Abstract
Secular variations inH at four Indian observatories near the regional focus of maximum horizontal intensity show that a reversal of the increasing trend occurred from about, 1965. Broad agreement in the secular trends is seen with some differences in detail. The changes observed at the observatories do not appear to be due to positional shift of the focus. The differences in the trends are attributable to secondary induced current effects in the earth's upper mantle or crust. An apparent long-period variation of 110 years is shown to be part of a much longer period trend.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have