Cloud suck is a phenomenon commonly known in

paragliding Paragliding is the recreational and competitive adventure sport of flying paragliders: lightweight, free-flying, foot-launched glider aircraft with no rigid primary structure. The pilot sits in a harness or lies supine in a cocoon-like 'po ...

hang gliding Hang gliding is an air sport or recreational activity in which a pilot flies a light, non-motorised foot-launched heavier-than-air aircraft called a hang glider. Most modern hang gliders are made of an aluminium alloy or composite frame covered ...

, and

sailplane A glider or sailplane is a type of glider aircraft used in the leisure activity and sport of gliding (also called soaring). This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude. Sailplan ...

flying where pilots experience significant

lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people or goods ** Paternoster lift, a type of lift using a continuous chain of cars which do not stop ** Patient lift, or Hoyer lift, mobile ...

due to a

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

under the base of

cumulus Cumulus clouds are clouds which have flat bases and are often described as "puffy", "cotton-like" or "fluffy" in appearance. Their name derives from the Latin ''cumulo-'', meaning ''heap'' or ''pile''. Cumulus clouds are low-level clouds, gener ...

clouds, especially towering cumulus and

cumulonimbus Cumulonimbus (from Latin ''cumulus'', "heaped" and ''nimbus'', "rainstorm") is a dense, towering vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful Buoyancy, buoyant air ...

. The vertical extent of a cumulus cloud is a good indicator of the strength of lift beneath it, and the potential for cloud suck. Cloud suck most commonly occurs in low pressure weather and in humid conditions. Cloud suck is typically associated with an increase in thermal updraft velocity near

cloud base A cloud base (or the base of the cloud) is the lowest altitude of the visible portion of a cloud. It is traditionally expressed either in metres or feet above mean sea level or above a planetary surface, or as the pressure level corresponding to ...

. As a parcel of air lifted in a thermal rises, it also cools, and water vapour will eventually condense to form a cloud if the parcel rises above the

lifted condensation level The lifted condensation level or lifting condensation level (LCL) is formally defined as the height at which the relative humidity (RH) of an air parcel will reach 100% with respect to liquid water when it is cooled by dry adiabatic lifting. The ...

. As the water vapour condenses, it releases its

latent heat of vaporization The enthalpy of vaporization (symbol ), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. T ...

, thereby increasing the buoyancy of the parcel. The updraft is amplified by this latent heat release. Although the process that causes this amplification happens above cloud base height, the effect is often noticeable as much as 300 m (1,000 feet) below cloud base. In fact, it is this effect ''below'' cloud base, not the effect ''within'' the cloud, that is generally referred to by pilots as cloud suck. The telltale signs for a pilot climbing in the thermal under a "sucking" cloud are (1) lift strengthening, (2) lift getting smoother, and (3) widening of the thermal. Paraglider pilots have reported being unable to descend in strong cloud suck, even after bringing their canopies into deep spiral, which would normally result in a rapid vertical descent. Cloud suck is especially dangerous for paraglider pilots, whose maximum speed is less than 30 knots, because storm clouds (Cumulonimbus) can expand and develop rapidly over a large area with accompanying large areas of strong lift. On 14 February 2007 while practising for a paragliding contest in Australia, Polish-born German team pilot Ewa Wiśnierska-Cieślewicz was sucked into a cumulonimbus cloud, climbing at up to 20 m per second (4,000 feet per minute) to an altitude of 9,946 m (32,600 feet). She lost consciousness due to

hypoxia Hypoxia means a lower than normal level of oxygen, and may refer to: Reduced or insufficient oxygen * Hypoxia (environmental), abnormally low oxygen content of the specific environment * Hypoxia (medical), abnormally low level of oxygen in the tis ...

, but regained consciousness after 30 minutes to an hour, and landed still covered in ice after a three and a half hour flight. In the same storm, 42 year old Chinese paraglider pilot He Zhongpin died after being sucked into the same storm system and struck by lightning at 5900 m (19,000 feet). His body was found the next day from his last known position prior to entering the cloud. In 2014 Italian paraglider Paolo Antoniazzi, 66 years old retired Army general, died after being sucked into a thunderstorm. Compared with hang-gliders and paragliders,

sailplanes A glider or sailplane is a type of glider aircraft used in the leisure activity and sport of gliding (also called soaring). This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude. Sailplan ...

have much higher top speeds (often over 250 km/h), and can more easily escape powerful cumulonimbus clouds by flying away quickly or by using very effective air brakes. A sailplane also has the added benefit of the pilot being able to put the sailplane into a spin to descend rapidly without over speeding. Shenandoah Disaster

Cloud suck is also a concern for powered aircraft but is usually not a lethal hazard, except in extreme weather situations. The USS ''Shenandoah'', the first rigid

airship An airship or dirigible balloon is a type of aerostat or lighter-than-air aircraft that can navigate through the air under its own power. Aerostats gain their lift from a lifting gas that is less dense than the surrounding air. In early ...

built in the United States, and the first in the world to be inflated with

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

, was lost in a cloud suck accident associated with a

squall line A squall line, or more accurately a quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accompa ...

. At about 6:00 AM on 3 September 1925, near Ava in northern Noble County,

Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...

, the ''Shenandoah'' was suddenly caught in a violent updraft while at an altitude of 2,100 feet, rising at the rate of a meter per second. At about 6,200 feet the ascent was checked, but the ship began to descend. When halfway to the ground it was hit by another updraft and began to rise rapidly at an even faster rate. Ultimately the keel snapped, and the ship broke up while still more than a mile above the ground. ''Shenandoah'''s commanding officer and 13 other officers and men were killed. Twenty-nine members of the crew survived the break-up, although some received serious injuries.

References

{{Reflist, 2

External links

* Steve Roti
How to Avoid Cloud Suck
article on

USHPA The United States Hang Gliding and Paragliding Association ''(USHPA)'' is a non-profit organization supporting foot-launched soaring flight in the United States. It began in 1971 as the Southern California Hang Gliding Association and became natio ...

website, first published in Paragliding Magazine, January 2001 Cloud and fog physics Gliding technology Hang gliding Paragliding Weather hazards to aircraft

See also

References

External links