Coronal evolution during the sunspot cycle: Coronal holes observed with the Mauna Loa K-coronameters
The white-light corona was observed regularly at the Mauna Loa Observatory during the years 1965--1967 and 1969--1978. Display of the measured polarization brightness in the form of synoptic maps permits the identification of large coronal holes and the study of their slow evolution during the sunspot cycle. The polar coronal holes were clearly seen to shrink in size during the ascending phase of cycle 20 (1965--1967), to be absent during a two-year period (1969--1970) just after sunspot maximum, to reappear near the end of 1970, and to remain as prominent features of the corona for the years 1971--1978. During the sunspot maximum epoch the corona was dominated by 'mid-latitude' holes, elongated in the direction parallel to the solar equator. Large equatorial holes or equatorward extensions of the polar holes were observed during the ascending, maximum, and descending phases of cycle 20 and appear to be sources of solar wind streams with maximum speeds over 600 km s/sup -1/ at all of these epochs. The lifetimes of these holes and streams were greatest during the descending phase of the cycle, or in 1974--1975.
- Research Organization:
- High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado 80307
- OSTI ID:
- 6386445
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 86:A4
- Country of Publication:
- United States
- Language:
- English
Similar Records
Atmospheric carbon dioxide and radiocarbon in the natural carbon cycle. I. Quantitative deductions from records at Mauna Loa Observatory and at the South Pole
Study of extreme-ultraviolet emission and properties of a coronal streamer from PROBA2/SWAP, HINODE/EIS and Mauna Loa Mk4 observations