The conventional view has been that the lower atmosphere influences the stratosphere primarily through planetary waves that emerge from the troposphere in middle and high latitudes. Recently, however, evidence has emerged that the leading modes of variability of the tropical troposphere, the El Nino-Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO), influence the tropical and extratropical stratosphere. Multiple pathways have been proposed for such influences. In this project these pathways will be explored using observational data and the output from troposphere-stratosphere global climate models (GCMs). Observations will comprise the ERA-40 analyses of meteorological fields and ozone from the European Center for Medium Range Weather Forecasting (ECMWF) and satellite observations of outgoing long-wave radiation to characterize convection.
Weare and his collaborators will establish indices of the key ENSO and MJO modes. Statistical techniques will be used to determine the dominant patterns of variability in the stratosphere. Using an extension of the singular value decomposition (SVD) method that incorporates multiple variables and data at temporal lags, they will describe the three dimensional relationships between tropical convection, as it is modulated by the MJO and ENSO, and the meteorology of the stratosphere and the distribution of stratospheric ozone. Based on the relationships that appear in these exploratory analyses, they will develop diagnostic tests of specific proposed pathways for tropical influences on the stratosphere.
GCM output will be selected from one or more models, based on the quality of the simulations of stratospheric variability and the model representations of ENSO and the MJO. The troposphere-stratosphere coupling in this, or these, GCMs will be analyzed, in order to identify deficiencies in their simulation(s) of this coupling, with the goal of suggesting model improvements that could yield model troposphere-stratosphere coupling that is more consistent with observations.
Broader impacts of this project are in validating widely used stratospheric data sets, improving our understanding of the processes that influence trends in stratospheric ozone, and, to the extent that troposphere-stratosphere coupling is an important aspect of climate change, improving projections of future climate. Two graduate students will be trained.
