variability. Several outstanding questions and challenges have been highlighted: (i) large, seemingly stochastic, day-to-day variability of tides in the TI; (ii) control of model error in the TI region by the lower atmosphere; and (iii) the increasing importance of processes with shorter spatial and temporal scales at higher altitudes. Addressing these challenges requires model capabilities to assimilate observations of both lower and upper atmosphere and higher model resolution to capture complex interactions among processes over a broad range of scales and extended altitudes.

/pdf/variability-and-predictability-of-the-space-environment-as-3lx2m563ju.pdf

Variability and predictability of the space environment as related to lower atmosphere forcing

[1] We model the gravity waves (GWs) excited by Tropical Storm (TS) Noel at 0432 UT on 30 October 2007. Using forward ray tracing, we calculate the body forces which result from the saturation and dissipation of these GWs. We then analyze the 59 traveling ionospheric disturbances (TIDs) observed by the TIDDBIT ionospheric sounder at 0400-1000 UT near Wallops Island. These TIDs were located at the bottomside of the F layer at z = 230–290 km, had periods of τr = 15 to 90 min, horizontal wavelengths of λH = 100 to 3000 km, and horizontal phase speeds of cH = 140 to 650 m/s. 33 (∼60%) of the TIDs were propagating northwest(NW) and north(N)ward, from the direction of TS Noel 1700–2000 km away. We show that these TIDs were likely GWs. 40% of these GWs had phase speeds larger than 280m/s. This precluded a tropospheric source and suggested mesospheric and thermospheric sources instead. Using reverse ray tracing, we compare the GW locations with the regions of convective overshoot, mesospheric body forces, and thermospheric body forces. We identify 27 of the northwest/northward propagating GWs as likely being secondary GWs excited by thermospheric body forces. Three may have originated from mesospheric body forces, although this is much less likely. None are identified as primary GWs excited directly by TS Noel. 11 of these GWs with cH < 205 m/s likely reflected near the tropopause prior to detection. This secondary GW spectrum peaks at λH ∼ 100–300 km and cH ∼ 100–300 m/s. To our knowledge, this is the first identification and quantification of secondary GWs from thermospheric body forces.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009JA015053

Sources of the traveling ionospheric disturbances observed by the ionospheric TIDDBIT sounder near Wallops Island on 30 October 2007

/pdf/thermospheric-responses-to-gravity-waves-arising-from-2a3u2xf5sj.pdf

Thermospheric responses to gravity waves arising from mesoscale convective complexes

A time-dependent, nonlinear, fully compressible, axisymmetric, ƒ-plane, numerical model is used to simulate the generation of small-scale gravity waves in the upper mesosphere and lower thermosphere by intense deep convection in the troposphere. The simulations show that major convective storms in the tropics excite a broad spectrum of upper mesosphere-lower thermosphere gravity waves above the storm centers. The wave field includes a component that is guided in a thermal duct in the lower thermosphere and propagates horizontally outward from above the storm. Storms excite oscillations over the source which are initially confined to a stratospheric duct but leak into the thermospheric duct over time generating a long train of small-scale-ducted waves. This ringing phenomenon persists for several hours after the storm has ended. The ducted disturbances may propagate large distances from the source and explain observations of a strong summertime anisotropy favoring southward propagation of small-scale waves observed in the airglow over Adelaide more than 2000 km to the south of the storm events.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JD000131

Small‐scale gravity waves in the upper mesosphere and lower thermosphere generated by deep tropical convection

[1] A time-dependent, nonlinear, fully compressible, axisymmetric, f-plane, numerical model is used to simulate the propagation of acoustic waves in the mesosphere and thermosphere by intense deep convection in the troposphere. The simulations show that major convective storms in the tropics launch acoustic waves into the mesosphere-thermosphere directly above the storm centers. The principal feature of the overhead acoustic wave field in the period interval of ∼3 to 5 min is a trapped oscillation below about 80 km altitude with a period of ∼5 min and a nearly vertically propagating wave with about a 3-min period above this height. Acoustic oscillations in the troposphere-mesosphere duct have a standing wave character directly over the storm; the oscillations that propagate off vertical mainly reflect off the top and bottom of the duct resulting in a horizontally propagating acoustic field within the duct. The acoustic oscillations that are mainly confined to the troposphere-mesosphere duct persist for about an hour after the storm has ended. The vertically propagating thermospheric acoustic oscillations are waves propagating upward from the thunderstorm source through the stratosphere-mesosphere. These predominantly 3-min waves are strongly driven for ∼30 min after the storm event and weaken with time thereafter. The vertically propagating thermospheric acoustic waves may be the source of the F-region 3-min oscillations. Intense acoustic disturbances directly above thunderstorms may be responsible for localized heating of the thermosphere.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2003JA010065

Acoustic waves in the upper mesosphere and lower thermosphere generated by deep tropical convection

Wave Disturbances from the Comet SL-9 Impacts into Jupiter's Atmosphere

[1] We have used a model of thermospheric gyres with simplified geometry (azimuthally symmetric cylindrical coordinate) to study dynamical adjustment for high-latitude gyres spun-up into rapid motion by ion drag. In our simulations, winds are spun-up for an hour subject only to circumgyre ion drag forcing from strong radial electric fields with peak values of ±75 mV m−1 centered at a radial distance of 1500 km. The winds in the core of the jets approach 500 m s−1. The major finding is that the imbalance between the inertial forces (centrifugal and Coriolis) and the pressure gradient force during the spin-up of high-latitude gyres drives a strong radial circulation, and this circulation is a significant contributor to the radial circulation forced by all sources. This agradient circulation attempts to establish a gradient-wind balance between the inertial and pressure gradient forces. A feature of general circulation model simulations of the high-latitude lower thermosphere is that, subtracting the warming of the whole polar cap due to Joule heating, the counterrotating gyres driven into motion by ion convection have opposite thermal polarities, with the cyclonic gyre developing a cold core (low density) and the anticyclonic gyre a warm core (high density). We suggest that this is accomplished by the radial circulation forced by the aforementioned imbalance between the inertial and pressure gradient forces. While diabatic heating over the polar cap acts to elevate the temperature (raise the density) over the polar cap as a whole, the changes induced by the dynamically induced circulation account for the fact that cyclonic gyres in the lower thermosphere are relatively colder and denser and the anticyclonic gyres are relatively warmer and less dense. We also examine the radial circulation forced by the initial stages of spin-down and show that the spin-down circulation is significant.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2007JA012682

D. G. Brinkman

Papers

Small‐scale gravity waves in the upper mesosphere and lower thermosphere generated by deep tropical convection

Acoustic waves in the upper mesosphere and lower thermosphere generated by deep tropical convection

Wave Disturbances from the Comet SL-9 Impacts into Jupiter's Atmosphere

Spin‐up circulation of high‐latitude ion drag‐driven gyres

Spin-down circulation of high-latitude ion drag-driven gyres: GYRE SPIN-DOWN