Wavelet analysis of long period oscillations in geomagnetic field over the magnetic equator

Abstract

In this paper the complex Morlet Wavelet Transform is used to identify long period oscillations in the horizontal component ( H) of the geomagnetic field over the magnetic equatorial location of Trivandrum (8.5°N; 77°E; dip lat. 0.5°N) during the solar maximum period 1990/1991 and solar minimum period 1995/1996. The Morlet WT of the geomagnetic data set indicates the presence of multiple timescales, which are localized in both frequency and time. Extra long period oscillations are observed in the period range of 40–80, and 80–130 days during 1995/1996 (October–April), and 30–60, 130–180 days during 1990/1991 (October–April). This is one of the first such observations in the nature of long period oscillations in the earth's magnetic field. These observations on the existence of different long wave periods in the geomagnetic field are consistent with their findings in the lower and middle atmosphere (J. Atmos. Sol. Terr. Phys. 63 (2001) 835; J. Atmos. Sci. 29 (1972) 1109). This analysis also brings out clearly the merging of long period oscillations with short period oscillations during conditions of geomagnetic disturbance.