Vertical structure and dynamical regimes of Mediterranean extreme warm events from surface to high troposphere

Abstract. Climate change is rapidly accelerating the frequency of Extreme Warm Events (EWEs) across the Mediterranean, yet their vertical thermodynamic structure and dynamical evolution remain poorly understood. This study investigates the three-dimensional patterns of EWEs over Rome during the 1991–2025 period using ERA5 temperature data at 1000 hPa (near-surface), 500 hPa (middle troposphere), and 300 hPa (high troposphere).

EWEs were identified through percentile- and persistence-based criteria and classified using a K-means clustering approach. Their evolution was further investigated through precursor analysis, synoptic composites, and HYSPLIT backward trajectories. Five Extreme Warm Regimes (EWRs) were identified, spanning from shallow boundary-layer warming to vertically coherent deep-column structures. These regimes naturally separate into two broader classes: vertically coupled events, characterized by warming throughout the tropospheric column, and vertically decoupled events, in which thermal anomalies remain confined to specific atmospheric layers.

Trend analysis reveals a marked increase in the frequency of vertically coupled regimes after 2015, particularly during summer and autumn. While the average duration and mean thermal intensity of episodes have remained remarkably stable over the 35-year period, the higher recurrence of deep-column anomalies is effectively extending summer-like atmospheric conditions into autumn months. Representative case studies show that the coupled regimes develop through different pathways, involving persistent blocking, subsidence, and/or subtropical warm-air advection, while the remaining regimes maintain persistent vertical decoupling throughout their evolution.

Overall, these findings indicate a progressive climatic transition toward more vertically organized and synoptically controlled EWEs, providing key information on the physical nature of Mediterranean heat extremes that cannot be inferred from near-surface temperatures alone. This three-dimensional framework offers a physically based approach for interpreting, classifying, and improving the prediction of EWEs in Mediterranean environments.