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Why the tornado circling with a vacated circle inside it?

Hi Wil

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"The observed "descent" of cloud to form the funnel-shaped cloud of a tornado is also not associated with true descent. As the vortex intensifies, its central pressure falls. When the pressure is reduced to that which permits condensation of water vapor into cloud material, the funnel-shaped cloud appears. It often appears to descend for perhaps two distinct reasons: 1) Near cloud base, the pressure doesn't have to fall as far for the air in the vortex to reach condensation as it does further down, or 2) The circulation intensity is actually increasing downward. We do not know the actual distribution of pressure in tornadoes, of course, and the tornadic pressure field may have many complexities. However, it is unlikely that clouds from above are descending to create the funnel-shaped cloud ... generally, descent dissipates clouds. Of course, it could be that descent in the core of a two-celled vortex might produce a funnel-shaped cloud simply by pulling down cloud matter in a way that evaporation of the cloud droplets is relatively slow along the axis and relatively faster along the margins, resulting in a tapered funnel. Someday, perhaps we can get some answers ... .

The public at large has many misconceptions about tornadoes, a notable one being that unless the condensation cloud associated with that rotating column of air is touching the surface, it is not a tornado. This is manifestly untrue, as many storm chasers realize fully. Since it is the wind associated with the rotating air column that does the damage, it is the moving air (wind) and not the cloud that constitutes the tornado. Many tornadoes have been observed (Fig. 1 is but one of countless examples) that do not have condensation funnels all the way to the surface, but which clearly are in contact with the ground. It is quite possible for the circulation to be more or less completely invisible for at least some portion of the life cycle of the event. In the case of waterspouts (see below), this is frequently the case, but such events also occur in the dusty, dry mid-continental plains (Fig. 2). Chasers may refer to these events with such slang terms as "dust bowls" or "dirt-daubers.""

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Donald Rosenfeld


Any questions (except private) answered from the 1st grade level on up pertaining to any aspect of Weather. I am a 20 year member of the American Meteorological society and a long time forecaster of eastern United States snow storms and Hurricanes.

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