Presentation Abstract

Session: Solar Interior
Presentation Number: P16.10
Title: Large-scale Zonal Flows During the Solar Minimum -- Where Is Cycle 25?
Presentation Start: 6/13/2011 7:30:00 AM
Presentation End: 6/16/2011 8:30:00 AM
Authors: Frank Hill1, R. Howe2, R. Komm1, J. Christensen-Dalsgaard3, T. P. Larson4, J. Schou4, M. J. Thompson5
1National Solar Obs., 2University of Birmingham, United Kingdom, 3Aarhus University, Denmark, 4Stanford University, 5High Altitude Observatory.
Abstract: The so-called torsional oscillation is a pattern of migrating zonal flow bands that move from mid-latitudes towards the equator and poles as the magnetic cycle progresses. Helioseismology allows us to probe these flows below the solar surface. The prolonged solar minimum following Cycle 23 was accompanied by a delay of 1.5 to 2 years in the migration of bands of faster rotation towards the equator. During the rising phase of Cycle 24, while the lower-level bands match those seen in the rising phase of Cycle 23, the rotation rate at middle and higher latitudes remains slower than it was at the corresponding phase in earlier cycles, perhaps reflecting the weakness of the polar fields. In addition, there is no evidence of the poleward flow associated with Cycle 25. We will present the latest results based on nearly sixteen years of global helioseismic observations from GONG and MDI, with recent results from HMI, and discuss the implications for the development of Cycle 25.