Intraseasonal to interannual variations of the temperature structure around the tropical tropopause and their relationships with convective activities

East-West Center, University of Hawai'i at Manoa (Honolulu, Hawai'i)

Space-time variability in the tropical tropopause temperatures and its relationship with convective activities are examined by using the ERA40/ERA-interim re-analysis and NOAA/OLR data sets. Low temperatures around the tropical tropopause generally occur over the equator and extend northwestward and southwestward in the subtropics to form the horseshoe-shaped structure. This structure resembles a stationary wave response known as the Matsuno-Gill pattern, which is a superposition of the Rossby and Kelvin responses. Because of this, the two preliminary indices are first defined to represent the two responses. The horseshoe-shaped structure index is then calculated from the two indices. The seasonal and interannual variability in the horseshoe-shaped structure index is related to that observed in convective activities adjacent to three monsoon regions: the South Asian monsoon (SoAM) and the North Pacific monsoon (NPM) areas during the northern summer and the Australian monsoon area during the southern summer. The convective activities in the SoAM and NPM areas individually influence the horseshoe-shaped structure. During the southern summer the horseshoe-shaped structure index is also related to convective anomalies associated with the ENSO cycle and intraseasonal oscillation.