Quasi-Stationary Temperature Structure in the Upper Troposphere over the Tropical Indian Ocean

Vertical fine structure of the tropical circulation in the upper troposphere was analyzed with using the dry temperature data obtained by Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Global Positioning System Radio Occultation (GPS-RO). The data have very high vertical resolution and global coverage. One-year record during 2007 was utilized to detect statically stable layers in the upper troposphere. Vertically thin quasi stationary stable layer separated from the deep stratospheric stable layer, is detected, over the equatorial western Indian Ocean during the boreal summer. The stable layer is found to be inclined to the horizontal surface and the center tilts eastward with increasing height.

We also conducted statistical analysis with objective reanalysis data made by ECMWF (ERA-40, 1979-2001). Low height anomaly at 150 hPa associated with the stable layer is located at the western edge of the strong easterly jet on the equator during the boreal summer. The magnitude of low height anomaly in each year has high correlation with that of the easterly jet around 20N. We discussed possible mechanisms to produce these vertical fine structures from the viewpoints of monsoon circulation and stationary equatorial-trapped Kelvin wave.