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R. Wolfson (CSSA Stanford University \& Middlebury College), C.B. Roald, P.A. Sturrock (CSSA Stanford University)
We have formed time series of photospheric magnetic field data from the Michelson Doppler Imager (MDI) on SOHO and of coronal X-ray flux from the Soft X-ray Telescope (SXT) on Yohkoh. The data are averaged to give one datum per day for each of nine latitude bins on the central meridian, for the mean SXT energy flux, the mean magnetic field B, and the mean field magnitude |B|. Data from both instruments overlap for a 521-day period beginning 25 July 1996. Analyzing the two time series for this period, we find strong correlations between coronal X-ray brightness and the magnitude of the photospheric magnetic field at all but extreme latitudes, and these correlations persist when the general trend in the data—presumably due to the solar cycle—is removed. The inferred relation between X-ray flux and the field magnitude |B| takes the form of a power law, which we compare with simple models that also predict a power-law relation. We have also formed cross correlations involving different time or latitude bins. The former show that the strongest correlations always occur for SXT and MDI data from the same time. Strong correlations also result when data are separated in time by integer multiples of a solar rotation, suggesting the presence of persistent structures at the photosphere and/or in the corona. The spatial analysis shows that at low latitudes the strongest correlation occurs between SXT and MDI data from the same latitude bins. At higher latitudes, however, the SXT data correlate most strongly with MDI data from lower latitudes, suggesting that the magnetic field spreads from the low-latitude photosphere to higher latitudes in the corona.
This work was supported by NASA grants NAG5-6118 and NAS 8-37334.
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