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.