21 May 2015

A Review of Temperature Extremes and their Large-Scale Meteorological Patterns


The statistical methods, dynamics, modeling efforts and trends related to extreme temperature events (ETEs) are reviewed with a focus upon intraseasonal ETEs over North America and the large scale meteorological patterns (LSMPs) associated with their occurrence. Methods to delineate ETEs, ETE statistics and their associated LSMPs are presented. Recent advances in statistical techniques to connect LSMPs to ETEs through appropriately defined covariates are reviewed.  The LSMPs associated with extreme temperature events range from synoptic to planetary scale circulation structures. The current knowledge about the synoptic behavior and dynamical mechanisms leading to these LSMPs is incomplete. There is a scientific need for systematic studies of the physics of LSMP life cycles as well as a comprehensive model assessment of LSMP properties and LSMP-ETE linkages.

Generally, climate models capture observed properties of heat waves and cold air outbreaks with some fidelity, with some tendency to overestimate warm wave frequency, underestimate cold air outbreak frequency and underestimate the impact of low frequency modes on temperature extremes. Although modeling studies have identified the impact of particular large-scale circulation anomalies and land-atmosphere interactions on changes in ETEs, few studies have examined the specific role of LSMPs in long term changes in ETEs. Even though LSMPs are resolvable by global and regional climate models, they are not necessarily well simulated by these models.

Richard Grotjahn
University of California at Davis (UC Davis)