On the nature of equatorial slant sporadicE

Abstract

Two features of the daytime sporadic E echoes observed on ionograms obtained near the magnetic equator have been termed ‘equatorial sporadic E’ and ‘equatorial slant sporadic E.’ These are traces that project from the E‐layer trace and have equivalent ranges independent of frequency and proportional to frequency, respectively. Radar studies in Peru indicate that a thin stratum of magnetic‐field‐aligned irregularities embedded in the E layer is responsible for the entire sporadic E configuration. The increased equivalent ranges of the slant trace are attributed to oblique propagation in the east‐west plane orthogonal to the irregularities. By accounting for the refraction and retardation imposed by the E layer, the entire configuration can be simulated in detail. It is established from this analysis that the equatorial electrojet flows within the equatorial E layer, and that its first‐order current variations are coherent over distances of 500 km or more along the magnetic equator.

Unique examples of solar flare effects in geomagnetic H field during partial counter electrojet along CPMN longitude sector

“…Bartels and Johnston (1940a, b) demonstrated an abnormally large lunar variation on the daily variation of H (SqH) at Huancayo such that on certain days the daytime values of H decreased below the nighttime value suggesting the reversed EEJ current direction. Cohen et al (1962) showed an association between the disappearance of Es-q and a decrease of the H field. Gouin (1962) reported a depression of H on magnetogram at local noon at Addis-Ababa well below the night level on a very quiet day.…”

Equatorial Sporadic E Layer during Geomagnetic Storms

“…Through the use of antenna lobing technique, BOWLES and COHEN (1962) confirmed this for irregularities giving rise to equatorial sporadic E. COHEN et al (1962) explained both the q-type and slant-type Es configuration in the ionograms on the model of the thin stratum of the magnetic-field-aligned irregularities embedded in the equatorial E layer. BOWLES et al (1963) showed that, when the VHF radar is not pointing vertically, the frequency spectrum of the echoes usually consists mainly of a fairly sharp peak at a discrete Doppler shift, the magnitude of which is independent of the angle between the beam and the jet current, the sign depending on whether one is looking East or West.…”

“…Sudden disappearance of Es-q during a decrease of geomagnetic H component was noticed by COHEN et al (1962). Examining the sonograms and magnetograms of Huancayo, BANDYOPADHYAY and MONTES (1963) found that about 82% of the disappearance of Es could be associated with the troughs in the H trace.…”

VHF radar studies of the equatorial electrojet 3-m irregularities over São Luís: day-to-day variabilities under auroral activity and quiet conditions

“…The characteristics of the plasma instabilities of the EEJ and the resulting plasma irregularities have been investigated extensively using VHF radars and rocket born experiments that have clarified many outstanding features of the dynamics and morphology of these irregularities (see for example, Cohen et al, 1962;Balsley, 1966;Balsley and Woodman, 1969;Fejer et al, 1975;Farley, 1985;Reddy, 1981;Prakash et al, 1971;Pfaff et al, 1987). Theoretical considerations on the plasma instabilities and the electrodynamics of the EEJ can be found in Matsushita (1951), Farley (1963), Buneman (1963), Fejer and Kelley (1980), Forbes (1981), Kudeki et al (1985), Fejer (1996).…”