Structure Of Tropical Tropopause Layer And Its Variations

Using the European Centre for Midium-range Weather Forecasting (ECMWF) Interim Re-Analysis (ERA-Interim) data and the model simulations from a chemistry-climate model, properties and trends of the tropical tropopause layer (TTL) are analyzed. The impact of Quasi-biennial oscillation (QBO) on the TTL is also analyzed using ERA-Interim. A series of model simulations from CAM3.0 model are used to analyze the radiative impact of ozone and green house gases (GHGs) changes as well as Sea Surface Temperature (SST) changes on TTL. The main conclusions of this study are as follows:It is found that the TTL properties have significant seasonal and spatial variations and the quasi-biennial oscillation signals are also found in TTL. The thickness of the TTL in summer and autumn is the thinnest in the Northern Hemisphere and it has the largest seasonal variability in winter in the Northern Hemisphere. The analysis of ERA-Interim data indicates that the TTL temperature increased significantly in 1991 because of the Pinatubo volcanic eruption, and after that the temperature decreased from 1992 to 1995. The TTL temperature has been increasing since 1996 without considering the impact of Pinatubo volcanic eruption. In recent years the TTL is getting higher, warmer and thinner, and the stratospheric water vapor is also increasing. The chemistry-climate model simulations show the same trends.The QBO, ozone changes, increasing GHGs and SST all have an impact on the TTL:the meridional circulation anomalies induced by QBO can effect TTL, especially the upper TTL, during east-west transitions of the wind. The upper TTL gets higher/lower and colder when east/west wind changes to west/east.The upper TTL gets lower and warmer when global ozone increases. Higher sea surface temperature (SST) produces a higher TTL but the temperature of the TTL only slightly increases. SST increases associated with increasing atmospheric greenhouse gases (GHGs) tend to warm the TTL, but this effect varies with the season. While the radiative effect of the CO2 doubling have little effect on TTL without corresponding SST changes.