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Thermal
A relatively small-scale, rising air current produced when the Earth's surface is heated. Thermals are a common source of low level turbulence for aircraft.
Thermal Belt
A zone of high nighttime temperatures (and relatively low humidities) that is often experienced within a narrow altitude range on valley sidewalls, especially evident during clear weather with light winds.
Thermal High
Area of high pressure that is shallow in vertical extent and produced primarily by cold surface temperatures.
Thermal Low
Area of low pressure that is shallow in vertical extent and produced primarily by warm surface temperatures.
Thermal Wind
It is a theoretical wind that blows parallel to the thickness lines, for the layer considered, analogous to how the geostrophic wind blows parallel to the height contours. The closer the thickness isopleths, the stronger the thermal wind. Cold air is always located to the left of the thermal wind (as you face downstream) and the warm air is located on the right. Since thickness contours are tighter on the cold side of thermal wind, your lower thickness values will be found on the left side of the thermal wind. The speed and direction of the thermal wind are determined by vector geometry where the geostrophic wind at the upper level is subtracted from the geostrophic wind at the lower level.
Thermally Driven Circulation
A diurnally reversing closed cellular wind current resulting from horizontal temperature contrasts caused by different rates of heating or cooling over adjacent surfaces; includes along-slope, cross-valley, along-valley, mountain-plain and sea breeze circulations.

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     Page last Modified: 25 June, 2009 1:01 PM