ALBERT

Description: Equatorial anomaly and atmospheric winds in F 2 region

Description: Examples illustrating the effects of large scale energy and mass transport in the thermosphere discussed include: (1) The seasonal variations reveal temperature, composition, and ionospheric anomalies involving energy exchange between the thermosphere and mesosphere. (2) The midnight temperature maximum in the thermosphere is interpreted as a signature of tidal waves emanating from the mesosphere and momentum coupling associated with ion drag. (3) The ionospheric storm in the F region illustrates the intricate effects of large scale atmospheric winds driven by magnetospheric energization processes. (4) Atmospheric signatures of Joule heating and electric field momentum coupling are markedly different.

Description: The dynamics of the equatorial thermosphere and the F-region plasma are reviewed, highlighting some features observed with the San Marco satellite, the AE-E, and the DE-2, as well as with ground-based facilities at Arecibo and Jicamarca. Particular attention is given to the midnight temperature maximum and related phenomena, and to results on zonal neutral and plasma flows at F-region heights.

Description: Based on modeling some interactions between the middle atmosphere and thermosphere are presented. The interactions studied include the thermospheric circulations driven by radiative and auroral heating affecting the O concentration and temperature of the upper mesosphere through the exchange of chemical energy. Considering Kellog's mechanism, an interaction between the mesosphere and thermosphere that is driven by Joule heating is discussed.

Description: Data obtained from the WATS (Wind and Temperature Spectrometer) and LP (Langmuir Probe) experiments on board DE-2 (Dynamic Explorer) during high solar activity show evidence of anomalous latitudinal variations in the zonal winds and temperature at low latitudes. The zonal winds exhibit a broad maximum centered around the dip equator, flanked by minima on either side around 25 degrees; while the temperature exhibits a pronounced bowl-shaped minimum at the dip equator which is flanked by maxima. The two minima in the zonal winds and the corresponding maxima in the temperature are nearly collocated with the crests of the well known Equatorial Ionization Anomaly (EIA). The maximum in the zonal winds and the minimum in the gas temperature are collocated with the trough of the EIA. The differences between the maxima and minima in temperature and zonal winds, on many occasions, are observed to exceed 100 K and 100 m/s, respectively. The characteristics of this new phenomenon have eluded present day empirical models of thermospheric temperature and winds. The connection among these variables can be understood from the ion-neutral drag effect on the motions of the neutrals that in turn affect their energy balance.

Description: The observation of a geomagnetic signature in the zonal eastward plasma flow, which is a striking feature of the equatorial ionosphere in the evening quadrant is reported. These observations were derived fronm (E x B)/B-squared measurements made with the cylindrical double-floating-probe experiment carried on the Dynamics Explorer 2 satellite. The signature consists of a crest-trough-crest effect in the latitude dependence of the eastward plasma flow with the crests at + or - 8 dip latitude and the trough nearly centered at the dip equator at all geographic longitudes. This phenomenon can be readily interpreted in terms of the altitude dependence of the F region dynamo electric field, and it is related to dip equator signatures in the plasma density and the magnetic declination which have been reported earlier.

Description: Evidence is presented for strong coupling between the diurnal components of zonal neutral winds and ion drifts, suggesting that the relative importance of the E- and F-region dynamos be reevaluated. Measurements of zonal neutral winds in the equatorial region of the earth's thermosphere at an average altitude of about 350 km show that the nighttime zonal winds are very similar to the zonal ion-drifts. That similarity is examined, comparing the corresponding tidal components of the 24 hr variations of these two parameters. The amplitude spectrum of the neutral winds exhibits primary and secondary maxima at the diurnal and ter-diurnal frequencies respectively, while the ion-drift spectrum shows only the diurnal maximum. It is found that the simularity between neutral winds and ion-drifts is strongest in the diurnal mode where the phases differ by less than one half hour, the amplitude of the ion-drift being between 70 percent and 80 percent that of the neutral wind, suggesting a first-order relation between the two quantities. The largest difference is found in the steady component representing superrotation; under similar conditions of solar activity, the ions superrotate with a velocity of about 30 m/s and the neutrals with 10 m/s. For the ions, the steady component, the phase of the semi-diurnal component and the amplitude of the ter-diurnal component appear to be sensitive to solar activity and are responsible for the observed solar cycle variations in the times of eastward-to-westward reversals between 0400 and 0700 LT. The ion-drift diurnal amplitude and phase are relatively insensitive to changes in solar activity.

Description: An analysis of the data on the asymmetries of the terrestrial thermospheric semiannual oscillation (SAO), recorded by satellites, radar stations, and rocket soundings (Hedin, 1983), is presented. The possible sources for the thermospheric SAO are discussed. An interpretation is presented of the hemispheric asymmetries of the thermospheric SAO in terms of gravity-wave activities, in which the proposed mechanism is associated with the hemispheric asymmetries in the atmospheric circulation due to the orographic differences between the two hemispheres. Consideration is given to the energy requirements for the observed hemispheric difference in the thermospheric SAO. The overall evidence supporting the proposed interpretation is discussed.

Description: Wavelike fluctuations in neutral composition data obtained with the neutral atmospheric composition system quadrupole mass spectrometer carried aboard the Dynamics Explorer (DE 2) satellite are at a maximum in the vicinity of the magnetic poles. Typical rms amplitudes near the poles for N2, O, He, and Ar fluctuations in the 400- to 4000-km-wavelength band are found to be 11, 6, 6, and 20 percent, respectively. Amplitudes near the equator are roughly a third of the polar amplitudes, and activity in the 50- to 400-km-wavlength band is roughly 20 percent of the longer-wavelength activity.

Description: A linear trasnfer function model of the earth's thermosphere which includes the electric field momentum source is used to study the differences in the response characteristics for Joule heating and momentum coupling in the thermosphere. It is found that, for Joule/particle heating, the temperature and density perturbations contain a relatively large trapped component which has the property of a low-pass filter, with slow decay after the source is turned off. The decay time is sensitive to the altitude of energy deposition and is significantly reduced as the source peak moves from 125 to 150 km. For electric field momentum coupling, the trapped components in the temperature and density perturbations are relatively small. In the curl field of the velocity, however, the trapped component dominates, but compared with the temperature and density its decay time is much shorter. Outside the source region the form of excitation is of secondary importance for the generation of the various propagating gravity wave modes.