Physics
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsh13a..11t&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #SH13A-11
Physics
2134 Interplanetary Magnetic Fields, 2169 Sources Of The Solar Wind, 2784 Solar Wind/Magnetosphere Interactions, 7509 Corona, 7524 Magnetic Fields
Scientific paper
The well established existence of an inverse correlation between the solar magnetic flux tube expansion factor (FTE) and the solar wind speed (SWS) at the Earth allows for the possibility to predict the SWS using observed solar photosphere magnetograms. A widely used method to compute the FTE is the potential field source surface (PFSS) model. Current PFSS models, however, do not always produce good agreement between the observed and predicted SWS. One complication is that traditional synoptic maps, used as input in the PFSS models, use the Carrington coordinates as the horizontal and vertical axes of the synoptic chart. Unfortunately, this choice leads to a mix of the time and space coordinates unless differential rotation is included in the tracking of magnetic features. We show here that the heliographic maps (longitude vs latitude or sine latitude) may be a better choice for the PFSS models. An additional problem is that the photospheric foot points and the FTE calculated from the PFSS models depend on Nmax, the number of multipole components used in the analysis. Current analyses use a combination of low resolution maps and small values of Nmax, typically around 30. We find that using a small Nmax produces fringing patterns in the reconstructed photospheric magnetic map. These fringing patterns alter the locations of the computed foot prints and the computed magnetic values on the photosphere as well as the predicted FTE. Increasing the Nmax value will then improve the reconstructed map and reveal more detail. In our analysis, we use high resolution synoptic and heliographic maps, which are 512 by 256, and Nmax up to 255. A typical simplification in previous analyses is to assume that the line-of-sight component of the solar magnetic field in the observed photospheric maps does not have a north-south contribution. This assumption may not be correct if one wants to reconstruct the north-south component map from the calculated coefficients using PFSS model. We use the Shrauner-Scherrer method to create both line-of-sight component and transverse component from the same observations. With the assumption (∇ × ěc{B}) = 0, we aim to obtain the north-south map from the transverse map and remove the north-south component from the line-of- sight component.
Bertello Luca
Boyden John E.
Tran Tan Van
Ulrich Richard K.
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