19 May 2015

The Synoptic Behavior of Temperature Regime Onset over the Southeast


During winter anomalous temperature regimes (ATRs), including cold air outbreaks (CAOs) and warm waves (WWs), provide important societal impacts in the Southeast United States. Using composite time-evolution analyses, the study characterizes the structural and dynamical development of ATRs occurring during 1949-2011 in the Southeast. Events are first categorized by the sign and amplitude of relevant low-frequency modes. During the development of CAOs (WWs), a negative (positive) geopotential height anomaly pattern is observed in the upper troposphere over the Southeast with oppositely-signed height anomalies found in the lower troposphere over the central US. In most cases, there is a near-surface east-west height anomaly dipole that provides anomalous northerly (CAO) or southerly (WW) flow into the Southeast leading to the local formation of cold or warm surface air temperature anomalies, respectively. Companion potential vorticity analyses reveal prominent anomaly features in the mid- to upper-troposphere that are related to the coincident geopotential height anomaly patterns. The composite analyses reveal that (a) synoptic-scale disturbances serve as dynamic triggers for ATR events while (b) low-frequency modes provide a favorable environment conducive to ATR onset.

Rebecca M Westby
Georgia Institute of Technology School of Earth and Atmospheric Sciences