Air Temperature Extremes in the Mediterranean Region (1940–2024): Synoptic Patterns and Trends
Journal
Atmosphere
Date Issued
July 13, 2025
Author(s)
DOI
10.3390/atmos16070852
Abstract
Extreme air temperatures along with the synoptic conditions leading to their appearance are
examined for the Mediterranean region for the 85-year period of 1940–2024. The data used
are daily (04UTC and 12UTC) grid point (1◦ × 1◦) values of 2 m air temperature, 850 hPa
air temperature, and 1000 hPa and 500 hPa geopotential heights, obtained from the ERA5
database. For 12UTC and 04UTC, the 2 m air temperature anomalies are calculated and
are used for the definition of Extremely High Temperature Days (EHTDs) and Extremely
Low Temperature Days (ELTDs), respectively. Overall, 3787 EHTDs and 4872 ELTDs are
defined. It is found that EHTDs are evidently more frequent in recent years (increased by
305% since the 1980s) whereas ELTDs are less frequent (decreased by 41% since the 1980s),
providing a clear sign of warming of the Mediterranean climate. A multivariate statistical
analysis combining factor analysis and k-means clustering, known as spectral clustering,
is applied to the data resulting in the definition of nine EHTD and seven ELTD clusters.
EHTDs are mainly associated with intense solar heating, blocking anticyclones and warm
air advection. ELTDs are connected to intense radiative cooling of the Earth’s surface, cold
air advection and Arctic outbreaks. This is a unique study for the Mediterranean region
utilizing the high-resolution ERA5 data collected since the 1940s to define and investigate
the variability of both high and low temperature extremes using a validated methodology.
examined for the Mediterranean region for the 85-year period of 1940–2024. The data used
are daily (04UTC and 12UTC) grid point (1◦ × 1◦) values of 2 m air temperature, 850 hPa
air temperature, and 1000 hPa and 500 hPa geopotential heights, obtained from the ERA5
database. For 12UTC and 04UTC, the 2 m air temperature anomalies are calculated and
are used for the definition of Extremely High Temperature Days (EHTDs) and Extremely
Low Temperature Days (ELTDs), respectively. Overall, 3787 EHTDs and 4872 ELTDs are
defined. It is found that EHTDs are evidently more frequent in recent years (increased by
305% since the 1980s) whereas ELTDs are less frequent (decreased by 41% since the 1980s),
providing a clear sign of warming of the Mediterranean climate. A multivariate statistical
analysis combining factor analysis and k-means clustering, known as spectral clustering,
is applied to the data resulting in the definition of nine EHTD and seven ELTD clusters.
EHTDs are mainly associated with intense solar heating, blocking anticyclones and warm
air advection. ELTDs are connected to intense radiative cooling of the Earth’s surface, cold
air advection and Arctic outbreaks. This is a unique study for the Mediterranean region
utilizing the high-resolution ERA5 data collected since the 1940s to define and investigate
the variability of both high and low temperature extremes using a validated methodology.
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