The International Cloud Atlas fifth edition, published in 2017, has included cloud types that were not recognized before, including types that are caused by humans and other unexpected sources. I’ve already posted on cirrus homogenitus, upper etage clouds forming from the condensation trails of aircraft. Today’s post is about cumulus flammagenitus, cumulus clouds formed by convection caused by a heat source. The heat source could be a wildfire or a volcano, for example, but the cloud can’t be just smoke or ash. It must include water droplets to qualify as a cloud. This type of cloud is also known by the name “pyrocumulus,” or “fire cloud,” which combines fire and the basic cloud type.
Wikipedia has a more in-depth article on flammagenitus than does the Cloud Atlas. As with other cumulus clouds, the convective clouds of the lower etage, flammagenitus can vary in vertical development, with bigger clouds being named accordingly. So we can have cumulus congestus flammagenitus, also known as towering cumulus flammagenitus, and cumulonimbus flammagenitus, complete with the lightning, wind and precipitation associated with thunder clouds.
Credit Jan Knight – World Meteorological Organization
Here’s another example. This flammagenitus is also referred to as pyrocumulonimbus. That is, a cumulonimbus cloud formed from fire. Tap for large original.
Eric Neitzel – CC-BY-SA
I have seen flammagenitus rising above forest fires, and it is impressive. The heat is so intense that the smoke, combined with the water driven out of the burning trees, can be driven rapidly high into the atmosphere. These clouds easily rival regular towering cumulus and cumulonimbus in their size and appearance.
Cavum is one of the new clouds that show up in the latest edition of the World Meteorological Organization’s International Cloud Atlas. I reported on the release of the new edition in this post. Cavum is really just a new name for a cloud type previously known as a fall streak hole, which I reported on here. There are more great pictures in that post. The full name for the example shown in this post is altocumulus stratiformis perlucidus translucidus cavum. That is, the middle etage cloud altocumulus (my previous post on altocumulus) which is in a layer thin enough to allow light through, and which has gaps between its elements and a great big hole with virga in it. Here’s how cavum is described in the International Cloud Atlas.
A well-defined generally circular (sometimes linear) hole in a thin layer of supercooled water droplet cloud. Virga or wisps of Cirrus typically fall from the central part of the hole, which generally grows larger with time. Cavum is typically a circular feature when viewed from directly beneath, but may appear oval shaped when viewed from a distance.
When resulting directly from the interaction of an aircraft with the cloud, it is generally linear (in the form of a dissipation trail). Virga typically falls from the progressively widening dissipation trail.
Occurs in Altocumulus and Cirrocumulus and rarely Stratocumulus.
And here’s the description of the image from the International Cloud Atlas.
This thin, translucent and extensive layer of cloud is Altocumulus stratiformis translucidus. In the top part of the picture it also displays the variety perlucidus, as there are the gaps between the cloud elements. However, the most striking feature is the large, roughly circular hole beneath which there is virga. The large hole is the supplementary feature cavum, popularly known as a “fallstreak hole” or “hole-punch cloud”. The full classification for the cloud is therefore Altocumulus stratiformis perlucidus translucidus cavum.
Also of note is a linear gap in the cloud between the fallstreak hole and the horizon. This is an aircraft dissipation trail, or distrail, formed as a result of an aircraft flying through the cloud layer. Informally this is sometimes known as a “canal cloud”. It later transformed into a circular-type hole.
The supplementary feature cavum is formed when glaciation occurs in a thin cloud layer consisting of supercooled water droplets that are in a liquid state and at a temperature below 0 °C. As the supercooled water drops glaciate, the resulting ice crystals fall from the cloud layer to a lower level as virga, or fallstreaks. The resulting cloud hole typically grows larger with time while the glaciation process continues.
I think HobbyHelp is selling itself short by limiting its audience to beginners “looking to start a new hobby.” I think their site would be useful to people who are already involved in a hobby, too. People who are trying to expand their knowledge, or who are contemplating taking the next step in their experience. That is certainly true of Jenny’s post mentioned above. The depth of her research is plain to see. The care in the writing is obvious. While useful to someone taking their first steps in the hobby of astronomy, her piece would also be useful to people further along.
If you’re looking for a new hobby, visit the HobbyHelp website. If you’re interested in astronomy, visit Jenny’s post. Either way I think you’ll be rewarded for your effort.
August 5, 2019
I got a note from Charles Wade of the NightSkyPix website asking if I would like to add a link to his site to offer my readers an additional source of information. From the site:
NightSkyPix is dedicated to learning and teaching all aspects of astrophotography and night-time imagery.
I had a look at the site and could see no obvious reason why I shouldn’t link to it. It looks like a thorough and professionally-crafted site dedicated to astrophotography.
Credit Stefan Xp – CC-BY-SA – Self-made UFO over Meersburg
It was a good year for aliens. Whether it was the fluctuations in the brightness of Tabby’s star, the oddly shaped interstellar visitor that passed through the Solar System, or a spate of sightings of UFOs, aliens received a lot of nominations. As always with the advocates of alien visitations, they want us to prove that it isn’t aliens. They say, “How do you know it isn’t? Can you prove it isn’t?” They always get that backwards, don’t they?
From the Scientific American article:
What do a strangely fading faraway star, an oddly shaped interstellar interloper in the solar system and a curious spate of UFO sightings by members of the U.S. military all have in common?
Far from being close-minded killjoys, most scientists in the “never aliens” camp desperately want to be convinced otherwise. Their default skeptical stance is a prophylactic against the wiles of wishful thinking …
Finding aliens—or coming up empty in our searches—has profound implications for our own ultimate cosmic fate.
UFO detections have remained marginal for decades; they’ve just gone from being blurry shapes on film cameras to blurry shapes on the digital infrared sensors of fighter jet gun cameras. This, in spite of the fact that the world’s total imaging capacity has expanded by several orders of magnitude in the past 20 years.
Hypothetical aliens with advanced technology could do that, of course. But then you have to ask why they would choose to remain marginally undetectable rather than just being undetectable.
It was a good year for alien hunters, but not good enough. They still haven’t come up with solid proof that their beliefs are true. I guess that’s why they keep asking us to prove that they aren’t, even though that’s the wrong way ’round.
You might be aware of the website dedicated to the Astronomy Picture of the Day (APOD.) You can visit the site and see another great picture every day. Some people even set things up so their computer’s desktop image is the APOD changing daily. It’s a NASA website and just one of the ways that organization shares its discoveries with the public. Today I’m going to direct you to another one called the NASA Image and Video Library. They have brought together about sixty of their media archives into one source. Here’s an article on Space.com about the library.
Here are some samples of the images available. They link to the much larger originals. These images are Public Domain.