TORNADOES

THE EXPLAINER

- PROF DANN MITCHELL

WHAT IS A TORNADO AND HOW DOES IT FORM?

Tornadoes, sometimes called twisters or whirlwinds, are intense vortices stretching from the Earth's surface to the base of stormy, cumulonimbus clouds - these clouds extend deeply in the vertical and often have an anvil-shaped top. Typically, tornadoes measure around 100 metres in diameter, travelling on average around five kilometres before they dissipate. Tornadoes form from mesocyclones, large-scale regions of rapidly rotating air that flow within the cumulonimbus clouds. Cool, dry air can wrap around these mesocyclones, creating a strong temperature contrast which intensifies the spinning, drops the central pressure and extends the vortex to the ground, thus the tornado is born. As tornadoes are made up of air, they are invisible to the naked eye unless they are transporting some other material, such as condensed water in the form of water vapour, dust, or larger debris, so more often than not take on a dark appearance. Given the chaotic nature of tornadoes, they are a nightmare to predict, so often it is the original mesocyclone that will start to alert the forecasters on where to look.

WHAT ARE THE DIFFERENT TYPES OF TORNADO?