Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Atmospheric Blocking and Intercomparison of Objective Detection Methods: Flow Field Characteristics

TitleAtmospheric Blocking and Intercomparison of Objective Detection Methods: Flow Field Characteristics
Publication TypeJournal Article
Year of Publication2019
JournalClimate Dynamics
Volume53
Number7-8
Pages4189-4216
Abstract / Summary

Objective methods for identifying and quantifying atmospheric blocking have been developed over recent decades, primarily targeting North Atlantic blocks. Differences arise from these methods, leading to changes in the resultant blocking climatology. To understand these differences, and better inform future assessments built on quantitative detection of blocks, this paper examines blocking properties produced by three different objective detection algorithms over the global extratropics. Blocking criteria examined include 500 hPa geopotential height anomaly (Z*), column-averaged potential vorticity anomaly (PV*), and 500 hPa geopotential height gradient (AGP). Results are analyzed for blocking climatologies and for instantaneous blocking patterns, as well as distributions of block size, speed, duration, and distance traveled. The results emphasize physical characteristics of the flow field and the subsequent blocking regions that emerge; overall, PV* and Z* blocked regions often have higher pattern correlation and spatial similarity, though these two methods also display high agreement with AGP in some instances. Z* finds the largest (and greatest number of) blocked regions, while PV*-detected regions are smallest in all instances except Southern Hemisphere winter. In some cases, PV* tracks a nearby jet streak, leading to differences with height-based algorithms. All three algorithms detect some questionable low-latitude blocks that are stationary and persist but do not impair zonal flow, although at different times. Therefore, careful consideration of the algorithm biases is important in future blocking studies. For example, linking extreme weather to detected blocking could vary substantially depending on the algorithm used.

URLhttp://dx.doi.org/10.1007/s00382-019-04782-5
DOI10.1007/s00382-019-04782-5
Journal: Climate Dynamics
Year of Publication: 2019
Volume: 53
Number: 7-8
Pages: 4189-4216
Publication Date: 10/2019

Objective methods for identifying and quantifying atmospheric blocking have been developed over recent decades, primarily targeting North Atlantic blocks. Differences arise from these methods, leading to changes in the resultant blocking climatology. To understand these differences, and better inform future assessments built on quantitative detection of blocks, this paper examines blocking properties produced by three different objective detection algorithms over the global extratropics. Blocking criteria examined include 500 hPa geopotential height anomaly (Z*), column-averaged potential vorticity anomaly (PV*), and 500 hPa geopotential height gradient (AGP). Results are analyzed for blocking climatologies and for instantaneous blocking patterns, as well as distributions of block size, speed, duration, and distance traveled. The results emphasize physical characteristics of the flow field and the subsequent blocking regions that emerge; overall, PV* and Z* blocked regions often have higher pattern correlation and spatial similarity, though these two methods also display high agreement with AGP in some instances. Z* finds the largest (and greatest number of) blocked regions, while PV*-detected regions are smallest in all instances except Southern Hemisphere winter. In some cases, PV* tracks a nearby jet streak, leading to differences with height-based algorithms. All three algorithms detect some questionable low-latitude blocks that are stationary and persist but do not impair zonal flow, although at different times. Therefore, careful consideration of the algorithm biases is important in future blocking studies. For example, linking extreme weather to detected blocking could vary substantially depending on the algorithm used.

DOI: 10.1007/s00382-019-04782-5
Citation:
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.  https://doi.org/10.1007/s00382-019-04782-5.