Solar Cycle and Quasi-biennial Variations in Helioseismic Frequencies

Tripathy Sushanta, stripathy@nso.edu, National Solar Observatory, Tucson, USA
Jain Kiran, jain@nso.edu, National Solar Observatory, Tucson, USA
Simoniello Rosaria, rosaria.simoniello@pmodwrc.ch, CEA/DSM/IRFU/SAp-AIM, CE Saclay, France
Hill Frank, fhill@nso.edu, National Solar Observatory, Tucson, USA
Turck-Chieze Sylvain, sylvaine.turck-chieze@cea.fr, CEA/DSM/IRFU/SAp-AIM, CE Saclay, France

Abstract
The prolonged period of solar minimum between cycles 23 and 24 has invoked a great deal of interest to understand the origin of the unusually low solar activity. Since the origin of solar activity is believed to lie in the shear layer at the base of the convection zone, the analysis of helioseismic data is important to probe these regions. In this analysis, using both low- and intermediate degree modes we show that there were two minima in oscillation frequencies depending on the penetration depth of the modes. This also brings up the question regarding the possible role of the relic magnetic field in modifying the oscillation frequencies. Further, in order to provide additional constraints on the solar dynamo models, we probe the signature of the quasi-biennial periodicity, seen in the oscillation frequencies, at different depths and over different phases of the solar cycle.