Abstract
The MgII index is an important proxy for solar activity; in particular it correlates well with the EUV which is important for understanding the upper atmosphere. We compare the measurements from all of the instruments making daily measurements during the most recent solar minimum. After adjustments to the data to account for instrumental effects, we find that there are still some discrepancies between the various time series. The data from the primary channel of the SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) on SORCE requires a correction factor starting in early 2006 in order to bring it into agreement with the redundant SOLSTICE channel and with the other datasets. Once this correction has been applied, all the MgII measurements are in good agreement throughout the solar minimum interval.
Highlights
The primary energy input to the upper atmosphere of the Earth is extreme ultraviolet (EUV; 10–121 nm) radiation from the Sun
During the solar minimum between cycles 23 and 24, there were many instruments measuring the MgII core-to-wing ratio. This wealth of observational datasets has allowed us to uncover an instrumental trend in the measurements from SOLSTICE A. After this correction using observations from SOLSTICE B, the time series from SOLar Radiation and Climate Experiment (SORCE) is in good agreement with the Bremen composite
Comparison between the different instruments will guide the creation of the new composite as much as possible, but the number of available datasets will be much fewer than we had during solar minimum
Summary
The primary energy input to the upper atmosphere of the Earth is extreme ultraviolet (EUV; 10–121 nm) radiation from the Sun. Heath & Schlesinger (1986) identified the Magnesium II core-to-wing ratio as a useful proxy for the solar EUV irradiance. This ratio is known as the MgII index and for a low-resolution (1.1 nm) instrument is defined as: I1⁄4. The spectral resolution of the instrument making the observation and the sampling of the spectrum can have an impact on the precision of the MgII index measurement (Snow & McClintock 2005; Snow et al 2005). The goal of this paper is to combine these observations into a single consistent time series that best represents the solar activity. We will have a single consistent MgII time series from 1978 through the present covering more than 35 years
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