East Atlantic Pattern

East Atlantic Pattern. The East Atlantic Pattern is a prominent mode of low-frequency variability in the atmospheric circulation over the North Atlantic and Europe. It is identified as the second empirical orthogonal function of geopotential height anomalies in the region and is characterized by a north-south dipole of pressure anomalies. This pattern significantly influences seasonal weather conditions, particularly during the winter months, affecting temperature and precipitation distributions across the European continent.

Definition and characteristics

The pattern is formally defined through statistical analysis, such as rotated principal component analysis, applied to fields like monthly mean 500 hPa geopotential height. Its primary characteristic is a dipole structure with one center over the British Isles and another of opposite sign spanning from Iberia to the Mediterranean Sea. The positive phase features anomalously low pressure over the Azores and high pressure over Scandinavia, while the negative phase exhibits the reverse configuration. This structure is distinct from, though sometimes correlated with, the classic North Atlantic Oscillation. The pattern's index is often calculated using standardized pressure differences between specific stations or through empirical orthogonal function projections, with its activity peaking during the boreal winter from December to February.

Climate impacts

The phase of this pattern exerts a strong control on regional climate anomalies. During its positive phase, enhanced southwesterly flow brings mild, moist Atlantic air across Western Europe, leading to above-average winter temperatures in countries like the United Kingdom, France, and Germany. Concurrently, conditions become drier and cooler over Southern Europe and the Mediterranean Basin, including regions like Spain, Italy, and Greece. The negative phase is associated with a weakened westerly flow, resulting in colder, drier conditions over Northwestern Europe and wetter weather toward the Alps and the Mediterranean. These shifts directly impact agriculture, water resources, and energy demand across the continent.

Causes and mechanisms

The dynamics are linked to interactions between mid-latitude storm tracks, Rossby wave trains, and underlying sea surface temperature anomalies. Variability in the North Atlantic Current and conditions in the subtropical Atlantic can influence the pattern's persistence. Mechanisms involve modulations of the jet stream and atmospheric blocking events over the Eastern Atlantic. Furthermore, it can be forced or modulated by larger-scale phenomena such as the El Niño–Southern Oscillation through teleconnection pathways that affect the Atlantic Multidecadal Oscillation. Internal atmospheric variability and interactions with the stratosphere, including sudden stratospheric warming events, also contribute to its initiation and maintenance.

Variability and trends

The pattern exhibits significant variability on intraseasonal, interannual, and decadal timescales. Its behavior is not strictly periodic, but periods of persistent positive or negative phases can last for several weeks or even entire seasons. Long-term studies, including analysis of reanalysis data sets like ERA5 from the European Centre for Medium-Range Weather Forecasts, have investigated potential trends linked to anthropogenic climate change. Some research suggests a possible tendency toward more frequent positive phases in recent decades, which may be associated with changes in Arctic amplification and alterations to North Atlantic storm tracks, though natural variability remains a dominant factor.

Related patterns

This pattern is one of several major teleconnection patterns that govern Northern Hemisphere climate variability. It is closely related to, but independent from, the North Atlantic Oscillation, with which it sometimes shares a quadrature relationship. Other associated patterns include the Scandinavian Pattern and the East Atlantic/West Russia Pattern, each describing different dipole or tripole structures over the Euro-Atlantic sector. It also interacts with remote patterns like the Arctic Oscillation and the Pacific–North American pattern, contributing to complex hemispheric climate linkages studied by institutions like the National Oceanic and Atmospheric Administration and the World Meteorological Organization.

Category:Climate patterns Category:Atmospheric dynamics Category:Climate of Europe