Vb Cyclones Synchronized With the Arctic-/North Atlantic Oscillation.

Area of Science:

• Meteorology and Climatology
• Atmospheric Science
• Ocean-Atmosphere Interactions

Background:

• Vb cyclones are significant weather phenomena originating in the Western Mediterranean, impacting Central Europe.
• Understanding their temporal occurrence is crucial for climate and weather forecasting.
• Previous studies have highlighted their impact but lacked detailed temporal analysis.

Purpose of the Study:

• To investigate the temporal characteristics and occurrence patterns of Vb cyclones.
• To identify clustering and hiatus periods in Vb cyclone activity.
• To explore the relationship between Vb cyclone occurrence and large-scale atmospheric circulation patterns, including the Northern Atlantic Oscillation (NAO) and Arctic Oscillation (AO).

Main Methods:

• Analysis of Vb cyclone tracks at Z700 and sea level pressure using JRA-55 reanalysis data (1959-2015).
• Identification of distinct clusters and hiatus periods in cyclone occurrence.
• Correlation analysis with atmospheric circulation indices (NAO and AO) at different pressure levels.

Main Results:

• Vb cyclone risk was highest in the 1960s, decreasing thereafter.
• Cyclone occurrences are not random, exhibiting 11 distinct clusters and 11 hiatus periods.
• Clustering is particularly evident for Genoan cyclones in summer and those near the Iberian Peninsula/North African coast in winter.
• Superposition of polar and subtropical jet streams over the Western Mediterranean is a key feature at Vb onset.
• Vb cyclone occurrence is synchronized with negative phases of NAO and AO, with reduced frequency during positive phases.

Conclusions:

• Vb cyclone activity exhibits significant temporal variability and non-random clustering.
• Large-scale atmospheric circulation, particularly jet stream configuration and phases of NAO/AO, strongly influences Vb cyclone occurrence.
• The findings provide insights into the predictability and behavior of these impactful weather systems.