Fueled by drought, wildfires have been blazing across the American West all summer. Sixteen are currently burning in California alone. While hiking in Kings Canyon National Park in the state’s rugged Sierra Nevada Mountains recently, I crossed paths with the “Rough Fire” and saw it produce a billowing pyrocumulus cloud.
Pyrocumulus clouds form when intense heat at the surface – usually from a wildfire or volcanic eruption – causes air to rise rapidly. As it travels upward, water vapor in the air condenses into droplets and forms a cloud. Filled with ash and smoke, the swelling cloud generally appears more grey than white.
Ignited by lightning over three weeks ago, the Rough Fire continues to spread and has even caused parts of Kings Canyon National Park to close. According to the NPS, smoke from the massive fire has also impacted the air quality in and around the park. To date, the fire has charred close to 50,000 acres and is only 17% contained.
Pyrocumulus cloud rising over California’s Rough Fire in Sierra National Forest and Kings Canyon National Park, August 2015. Credit: The Weather Gamut.
There may be a new variety of cloud floating in the skies overhead – the undulatus asperatus.
According to the Cloud Appreciation Society (CAS) – an international group of weather enthusiasts – this new cloud resembles an agitated wave that covers most of the sky. First photographed in 2006 by a cloud-watcher in Iowa, it has since been spotted several times around the globe. The CAS is now lobbying the World Meteorological Organization (WMO) to acknowledge the undulatus asperatus as an official new variety of cloud.
There are currently ten cloud types officially recognized by the WMO. Most of these have a number of sub-varieties – specific Latin adjectives to describe their formation. If the undulatus asperatus is accepted as a new variety, it will be the first new cloud added to the WMO’s International Cloud Atlas since 1951.
Undulatus Asperatus Clouds
Image Credit: Cloud Appreciation Society/Ken Prior
While traveling among the Hawaiian Islands, I had the opportunity to visit Haleakalā National Park. Ascending its volcanic slopes, I was struck by its summit region known as “kua mauna”, the land above the clouds. Its unique view is made possible by an elevated temperature inversion.
In the troposphere, the weather layer of our atmosphere, air temperature usually decreases with height. An inversion occurs when something causes that situation to reverse and allows air temperature to increase with height.
At Haleakalā , the inversion is caused by a large-scale subsidence in the Trade Winds. Blowing from centers of high pressure across the Pacific, cool, dense air aloft is warmed by compression as it descends to lower altitudes. In opposition, solar heating warms air near the surface allowing it to rise and cool, forming clouds. When these cool clouds meet the warmer air above them, an inversion layer is formed.
The inversion layer acts like a cap for cloud convection. Therefore, the summit of Haleakalā (10,023 feet), rising above the inversion altitude, stands out like an island in a sea of clouds.
View from the summit of Haleakalā, Maui, Hawai'i
Photo Credt: MF at The Weather Gamut
Clouds are visual indicators of what is going on in the atmosphere. They are also aesthetically interesting.
Mammatus clouds are one of the more striking sights in the sky. Technically, they are a supplementary feature of a variety of other large clouds. However, they are most dramatic when they line the underside of a cumulonimbus. Shaped like giant udders, they form when parts of the anvil cool and sink into warmer air. In general, the more plump the udders, the more severe the recent or nearby thunderstorm.
Below is a photo of the remnants of the first Mammatus cloud I ever saw in person. It was taken in New York City shortly after a violent summer thunderstorm a few years ago.
Photo Credit: MF at the Weather Gamut
On a recent visit to the Yale Center for British Art, I was enchanted by the cloud studies of John Constable. He was an English Romantic painter who believed, “…the sky is the source of light in nature, and governs everything.”
Constable is well known for his grand landscapes that emphasize atmospheric phenomena and mood. His sketch canvases, however, tell us even more about his fascination with the weather. On the back of his cloud studies, he recorded the weather conditions that existed while he painted. For example, on the back of the cloud study painted on September 13, 1821, the artist wrote, “1 o’clock, slight wind at NW, which became tempestuous in the afternoon, with rain all the night following.”
Interested in the developments of the atmospheric sciences of his time, Constable is reported to have owned a copy of Thomas Forster’s Researches About Atmospheric Phenomena. This book included Luke Howard’s 1802 scientific paper, Essay on the Modification of Clouds, which outlines the classification system for clouds that is still used today. A self described “man of clouds”, Constable believed, “we see nothing truly till we understand it.”
Constable's "Study of Cirrus Clouds"
Constable's "Seascape Study with Rain Cloud"
Image Credit: John Constable via Wikipedia
After two days of cloudy skies and heavy rain, it was nice to have a bright sunny day for the Thanksgiving holiday here in New York City.
This quick turnaround in the weather reminded me of a piece of poetry that I recently came across. The poem is called The Cloud and was written by Percy Shelley in 1820. It uses the weather as a metaphor, but highlights the fact that the atmosphere is in a continuous state of change. Clouds, visual indicators of atmospheric activity, are diverse in their forms and functions, but are nonetheless ephemeral phenomena. A cumulus cloud, for example, usually only lasts between five and forty minutes, depending on the wind and other environmental conditions. Enjoy the poem.
Below is the final verse of the six stanza poem:
I am the daughter of Earth and Water,
And the nursling of the Sky;
I pass through the pores of the ocean and shores;
I change, but I cannot die.
For after the rain when with never a stain
The pavilion of Heaven is bare,
And the winds and sunbeams with their convex gleams
Build up the blue dome of air,
I silently laugh at my own cenotaph,
And out of the caverns of rain,
Like a child from the womb, like a ghost from the tomb,
I arise and unbuild it again.
Clouds are mostly made of water-vapor, but a dash of something extra is needed to complete their formation.
As air rises through the atmosphere, it cools. When it reaches its dew point, it is ready to form a cloud if it can find a condensation nuclei. These are free floating microscopic particles in the air, like dust, salt, or smoke . A cloud droplet is born when a water-vapor molecule lands on one of these tiny non-gaseous surfaces and condenses. As cloud droplets gather together in massive numbers, they become visible.
There are a variety of potential condensation nuclei in the air. Their size, composition, and capacity to attract and hold water molecules impact their ability to form clouds. Salt particles, for example, are very good at absorbing water while carbon based particles are not. Without the presence of condensation nuclei in the air, cloud development would be limited to areas of significantly colder air temperatures.
Photo Credit: cmmap.org
The phrase, “to be on cloud nine”, generally means that someone is so elated that they are walking on a cloud. With all the clouds in the sky, why did they choose number nine?
I have heard a number of origins for this popular saying, but the one that makes the most sense to me comes from the pioneering days of meteorology. According to this theory, cloud number nine refers to a cumulonimbus cloud … the towering anvil shaped cloud of violent thunderstorms.
The story goes back to 1802 when an amateur British meteorologist named Luke Howard developed a basic nomenclature for clouds. He gave us names like cumulus, stratus, and cirrus. His system followed the Linnaean ideas already in use with flora and fauna. As the science of meteorology developed, different nations soon created their own weather vocabularies and classification systems. This lack of consistency was creating confusion, especially since weather does not recognize national boundaries. Before we had radar and satellites, the study of weather and early forecasting relied on cloud identification and communications between weather stations. To function properly and advance the science, these communications needed a uniform system of identification and measurement.
In 1896, an International Meteorology Conference was held in Paris to establish a uniform standard of cloud classification. The committee built on Luke Howard’s Latin-based scientific names and set up the convention of grouping clouds according to their altitude. The product of this conference was the The International Cloud Atlas. This reference book used photographs and drawings to identify the ten cloud types agreed upon by the committee. Cumulonimbus was number nine on their list.
A cumulonimbus is the tallest of all cloud types. So, to be on cloud nine is to be on the highest cloud in the sky. In a later edition of the Cloud Atlas, the order of list was re-arranged and cumulonimbus was moved to number ten. The phrase, however, is still with us.
The International Meteorological Committee still exists today in the form of the World Meteorological Organization within the U.N. They continue to publish The International Cloud Atlas.
The Ten Cloud Types
Photo Credit: Cloudloverclub