Atmospheric blocking and intercomparison of objective detection methods: flow field characteristics.

Area of Science:

• Atmospheric Science
• Climatology
• Meteorology

Background:

• Objective methods for identifying atmospheric blocking have proliferated, mainly focusing on the North Atlantic.
• Discrepancies among these methods lead to variations in blocking climatology.

Purpose of the Study:

• To compare blocking properties derived from three distinct objective detection algorithms globally.
• To analyze differences in blocking climatologies, instantaneous patterns, size, speed, duration, and travel distance.

Main Methods:

• Examined blocking using 500 hPa geopotential height anomaly (Δ500), column-averaged potential vorticity anomaly (ΔPV), and 500 hPa geopotential height gradient (AGP).
• Analyzed results for blocking climatologies, instantaneous patterns, and distributions of block characteristics across global extratropics.

Main Results:

• Δ500 and ΔPV methods showed higher spatial similarity in detected blocking regions.
• Δ500 identified the largest and most numerous blocked regions, while ΔPV-detected regions were generally smallest.
• All algorithms detected some questionable low-latitude blocks; Δ500 sometimes tracked jet streaks, differing from height-based methods.

Conclusions:

• Algorithm choice significantly impacts blocking detection and characterization, influencing derived climatologies.
• Careful consideration of algorithm biases is essential for future blocking research and linking blocking to extreme weather.
• Methodological differences necessitate caution when interpreting blocking events and their impacts.