Auroral heating and the composition of the neutral atmosphere

Hays, P. B.; Jones, Richard; Rees, M. H.

doi:10.1016/0032-0633(73)90070-6

Cited by 204 publications

(111 citation statements)

References 17 publications

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“…However, a quantitative understanding of whether the Joule and particle heating energies are sufficiently abundant to cause such large vertical motions in the lower thermosphere remains as a fundamental question. Hays et al (1973) presented a simple way of estimating the vertical speed caused by "vertical" thermal expansion, in which all deposited energies are dissipated for thermospheric expansions in the vertical direction. The calculation under the first law of thermodynamics provided a vertical speed of 1-10 cm s −1 at the 120-km level.…”

Section: A Physical Process For Generating Wind Variationsmentioning

confidence: 99%

Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

et al. 2008

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Abstract. Lower-thermospheric winds at high latitudes during moderately-disturbed geomagnetic conditions were studied using data obtained with the European Incoherent Scatter (EISCAT) Kiruna-Sodankylä-Tromsø (KST) ultrahigh frequency (UHF) radar system on 9-10 September 2004. The antenna-beam configuration was newly designed to minimize the estimated measurement error of the vertical neutralwind speed in the lower thermosphere. This method was also available to estimate the meridional and zonal components. The vertical neutral-wind speed at 109 km, 114 km, and 120 km heights showed large upward motions in excess of 30 m s −1 in association with an ionospheric heating event. Large downward speeds in excess of −30 m s −1 were also observed before and after the heating event. The meridional neutral-wind speed suddenly changed its direction from equatorward to poleward when the heating event began, and then returned equatorward coinciding with a decrease in the heating event. The magnetometer data from northern Scandinavia suggested that the center of the heated region was located about 80 km equatorward of Tromsø. The pressure gradient caused the lower-thermospheric wind to accelerate obliquely upward over Tromsø in the poleward direction. Acceleration of the neutral wind flowing on a vertically tilted isobar produced vertical wind speeds larger by more than two orders of magnitude than previously predicted, but still an order of magnitude smaller than observed speeds.

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Section: A Physical Process For Generating Wind Variationsmentioning

confidence: 99%

Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

et al. 2008

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“…Fuller-Rowell, 1985]. Upwelling in the resultant circulation cells brings oxygen poor air from below and causes a reduction in the atomic oxygen to molecular nitrogen ratio O/N 2 [Mayr and Volland, 1973;Hays et al, 1973]. Downwelling results in the opposite effect observed as an increase in the O/N 2 ratio during geomagnetic storms [Bums et al, 1995].…”

Section: Introductionmentioning

confidence: 99%

Depletion of oxygen in aurora: Evidence for a local mechanism

Christensen¹,

Hecht²,

Walterscheid³

et al. 1997

J. Geophys. Res.

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Abstract. A ground-based and rocket investigation of the response of the neutral atmosphere to E region auroral heating has been carried out at Poker Flat, Alaska. The temporal evolution of the atomic oxygen to molecular nitrogen ratio (O/N2) in the lower thermosphere has been monitored using the optical emissions from the aurora as a diagnostic. Comparisons between the changes in the O/N 2 ratio and the auroral Joule and particle heating have shown several examples of close similarity between the durations of the heating events and the depletions. Using the thermospheric winds measured during the rocket flights and the temporal structure of the depletions, the upper limit on the horizontal scale size of the depletions has been estimated at 200-400 km. Moreover, in situ rocket measurements of atomic oxygen showed significant differences at points separated horizontally by approximately 220 km. It is also concluded from the near coincidence between the depletion events and the Joule heating events that the dynamical mechanism(s) that drive the depletions were not far distant from the observing site, that is, local processes are sometimes dominant • during periods of moderate auroral activity.We suggest that the observation of a strong wind shear in the 100-to 120-km altitude region [Larsen et al., 1997] could be responsible for turbulence that contributes to the changes in minor constituent composition.

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“…The high-latitude thermosphere, accelerated by the convecting plasma through ion-neutral momentum transfer and thermal pressure imbalances caused by auroral particle precipitation, generates winds in the mid-latitude thermosphere Roble, 1978, 1984). Such an affect can clearly be seen in the ''storm time circulation'' pattern (Duncan, 1969;Mayr and Volland, 1972;Hays et al, 1973). In addition to being accelerated, the high-latitude neutral thermosphere undergoes heating.…”

Section: Introductionmentioning

confidence: 99%

Ionospheric and geomagnetic responses to changes in IMF <i>B<sub>Z</sub></i>: a superposed epoch study

et al. 1997

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Abstract. Superposed epoch studies have been carried out in order to determine the ionospheric response at mid-latitudes to southward turnings of the interplanetary magnetic field (IMF). This is compared with the geomagnetic response, as seen in the indices K p , AE and Dst. The solar wind, IMF and geomagnetic data used were hourly averages from the years 1967-1989 and thus cover a full 22-year cycle in the solar magnetic field. These data were divided into subsets, determined by the magnitudes of the southward turnings and the concomitant increase in solar wind pressure. The superposed epoch studies were carried out using the time of the southward turning as time zero. The response of the mid-latitude ionosphere is studied by looking at the F-layer critical frequencies, f o F2, from hourly soundings by the Slough ionosonde and their deviation from the monthly median values, f o F2. For the southward turnings with a change in B z of B z > 11:5 nT accompanied by a solar wind dynamic pressure P exceeding 5 nPa, the F region critical frequency, f o F2, shows a marked decrease, reaching a minimum value about 20 h after the southward turning. This recovers to pre-event values over the subsequent 24 h, on average. The Dst index shows the classic storm-time decrease to about )60 nT. Four days later, the index has still to fully recover and is at about )25 nT. Both the K p and AE indices show rises before the southward turnings, when the IMF is strongly northward but the solar wind dynamic pressure is enhanced. The average AE index does register a clear isolated pulse (averaging 650 nT for 2 h, compared with a background peak level of near 450 nT at these times) showing enhanced energy deposition at high latitudes in substorms but, like K p , remains somewhat enhanced for several days, even after the average IMF has returned to zero after 1 day. This AE background decays away over several days as the Dst index recovers, indicating that there is some contamination of the currents observed at the AE stations by the continuing enhanced equatorial ring current. For data averaged over all seasons, the critical frequencies are depressed at Slough by 1.3 MHz, which is close to the lower decile of the overall distribution of f o F2 values. Taking 30-day periods around summer and winter solstice, the largest depression is 1.6 and 1.2 MHz, respectively. This seasonal dependence is confirmed by a similar study for a Southern Hemisphere station, Argentine Island, giving peak depressions of 1.8 MHz and 0.5 MHz for summer and winter. For the subset of turnings where B z > 11:5 nT and P 5 nPa, the response of the geomagnetic indices is similar but smaller, while the change in f o F2 has all but disappeared. This confirms that the energy deposited at high latitudes, which leads to the geomagnetic and ionospheric disturbances following a southward turning of the IMF, increases with the energy density (dynamic pressure) of the solar wind flow. The magnitude of all responses are shown to depend on B z . At Slough, the peak depression alwa...

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Auroral heating and the composition of the neutral atmosphere

Cited by 204 publications

References 17 publications

Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

Depletion of oxygen in aurora: Evidence for a local mechanism

Ionospheric and geomagnetic responses to changes in IMF <i>B<sub>Z</sub></i>: a superposed epoch study

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Auroral heating and the composition of the neutral atmosphere

Cited by 204 publications

References 17 publications

Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance

Depletion of oxygen in aurora: Evidence for a local mechanism

Ionospheric and geomagnetic responses to changes in IMF &lt;i&gt;B&lt;sub&gt;Z&lt;/sub&gt;&lt;/i&gt;: a superposed epoch study

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Ionospheric and geomagnetic responses to changes in IMF <i>B<sub>Z</sub></i>: a superposed epoch study