Assalamualaikum Wr. Wb.
Hi Guys, today im going to write about Natural Phenomenon
So, recently we were shocked by Airplane crash accident that involved Air Asia's QZ8501 Airplane. What i heard from the news this accident was caused by a cloud that called Cumulonimbus Cloud.
Im interested to search and find out any information about this cloud. So here is some explanation about Cumulonimbus Cloud and why it's dangerious for flight.
 |
| Cumulonimbus Cloud |
Cumulonimbus, from the Latin cumulus ("heap") and nimbus ("rainstorm", "storm cloud"), is a dense towering vertical cloud [1]associated with thunderstorms and atmospheric instability, forming from water vapor carried by powerful upward air currents. Cumulonimbus can form alone, in clusters, or along cold front squall lines. These clouds are capable of producing lightning and other dangerous severe weather, such as tornadoes. Cumulonimbus progress from overdeveloped cumulus congestus clouds and may further develop as part of a supercell. Cumulonimbus is abbreviated Cb and are designated in the D2 family.
Towering cumulonimbus clouds are typically accompanied by smaller cumulus clouds. The cumulonimbus base may extend several miles across and occupy low to middle altitudes- formed at altitude from approximately 500 to 13,000 ft (200 to 4,000 m). Peaks typically reach to as much as 20,000 ft (6,000 m), with extreme instances as high as 75,000 ft (23,000 m).[2] Well-developed cumulonimbus clouds are characterized by a flat, anvil-like top (anvil dome), caused by wind shear or inversion near the tropopause. The shelf of the anvil may precede the main cloud's vertical component for many miles, and be accompanied by lightning. Occasionally, rising air parcels surpass the equilibrium level (due to momentum) and form an overshooting top culminating at the maximum parcel level. When vertically developed, this largest of all clouds usually extends through all three cloud regions. Even the smallest cumulonimbus cloud dwarfs its neighbors in comparison.
Thunderstorms represent some of the worst dangers in aviation. The effects they have are most likely to be found in the form of turbulence, downburst, microburst, tornadoes, icing, lighting, hail, heavy rain, surface wind gusts, runway contamination, low status and bad visibility.
Turbulence
Severe turbulence is caused by mixing of up- and downward moving air and can be expected anywhere in and under the Cb, even at distances of 25 NM ahead of and 10000 feet above the shower depending of its intensity.
Downburst
A huge amount of cold air flows out of a Cb causing a strong downdraught with a cross section of 2 - 5 NM in center and horizontal wind shear and updraught around the center and with severe horizontal wind shear outside of the Cb. The total affected area may have a radius of more than 15 NM. The horizontal wind shear component may be as large as 6 kts per second over a period of 16 seconds, which exceeds the acceleration of any aircraft.
Microburst
This is like a downburst but on a much smaller scale and with a cross-section of 0.5 - 2 NM. The horizontal wind may average at 45 kts with a maximum of 90 kts. It is very dangerous as the phenomena is concentrated over a small area.
Tornadoes
These may develop under a shower visible by dust or moist but they can be invisible too when the air is dry under the convective condensation level. Typical horizontal dimension is several hundreds of meters and windspeeds of over 150 kts are not uncommon. Lifetime may last from several minutes to hours. Smaller types like the waterspout have a radius of 25 to 50 meters and a lifespan of about an hour.
Icing
Since the most severe icing occurs in an environment of supercooled water droplets. In a Cb this will be between levels where the temperature is around zero and minus 23° Celsius. Icing may also occur at higher level altitudes, near the top of the Cb where mixed water and ice particles may stick to the cold airframe.
Hail
Hail may be present in temperatures well above zero Celsius, the occurrence at +20° Celsius is quite normal. As hail is formed by the Bergeron Findeisen and coalescence processes, requiring supercooled water droplets, it will typically be present in the lower and medium levels of a Cb, since these droplets are scarce above the -23° Celsius level.
Heavy rain
If rain is present in the lower parts of the Cb it may cause engine flame outs and reduced visibility from the cockpit.
Gusty winds
This may cause heavy turbulence, severe down draughts and may exceed crosswind limitation of the aircraft. Wind gusts can be present in a range of 25 NM ahead of and 15 NM around a Cb.
Runway contamination
The presence of rain, hail or snow may result in a poor braking action. As a Cb is relative short lived phenomenon braking action coefficients are hardly ever measured and actual braking action may be unexpectedly poor.
Lightning
Aluminum aircraft form a Faraday cage and are relatively safe from a lightning strike. If it does happen then this will result in compass deviations, electronic failures and such. Composite aircraft, fly by wire systems, computerized navigation and the like may make an aircraft more vulnerable to a lightning strike. Lightning will occur near or in (70% of lightning occurs within the Cb).
An electrically charged aircraft (static electricity) can be detected by static VHF disturbances on the radio and or St Elmo's fire, at this point it is more prone to a lightning strike. Charging can also occur when flying in Cirrus clouds near Cb's.
To electrically discharge an aircraft static wicks are used. They are connected to the airframe and release the electrons back to the atmosphere, thus reducing radio interference.
Low stratus
Often seen near a shower in moist areas and affects the ceiling limits. Results in sudden visibility reduction in mountainous terrain making flight below MOCA (Minimum Obstacle Clearance Altitude) impossible without ground violations.
Poor visibility
This will occur in heavy precipitation fog or stratus over high ground.
