Darbas:

droplets and ice crystals are being carried upwards or are kept suspended by the strong updrafts.

2.3.1.2 MATURE STAGE:
The mature stage typically lasts between 25 and 30 minutes. During this stage downdrafts develop, and after some time strong updrafts can be found at the leading part and pronounced downdrafts at the rear part of the Cb. The development of downdrafts is a consequence of the cooling by evaporation of the cloud droplets due to entrainment, as well as the falling rain droplets, which accelerate the downdraft even more.
Therefore the strongest downdraft can be found within the lower layers of the Cb. At the same time the updraft steadily weakens. The air beneath the cloud base is saturated due to the evaporation of the rain droplets. The downward transported air of the downdraft spreads horizontally after it reaches the surface, which may lead to the development of squall lines. The end of the mature stage is reached when the out flowing dry air cuts off the incoming supply of moist air. During the mature stage of the Cb the weather events are most intense. Although each cell may last only 20 minutes, the cluster may last several hours. These can produce heavy rainfall, downbursts, moderate-sized hail, and occasional weak tornadoes.
2.3.1.3 DISSIPATING STAGE:

The last stage, the dissipating stage, of a Cb is reached when the updrafts in the lower levels of the Cb are replaced by downdrafts. The Cb dissipates, as there is no supply of warm moist air for the updraft.


2.4 THUNDERSTORM TYPES
2.4.1 Multi-cells Storms
Although there are times when a thunderstorm consists of just one ordinary cell that transitions through its life cycle and dissipates without additional new cell formation, thunderstorms often form in clusters with numerous cells in various stages of development merging together.

Unlike ordinary single cells, cluster storms can last for several hours producing large hail, damaging winds, flash flooding, and isolated tornados. However this kind of thunderstorm has a very long life span due to the continuous development of new cells, so-called daughter cells. In most cases these daughter cells develop in the right leading part, but sometimes they can also develop on the left side. According to studies, every 5 to 10 minutes such a daughter cell develops. These new cells have a diameter between 3 and 5 km, and the distance to the center of the thunderstorm is approximately 30 km. The daughter cells develop very rapidly and after a short time become the new center of the Multi-Cell Storm (mother cell). This rapid development takes place because the daughter cells develop immediately in front of the mother cell; therefore no kinetic energy is taken away from the cloud. Although the older cells dissolve at the rear part of the complex, the Multi-Cell Storm is still active due to the continuous new development of daughter cells. Investigations have shown that during the life span of a Multi-Cell Storm 30 or more cells can develop. If the sequence of the cells is short the Multi-Cell Storm can change to a Super Cell Storm.
The diagram shows that the daughter cell (n) develops from the so-called shelf cloud (n+1). This lasts approximately 15 minutes. After an additional 15 minutes the daughter cell becomes the center of the Multi-Cell Storm. The center of the storm is shown with the cell (n-1). The cell is now in its mature stage and strong up and downdrafts can be found. 15 minutes later the cell has finished its mature stage and dissolves at the rear part of the Multi-Cell Storm (n-2).

2.4.2 The Super cell Storm
Super cell thunderstorms are a special kind of single cell thunderstorm that can persist for many hours. Super cells are also known to produce extreme winds and flash flooding. They are characterized by a rotating updraft (usually cyclonic), which results from a storm growing in an environment of significant vertical wind shear.
Wind shear occurs when the winds are changing direction and increasing with height.



The most ideal conditions for super cells occur when the winds are veering or turning clockwise with height. For example, in a veering wind situation the winds may be from the south at the surface and from the west at 15,000 feet. Beneath the super cell, the rotation of the storm is often visible as well. This rotating updraft is called a mesocyclone.

The lowering in the photograph (bottom) represents the wall cloud.

2.4.3 Squall Lines
Sometimes thunderstorms will form in a line, which can extend laterally for hundreds of miles. These "squall lines" can persist for many hours and produce damaging winds and hail.
The rain cooled air or "gust front" spreading out from underneath the squall line acts as a mini cold front, continually lifting warm moist air to fuel the storms.

Often along the leading edge of the line a low hanging arc of cloudiness will form called the shelf cloud. Gusty, sometimes damaging outflow winds will spread out horizontally along the ground behind the shelf cloud.

2.4.4 Wall Clouds

Wall clouds are a visible manifestation of the mesocyclone at low levels, another words, the wall cloud contains significant rotation The tornado often forms from within the wall cloud, with the funnel cloud descending to the ground


2.4.5 Tornadoes and funnel cloud
A tornado is a vortex of rapidly moving air associated with some severe thunderstorms Tornadoes that travel across lakes or oceans are called waterspouts. Winds within the tornado funnel may exceed 500 kilometers per hour. High velocity winds cause most of the damage associated with these weather events.

Tornadoes also cause damage through air pressure reductions. The air pressure at the tornado center is approximately 800 millibars (average sea-level pressure is 1013 millibars). The destructive path of a tornado is usually about half a kilometer wide, and usually no more than 25 kilometers long.


3.CAUTIONS AND NOTIFICATIONS FOR AIRMAN

3.1 THE DANGERS OF FLYING IN OR CLOSE TO A THUNDERSTORM

Visual observations of the weather within the thundercloud from aircraft are difficult because of the speed with which they pass through the thunderclouds, and man has yet to devise an instrument that will measure all hydrometers in the cloud.
As you all know AIRSPEED = GROUND SPEED + WIND SPEED
So it is obviously that a sudden change of wind speed can change the airspeed and therefore, change the amount of lift keeping the airplane in the air. If the airplane is going slow, like on take off or landing, this can be very dangerous. Most of the Microburst incidents happen in a thunderstorm. An aircraft flying through a downburst may experience the following sequence of events. As the aircraft enters the edge of the downburst, it encounters an increased headwind. This headwind increases the lift of the aircraft and therefore the altitude of the aircraft. The flight crew may attempt to correct the altitude increase with a decrease in engine power or increase in descent angle.
Next, the aircraft passes through the microburst core where it encounters an abrupt change from headwinds to down flow winds, which results in a loss of lift and altitude. Soon afterward, the aircraft crosses into a region of tailwinds. This additional wind change further decreases lift, causing the aircraft to lose more altitude.

Altitude loss is even greater if flight corrections to compensate for the initial headwind are still taking place. If the wind shear encounter began at a low altitude, such as it would during a takeoff or landing, the overall loss of altitude may cause the aircraft to fly directly into the ground with catastrophic results.
Turbulence. Turbulence, associated with thunderstorms, can be extremely hazardous, having the potential to cause overstressing of the aircraft or loss of control. Thunderstorm vertical currents may be strong enough to displace an aircraft up or down vertically as much as 2000 to 6000 feet. The greatest turbulence occurs in the vicinity of adjacent rising and descending drafts. Gust loads can be severe enough to stall an aircraft flying at rough air (maneuvering) speed or to cripple it at design cruising speed.
Maximum turbulence usually occurs near the mid-level of the storm, between 12,000 and 20,000 feet and is most severe in clouds of the greatest vertical development.
Severe turbulence is present not just within the cloud. It can be expected up to 20 miles from severe thunderstorms and will be greater downwind than into wind. Severe turbulence and strong out-flowing winds may also be present beneath a thunderstorm. Micro bursts can be especially hazardous because of the severe wind shear associated with them.
The turbulence associated with clouds types is:
· St – slight
· Ci, Cs, Cc, Ac, As – nil or slight except when Ac cas or when merging into Cb
· Sc – moderate
· Ns – moderate but may be severe near base
· Cu, TCu, and Cb – Generally severe but may be catastrophic and include the downbursts
Lightning. Static electricity may build up in the airframe, interfering with operation of the radio and affecting the behavior of the compass. Trailing antennas should be wound in. Lightning blindness. may affect the crew's vision for 30 to 50 seconds at a time, making instrument reading impossible during that brief period. Lightning strikes of aircraft are not uncommon.
The probability of a lightning strike is greatest when the temperature is between -5ºC and 5°C. If the airplane is in close proximity to a thunderstorm, a lightning strike can happen even though the aircraft is flying in clear air. Lightning strikes pose special hazards. Structural damage is possible. The possibility of lightning igniting the fuel vapor in the fuel cells is also considered a potential hazard.

The lightning first occurs between the upper positive charge area and the negative charge area immediately below it. Lightning discharges are considered to occur most frequently in the area bracketed roughly by the 32°F and the 15°F temperature levels. However, this does not mean that all discharges are confined to this region; as the thunderstorm develops, lightning discharges may occur in other areas and from cloud to cloud, as well as from cloud to ground.
St. Elmo’s fire. If an airplane flies through clouds in which positive charges have been separated from negative charges, it may pick up some of the cloud's overload of positive charges. Weird flames may appear along the wings and around the propeller tips. These are called St. Elmo's fire. They are awe-inspiring but harmless. It the airplane flies in the vicinity of a cloud where negative charges are concentrated, its positive overload may discharge into the cloud. In this case, it is the airplane, which strikes the cloud with lightning! The electricity discharges cause a noisy disturbance in the lower frequency radio bands