Solar Cycle Variation of Ephemeral Regions.
Abstract
Ephemeral active regions (ER) have been identified and counted for selected periods from 1970 to mid-1984 using the daily, full-disk photospheric magnetograms taken by the National Solar Observatory. The number of ephemeral regions varies nearly in phase with the solar cycle. At solar minimum, ER are distributed almost uniformly in latitude; by solar maximum, peaks in the latitude distribution are observed in the sunspot zones and in higher latitude bands. In the quiet sun, 37% of the He I lambda 10830 'dark points', used as a proxy for X-ray bright points (XBP), are associated with ER; 63% overlie bipoles that appear to be the chance encounter of opposite polarity network. The percentages are somewhat different in coronal holes; 21% of the dark points in He I are associated with ephemeral regions and 79% with bipoles that apparently result from chance encounters of flux. The dark points observed in the quiet sun and in coronal holes, vary anti-correlated with the solar cycle. Little relations was found between the areal density of He I dark points and ephemeral regions within the boundaries of coronal holes and parameters of the high speed solar wind streams associated with coronal holes. This study suggests that (1) ephemeral regions are not small active regions and that they may be primarily a surface phenomena, possibly resulting from convection interacting with sub-photospheric fields, and (2) He I 'dark points', and therefore, XBP, are more often associated with the encounter of existing opposite polarity network flux, the occurrence of which is related to the amount of mixed polarity areas which varies inversely with the solar cycle. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1984
- Accession Number
- ADA154967
Entities
People
- K. L. Harvey
Organizations
- National Oceanic and Atmospheric Administration