Part 4. Disturbances. Chapter 11 Lightning, Thunder, and Tornadoes. Annual distribution of lightning strikes. There are about 40,000 thunderstorms daily on the Earth that produce lightning. A few produce tornadoes. Development of lightning and thunder.
Lightning, Thunder, and Tornadoes
There are about 40,000 thunderstorms daily on the Earth that produce lightning. A few produce tornadoes.
(a) Positive and negative charges separate in the cloud.
(b) The step leader is a flow of negative charges (electrons) toward positive charges.
(c) A flow of positive charges moves toward the step leader.
As the positive and negative charges combine, the lightning stroke is seen.
A dart leader is a secondary stroke just after the first.
Thunder arises from the rapid heating of the air by the lightning stroke, which sends out a sound wave at 5 miles/sec.
Safest areas from lightning -- indoors or in an automobile. Outdoors, do not stand under tall objects. Do not touch telephones or electrical appliances. Lightning can strike in the same place twice!
A positive stroke can occur when thunderstorms become tilted
Air Mass thunderstorm lifecycle
Air Mass thunderstorms form in humid, unstable air. Each cell lasts no more than a few hours from development to dissipation.
Outflow boundaries -- front edge of cold air flowing out away from a thunderstorm; a gust front occurs at an outflow boundary
Thunderstorm movement in an MCC
Movement and lifecycle of individual thunderstorm cells (A, B, C, D, E, F, and G) and how they change with time
Direction of movement of the line of thunderstorms
This squall line is probably along or ahead of an advancing dry line
Wind shear and vertical motions in a squall line thunderstorm
Vertical wind profile in (a) here
Gust front-induced shelf and roll cloud thunderstorm
Internal structure of a supercell thunderstorm
A supercell thunderstorm is an extremely powerful thunderstorm cell. Supercell thunderstorms can spawn tornadoes.
The above are map views of a supercell thunderstorm.
Microbursts create aviation hazards thunderstorm
Tornado-producing supercell thunderstorm
Tornadoes typically drop out of the wall cloud on the southwest side of a supercell
A possible mechanism of tornado thunderstorm
Tornado development along a convergence boundary thunderstorm
Circular areas shows places where thunderstorm inflow and outflow circulation resulted in vorticity and tornado development
Global tornado frequency thunderstorm
Most of Earth’s tornadoes occur in the lower elevation areas of North America
“Tornado Alley” thunderstorm
Most tornadoes occur in the springtime, when the contrast between warm and cold air in the atmosphere is the greatest
-- Most injuries and deaths in tornadoes are in automobiles and mobile homes and are caused by flying debris
-- US averages 91 tornado deaths each year
-- Safest area in a tornado is in a basement or an interior room, away from windows
Multiple suction vortices greatly increase damage and mobile homes and are caused by flying debris
Linear tornado damage path and mobile homes and are caused by flying debris