Astronomy and Astrophysics – Astronomy
Scientific paper
May 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997spd....28.0254p&link_type=abstract
American Astronomical Society, SPD meeting #28, #02.54; Bulletin of the American Astronomical Society, Vol. 29, p.902
Astronomy and Astrophysics
Astronomy
Scientific paper
Understanding the magnitude and temporal structure of variations in solar ultraviolet irradiance is a key component of understanding the Sun as a variable star and is critical to understanding solar forcing of the Earth's upper and middle atmosphere. We have used indices derived from the daily, spatially resolved, magnetograms taken at the Mount Wilson Observatory to develop models of UV observations. These magnetograms, which have been taken in the magnetically sensitive FeI 525.0 nm line on a daily basis since 1968, offer the possibility of long term modeling of solar UV variations, including periods for which satellite observations are unavailable or unreliable. One index used in this modeling is the "Magnetic Plage Strength Index" (MPSI), which is defined as the sum of the absolute magnetic fields of all pixels with magnetic strength between 10 and 100 gauss and is associated with the strong fields of plage/facular regions. We have found the MPSI to describe reasonably well both short and long term variations in the UV irradiance observations from the Solar Mesosphere Explorer, Nimbus-7, NOAA9, and Upper Atmosphere Research Satellites with correlation coefficients of from 0.93 to over 0.98. However, there remains a substantial fraction of solar UV variations which appears not to be associated with these strong fields. In this paper we describe our efforts to improve on the MPSI model of these satellite observations by (1) using different field strength limits for a plage index, (2) creating new and improving on old magnetic indices by including in the model surface magnetic features with field strengths lower and higher than associated with the MPSI, and (3) correcting the Mount Wilson indices for certain changes in the observation protocol. Since the bulk of the magnetogram pixels have field strengths between 0.5 and 2.0 gauss as measured at 525.0 nm, and since pixels with field strengths between 2.0 and 10 gauss may be associated with active network, we think, and our results so far confirm, that indices based on fields lower than 10.0 gauss will significantly improve modeling of UV variations.
Floyd Linton E.
Pap Judit M.
Parker Gary D.
Prinz Dianne K.
Ulrich Richard K.
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