The proton flare of August 28, 1966

Abstract

The proton flare of August 28, 1966 began on Ha records at 15h21m35 ~ UT. It presented an unusually complex development with flare emission occurring in two distinct plages. The brightest part of the flare attained maximum intensity, 152 % of the continuum, between 15h30 TM and 15h32 m UT. Photometric measurements show that a long-enduring part of the flare continued to decline in intensity until at least 21h20 TM UT.The flare developed first in parts of the plages that were near the extremities of a filament and a complex system of curvilinear absorption structures, possibly an eruptive prominence in projection. During the rise to maximum intensity a large expanding feature moved southward from the site of the flare with a velocity ~ 700 km/sec. Its appearance on monochromatic records of the chromosphere made in the center of Hc~ and 0.5 A on either side was consistent with the effect of an advancing phenomenon that induces a small shift of the Hc~ absorption line, first to longer, and then to shorter wavelengths.Two bright flare-filaments were obvious aspects of the event by 15~128m and dominated the main phase of the flare. Loop-type prominences were observed in absorption as early as 15h40 m. General Description of Outbreak and Development of the H~ FlareThe proton flare of August 28, 1966 (Imp. 2B or greater, N22 E05) occurred in two well-defined plages, each with separate spot groups, and presented an unusually complex development. The first evidence of flare-emission on the He patrol films of the McMath-Hulbert Observatory (0.5 A band pass) occurred at 15h21 m35 s UT ** when a small area, region 1 in Figure 1A, on the North side of filament F ( Figure 1B) suddenly increased in intensity. Thirty seconds later another small point, region 2, directly across the filament and on the South side was also the site of flare-emission. These two initial brightenings were in the plage surrounding the dying/3 spot group (Mt. Wilson No. 16111) that preceded by approximately 15 ~ the large/37 spot (Mt. Wilson No. 16114) near which the principal He emission of this proton flare would occur. By 15h22m35 S flare-emission had started at regions 3 and 4 within the large bright plage surrounding the/~7 spot. The flare then broke out in numerous small bright points, some of which are indicated in Figure 1. Intensity increased rapidly at 15h24 TM and 15h25 m UT and maximum intensity was reached between 15h3ff n and 15h32 m UT. (See Figure 2.)The regions of enhanced emission for this flare fall naturally into two parts, the

Flare waves observed in Helium I 10 830 Å

“…The plasma is pushed down, but due to inertia it takes some time to get maximum compression. In this period of downward plasma motion the Moreton wave is seen in absorption in the red wing of the Hα line and in emission in the blue wing (Dodson & Hedeman 1968). In the line center, the maximum ∆I in Hα is reached (r = 3 in Fig.…”

Sequential Chromospheric Brightenings beneath a Transequatorial Halo Coronal Mass Ejection

“…The downward and upward oscillation of the chromosphere damps out after only one to two oscillations. Similar sudden vertical oscillations in filaments (Dodson & Hedeman 1964;Ramsey & Smith 1966) had been first seen in H line-center images as ''winking '' filaments that momentarily flickered out and back into view, always within minutes of an exceptionally bright flare in a neighboring region (Dodson 1949;Bruzek 1951; see references in Smith & Harvey 1971). The measured speed of the visible chromospheric waves were initially found to be in the range 500-2000 km s À1 , and the propagating front was thought to be confined within a $90 sector angle (Moreton 1960;Athay & Moreton 1961).…”

“…The classic chromospheric flare wave, also known as a Moreton wave (Moreton 1960;Athay & Moreton 1961;Dodson & Hedeman 1964;Dodson & Hedeman 1968;Smith & Harvey 1971), appears in images in the wings of H as both bright and dark parallel fronts propagating in an arc, away from the site of solar flare. The bright /dark front (or dark / bright in the opposite wing of H) is due to the successive depression and relaxation of chromospheric structures caused by the pressure of an overlying coronal wave assumed to propagate at high velocity through the corona from the site of a solar flare.…”

On the Origin of the Solar Moreton Wave of 2006 December 6

“…Moreton waves, large-scale waves observed in Hα emanating from the sites of major solar flares, were first reported 50 years ago (Moreton 1960(Moreton , 1961(Moreton , 1964Moreton & Ramsey 1960;Athay & Moreton 1961;Dodson & Hedeman 1964;Ramsey & Smith 1966;Dodson & Hedeman 1968). Such waves have characteristic speeds of ∼1000 km s −1 and tend to be directional, with angular widths typically in the range from 60 • to 150 • (Smith & Harvey 1971;Warmuth et al 2004a;Veronig et al 2006), although cases with fragmented arcs collectively spanning larger angles have been reported (Pick et al 2005;Balasubramaniam et al 2007;Muhr et al 2008Muhr et al , 2010.…”