Study of equatorial E region irregularities using rare daytime VHF scintillation observations

Abstract

Scintillations on VHF radio signal are sparsely observed during daytime due to unavailability of strong electron density irregularities in equatorial E or F region. Type I/II irregularities observed at E region altitudes during the daytime are linked with either two‐stream or gradient drift instability. The occurrence of these irregularities in presence of strong blanketing Es (Esb) can produce weak‐moderate scintillations on VHF signal during daytime. Such sparse daytime VHF scintillations are used in the present study to retrieve information about E region irregularities, which are generally examined with radar observations. We use spaced receiver scintillation observations on 251 MHz signal transmitted from geostationary satellite UFO2 (71.2°E) and recorded at Tirunelveli (8.5°N, 77.8°E, dip latitude 0.6°N). Ionosonde data from Trivandrum (8.5°N, 76.6°E, dip latitude 0.5°N) during 2003–2005 is used to confirm the association of daytime scintillations with Esb. The daytime scintillations last for 15–45 min during postnoon hours. Their occurrence closely matches the peak occurrence time of Esb. For the first time, spatial scale lengths of E region irregularities are obtained using the technique introduced by Bhattacharyya et al. (2003). The observed spatial scales are validated using theoretical model. The theoretical model manifests 6–19% density fluctuations in the E region to produce weak scintillations (0.15 ≤S4≤ 0.4) on 251 MHz. The study reveals that scale lengths of E region irregularities are smaller on counter equatorial electrojet (CEEJ) days than non‐CEEJ days, which could be resulting from lower electron temperatures in E region on CEEJ days.

Characteristics of the equatorial plasma drifts as obtained by using Canadian Doppler ionosonde over southern tip of India

“…Similarly, using spaced receiver VHF scintillation measurements, recently, Yadav et al . [] have shown that zonal drifts are having drift speeds on the order of 120 m/s. On the other hand, the temporal variations of zonal drifts also suggest higher eastward drifts during evening hours at PRE times, while they show slow reduction of these drifts to westward in the late nights.…”

Structuring of intermediate scale equatorial spread F irregularities during intense geomagnetic storm of solar cycle 24

“…This technique is applicable to both weak and strong scintillations unlike power spectral analysis technique, which is valid for only weak scintillations. Recently, Yadav et al [] examined the spatial structures of E region long‐wavelength irregularities using daytime spaced receiver VHF scintillation observations. Besides this it can be used to get the zonal irregularity drift.…”

Quiet and Disturbed Time Characteristics of Blanketing Es (Esb) During Solar Cycle 23

“…Arras () estimated global Es occurrence using GPS radio occultation technique, which indicates that Es occurrence is maximum at mid latitudes in local summer. On rare occasions E region irregularities, in presence of Esb, can produce scintillations of radio signals in VHF band (Yadav et al, ). The main difference is that, unlike Esb layer, the ionization in nonblanketing Es layers is not high enough to blanket the upper ionospheric layers to the radio signal transmitted from ground‐based ionosonde.…”