All posts tagged meteorology

Cloud of the Day – International Cloud Atlas

The International Cloud Atlas has recently published a new edition, the first in thirty years. The 2017 edition is only the fifth one, with the first coming out in 1939, so it’s pretty special. The International Cloud Atlas is a product of the World Meteorological Organization, an agency of the United Nations. The Atlas takes much the same approach as I do in their definition of what is a “cloud.” In my Cloud of the Day series I have included many things that aren’t strictly clouds, such as rainbows, haloes and sprites. The Atlas collects them all under the umbrella of meteors. So we have hydrometeors — meteors composed of water — that include things other than clouds, such as fog and rain. And there are photometeors, that are made by light, such as rainbows, etc . Electrometeors include auroras and Saint Elmo’s fire. There are even lithometeors, made of dry particles, like dust and haze. I don’t feel quite so bad now. If the UN can do it, who am I to cavil?

The existing classifications have been reviewed and all have been retained. Several new, formal cloud classifications have been introduced. These include one new species (volutus), five new supplementary features (asperitas, cauda, cavum, fluctus and murus), and one new accessory cloud (flumen). The species floccus has been formally recognized as being able to occur in association with stratocumulus. The separate section on Special Clouds has been removed, and the cloud and meteor types previously discussed within this section have been integrated into the cloud classification scheme as cataractagenitus, flammagenitus, homogenitus, silvagenitus, and homomutatus.

This edition of the International Cloud Atlas includes new additions, including one you might remember seeing here when it hadn’t yet been accepted as a unique type. I wrote about it as asperatus, but they’ve changed the spelling to asperitas. This cloud was championed by the Cloud Appreciation Society, a collection of enthusiastic amateurs, and great photographers.

Photo credit – NASA – PD

Enjoy this fresh edition of the International Cloud Atlas. It has a searchable image gallery.


Photo credit - Deven Stross CC-BY-NC-ND

Photo credit – Deven Stross CC-BY-NC-ND

Cloud of the Day – Aurora

Aurora is not clouds. Clouds can’t form in the tenuous wisps of atmosphere found at the heights, approximately 90 – 1,000 kilometers, where aurora occurs. Therefore, it is wrong for me to call aurora the cloud of the day. Naughty me. It’s a meteorological phenomenon, and it’s beautiful. I’ll call it the cloud of the day if I want.

Photo credit - Alan C Tough

Photo credit – Alan C Tough

Photo credit - Andia Frh

Photo credit – Andia Frh

The Northern Lights, aurora borealis, were named in 1621 by Pierre Gassendi, a French scientist, priest and philosopher. Boreas was the Greek name for the north wind, and Aurora was the Roman goddess of the dawn. The Northern Lights are mirrored around the south pole by aurora australis, the Southern Lights.

Photo credit - 14jbella Click image for huge poster

Photo credit – 14jbella
Click image for huge poster

Photo credit - John Freddy

Photo credit – John Freddy

The aurorae work on the same principle as a neon lamp. Energized atoms release the excess energy as photons of light. In a neon lamp, the atoms are energized by electricity. In aurorae, nitrogen and oxygen atoms are energized by the solar particles that are trapped and funneled into the upper atmosphere by Earth’s magnetic field. When intense enough to be more than a whitish glow, the most common colors are green from oxygen and red from nitrogen. Other colors result from mixing of the main colors, or from variations in the excitation-release mechanism. For example, the rare blue that sometimes comes from nitrogen.

Photo credit - Aaron Kaase - Public domain

Photo credit – Aaron Kaase – Public domain

Although it might be interesting, there is no precipitation from aurora.