Pyramidal halos over Frankfurt am Main

Andreas Zeiske observed a pyramidal halo on 6 June 2011 in Frankfurt am Main. In the images, the 22° halo, 18° halo and the left 18° lateral arc can be seen about the St.-Katharinen-Church. The phenomenon formed on a thin field of Cirrus clouds and lasted for 10 minutes at around 08.00 CET. About 5 hours later a cold front with rain showers and thunderstorms swept across the city of Frankfurt. ( 1 - 2 )

Andreas Zeiske, Germany

Atmospheric Phenomena Blog

The blog on atmospheric optics has moved to a new address ( 1 ), and has recently been updated with many interesting observations. As a teaser, Michael Großmann's image of a tertiary order rainbow can be seen on the right.

Pyramidal halo from Thailand

The above image was photographed by Pitan Singhasaneh on 5 June in Bangkok, Thailand.

Simultaneous upper tangent arc and rainbows

On 4 June 2011 Pietari Puranen observed these rainbows in Jyväskylä. When he turned around to see the sky around the sun, he observed an upper tangent arc. Remarkably, the arc formed in virga precipitating from the same low clouds around the rainbow forming cumulonimbus. It is rare to see halos in virga so close to rainbows.

As column crystals are formed in temperatures relatively close to 0 degrees Celsius we may assume the Virga has been born in temperatures around, say, -4 to -9 degrees Celcius. At least in those temperatures diamond dust close to the ground seems to most often exhibit column crystals.

Double sun effect

On May 1st 2011 cumulonimbus clouds precipitating hail were commmon. These clouds exhibited clear praecipitatio and later in the evening they featured prominent virga. In these virga a sun pillar formed and as the sun descended behing stratocumulus a double sun effect was seen. A series of images is provided to see the progression of the effect. The real sun can be seen descending behing the stratocumulus.

The first observation of this effect was by Giovanni Cassini in 1693 (see e.g. Riikonen 2011 (1)). By clicking the above image a larger version can be seen. A full image gallery is available online (2). Marko Riikonen also captured images from the other side of the lake (3).