Longitudinal variations of thermospheric composition indicating magnetic control of polar heat input

Self Cite

Measurements of N2, O, He, and Ar densities from neutral gas mass spectrometers on four satellites (Ogo 6, Aeros A, AE‐C, and AE‐D) and inferred O2 and H densities from an ion mass spectrometer on AE‐C have been combined to produce a model of longitude/universal time (UT) variations in thermospheric neutral temperature and composition. The longitude/UT model is an extension of the mass spectrometer‐incoherent scatter thermospheric model and uses spherical harmonic terms dependent on geographic latitude, longitude, and universal time. The terms which depend only on longitude indicate a temperature enhancement of about 30°K somewhat equatorward of the magnetic poles. The temperature varies also in universal time, the greatest enhancement being about 30°K near 2130 UT in the northern hemisphere and about 70°K near 0930 UT in the southern hemisphere. The extrapolated 120‐km variations are generally in phase for Ar and O2 and out of phase for He, O, and H. Changes during magnetic storms are relatively small. The combined longitude and UT variations reflect the influence of the earth's magnetic field but indicate that the variations may not be simply represented in magnetic coordinates. The longitude/UT model helps reduce differences in the local time variation between the incoherent scatter stations.

Section: Introductionmentioning

confidence: 97%

Global model of longitude/UT variations in thermospheric composition and temperature based on mass spectrometer data

Hedin¹,

Reber²,

Spencer³

et al. 1979

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“…All averages used in the model are based upon at least 20 density points. The averaging procedure eliminates longitudinal/UT effects [Hedin and Reber, 1972] in the data and reduces the amount of data handled, but does not eliminate local time effects since the orbit plane changes quite slowly with respect to the sun (2°/day).…”

Section: Data Selection and Coveragementioning

confidence: 99%

Empirical model of global thermospheric temperature and composition based on data from the Ogo 6 quadrupole mass spectrometer

Hedin¹,

Mayr²,

Reber³

et al. 1974

Self Cite

231

An empirical global model for magnetically quiet conditions has been derived from longitudinally averaged N2, O, and He densities by means of an expansion in spherical harmonics. The data were obtained by the Ogo 6 neutral mass spectrometer and cover the altitude range 400–600 km for the period June 27, 1969, to May 13, 1971. The accuracy of the analytical description is of the order of the experimental error for He and O and about 3 times the experimental error for N2 and thus provides a reasonable overall representation of the satellite observations. Two model schemes are used: one representing densities extrapolated to 450 km and one representing densities extrapolated to 120 km with exospheric temperatures inferred from N2 densities. Features in the thermospheric structure brought out by the model include a near 1000 hour local time maximum for He and a 1600 hour maximum for N2 at 450 km, a winter maximum in the O to N2 ratio at 120 km, and a 400°K summer to winter exospheric temperature difference with the diurnal temperature bulge located at high latitudes in summer.

“…that would accompany atmospheric heating. There is ample evidence that such heating occurs at higher latitudes, even during magnetically quiet periods [Hedin and Reber, 1972], an effect that appears to involve direct heating by precipitation as well as Joule heating caused by electric fields. Reber et al [1973] have reported that this heating extended down to the lowest latitudes during a large substorm, increasing the N•.…”

mentioning

confidence: 99%

Deformation of the night side plasmasphere and ionosphere during the August 1972 geomagnetic storm

Brace¹,

Maier²,

Hoffman³

et al. 1974

Isis 2 satellite measurements of electron and ion temperatures and densities and of airglow emissions have resolved certain features of the response of the night side ionosphere to the major magnetic storm of August 4–6, 1972, an event in which Kp reached 9o at one point. The near‐polar orbit of Isis 2 is circular at about 1400‐km altitude and at the time of the storm was oriented in the 0500–1700 LT plane. During the initial phases the plasmapause moved equatorward from L=4.5 to about 2.7, followed by a further compression to L=1.9–2.0 at the peak of the storm and a slow recovery during the ensuing days. The plasmapause was identified by an abrupt decline in H+ accompanied by a sharp peak in both Te and Ti, Te approaching 6000°K and Ti exceeding 3000°K in some passes. A pronounced trough developed within the plasmasphere during the days of greatest disturbance. Equatorial temperatures were also enhanced from normal values, Te exhibited great spatial variation there on some passes, and this variation was associated with the development of troughs of Ne at the dip equator. On the most disturbed day (August 5), when the plasmapause had fallen to L=2.3, a deep trough developed in the region L=1.3‐1.8, Ne falling below 1 × 10² cm−3, more than 2 orders of magnitude below the normal protonosphere concentration at this altitude. Top side sounder observations of radio breakthrough from the ground indicated that the trough extended through the F region as well. A red arc observed on this day at L=1.23 apparently was associated with an equatorial trough in Ne and enhancement in Te. Whether the arc and the troughs were caused by magnetospheric processes or by enhanced recombination within the F region is not clear.