Solar Flaring in SC24: End of an Era?

Presenter(s): harry roberts

Affiliation(s): ASNSW, SCS(BAA, NSW), Shoalhaven Astronomers

Session details: Posters

Abstract

This paper revisits the question of Solar Flaring where the NACAA2008 paper, “Anomalous Flaring in Solar Cycle 23”, left off. That paper concluded that flaring in solar cycle 23 (SC23, 1997-2008) was unusually strong compared to earlier cycles. Reasons for this were advanced. As well as being a thermonuclear reactor, the Sun contains a dynamo, and magnetism drives most solar activity – including sunspots and their flares. Data collected since SC23 (2008 – 2016) will show that the power of current flaring in SC24 (GOES satellite X-ray flux, 2008 – 2016) has fallen dramatically when compared to the earlier cycles, particularly SC23: indeed to levels not seen since X-ray flux data have been available (~40yrs). We examine some of the strong flares of SC24, as logged in H-alpha, contrasting them with earlier SC23 events. This will be supported by data from other channels, notably the strength of sunspot umbral-fields from Mt Wilson and Kitt Peak facilities. We will conclude that an era of steadily increasing flare power peaked in SC23, and that SC24 activity is now about an order of magnitude weaker by comparison. This prompts the idea that the Sun has a way of accumulating magnetic power over several solar cycles, despite the general belief that no such mechanism exists. A mechanism for the steady increase in flare power over the latter part of the 20thC will be suggested. The paper will support the 2008 conclusion that flaring in SC23 was anomalously strong. It will also confirm that an era of steadily stronger flaring, over successive solar cycles, ended in 2008 – suggesting a reason for that abrupt decline.

Biography

Harry Roberts Born in Adelaide in 1946, at a time of intense solar activity, Harry has the Sun ‘in his veins’. His first images were projected with a small ‘scope and later a larger reflector in the 1960’s, making occasional observations over the next two decades. In the 1980’s an 8”SCT with ND filter was used to photograph spot groups in detail. In 2000 he commenced daily recording and measurement of sunspots. In 2001 he upgraded the 8” ‘scope by adding an H-alpha filter, taking his first steps into the bizarre world of high velocity ejections and solar flares. These investigations led to numerous articles in the journals of the RASNZ “Southern Stars” and the ASNSW, as well as presentations to various amateur groups and public outreach.

His favourite solar event was following an ejecting filament from the Sun’s surface to a point over one solar radius away: material shown to be moving at ~300 km/sec! Through the early 21stC he made detailed logs of complex sunspots liable to flare (‘Delta’ groups) and, at times, multiple logs of the evolution of flares in such groups, incorporating online sunspot polarity data. In 2008 he submitted a poster paper to NACAA on “Anomalous Flaring”.

Awards: ASNSW Southern Cross Award 2003, NACAA poster prize 2008 (“Anomalous Flaring in Cycle 23”). ASNSW Mike Kerr Medal 2009 for observational astronomy. McNiven Medalist 2012.