Asymmetries in periodicities of the photospheric magnetic field of the sun: A probe to the unusual solar minimum prior to the solar cycle 24

Bisoi Susanta Kumar, bisoi.susanta@gmail.com Physical Research Laboratory, Ahmedabad, India
Padmanabhan Janardhan, jerry@prl.res.in, Physical Research Laboratory, Ahmedabad, India

Abstract
The solar cycle 23 minimum has been long debated for its unusualness and extended behaviour. The recent work has shown that solar polar fields have been steadily declining since around 1995, well supported by the fact that a similar decline in the turbulence level was observed, through IPS observations, in the entire inner heliosphere around 1995. We investigate the temporal variations in periodic activity observed in the photospheric magnetic field of the sun covering years from 1975 to 2009 using the wavelet and Fourier time-series techniques. A north-south asymmetry in periodicities is noticed for the polar field (latitude 450-780) obtained before 1995 and those after 1995 with significant shifting of spectral power between the solar hemispheres. We don’t find any such signatures in the periodicities for the toroidal field (latitude 00-450). The asymmetry, thus reported around 1995, coupled with the fact that the solar polar fields of the sun and the turbulence levels in the entire inner heliosphere started decreasing around 1995 suggests certain active changes, occurred in the underlying physical processes of the sun, eventually leading to the initiation of the unusual solar minimum at the end of the solar cycle 23.