Thermospheric mass density: A review

Emmert, J. T.

doi:10.1016/j.asr.2015.05.038

Cited by 206 publications

(235 citation statements)

References 364 publications

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“…These results illustrate that the thermospheric annual asymmetry should be associated with the varying Sun-Earth distance. Actually, previous studies suggested that the difference of solar radiation associated with the difference of Sun-Earth distance between June and December would contribute to the annual asymmetry (Qian et al, 2012;Lei et al, 2013Lei et al, , 2016Emmert, 2015;Calabia et al, 2016). Moreover, Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Wang et al (2014) investigated the seasonal variations of globally averaged thermospheric mass density at 400 km during 1996-2006 using an artificial neural network (ANN), and concluded that there exist strong linear relations between the annual/semiannual amplitudes and the solar activity. Emmert (2015) reviewed the studies of the thermosphere between 2000 and 2014, summarized several possible mechanisms to explain the seasonal variations, and demonstrated that further investigations are required to understand the seasonal variations of the thermosphere. Recently, Calabia et al (2016) investigated the thermospheric mass density variations from GRACE data for the period 2003-2016 by using the principal component analysis (PCA) method, and discussed the annual variation for different local solar times (LSTs) and solar activities.…”

Section: Introductionmentioning

confidence: 99%

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Seasonal variations of thermospheric mass density at dawn/dusk from GOCE observations

et al. 2018

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Abstract. Thermospheric mass densities from the GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite for Sun-synchronous orbits between 83.5 • S and 83.5 • N, normalized to 270 km during 2009-2013, have been used to develop an empirical mass density model at dawn/dusk local solar time (LST) sectors based on the empirical orthogonal function (EOF) method. The main results of this study are that (1) the dawn densities peak in the polar regions, but the dusk densities maximize in the equatorial regions; (2) the relative seasonal variations to the annual mean have similar patterns across all latitudes regardless of solar activity conditions; (3) the seasonal density variations show obvious hemispheric asymmetry, with large amplitudes in the Southern Hemisphere; (4) both amplitude and phase of the seasonal variations have strong latitudinal and solar activity dependences, with high amplitude for the annual variation at higher latitudes and semiannual variation at lower latitudes; (5) the annual asymmetry and effect of the Sun-Earth distance vary with latitude and solar activity.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Seasonal variations of thermospheric mass density at dawn/dusk from GOCE observations

et al. 2018

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“…Many authors have evaluated the efficacy of these proxies for thermospheric modelling, see the review by Emmert (2015b). While the EUV flux from SEM and the MgII index perform slightly better at time scales of a few months and below, F10.7 is still preferred by most for its good overall results and for its long-term stability.…”

Section: Comparison With Solar Proxiesmentioning

confidence: 99%

“…The relationship between average solar forcing and average density is nonlinear but monotonic (Emmert 2015b), which allows us again to rely on the convenient framework of the cross-coherence. The true picture, however, is blurred by the contribution of geomagnetic activity, which also strongly affects the density, but does so more intermittently and mostly independently of the UV flux.…”

Section: Comparison With the Thermospheric Densitymentioning

confidence: 99%

“…Particular attention will be given here to satellite drag modelling for satellite operators. Satellite drag is proportional to the thermospheric neutral density, whose variations are mainly driven by the solar UV flux and by geomagnetic activity (Emmert 2015b). Although F10.7 is the most commonly used indicator of thermospheric density variations on time scales of several months and beyond, the reasons leading to the better efficacy of F10.7 have remained elusive.…”

Section: Introductionmentioning

confidence: 99%

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The 30 cm radio flux as a solar proxy for thermosphere density modelling

Wit

Bruinsma²

2017

J. Space Weather Space Clim.

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The 10.7 cm radio flux (F10.7) is widely used as a proxy for solar UV forcing of the upper atmosphere. However, radio emissions at other centimetric wavelengths have been routinely monitored since the 1950 s, thereby offering prospects for building proxies that may be better tailored to space weather needs. Here we advocate the 30 cm flux (F30) as a proxy that is more sensitive than F10.7 to longer wavelengths in the UV and show that it improves the response of the thermospheric density to solar forcing, as modelled with DTM (Drag Temperature Model). In particular, the model bias drops on average by 0-20% when replacing F10.7 by F30; it is also more stable (the standard deviation of the bias is 15-40% smaller) and the density variation at the the solar rotation period is reproduced with a 35-50% smaller error. We compare F30 to other solar proxies and discuss its assets and limitations.

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Traveling planetary‐scale waves in the lower thermosphere: Effects on neutral density and composition during solar minimum conditions

2016

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The effects of breaking of traveling, planetary scale Rossby waves (TPWs) in the lower thermosphere are investigated with respect to the mixing of neutral constituents. We use numerical simulations of the Whole Atmosphere Community Climate Model, eXtended version, whose meteorology below 92 km is constrained by atmospheric specifications obtained from operational weather forecast/data assimilation system. The Fourier spectra show that the amplitude of TPWs with periods between 3 and 10 days are statistically significant in some years; the amplitude and phase of the band‐pass filtered behavior is consistent with the behavior of the 5 day wave. A wavelet analysis using the S‐transform shows that large variations with periods between 3 and 10 days can occur in relatively narrow temporal windows (20–30 days) during boreal winter. The momentum flux entering the lower thermosphere during the times of TPW amplification is shown to be large, and the amplifications of the TPWs in the thermosphere are not always associated with stratospheric sudden warming. The subtropical zonal accelerations are consistent with Rossby wave encountering a surf zone at low latitudes, resulting in wave breaking. The zonal acceleration is shown to be associated with a meridional diffusion, which is largest in the lower thermosphere where the wave activity and the wave breaking are also large. The ultimate effect on neutral density and composition is a meridional, down‐gradient mixing; although this horizontal diffusion is largest below 110 km, the effects on the composition are amplified with increasing altitude, due to the diffusive separation of the thermosphere.

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Thermospheric mass density: A review

Cited by 206 publications

References 364 publications

Seasonal variations of thermospheric mass density at dawn/dusk from GOCE observations

Seasonal variations of thermospheric mass density at dawn/dusk from GOCE observations

The 30 cm radio flux as a solar proxy for thermosphere density modelling

Traveling planetary‐scale waves in the lower thermosphere: Effects on neutral density and composition during solar minimum conditions

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