Crochet-associated flares.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Crochet-associated flares. Dodson, Helen W. ; Hedeman, Ruth E. Abstract The crochet is a relatively minor disturbance of the earth's magnetic field which occurs concomitantly with certain flares. lATME Bulletins for 1949-54 list 185 crochets. Solar or ionospheric data confirm 148. Ha flares were observed in 109 cases. The 109 crochet-flares occurred in 52 different centers of activity and constituted 10 per cent of the flares in those regions. Even though short-wave fades were reported with 87 per cent of the crochet flares, the crochet phenomenon does not satisfactorily delineate flares with the greatest ionospheric disturbances. Crochet flares exhibit an atypical distribution on the solar disk. Instead of the usual concentration near the center, crochet flares show highest frequency about 500 on either side of the central meridian. This double-humped distribution is not duplicated in the disk positions of 217 flares with "major" ionospheric disturbances. It is, however, very similar to the distribution of flares with wide Ha, and for crochet flares, the average width of Ha is large. The scarcity of crochet flares near the central meridian is not a simple result of masking of crochets by more severe geomagnetic disturbances since averaged geomagnetic indices were high during the western transit of the crochet regions but not during central meridian passage. The crochet does not assist in identifying flares that are followed by geomagnetic disturbances. However, averaged geomagnetic indices following crochet-flares with "major early bursts" at 200 Mc/s rise to a high maximum on day 2 even though crochet-flares are relatively far from the central meridian. The study indicates that crochet-flares do not form a random sample of important flares and that there are systematic differences between flares with crochets and those with "major" ionospheric disturbances. McMath-Hulbert Observatory, University of Michigan, Pontiac, Mich. Publication: The Astronomical Journal Pub Date: 1958 DOI: 10.1086/107666 Bibcode: 1958AJ.....63R.304D full text sources ADS |