LOOKS LIKE A STORM IS COMING
Primm Travel Blog› entry 4 of 4 › view all entries
My favorite type of clouds:
Cumulus humilis is what is commonly referred to as "fair weather cumulus". In hot countries and over mountainous terrain these clouds occur at up to 6000 meters altitude, though elsewhere they are typically found lower.
They are formed by rising warm air that has been heated by the ground, which in turn has been heated by the sun. They have a limited depth (technically known as showing no significant vertical development). This indicates that the temperature in the atmosphere above them either drops off very slowly or not at all with altitude (see Lapse rate). While cumulus humilis may be accompanied by other cloud types, when they appear in a clear sky (see picture), they are an indicator of pleasant weather for the next several hours.
Below the cloud base the air can be quite turbulent, giving occupants of light aircraft a rough ride. To avoid turbulence where such clouds are present, pilots may climb above the cloud tops. However glider pilots actively seek out the rising air to gain altitude.
Cumulus mediocris is a cloud form of the cumulus family, slightly larger in vertical development than Cumulus humilis. It may or may not show the cauliflower form characteristic of cumulus clouds. This cloud type does not produce precipitation, but may further advance into clouds such as Cumulus congestus and Cumulonimbus, which do.
A few clouds can be found above the troposphere; these include noctilucent and polar stratospheric clouds (or nacreous clouds), which occur in the mesosphere and stratosphere respectively.
Some clouds form as a consequence of interactions with specific geographical features. Perhaps the strangest geographically-specific cloud in the world is Morning Glory, a rolling cylindrical cloud which appears unpredictably over the Gulf of Carpentaria in Northern Australia. Associated with a powerful "ripple" in the atmosphere, the cloud may be "surfed" in unpowered glider aircraft.
A cloud field is simply a group of clouds but sometimes cloud fields can take on certain shapes that have their own characteristics and are specially classified. Stratocumulus clouds can often be found in the following forms:
* Actinoform, which resembles a leaf or a spoked wheel.
* Closed cell, which is cloudy in the center and clear on the edges, similar to a filled honeycomb.
* Open cell, which resembles a honeycomb, with clouds around the edges and clear, open space in the middle.
The color of a cloud tells much about what is going on inside the cloud. Clouds form when relatively warm air containing water vapor is lighter than its surrounding air and this causes it to rise. As it rises it cools and the vapor condenses out of the air as micro-droplets. These tiny particles of water are relatively densely packed and sunlight cannot penetrate far into the cloud before it is reflected out, giving a cloud its characteristic white color.
Other colours occur naturally in clouds.
A greenish tinge to a cloud is produced when sunlight is scattered by ice. A cumulonimbus cloud which shows green is an imminent sign of heavy rain, hail, strong winds and possible tornadoes.
Yellowish clouds are rare but may occur in the late spring through early fall months during forest fire season. The yellow color is due to the presence of smoke.
Red, orange and pink clouds occur almost entirely at sunrise/sunset and are the result of the scattering of sunlight by the atmosphere.
It has been suggested that Cloud feedback be merged into this article or section. (Discuss)
The recently recognized phenomenon of global dimming is thought to be caused by changes to the reflectivity of clouds due to the increased presence of aerosols and other particulates in the atmosphere.
New research From Dimming to Brightening: Decadal Changes in Solar Radiation at Earth's Surface by Martin Wild et al.
Global brightening is caused by decreased amounts of particulate matter in the atmosphere. With less particulate matter there is less surface area for condensation to occur. Since there's less condensation in the atmosphere and increased evaporation caused by increasing amounts of sunlight striking the water's surface there is more moisture, causing fewer but thicker clouds.
Clouds on other planets
Within our solar system, any planet or moon with an atmosphere also has clouds. Venus' clouds are composed entirely of sulfuric acid droplets. Mars has high, thin clouds of water ice. Both Jupiter and Saturn have an outer cloud deck composed of ammonia clouds, an intermediate deck of ammonium hydrosulfide clouds and an inner deck of water clouds. Uranus and Neptune have atmospheres dominated by methane clouds.
Saturn's moon Titan has clouds which are believed to be composed largely of droplets of liquid methane. The Cassini-Huygens Saturn mission has uncovered evidence of a fluid cycle on Titan, including lakes near the poles and fluvial channels on the surface of the moon.