Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling
21 July 2020

Understanding Automated Detection of Atmospheric Blocking Events

Long-term seasonally-averaged (JJA and DJF) blocking frequency from three different detection methods

Careful consideration of the algorithmic biases in objective tracking methods is important in future blocking studies. Differences in the definition of blocking produced widely varying climatologies, underscoring that different processes are relevant in different regions for connecting blocks to extreme weather.


Atmospheric blocks are obstructions to the normal flow pattern of the atmosphere, often associated with heatwaves and modified precipitation patterns.  Several objective methods for identifying blocks have been used throughout the literature to better understand how atmospheric blocking is a driver for extreme weather.  We characterize the blocking climatologies associated with each of these methods and understand which meteorological patterns result in similarities and differences among tracking algorithms.


Different objective methods have been developed over the years to better understand how atmospheric blocking -- associated with persistent redirection of the typical west-to-east flow -- is connected with local extreme weather events, particularly heat waves and dry spells.  However, most studies have focused on atmospheric blocking in the North Atlantic and the corresponding impacts to extreme weather in Europe.  In this study, we extend three atmospheric blocking algorithms to 2D and assess the characteristics of atmospheric blocking globally.  This study reveals that certain definitions of blocks, implied by the design of the underlying detection algorithm, are better suited for explaining the process drivers in particular regions.  This study further connects blocking features with local meteorological patterns so as to better understand why these differences arise.

Paul Ullrich
University of California - Davis
Pinheiro, MC, PA Ullrich, and R Grotjahn.  2019.  "Atmospheric Blocking and Intercomparison of Objective Detection Methods: Flow Field Characteristics."  Climate Dynamics 53(7-8): 4189-4216.