Day-to-day variability in the occurrence characteristics of Sq focus during d-months and its association with diurnal changes in the Declination component

S Alex,M M Jadhav

doi:10.1186/bf03352067

Abstract

AbstractScrutiny of the geomagnetic observations of the Declination component “D” from equatorial and low-latitude locations in the Indian longitude revealed anomalous variations during d-months. Examination of the Quiet day (Ap≤7) variations in the Declination component (Yin nT =HsinD) and Horizontal component (H) during the d-months (November, December, January, February) of the low solar activity year 1977 revealed the salient features associated with the day-to-day changes observed in Sq current system over the latitude chain in the Indo-Russian longitude. Diurnal variations in the east-west componentYand north-south componentHwere used to depict the effect of changes in the Sq current pattern for a selected set of Quiet days, which are classified into normal and abnormal days based on the trend in the variation of the Declination component. Normal days designated in the study clearly showed the expected pattern of variation in ΔY(eastward-directed field) in the morning hours and westward-directed field in the afternoon hours, and diurnal variation of ΔHsimultaneously showed the presence of northern Sq focus within the low-latitude range. In contrast, the abnormal days projected by the variation in ΔYand ΔHon certain days of d-months showed an almost complete absence of the focus formation within the expected latitude extent. Day-to-day variability characteristics of the Declination component discussed in the study are illustrated in relation to modifications in the expected Sq current system by the invasion of the prevalent southern hemisphere current whorl to the northern hemisphere during the winter months. Some of the anomalous changes observed in the day-to-day variation in the latitudinal pattern of ΔYand ΔHcomponents are also interpreted as suggesting an influence of high-latitude magnetospheric current systems on certain quiet days.

Highlights

The daily variation in the magnetic field at the Earth’s surface during the geomagnetic quiet condition is known to be generated by solar heating and results in tidal winds in the E-region of the ionosphere, where the magnitude of conductivity is appreciable
In an attempt to elucidate this component, we examined certain finer aspects of abnormal day-to-day characteristics of the Sq current system
The database used to depict the day-to-day variability is mainly restricted to the average hourly values of the H and D components for 1977 in terms of the availability of data for individual days spanning from the equator to high-latitude regions; the period of the study falls in the solar minimum, similar to the conditions of 1987

Summary

Introduction

The daily variation in the magnetic field at the Earth’s surface during the geomagnetic quiet condition is known to be generated by solar heating and results in tidal winds in the E-region of the ionosphere, where the magnitude of conductivity is appreciable. Normal days are designated as the Quiet days of a particular month with a well-defined eastward field (positive Y ) in the morning hours, changing over to westward-directed field during the noon hours at most of the low-latitude locations along the Indian longitude.

Results

Conclusion