The Fascinating World of Clouds.

“There’s a bright spot in every dark cloud.” — Bruce Beresford

There can barely be any weather phenomenon more common, yet also more changeable than clouds. They constantly waft across the sky, sometimes blocking the sun, sometimes bringing rain, sleet and snow. They seem to have their own moods and personalities. Weather watchers around the world are often transfixed by their variability.

Formation of Clouds

There are many types of clouds that are all generally formed in the same way — normally the sun heats the surface of the earth, causing invisible water vapor to rise that eventually condenses into visible water droplets or crystals to form clouds.

For this to happen, the rising air must be saturated, in other words, not be able to hold any more water in vapor form. Saturation can happen in two ways:

• Firstly, by increasing the water content of the air, usually through evaporation to a point where the air can hold no more water vapor.
• Secondly, and most commonly, by cooling the air to the ‘dew point’, which is the point that the air can hold no more water causing condensation to happen.

As the air rises, it expands in volume due to the lower atmospheric pressure. The energy used by this expansion causes the temperature to fall, and hence reach the dew point.

It is estimated that 67% of the earth’s surface is covered by cloud at any given time, with the mid-latitudes and the equator being the most cloudy. This is caused by the interaction of large masses of water, part of the world’s circulation process. Weather science has created complex models to predict their location, size and route around our skies.

Why are clouds white?

Clouds are white, the sun is orange and the sky is blue for the same reason. Light coming from the sun is actually white, though as it enters the confines of the earth’s atmosphere, small particles separate the blue light from the pure white sunlight, causing a blue sky and orange sun. The sky is slightly less blue at the horizon as the sunlight travels further through the atmosphere, further scattering the light wavelengths, and enabling some to re-combine to form larger levels of white light.

However, the droplets of water are far larger in clouds, this means that all spectrums of sunlight are scattered almost equally, meaning that no separation occurs, and the pure white sunlight brightens the clouds. So next time you lookup into the clouds, imagine that you are actually looking at sunlight as it really is.

Fire-Breathing Dragon

Although the heating of the air is normally caused by gradual warming by the sun, other geographical factors can create a more dramatic heating effect — wildfires and volcanoes can create a heat source that causes the rapid formation of clouds known as pyrocumulus. If there is enough water vapor in the air, dramatic thunderstorms, pyrocumulonimbus, and lightning can happen. The anvil shaped pyrocumulonimbus clouds actually contain the smoke from the fires, and can reach five miles high. These storms can act as a ‘funnel’, and through an effect known as “pyroCb”, can cause the previously earth-bound polluting particles to linger in the air, causing ill-effects to people and animals.

There have been a number of ‘mystery cloud’ phenomena, an example being one initially attributed to the 1991 eruption of Mount Pinatubo in the Philippines, that was actually caused by a pyrocumulonimbus storm originating in Canada.

Cloud Suck

The base of cumulus clouds are well known as places of potential danger for gliders, paragliders and hand-gliders. The strong thermal updrafts in these areas lead to a phenomena known as ‘cloud suck’. Pilots have reported being unable to descend in these conditions, even by using maneuvers that would normally cause a rapid descent, the clouds seem to be ‘sucking’ their aircraft higher and higher.

These conditions are especially dangerous for paragliders, whose speeds are typically less than 35mph. This was certainly the case for Eva Wiśnierska-Cieślewicz, who in February 2007 was sucked at speeds of 45mph into a cumulonimbus cloud, reaching a height of 10Km, almost that of a commercial airliner. Eva experienced temperatures of -50C, and briefly lost consciousness through hypoxia. Fortunately she managed to skilfully recover her aircraft, and land with only bruising from the impact of hailstones during her incredible journey. Being able to accurately predict the weather is vital in even some of the most extreme of sports!

Fallstreak Hole

This is a feature in a large circular or elliptical hole in a cirrocumulus or altocumulus cloud, and can be partially attributed to human behavior — namely flight.

As aircraft pass through clouds formed of supercooled water droplets that still exist as liquid water below 0C. These water droplets need a small particle to be able to freeze when the temperature goes below -40C. When an aircraft passes through the droplets, the air passing over the wing experiences an expansion and rapid drop in temperature. This drop in temperature is sometimes enough to trigger the supercooled water droplets to freeze, form a ribbon of ice crystals following the plane’s path, and then fall out of the cloud. As the ice falls, it has the effect of creating other crystals that also fall from the sky by a process known as the Bergeron Effect, creating holes in the cloud.

Tracking Clouds

Weather watchers and app developers can track clouds using the cloud layer of the OpenWeather Weather Maps 2.0. This easy to use API also provides a wealth of weather layer information on other parameters!

These customizable weather APIs provide global, accurate, feature-rich and graphical display of the progress, location and intensity of clouds, rain, and other weather phenomena can have uses in a number of different scenarios. OpenWeather presents a selection of six versatile weather map APIs, four of which are based on model data, and two on radar. If you are interested in learning more, please take a look at our earlier post on the maps that we currently offer.

Each map type can have many uses, even within the same industry. For example with food delivery, model maps can be used for the long-term planning of shift allocation for drivers, and the radar maps can be used for proactive reallocation of driver resources within a city for a particular day.

So the old saying that ‘every cloud has a silver lining’ may not be particularly true, each cloud certainly is unique, and is created by some incredible natural, and sometimes human phenomena.

About OpenWeather:

At OpenWeather, we create highly recognisable weather products, aimed at the needs of our customers, that make working with weather data effective and straightforward.

The wide variety of these products work across a multitude of enterprises, and include forecast, observation and historic information for any global location. Our industry-standard, fast, reliable APIs streamline flexible integration with enterprise systems. Our pricing and licensing is transparent.

Pricing and subscription details can be found here.