Oblique supernumeraries to the primary rainbow

August 1, 2015: Rainbow with oblique supernumeries. Photo: Claudia Hinz

August 1, 2015: Rainbow with oblique supernumeries. Photo: Claudia Hinz

Last fall, two AKM members observed a rainbow with supernumeraries, which were clearly oblique to the primary rainbow.

On August 1, 2015, they were observed by Claudia Hinz on a red rainbow just before sunset in the Fichtelgebirge / Erzgebirge mountains. A rain front had just passed and the last precipitation from the departing clouds evaporated in the air, so that the raindrops did not reach the ground anymore. Virga were clearly visible and at the same time an intensive Zero order glow could be seen at the Sun side.

On October 5, 2015, Sirko Molau observed in Günzburg/Bavaria a similar phenomenon. Also here the rain shower had already passed and a strip of blue skies was visible near the horizon. Over one hour after the rain Sirko was surprised to see a bright rudiment of the rainbow. On the first glimpse it looked like a split rainbow. However, a closer look revealed that two interference bows disemminated obliquely from the root of the rainbow.

1b-tile

October 5, 2015: Rainbow foot with oblique supernumeries. Photo: Sirko Molau

The oblique interference arcs can be explained best with different raindrop sizes. In both cases, the rainbow appeared after the rain had disapperead and just when the Sun showed up. We can assume that dry air had already moved in, causing the last drops to evaporate on their way to the ground. So the raindrops quickly reduced in size after they left the cloud. The simulation of Les Cowley shows that with reduced drop size not only the number, but also the distance of the interference bows decreases.

Authors: Claudia Hinz, Sirko Molau, Germany

Advertisements

Posted on February 9, 2016, in rainbow and fogbow and tagged , , , . Bookmark the permalink. 3 Comments.

  1. The tropical photos are wonderful.

  2. Hi guys,

    very nice pictures of a rare phenomenon! In July 2015 I made an indoor rainbow with a spray bottle, and accidently created a drop size gradient (small drops at the top, big drops at the bottom), as you can see from the supernumerary spacing:

    By the way, of course I continued spraying until I got a full circle:

    Best regards,
    Alex

  3. Barry Vanderhorst

    Cannot understand the oblique supernumeries. Do not observe them in the pics. Do not observe 2 rainbows from the same root. Oblique means at some strange angle. I see a primary and secondary bow, primary with supernumeries, as usual. In the second pic, observe just a primary. I know I’m blind, but please set me straight.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: