Medium‐scale gravity wave activity in the thermosphere inferred from GOCE data

Garcia, Raphaël; Bruinsma, Sean; Massarweh, Lotfi; Doornbos, Eelco

doi:10.1002/2016ja022797

Cited by 25 publications

(25 citation statements)

References 37 publications

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“…Here we discuss why the TEC variation and the GW activity are weaker in summer (SH) than that in winter (NH). The model study by Miyoshi et al () and the observational study by Forbes et al () and Garcia et al () demonstrated that the GW activity at middle and high latitudes in the thermosphere is stronger in winter than in summer. From these results, there are two plausible candidates for the seasonal difference in the GW activity.…”

Section: Discussionmentioning

confidence: 96%

Numerical Study of Traveling Ionospheric Disturbances Generated by an Upward Propagating Gravity Wave

et al. 2018

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Using a global atmosphere‐ionosphere coupled model, the characteristics and excitation source of traveling ionospheric disturbances (TIDs) during geomagnetically quiet periods are studied. This is the first paper concerning the simulation of TIDs generated by upward propagating gravity waves (GWs) that are spontaneously generated in the model. The dominant horizontal wavelengths of the simulated TIDs range from 700 to 1,500 km. The dominant periods and horizontal phase velocities of TIDs are 45–90 min and 250–300 m s−1, respectively. These features are the same as those of GWs in the 250–300 km height region. The phase of the electron density variations due to TIDs descends with increasing time, which is characteristic of the upward propagation of GWs. These electron density variations that are caused due to TIDs are explained by the transport processes of a neutral wind along a geomagnetic field line. These results indicate that the electron density variations respond locally to the passage of neutral wind fluctuations associated with upward propagating GWs. The GWs that excite TIDs are secondary GWs, which are generated in the mesosphere and lower thermosphere via the dissipation/breaking of tropospheric GWs. The magnitudes of TIDs at middle latitudes are larger in winter than in summer. The mechanisms of seasonal and day‐to‐day variations in TIDs that are caused due to GWs are discussed in this study.

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Section: Discussionmentioning

confidence: 96%

Numerical Study of Traveling Ionospheric Disturbances Generated by an Upward Propagating Gravity Wave

et al. 2018

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“…In addition to the dynamical forcing, GWs contribute to heating and cooling of the thermosphere above the turbopause (∼105 km) up to F 2 layer altitudes, reaching peak values of ∼170 K d −1 [ Yiğit and Medvedev , ]. Since the thermosphere is strongly susceptible to variations of solar activity, GW propagation and effects exhibit appreciable changes, as was predicted by general circulation models (GCMs) [ Yiğit and Medvedev , ] and recently demonstrated by satellite observations [ Park et al , ; Garcia et al , ]. Transient events in the lower and middle atmosphere, such as sudden stratospheric warmings, also alter propagation of GWs causing an increase of the GW activity in the upper thermosphere by more than a factor of 3 [ Yiğit and Medvedev , , ] and generating changes in the thermospheric circulation up to ±50% [ Yiğit et al , ].…”

Section: Introductionmentioning

confidence: 95%

Influence of parameterized small‐scale gravity waves on the migrating diurnal tide in Earth's thermosphere

Yiğit

Medvedev

2017

JGR Space Physics

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Effects of subgrid‐scale gravity waves (GWs) on the diurnal migrating tides are investigated from the mesosphere to the upper thermosphere for September equinox conditions, using a general circulation model coupled with the extended spectral nonlinear GW parameterization of Yiğit et al. (). Simulations with GW effects cut off above the turbopause and included in the entire thermosphere have been conducted. GWs appreciably impact the mean circulation and cool the thermosphere down by up to 12–18%. GWs significantly affect the winds modulated by the diurnal migrating tide, in particular, in the low‐latitude mesosphere and lower thermosphere and in the high‐latitude thermosphere. These effects depend on the mutual correlation of the diurnal phases of the GW forcing and tides: GWs can either enhance or reduce the tidal amplitude. In the low‐latitude MLT, the correlation between the direction of the deposited GW momentum and the tidal phase is positive due to propagation of a broad spectrum of GW harmonics through the alternating winds. In the Northern Hemisphere high‐latitude thermosphere, GWs act against the tide due to an anticorrelation of tidal wind and GW momentum, while in the Southern high‐latitudes they weakly enhance the tidal amplitude via a combination of a partial correlation of phases and GW‐induced changes of the circulation. The variable nature of GW effects on the thermal tide can be captured in GCMs provided that a GW parameterization (1) considers a broad spectrum of harmonics, (2) properly describes their propagation, and (3) correctly accounts for the physics of wave breaking/saturation.

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“…For the T/I region thus dedicated experimental evidence is needed to compare GW distributions in the middle atmosphere and in the T/I. Until recently, several observational studies of GWs in the T/I have been performed (e.g., Bruinsma and Forbes, 2008;Park et al, 2014;Forbes et al, 2016;Garcia et al, 2016). In particular, Park et al (2014) derived global GW distribution using CHAMP mass density and performed a first comparison with a global distribution of GW temperature variances in the stratosphere.…”

Section: Q T Trinh Et Al: Satellite Observations Of Vertical Couplmentioning

confidence: 99%

Satellite observations of middle atmosphere–thermosphere vertical coupling by gravity waves

et al. 2018

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Abstract. Atmospheric gravity waves (GWs) are essential for the dynamics of the middle atmosphere. Recent studies have shown that these waves are also important for the thermosphere/ionosphere (T/I) system. Via vertical coupling, GWs can significantly influence the mean state of the T/I system. However, the penetration of GWs into the T/I system is not fully understood in modeling as well as observations. In the current study, we analyze the correlation between GW momentum fluxes observed in the middle atmosphere (30-90 km) and GW-induced perturbations in the T/I. In the middle atmosphere, GW momentum fluxes are derived from temperature observations of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument. In the T/I, GW-induced perturbations are derived from neutral density measured by instruments on the Gravity field and Ocean Circulation Explorer (GOCE) and CHAllenging Minisatellite Payload (CHAMP) satellites. We find generally positive correlations between horizontal distributions at low altitudes (i.e., below 90 km) and horizontal distributions of GW-induced density fluctuations in the T/I (at 200 km and above). Two coupling mechanisms are likely responsible for these positive correlations: (1) fast GWs generated in the troposphere and lower stratosphere can propagate directly to the T/I and (2) primary GWs with their origins in the lower atmosphere dissipate while propagating upwards and generate secondary GWs, which then penetrate up to the T/I and maintain the spatial patterns of GW distributions in the lower atmosphere. The mountain-wave related hotspot over the Andes and Antarctic Peninsula is found clearly in observations of all instruments used in our analysis. Latitude-longitude variations in the summer midlatitudes are also found in observations of all instruments. These variations and strong positive correlations in the summer midlatitudes suggest that GWs with origins related to convection also propagate up to the T/I. Different processes which likely influence the vertical coupling are GW dissipation, possible generation of secondary GWs, and horizontal propagation of GWs. Limitations of the observations as well as of our research approach are discussed.

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Medium‐scale gravity wave activity in the thermosphere inferred from GOCE data

Cited by 25 publications

References 37 publications

Numerical Study of Traveling Ionospheric Disturbances Generated by an Upward Propagating Gravity Wave

Numerical Study of Traveling Ionospheric Disturbances Generated by an Upward Propagating Gravity Wave

Influence of parameterized small‐scale gravity waves on the migrating diurnal tide in Earth's thermosphere

Satellite observations of middle atmosphere–thermosphere vertical coupling by gravity waves

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