Boundaries of the tropical tropopause layer (TTL) identified by the ozone-water vapor relationship

Application of the tracer-tracer correlation technique has been successful in characterizing the chemical transition layer between the troposphere and stratosphere in mid to high latitudes. In this work, we present the method of using ozone-water vapor relationship to characterize the upper and lower boundaries of TTL. These boundaries have been defined using thermal and dynamical fields. There are two schools of thoughts – one based on the temperature lapse rate, and the other based on radiative forcing or the net heating. The results of the tracer analysis shows that the tracer behavior supports the level of the minimum stability to be the lower boundary of the transition layer and the cold point to be a good proxy of the upper boundary. We further use the method to examine the chemical transition across the tropopause in the Asian summer monsoon region and compare to that of the tropics. The Asian summer monsoon region has been known to behave similarly to the TTL in its very high convectively driven tropopause and potentially is an alternative transport pathway for water vapor and pollutants entering into stratosphere. The comparison between observations in the Asian summer monsoon (Kunming, China) and the TTL (TC4 and TCSP, Costa Rica) shows that the transition layer in the Asian monsoon region is narrower but at higher potential energy levels compared to that of TTL. The possible applications of this method to understanding the global TTL structure will be discussed.