LIMITS TO THE ACCURACY OF THE 10.7 CM FLUX

被引:52
作者
TAPPING, KF
CHARROIS, DP
机构
[1] Dominion Radio Astrophysical Observatory, National Research Council, Penticton, V2A 6K3, B.C.
[2] Legal, Alberta, T0G 1L0
关键词
D O I
10.1007/BF00712892
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
The 10.7 cm flux data, which are widely used as an index of solar activity, are actually spot measurements of the solar flux density at 10.7 cm wavelength, made three times each day, usually at 17:00, 20:00, and 23:00 UT. These values, or the 20:00 UT determination alone, are frequently used as the average flux for that day. Since each spot measurement takes about one hour to make, and the Sun's emissions at that wavelength can vary over time scales shorter than the intervals between the measurements, the data are unavoidably undersampled. Radio emissions from transient events, such as flares, are defined as contaminants of the flux, and largely-empirical procedures have evolved which are used to filter them from the data. The utility of the F10.7 index over more than 40 years suggests that the consequences of the undersampling and the use of largely-empirical data filters are not serious. However, as new applications of the flux data appear, and existing ones become more quantitative, we need to better understand the accuracy of data as estimates of the 10.7 cm flux index, and to know how much precision we can reasonably expect to attain. In this paper we describe part of a study aimed at estimating how good the spot measurements are as estimators of the 'daily-average' flux. By a combination of measurement and modelling, the contributions to the flux monitor output truly due to the Sun are separated from the non-solar signals. We then derive the daily average 10.7 cm flux values and compare them with the spot measurements. We find that in general, the spot measurements are usually within a percent or so of the daily-average fluxes.
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页码:305 / 315
页数:11
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