Atmospheric Forcing of Coastal Upwelling in the Southern Baltic Sea Basin

Ewa Bednorz,Marek Półrolniczak,Arkadiusz M Tomczyk,Bartosz Czernecki

doi:10.3390/atmos10060327

Ewa Bednorz, Marek Półrolniczak + Show 2 more

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https://doi.org/10.3390/atmos10060327

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Journal: Atmosphere	Publication Date: Jun 17, 2019
Citations: 8	License type: CC BY 4.0

Affiliation: Adam Mickiewicz University in Poznań

Abstract

This study analyzes the atmospheric forcing of upwelling occurrence along differently oriented coastlines of the southern Baltic Sea basin. The mean daily sea surface temperature (SST) data from the summer seasons (June–August) of the years 1982–2017 made the basis for the detection of upwelling cases. For the atmospheric part of the analysis, monthly indices of four macroscale circulation patterns were used: North Atlantic Oscillation (NAO), Scandinavian (SCAND), East Atlantic (EA) and East Atlantic/Western Russia (EATL/WRUS). In order to identify the local airflows and wind conditions, zonal and meridional regional circulation indices were constructed and introduced to the analysis. Within the southern Baltic Sea basin, upwelling occurs most frequently along the zonally oriented southern coasts of Sweden, and least frequently along the southern (Polish) and eastern (Lithuanian-Latvian) coasts. Among the macroscale circulation patterns, the SCAND has the strongest impact on the horizontal flow of surface sea waters in the southern Baltic, which triggers upwelling. The summer NAO and EA appeared to have a weak effect on upwelling occurrence, and EATL/WRUS have the smallest impact. Local circulation indices allowed us to recognize the atmospheric control of upwelling frequency better than the indices of the macroscale patterns. Anomalies in upwelling frequency are their highest at the positive/negative phase of the zonal circulation, particularly along the southern and eastern coast of the southern Baltic Sea basin.

Highlights

Upwelling occurs in oceanic and sea waters, and is defined as a process of “an ascending motion of subsurface water by which water from deeper layers is brought into the surface layer and is removed from the area of upwelling by a divergent horizontal flow” [1]
This study aims to contribute to the research of the sea-atmosphere coupling by finding out the atmospheric forcing of the sea waters’ circulation and sea surface temperature along the differently oriented coastlines of the southern Baltic Sea basin
This study’s results proved that both local and macroscale circulation patterns control the occurrence of coastal upwelling within the southern Baltic Sea basin

Summary

Introduction

Upwelling occurs in oceanic and sea waters, and is defined as a process of “an ascending motion of subsurface water by which water from deeper layers is brought into the surface layer and is removed from the area of upwelling by a divergent horizontal flow” [1]. The nutrients fertilize surface waters, and as a result the areas of upwelling often have high biological productivity. In this way upwelling can have economic relevance, providing good fishing grounds in areas where it is common. Upwelling may take place in the open ocean, or along coastlines In the latter case, it appears where the wind, blowing alongshore, has the coast on its left [2,5,6]. It appears where the wind, blowing alongshore, has the coast on its left [2,5,6] This general rule works as described in the Northern Hemisphere, where the Coriolis Force turns the water or air-flows to the right. The direction of the air and water current within the Ekman Spiral is rotating due to the effect of the Earth’s rotation and frictional forces, and it is integral with the current down

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