The nature of association of equatorial spread F with magnetic activity

Abstract

STATISTICAL studies based on a published data of f₀F₂ have revealed that equatorial spread F depends inversely on magnetic activity during the sunspot maximum period but tends to disappear or even become positive in some seasons during the sunspot minimum period^1–3. Somayajulu et al.⁴, using a different technique, considered the occurrence of spread F during different phases of magnetic storms, and they concluded that the initial storm phase does not have any inhibiting effect on spread F occurrence and that spread F occurs in general during the main phase of the magnetic storms. They observed that, during the recovery phase when the field value is quite different from the normal value, there is no spread F but it is present when the magnetic field value is close to its normal value. To investigate this discrepancy with the earlier results further, the spread F behaviour has been studied⁴ in relation to K_p indices, and for the Trivandrum data of 1970, and though the overall correlation between spread F and magnetic activity is negative, occurrence of spread F was found to decrease initially with increasing ΣK_P and then to start increasing at higher ΣK_P values. The effect of magnetic activity on equatorial spread F is reported here.