Lectures on Thunderstorms and Tornadoes. Chanh Q. Kieu Department of Atmospheric and Oceanic Science University of Maryland AOSC400, Fall 2008. Definition of thunderstorms.
Chanh Q. Kieu
Department of Atmospheric and Oceanic Science
University of Maryland
AOSC400, Fall 2008
Thunderstorms are rain showers with accompanied thunder. As thunder is a result of lighting, you can also define thunderstorms as rain showers with lighting (NOAA/NWS)
The typical lifecycle of a thunderstorm consists of three stages: towering, mature cumulus, and dissipating stage
Thunderstorms can be classified based on the numbers of principle updraft cores. The formation of different types of thunderstorm is caused by various combinations of above three conditions
Single-cell: There is one updraft core, so-called “cell”. Such single cell is usually formed in isolation with the other cells. Very often, there are more than just one cell if the environment is favorable for the development
Multi-cell cluster: Has more than one cell, formed by mergers of several storms. The multi-cell clusters are often associated with convective updrafts near mountain ranges or strong cold fronts. Sometimes, there is a “back building” storm upstream.
Multi-cell line (squall-line): multiple cells merge and form a line instead of a cluster. May be as long as several hundred miles, move very fast.
Supercell: a special kind of singlecell thunderstorm but stay as long as few hours. Have very organized and strong updrafts (100 mph) and downdraft cores. Extremely dangerous and responsible for nearly all of tornadoes
Thunderstorms are particular dangerous because of their products during their developments including hails, strong wind, heavy rain, tornadoes. Hails are produced by strong updrafts, which carry the raindrops continuously back into the cloud.
The most severe products of thunderstorms are tornadoes. By definition, a tornado is a violently rotating column of air extending from a thunderstorm to the ground.
The Fujita (F) Scale is the most commonly used scale for rating the damage of tornadoes, which is based on damage left behind by a tornado. There are some disadvantages of the F scale, and a recently revised scale, so-called Enhanced Fujita (EF) Scale seem to make improvements to the original F scale. This EF Scale has replaced the original F scale, which has been used to assign tornado ratings since 1971.
Before thunderstorms develop, vertical wind shear creates an invisible, horizontal spinning effect in the lower atmosphere
Updraft within the thunderstorm tilts the rotating tube from horizontal to vertical.
An area of rotation of few miles wide (mesocyclone) is formed within the storm. Most tornadoes form within this area of strong rotation
There are four basic types of tornadoes:
Multiple vortex tornado: a type of tornado in which two or more columns of spinning air rotate around a common center, very often observed in intense tornadoes. These vortices often create small areas of heavier damage along the main tornado path.
Satellite tornado: a weaker tornado which forms very near a large, strong tornado. The satellite tornado may appear to rotate around a larger tornado.
Waterspout: simply as a tornado over water. Can be divided into two smaller types: fair weather waterspout and tornado waterspout
Landspout: a tornado over the ground that is not associated with a mesocyclone. Share many defining characteristics, including relative weakness, short lifespan, and a small, smooth condensation funnel with fair weather waterspout