Variability in Tropical Tropopause Layer Temperatures from Intra-seasonal to Interannual Timescales

This work examines the processes and phenomena that contribute to variability in the tropical tropopause layer, the region of the atmosphere that marks the transition between the troposphere and stratosphere in the tropics. Our study is motivated by recent observational results that show a strong connection between the tropospheric Madden-Julian oscillation (MJO) and the stratospheric quasi-biennial oscillation (QBO): stronger MJO events in boreal winter are more likely when QBO winds in the lower stratosphere are easterly. Recent observational and modeling studies suggest that tropical tropopause layer temperatures could be key to understanding the MJO-QBO connection, and highlight the need for increased study of this region of the tropics.

We present results from a wide range of reanalysis, satellite, and sounding products that examine tropical tropopause layer temperature signals induced by several key modes of variability in the tropics: the MJO, the QBO, El Niño/Southern Oscillation, and the annual cycle. Of most interest in our findings is evidence of seasonal variations and long-term trends in QBO temperature anomalies that we believe have not been discussed in the literature: QBO temperature anomalies are stronger in boreal winter than the annual mean, and stronger in recent decades. These trends have implications for the MJO-QBO link, and underscore the degree to which the tropical tropopause layer is a dynamic region of the tropical atmosphere in which many modes interact on multiple timescales. Among the questions and hypotheses our results raise are the role of feedbacks in the tropical tropopause layer, why there is a seasonality in the MJO-QBO relationship, and whether the QBO is being altered by anthropogenic climate change.