Diagnosing Non‐Gaussian Temperature Distribution Tails Using Back‐Trajectory Analysis

Abstract

AbstractCoherent regions exhibiting non‐Gaussian 2‐m temperature distribution tails are present across the globe, indicating changes in extreme temperatures under future warming may manifest in more complex ways than were the underlying distributions symmetric about the mean. To further the understanding of physical processes that govern temperature distribution tail shape, this work utilizes a back‐trajectory model to diagnose mechanisms for extreme daily mean temperature development at select extratropical locations exhibiting non‐Gaussian tails. Although characteristics such as direction, distance, and temperature evolution vary among back‐trajectories associated with extreme temperature days, results reveal principal pathways for air parcel propagation associated with preferred patterns in large‐scale circulation. A relatively persistent synoptic setup leads to thermal advection, which interacts with local geographic features to produce a shorter‐ or longer‐than‐Gaussian tail. Significant relationships with recurrent modes of atmospheric and sea surface temperature variability further suggest the influence of teleconnection wave patterns and ocean temperatures on extreme daily temperature occurrence over land, though local, smaller‐scale processes are also important. Air parcels transporting extreme temperatures at short‐tailed locations often originate in marine environments, constraining the magnitude of the temperature extreme, while locations exhibiting long cold tails require rare meteorological conditions to transport the coldest air from poleward source regions often partially blocked by topography or downstream of the prevailing wind. Processes governing longer‐than‐Gaussian warm tails at locations examined are more subtle and not as obviously dominated by horizontal advection. Results provide added insight into our understanding of temperature extremes and how they may change in the future at regional scales.