“Fire Rainbows” (Circumhorizontal Arcs) & Cloud Iridescence
These phenomenons are and can be uncommon (especially depending on your location) and bloody cool! Like moon and sun halos, they work basically the same way: clouds in the atmosphere have ice crystals and water droplets that cause diffraction and scatter the light when the sun is at just the right angle. Circumhorizontal Arcs (aka “Fire Rainbows”) are more common than Cloud Iridescence, as the sun must be high in the sky for fire rainbows, which produce these massive halos that usually you can’t fully see due to your location or scattered clouds. Cloud Iridescence is with smaller crystals “closer” to the sun and in certain thin clouds. With that, classification of all these different phenomenons depends on the size of the crystals, degree of the sun (or moon), location (etc), giving us an awesome variety of atmospheric optical phenomenons to witness!
Shuttle Silhouette (Credit: NASA)
“In a very unique setting over Earth’s colorful horizon, the silhouette of the space shuttle Endeavour is featured in this photo by an Expedition 22 crew member on board the International Space Station, as the shuttle approached for its docking on Feb. 9 during the STS-130 mission.”
“The orbital outpost was at 46.9 south latitude and 80.5 west longitude, over the South Pacific Ocean off the coast of southern Chile with an altitude of 183 nautical miles when the image was recorded. The orange layer is the troposphere, where all of the weather and clouds which we typically watch and experience are generated and contained. This orange layer gives way to the whitish Stratosphere and then into the Mesosphere. In some frames the black color is part of a window frame rather than the blackness of space.”
Fierce dinosaurs may not have had to contend with many predators, but intense and frequent wildfires may have been a real threat during their reign, new research suggests. Wildfires seem to have left their mark on the archeological record in the form of charcoal deposits.
The researchers discovered these abundant and widespread fires by analyzing the amount of charcoal in the fossil record. They created a global database of charcoal deposits during the Cretaceous Period (the period from 145 million to 65 million years ago). Many of these charcoal deposits were associated with beds of dinosaur fossils.
“Charcoal is the remnant of the plants that were burnt and is easily preserved in the fossil record,” study researcher Andrew C. Scott, a professor from Royal Holloway University of London, said in a statement.
Definitely a cool article to read about the Cretaceous atmosphere and how it (in theory) affected the ecology. Like they said in the article, many people don’t first think about how fires (and other types of natural disasters/events) would affect the areas it took over. I remember a part in ‘Walking With Dinosaurs’ where they had a small section on a wildfire in the forest which took all the vegetation, some Diplodocus, and other countless lives. With those higher levels of oxygen and the general atmosphere back during the Mesozoic, we all know how that would heighten changes of fires or other weather conditions. Yes, I love dinosaurs very much, but the Mesozoic atmosphere and weather is just as interesting.
Some 2.7 billion years ago in what is now Omdraaisvlei farm near Prieska, South Africa, a brief storm dropped mild rain on a new layer of ash laid down by a recent volcanic eruption (not unlike ash from the 2010 Eyjafjallajökull eruption in Iceland) forming tiny craters. Additional ash subsequently buried the craters and, over eons, hardened to become rock known as tuff. Closer to the present, other rainstorms eroded the overlying tuff, exposing a fossil record of raindrops from the Archean eon, and may now have revealed the density of early Earth’s atmosphere.
By scanning with lasers the craters created by ancient raindrops—and comparing the indentations with those made by water drops sprinkled onto a layer of similar ash today—physicist Sanjoy Som of the University of Washington in Seattle and his colleagues have derived a measurement of the pressure exerted by the primitive atmosphere. The scientists report in Nature on March 29 that the ancient air could not have been much denser than the present atmosphere—and, in fact, may have been much less so. (Scientific American is part of Nature Publishing Group.)
“Air pressure 2.7 billion years ago was at most twice present levels, and more likely no higher than at present,” Som explains. The key to that determination is raindrop size. Back in 1851 pioneering geologist Charles Lyell suggested that measuring the fossilized indentations of raindrops might reveal details about the ancient atmosphere. These mini-craters are formed based on the size and speed of ancient raindrops. Because the atmosphere drags on each drop, constraining the speed of its descent based on its size, if one could determine an ancient raindrop’s size, one could determine how thick the atmosphere likely was.
Definitely an interesting article to read, and wonder more about Earth’s early atmosphere!