Maximum Frequency Of Occurrence Research Articles

SOME CHARACTERISTICS OF THE LOWER HYBRID RESONANCE NOISE BANDS OBSERVED BY THE ALOUETTE I SATELLITE

An investigation has been made of the occurrence as a function of latitude and time of lower hybrid resonance (LHR) noise bands as recorded during 1963 and 1964 by the very-low-frequency receiver aboard the Alouette I satellite. Two different types of LHR noise are observed—polar and mid-latitude. Polar LHR noise bands, with the maximum frequency of occurrence at about 75° invariant latitude, are observed approximately one half of the time throughout the year and during both night and day. Mid-latitude LHR noise bands have a maximum frequency of occurrence at about 55° and are observed mainly during the months of June–October and primarily at night. The differences in appearance and occurrence of these two types of LHR noise suggest different excitation mechanisms.

Regular Micropulsations of the Earth's Field at the Equator

THE diurnal variation of occurrence of regular pulsations, pc, of the Earth's magnetic field has been studied by many workers and it has been found, in all the cases reported, that the phenomenon is predominantly a day-time one. Typical of the results of magnetic measurements are those obtained in Germany by Angenheister1, for periods of 30–60 sec., which have a maximum frequency of occurrence at 10–12 hr. L.M.T. The measurements of Earth currents, obtained in the U.S.S.R. by Mme. Troitskaya2, are representative of that experimental approach and they show a maximum frequency of occurrence around 11–13 hr. L.M.T. Most of the results reported have been confined to mid-latitude stations.

Sporadic echoes from the E region over Ahmedabad (28° 02′ N, 72° 38′ E)

In this paper, a study is made of the sporadic E echoes observed in the ionospheric h′-ƒ records of Ahmedabad ( Φ = 13.6° N). From the analysis of the data for 1953–1954, a sunspot minimum period, it was found that three types of sporadic, namely 1. (i) Esc at 95–100 km, 2. (ii) Esn at 105–125 km, and 3. (iii) Ess at 115–125 km, occur in the E region. The overall behaviour of Es has been shown as being due to the combination of the characteristics of these three types. The sporadic ionization of type Esc has a maximum frequency of occurrence in the late evening hours, and has a thin structure. It is apparently evolved out of a downward drift of the residual ionization of the normal E layer. No correlation could be established with meteor activity. Esn shows a minimum in the afternoon and maximum in late-night hours before dawn. Ess is developed by the vertical downward movement of the E2 layer.

Geographic and temporal distribution of polar blackouts

Tabulations of hourly values of the ionospheric parameters for 18 northern-hemisphere stations have been used to derive diurnal variations in the occurrence of “blackout” conditions. Contour plots are presented showing the diurnal average percentage of time during which blackout conditions prevailed, the amplitude of the diurnal variation, and the time of maximum frequency of occurrence. Changes in the contours with season and with magnetic activity are discussed.