Ephemeral active regions

• Published in: Solar physics Vol. 32; no. 2; pp. 389 - 402
• Main Authors: Harvey, Karen L., Martin, Sara F.
• Format: Journal Article
• Language: English
• Published: Springer 01.10.1973
• Subjects: ASTRONOMY AND ASTROPHYSICS; DISTRIBUTION; LATITUDE EFFECT; PHOTOSPHERE- MAGNETIC FIELDS; SIZE; SUNSPOTS- MAGNETIC FIELDS
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/BF00154951

Ephemeral active regions attain maximum development within 1 day or less of their initial appearance and are typically observed for 1 to 2 days. They appear mostly as small bipolar regions having a typical dimension of about 30,000 km and a maximum total flux of the order of 1020 Mx. The ephemeral regions generally do not produce sunspots and flares, though they are identifted in H alpha as small active centers. Observations indicate that the ephemeral regions are frequently generated both near large active centers and in extensive quiet areas of the Sun. The location of emerging ephemeral regions does not appear to be associated with the distribution of the existing network fields. As many as 100 ephemeral regions may form per day. On the average, as much flux may erupt in the form of small ephemeral regions as erupts in larger active centers. The latitude distribution of ephemeral regions appears to be much wider than that of sunspots and major active centers. Their frequency of occurrence does not appear to follow the sunpot cycle.