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* How do tornados form?
*At the core of a thunderstorm, warm moist air is being sucked upward in the updraft which is usually near the rear (typically southeast) of the storm. This is called the inflow. Strong storms must have a significant inflow to feed themselves, and as a storm strengthens its updraft, and hence inflow, becomes more powerful and violent. Usually this process does not spawn tornados, but in some cases it does. When a new storm passes over this boundary, or passes along it, helicity develops. Helicity is the horizontal "rolling" rotation of air as the different air masses separated by the boundary tumble over each other along the surface. This rotation can be tilted up into the updraft of the storm and become vertical rotation, or vorticity. When vorticity is present in the updraft, an area of low pressure develops around the immediate area of the updraft and this is called a mesocylone. As the updraft strengthens, rotation increases and the pressure further drops. In order to get more air, the updraft begins to extend downward and the resulting low pressure causes moisture to condense in the rotating column of air which becomes visible as a "funnel cloud" extending from the cloud base (known as the "shelf cloud") and usually from a further lowered shelf known as a "wall cloud". Most people mistake funnel clouds for tornados, but a funnel cloud is not a tornado, though it is almost always found prior to tornado formation. A tornado isn't classified as such until the rotating air reaches the ground, and funnel clouds are usually visible prior to reaching the ground. If it does reach the ground, then it becomes a tornado, and will usually kick up debris into the updraft which is visible as a dark swirling mass at the surface known as the debris cloud - in a strong tornado, the debris cloud and funnel cloud are mixed together and extend all the way from the base of the wall cloud to the ground. *Tornados are classified according the Fujita scale based on its level of damage (although with new Doppler we are beginning to use wind speeds as the basis for classification) or the width of the damage path. F1 is the weakest, all the way to F5 which is the strongest (which can have winds of over 300mph).
Tornados are now being detected by new Doppler radar (NEXRAD). Weather radar measures the direction and the speed of moving objects, such as precipitation, and has the capacity to measure the velocity of the particles in order to determine the rate at which the particles are falling. Doppler radar works by detecting the presence and location of an object by bouncing a radio wave off of it and detecting the time it takes for the signal to return. Using the time value, and a knowledge of the speed of the wave, the distance traveled can be determined. These radar waves are bounced off of moving objects. In the case of weather, these objects are raindrops, snowflakes or other forms of precipitation. Using the Doppler effect, the change in frequency of the returning wave, as compared to the frequency of the wave that was sent out, yeilds the direction and the speed that the object is moving (radially) away from or towards the detector source. This data is then electronically converted into pictures showing the location and intensity of precipitation. These images help to demonstrate how doppler radar works:
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(radar
picture of a tornado)
