Tuesday, 1 February 2011

Halo observations by J. R. Blake in the Antarctic

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There are two books devoted to halo observations in the Antarctic in 1950's. One is by the Swedish meteorologist Göstä Liljequist and another by the Australian glasiologist Roger Blake. The images above are from Blake's book "Solar Halos in Antarctica", which I found for sale in an Australian antikvariat a few years ago. Blake was in a project called the "Souther Seismic Traverse", using the Australian research station Mawson as a base for the trips further south. The time he spent in the Antarctic spanned from 30 September 1958 to 17 January 1959 and halos were a sideline research for him, clearly inspired by the Liljequists's work in the early 50's. Above are shown three displays from Blake's book.

The first display, observed from a field trip at the location 70.1° S and 62.1° E on 21 November 1958, contains 9° halo. Blake wrote the following notes on it: "The parhelic circle extended only about 10° either side of the sun, being rather faint. It formed a closed semicircle with a very faint Hall's halo, the radius of that halo being approximately half that of the 22° halo, but observations being greatly impeded by the sun's brightness."

The second display was seen near the first display's location, on 28 November 1958. It has sunvex Parry arc and halos at the anthelic region: "Through the anthelic point was a bright, white vertical pillar, reaching the ground. Also visible was part of the parhelic circle, the intersection of the two arcs being a 'spot' of greater intensity. The parhelic circle did not exists elsewhere."

The third observation on 29 November 1958 was made in the same area as two previous ones. It has several interesting features: "The 22° and 46° halos were both very brightly coloured, and both 22° and 46° parhelia were present, both pair being very bright. The vertical pillar extended from the horizon to the top of the 22° halo, which was brilliant. From this point extended the upper contact arc which merged smoothly with Parry's Arc; both these arcs were coloured and very bright. [... ] The circumzenithal arc was also present, being very brightly coloured. A fairly bright, coloured arc, passing through or close to the zenith and concave to the sun was visible, the colours being very pure and distinct. Because of its position, it was difficult to obtain any estimates; however, it appeared to have approximately the same curvature as the 22° halo. The full 180° of the parhelic circle was visible on either side of the sun, being intersected approximately 90° from the sun by a pair of white pillars extending from the horizon slightly above the parhelic ring. The points of intersection resembled mock-suns, though white. Also at 180° there existed a somewhat fainter, white pillar extending to just above the horizon, the point of intersection with the parhelic circle again being brighter. The display disappeared as the cloud cover increased."

Now I could go on discussing what Blake really saw in 29th November display, but that would not lead anywhere. Suffice to say: a photograph would have been nice.

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