Dangers of Thunderstorms for Paragliders

Flying near thunderstorms is certainly not the best choice to make and flying a paraglider during a thunderstorm will shorten your life expectancy dramatically.
Cloud Suck
Thunderstorms produce enormous updrafts which can reach up to 160 Km/hour. If caught out in these updrafts your glider can be sucked up to 10 Km into the air where freezing temperatures and the lack of oxygen will be responsible that you never have to pay taxes again.
Turbulence
The turbulence in a thunderstorm are created by the tremendous updrafts and shear. They will collapse your canopy and create a highly critical flying situation with unforeseeable outcome.

Convection is a mechanical process produced by thermals. It involves the upward transfer of air masses of the atmosphere. Convection is essential for the formation of many types of clouds.

Precipitation: falling products of condensation in the atmosphere, as rain, snow, hail.

Thunderstorms

Picture left: Severe Thunderstorm approaching.

Did you know that our atmosphere generates 2,000 Thunderstorms at any given time which add up to 45,000 a day? (sources Dennis Pagen „Understanding the Sky”)

Thunderstorms are generated by temperature imbalances in the atmosphere.
Warming of the air near the earth's surface and/or cooling of the air above puts warmer, lighter air layers below colder, denser layers. The resulting instability causes convective overturning of the layers, with heavier, denser layers sinking to the bottom and the lighter warmer air rising rapidly.

Mechanical processes are also at work. Warm, buoyant air may be forced upward by the wedge-like undercutting of a cold air mass or by flowing up a mountain slope. Winds blowing into the center of a low-pressure area may force warm air near that center upward.

In the first stage of thunderstorm development, an updraft carries warm air to a level where the air becomes saturated with moisture and visible droplets appear as a cloud begins to form. Continued upward movement produces large clouds resembling rising mounds, domes, or towers, known as cumulus clouds. Strong winds above the developing clouds may further enhance the updraft or convection.

As the cloud forms, water vapor changes to liquid or frozen cloud particles. This results in a release of latent heat. The latent heat takes over as the principal source of energy for the developing cloud. Once the cloud starts to form by other forces, this release of heat helps keep it growing and finally becomes a cumulonimbus cloud.

The cloud particles grow by colliding and combining with each other, forming rain, snow, and hail. When the droplets become heavy enough to fall against the updraft, precipitation begins (rain or hail starts to fall).

Having reached its final stage of growth, the cumulonimbus cloud may be several kilometers across its base and often towers to altitudes of 10,000 meters or more. High level winds shred the cloud top into the familiar anvil form. These cloud towers are sometimes visible as lonely giants and at other times while moving several abreast are known as a squall line.

This final stage is also marked by a change in wind flow within the storm cells. The updraft which initiated the cloud's growth no longer prevails and is joined by a downdraft generated by the precipitation. This updraft-downdraft couplet constitutes a single storm "cell". Most storms are composed of several cells that survive for perhaps 20 minutes, and then die. New cells may replace old ones, and it's possible for some storms to last for several hours.

Strong gusts of cold wind from the downdraft or heavy precipitation often occur at the ground beneath and outward from the mature storm. Lightning always accompanies the thunderstorm. These are nature's warnings that the thunderstorm is in its most violent stage. Tornadoes may also be associated with the thunderstorm.

When the thunderstorm cell begin to die, the violent downdraft, having shared the circulation with the sustaining updraft, now strangles it. Precipitation weakens and the cold downdraft ceases. The thunderstorm cell, a short-lived creation spreads and dies.

pic1: freezing high up

Thunder

Thunder is the sound produced by explosive expansion of air heated by a lightning stroke. When lightning is close by, the thunder sounds like a sharp crack. More distant strokes produce growling and rumbling noises. Because the speed of light is about a million times that of sound, we see a lightning bolt before the sound of thunder reaches us. This makes it possible to estimate the distance (in Km) to a lightning stroke by counting the number of seconds between lightning and thunder and dividing by three (speed of sound=343m/second).

pic2.

Downdrafts

Downdrafts along the leading edge of a thunderstorm form the gust front. It is usually marked by gusty cool winds that can produce damage. Strong localized downdrafts are called down bursts. These are intense concentrations of sinking air which fan out on striking the earth's surface, producing damaging strong turbulent winds.

pic3

Hail

Hailstones are precipitation ( rain or hail starts to fall) in the form of lumps of ice that form during some thunderstorms. Hailstones range from pea size to the size of a grapefruit. They're usually round, but may also be conical, or irregular in shape, some with pointed projections. Hail is most devastating to crops but can also cause heavy damage to aircraft, automobiles, roofs, and windows.
top

pic4

Lightning

(Q1 Tower, Surfers Paradise Gold Coast)

Lightning is an effect of electrification within a thunderstorm. As the thunderstorm develops, interactions of charged particles produce an intense electrical field within the cloud. A large positive charge is usually concentrated in the frozen upper layers of the cloud, and a large negative charge, along with a smaller positive area, is found in the lower portions.

The earth is normally negatively charged with respect to the atmosphere. But as the thunderstorm passes over the ground, the negative charge in the base of the cloud induces a positive charge on the ground below and for several miles around the storm. The ground charge follows the storm like an electrical shadow, growing stronger as the negative cloud charge increases. The attraction between positive and negative charges makes the positive ground current flow up buildings, trees, and other elevated objects in an effort to establish a flow of current. But air, which is a poor conductor of electricity, insulates the cloud and ground charges, preventing a flow of current until huge electrical charges are built up.

Lightning occurs when the difference between the positive and negative charges--the electrical potential--becomes great enough to overcome the resistance of the insulating air and to force a conductive path for current to flow between the two charges. Electrical potential in these cases can be as much as 100 million volts. Lightning strokes proceed from cloud to cloud, cloud to ground, or, where high structures are involved, from ground to cloud.

Jorg Fedler can be reached under jfe@bigpond.net.au or visit the web site http://www.bollygum.com