The solar wind, as it flows out, carries along the coronal magnetic field frozen-in the plasma. The coronal magnetic field plays an important role in the structure and distribution of solar wind in the heliosphere but the exact nature of the controlling influence of the former on the latter is still being debated. A direct measurement of the coronal magnetic field is still limited to strong field regions owing to which connecting the Sun and Solar Wind becomes difficult. The structure and distribution of the coronal magnetic field is obtained by extrapolating the observed photospheric magnetic field using the assumption that between the photosphere and a certain height (source surface at about 2.5 R, R being the radius of the Sun) the magnetic field can be derived from a potential obeying LaPlace's equation. This was suggested by Schatten, Wilcox, and Ness in 1969, and independently by Altschuler and Newkirk the same year, and is known as Potential Field Source Surface (PFSS) model. This model has been extensively used in the study of global structures and phenomena. Though the results of the model agree with observations with a certain level of accuracy, the discrepancies are very significant.
One of the most recent application of this model is the prediction of solar wind speed at 1 AU. Levine, Altschuler and Harvey, in 1977, noticed that the fastest solar wind correlated with the least expanding magnetic flux tube. Wang and Sheeley, 20 years later, in the 1990s, made use of this correlation and obtained a more general correlation between the two. They established that the solar wind speed inversely correlated with the expansion rate of the magnetic flux tube between the photosphere and the source surface, using PFSS model. This inverse correlation has been made use of by C. N. Arge and V. J. Pizzo to predict solar wind speed and magnetic field at 1 AU. The observed and predicted quantities agree pretty well, but at the same time, the discrepancies are significant. We have carried out an extensive analysis on the causes of these discrepancies.
Another model of the solar corona, known as the Current Sheet Source Surface (CSSS) model, developed earlier at Stanford University, has many advantages over the PFSS model, though similar in many respects. Here is a comparison of the predicted solar wind speed using the two models and the observed solar wind at Earth I have computed. I am attempting to create a solar wind prediction scheme making use of the CSSS model along with the PFSS model.