Jack Slowey

Diurnal and seasonal latitudinal variations in the upper atmosphere

Abstract The variations with solar and geomagnetic activity have been eliminated by the use of appropriate models, and the diurnal variation has been isolated in the densities derived from the drag of seven artificial satellites with perigees between 250 and 650 km. An analysis of the diurnal variations leads to the following conclusions: 1. A. Contrary to previous suggestions, the diurnal bulge does migrate in latitude in phase with the subsolar point at all heights. 2. B. The diurnal bulge peaks at 2 pm. local solar time (LST) irrespective of solar activity; the minimum density occurs between 3 and 4 am. 3. C. The amplitude of the diurnal variation seems to fluctuate in a manner that cannot be entirely accounted for by variations in solar activity. 4. D. The significant high-latitude residuals from the diurnal-variation model observed on the drag of Explorer 19 and Explorer 24 may be explained by the formation at exospheric heights of a region of greater helium density above the poles during the winter months, caused by a seasonal variation in the height of the turbopause.

A study of the semi-annual density variation in the upper atmosphere from 1958 to 1966, based on satellite drag analysis

Abstract The semi-annual variation has been isolated in the drag data of six artificial satellites with perigee heights ranging from 250 to 658 km in the interval from 1958 through 1966 by suppression of all other known types of upper atmosphere variation with the help of empirical formulas. Although the shape of the curve is somewhat variable from year to year, the semi-annual oscillation is a very stable feature and can be followed without any major change in phase throughout the 8 yr covered by the observations. The temperature curves obtained from each of the six satellites are strictly in phase and show the same amplitude, irrespective of perigee height; peculiarities of the variation, such as an unusually broad minimum or a late maximum, are easily recognizable in each of the individual satellite curves. This shows that the semi-annual variation is worldwide and that the observed density variations are the result of temperature variations at essentially the same atmospheric level as those arising from the solar-activity effect. All previously known features of the semi-annual variation, such as the systematic inequality in the maxima and minima and the proportionality between the amplitude of the temperature variation and the 10.7-cm solar flux, are confirmed.

A study of the diurnal variation in the thermosphere as derived by satellite drag

Abstract An analysis was performed on 29,574 densities derived from the drag of 10 satellites to determine simultaneously the parameters of the solar-activity effect in the thermosphere on the one hand, and the amplitude and shape of the diurnal-variation curve on the other. This paper reports on the study of the diurnal variation only. Although a considerable amount of smoothing is inherent in the drag method, it seemed useful to see whether we could detect any change in the shape of the diurnal-variation curve with height, latitude and solar activity. None was detected: the curve remains remarkably stable, symmetric, with a maximum at 14 hr 20 min L.S.T. and a minimum at 2 hr 20 min L.S.T. A systematic variation of the temperature range with height is observed when static models are used to derive it.

Systematic winds at heights between 350 and 675 km from analysis of the orbits of four balloon satellites

Abstract Six values of the rate of rotation of the Earths upper atmosphere have been obtained by analysis of the orbital inclinations of four balloon satellites in the intervals just before the final decay of their orbits. The effective heights of these results range from about 350 to about 675 km. The values themselves range from 0·8 to 1·4 times the Earths rotation and correspond to zonal wind speeds between 100 m/sec westward and 200 m/sec eastward. All the results correspond to fairly specific local times and are consistent with a diurnal wind pattern in low latitudes having a strong eastward maximum near local midnight and a lesser westward maximum near 10:00 LT. They argue against the contention of a sharp decrease in the rate with respect to that of the Earth, which is supposed to begin at about 360 km. The factors involved in the determination of these values and the method used are discussed in considerable detail.