Quantifying the Role of Large-scale Atmospheric Circulation in Midlatitude Weather Extremes

Midlatitude extreme weather events are responsible for a large part of climate-related damage, yet our understanding of these extreme events is limited.  While extreme weather events are often identified by the probability distribution function (PDF) of meteorological variables (e.g., temperature or moisture) or the pattern of large-scale circulations (e.g., jet stream meandering or blocking), recent works (e.g., Neelin et al. 2010) have noted the non-Gaussian tails are common to the PDFs of dynamical or chemical tracers subject to the advection-diffusion processes.  In this talk, we will introduce a new approach to transform the prototypes of the advection-diffusion dynamics to the analysis in the tracer-based coordinates.  Such a transformation highlights the Lagrangian perspective of atmospheric dynamics and connects the PDF of weather events to the large scale atmospheric circulation quantitatively.  This framework reveals that the source of non-Gaussianity of near-surface temperature may be related to the nonlinear advection of temperature.  It also provides a useful diagnostic for the hydrological cycle in terms of the availability of column water vapor.