Polar Magnetic Field Elena E. Benevolenskaya Stanford University SDO Team Meeting 2009 Overview What we know about polar magnetic field? Polar magnetic field inferred from SOHO/MDI data SOLIS and HINODE polar magnetic field Toward the SDO Babcock & Babcock measured the polar magnetic field in solar cycle 19 (1955). It is observed the polar magnetic fields is their reversal during the maxima of 11-year sunspot cycles (Babcock and Livingston, 1958; Babcock, 1959). To understand the origin of the polar magnetic field reversals many investigators employed the mean-field dynamo theory (e.g. Dikpati et al., 2004). The solar magnetic field and, particularly, the polar magneticfield, is dominated by small magnetic elements of mixed polarities as has been shown by Severny (1971). During the last three cycles the polar magnetic field is continually decreased (WSO data). History MDI data Axisymmetrical Pattern of the Cycle 23 The polar magnetic field reversal in cycle 23 was in CR19752 (April 2001) in the North and in CR1980 2 (September 2001) in South. MDI WSO Scientific Task. Polar magnetic field: small-scale and large-scale pattern Major goals and significance The polar magnetic field is dominated by small magnetic elements of mixed polarities, while the Polar Regions may appear as unipolar in low-resolution magnetograms. During the solar minimum the polar magnetic field reaches their maxima and is appeared to be pronounced. The small-scale magnetic elements of the dominant polarity are coincided with polar faculae which display the solar cycle dependence. HMI will provide vector magnetic data near the solar limb and detect the intensity and polarity of small-scale elements more correctly to compare with line-of-sight component. The local helioseimology produces the polar synoptic maps of plasma motion near the poles beneath the photosphere and help to understand dynamics of small scale-elements. The goal of this investigation is to understand nature of the polar magnetic field and to answer on the question if any local dynamo is involved in the polar magnetic field pattern. It is important because of the polar field strength at solar minimum is perhaps the most important quantitative indicator used to forecast the strength of the oncoming solar cycle. MHD simulation and current-free coronal field modeling based on magnetograms will be carry out for constructing of polar magnetic field above the photosphere and investigate the configuration of large-scale magnetic fields in solar corona. One important objective of HMI is to examine these results and to understand relationship of magnetic configuration of large-scale and small-scale magnetic field during the solar cycle and define the polar magnetic field. Science team roles and responsibilities Dr J.Todd Hoeksema with his student Xudong Sun, and Dr Elena Benevolenskaya (international collaborator, Russia) will lead the investigation team which includes Xu Pu Zhao, K. Hayashi, Y. Liu, P. H. Scherrer, of Stanford University. They will carry out the investigation by synoptic analysis, MHD and potential field simulation. We are welcome!