Accession Number : ADA259978

Title :   The Variation of Solar FE XIV and FE X Flux Over 1.5 Solar Activity Cycles


Personal Author(s) : Altrock, Richard C

Full Text :

Report Date : Apr 1990

Pagination or Media Count : 8

Abstract : This paper presents a new source of data on the solar output, namely 'limb flux' from the one- and two-million degree corona. This parameter is derived from data obtained at National Solar Observatory at Sacramento Peak with the 40 cm coronagraph of the John W. Evans Solar Facility and the Emission Line Coronal Photometer. Limb flux is defined to be the latitude-averaged intensity in millionths of the brightness of disk center from an annulus of width 1.1' centered at a height of 0.15 R above the limb of emission from lines 6374A (Fe X) or 5303A (Fe XIV). Fe XIV data have been obtained since 1973 and Fe X since 1984. Examination of the Fe XIV data shows that there is ambiguity in the definition of the last two solar activity minima, which can affect the determination of cycle rise times and lengths. There is an indication a constant minimum or basal corona may exist at solar minimum. Cycle 22 has had a much faster onset than Cycle 21 and has now overtaken Cycle 21. The rise characteristics of the two cycles were very similar up until Jul-Aug 1989, at which time a long-term maximum occurred in Fe X and Fe XIV, which could possibly be 'solar maximum'. Another maximum is developing at the current time. Cycle 21 was characterized in Fe XIV by at least 4 major thrusts or bursts of activity, each lasting on the order of a year and all having similar maximum limb fluxes, which indicates coronal energy output is sustained over periods in which sunspot number declines significantly. Dramatic increases in the limb fluxes occur from minimum to maximum, ranging from factors of 14 to 21 in the two lines. Two different techniques to predict the epoch of solar maximum have been applied to the Fe XIV data, resulting in estimates of Apr 1989 (+ or - 1 mo) and May 1990 (+ or - 2 mo).


Subject Categories : Astrophysics

Distribution Statement : APPROVED FOR PUBLIC RELEASE