Cumulonimbus

Characteristics

It is this type of cloud which gives the Orage S. According to its development, it can be the seat of electric demonstrations like the Foudre, of falls of Grêle, Pluie, strong precipitations and in the most extreme cases, of Tornade S.

The cumulonimbus is the cloud more fears aeronauts. Even the largest airliners divert their road in order to avoid crossing the way of a cumulonimbus. Indeed, the Lightning, Hail, and forts Shearing S of winds inside cloud, add to risk of icing (present when the temperature of the surrounding air lies between -40 and 0 degrees Celsius), and would contribute to put in danger the plane (and its occupants), if the pilot of this last tried to pass to through. Moreover it is allowed that a pilot of Planeur should never use the ascending current existing in or under the cloud. There exist two kinds of dangers: one is related to the effects of shearing between ascents and descents which can break the Planeur. The second is more underhand: the ascending currents under a cumulonimbus can reach 20 m/s, be broad and be relatively not very turbulent. In this case there the sailplane is aspired in the cloud and the pilot finds himself in bad posture because of the loss of the visual reference marks (VFR). Moreover, the phenomenon of Rafale downward can appear in lower part of the cloud, plating the apparatus on the ground. A parachutist or parapentist who engages under a cumulonimbus takes the mortal and unquestionable risk to be aspired quickly until the top of this cloud: asphyxiated, struck down, frozen… If he escapes from it, he can have irremediable damage with the brain following a lack of oxygen.

Let us quote a fact, exceptional by its happy conclusion, which occurred on Wednesday, February 14, 2007: A German parapentist of Polish origin which accomplished a training flight with Manilla (Northern of Sydney, New South Wales, Australia) suddenly found herself at an altitude of 9950 meters, carried by the ascending violent one running of a storm and where reigned, according to the Australian services of weather a temperature of Less 40°C. Ewa Wisnierska, 35 years, survived the lack of oxygen, cold and with strong turbulences which characterize extreme altitudes. Victorious of the World cup of parapente in 2005, the young woman prepared, like the 200 other participants, for the championships of the world which begin on February 24th, 2007, when it was taken in a powerful ascent. A Chinese parapentist who was in the same sector did not have his chance. He was struck by the lightning and its body was found with 75km of its starting point. The authorities and the team on the ground of Ewa Wisnierska could follow the upward course of the champion thanks to her equipment GPS and to its radio. The parapentist thus passed from 760m to 9950m in the space of about fifteen minutes, which was worth to him to lose consciousness and to remain unconscious half an hour, fixed on a wing in perdition. Ewa Wisnierska returned to it to approximately 6000m of the ground and could be posed without encumber. Its face carried some traces of gelures and its combination was covered with ice. It however spent only one hour in observation to the hospital, following what it was declared ready to take part in the championships of the world. Sporting allemande explained that it had tried to circumvent the stormy zone, but in vain. Once inside the cloud, it had tried to resist the power of the currents, without managing to stop its rise. Surrounded by flashes, it estimated its chances of survival at “almost zero”. Arrived at 4000m of altitude, it had come into radio operator contact with his team. “I said to them: " I cannot anything faire" ”, she told with the press. “It rains, it hails and I continue to climb; I am lost!” Let us hail had the size of oranges! After having begun again knowledge, she remembers “to have seen the Earth approaching, as Apollo the 13…” director of the competition qualified the event of miracle and acknowledged to remain still incrédule. “Its chances of survival was equal to those which it had to gain ten times of continuation the first prize of the Lotto”, he commented on. The whole of the community of the Coasting flight (parapente, delta) perceives these facts like the result of enormous and dramatic error of the pilots, an example not to be followed even for the champions!

Formation

The cumulonimbus are clouds of convective origin , members of the class of the cumulus . It is acted in fact of cumulus of very strong vertical extension of which the upper part makes up of crystals of ice. Their formation is supported by hot and wet close to surface, but colder and dry conditions in altitude. These Orage S in general develops with the approach of a cold Front. The majority of the storms of winter are of this type. The cumulonimbus known as of Mass of air (typically storms in summer of end of the afternoon), which is relatively benign, are formed following the convection caused by the solar warming of the air close to the ground, in the absence of dynamic forcings. The presence of forcings due to atmospheric dynamics can destabilize the atmosphere more, which increases the probability of formation of cumulonimbus and the severity of the storms which result from it. The appearance of the anvil is the consequence of the spreading out of the cumulonimbus on the level of the Tropopause (name given to the limit between the Troposphère and the Stratosphère). The ascending currents inside the cloud are stopped or slowed down while arriving in this zone of the particularly stable atmosphere, and they are transformed then into horizontal currents. In the event of severe storm, the differential between the temperature of the ascending mass of air and the surrounding air can make that the ascending current can be propagated in the Stratosphère and it is then formed what one calls in English a overshooting dome .

List

Cumulonimbus calvus
Cumulonimbus capillatus
Cumulonimbus praecipitatio
Cumulonimbus virga
Cumulonimbus pannus
Cumulonimbus incus
Cumulonimbus mammatus
Cumulonimbus pileus
Cumulonimbus velum
Cumulonimbus arcus
Cumulonimbus tuba

External bonds

Photograph of cumulonimbus capillatus incus

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