Multidecadal Changes in the Relationship of Storm Frequency over Euro-Mediterranean Region and ENSO During Boreal Winter

Abstract

Background: The El Niño–Southern Oscillation (ENSO) influence over Euro-Mediterranean boreal winter season (December to February) precipitation anomalies has changed along the twentieth century. Purpose: The precipitation anomalies are closely associated with storm track frequency. The changing relationship between the interannual variability of storm track frequency and ENSO is investigated at interannual and multidecadal timescales. Methods: The Melbourne University cyclone tracking scheme (MS) is applied to reanalyse 200-hPa geopotential height (Z200) datasets to track the winter storms over the Euro-Mediterranean region for the period 1950–2016. Results: The maximum of climatological storm track frequency is found to prevail in the study domain with large interannual variability. The multidecadal changes show a phase shift in the relationship between storm track frequency and ENSO from the 1950s to the recent decades. The storm track frequency is negatively correlated (−0.24) to ENSO for the early period (1950–1979), whereas it is positively correlated with a maximum correlation value of 0.44 for the recent period (1987–2016). The correlation departure (0.68) between the two periods shows a significant change in the multidecadal relationship between storm track frequency and ENSO. Conclusion: The ENSO-associated significant changes are noted in the upper and lower tropospheric height anomalies over the North Atlantic and Euro-Mediterranean sector in the recent period with respect to the earlier period, which may largely influencing the storm activity (Frequency/Intensity) and precipitation anomalies over the Euro-Mediterranean region. The findings of this study can have important implications in Euro-Mediterranean seasonal predictability.