Tropical Upper Tropospheric Trough

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A Tropical Upper Tropospheric Trough (TUTT) is a trough in upper-level (at about 200 hPa) tropics. Its formation is usually caused by the expansion of the Trough of Westerlies Wind to the tropics. It can also develop from the inverted trough adjacent to a upper level anticyclone. TUTTs are different from mid-latitude troughs in the sense that they are maintained by subsidence warming near the tropopause which balances radiation cooling.

TUTTs sometimes bring a large amount of vertical wind shear over tropical disturbances and cyclones so TUTTs can reduce cyclone development. But, there are also times when TUTTs help start tropical cyclones or make them stronger by providing additional forced ascent near the storm center and an efficient outflow channel in the upper troposphere. Moreover, under specific circumstances, TUTTs can grow into upper cold lows and may enhance the development of low level disturbances.

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