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Abstract
The sea surface temperature (SST) front in the Gulf Stream (GS) extension region is important to synoptic variations in atmosphere. In winter, large amounts of heat and moisture are released from the SST front, modulating the baroclinicity and humidity of the atmosphere, which is important for extratropical cyclones and atmospheric rivers (ARs). In this study, the variation of SST in the North Atlantic in winters since 1981 is investigated using satellite and reanalysis datasets, and a 23-year (1997 to 2019) warming trend of SST in the GS extension region is detected. The increase of SST is mainly distributed along the SST front, with more than 2 °C warming and a northward shift of the SST gradient from 1997 to 2019. Connected with the SST warming, significant increases in turbulent heat flux and moisture release into the atmosphere were found along the ocean front. As a result, baroclinic instability, upward water vapor flux and AR occurrence frequency increased in recent decades. Meanwhile, there was an increase in extreme rainfall along with the increase in AR landfalling on continental Western Europe (especially in the Iberian Peninsula and on the northern coast of the Mediterranean Sea).
Highlights
The Gulf Stream (GS) extension region is a strong mid-latitude western boundary current with a sharp ocean sea surface temperature (SST) front and active oceanic mesoscale eddies
It is worth noting that as the main purpose of this paper is to assess the effect of SST warming in the Gulf Stream extension region on atmospheric rivers (ARs), we focus on the increase of SST value in recent decades and its effect on atmosphere
The eddy kinetic energy (EKE) increased about 20–30 m2 s−2 in 23 years, which is over 10% of the mean, indicating the locally strengthened and eastward expansion of the storm track in the North Atlantic (Figure 5a)
Summary
The Gulf Stream (GS) extension region is a strong mid-latitude western boundary current with a sharp ocean sea surface temperature (SST) front and active oceanic mesoscale eddies. Many studies revealed the importance of ocean fronts on ECs, few referred to their impact on ARs. Matthews et al.’s work [28] found an extremely strong AR related to a higher SST than in other ARs assessed at their uptake locations. As for the changes in GS SST fronts, their meridional shift was revealed to be a stimulator of the shift in storm tracks on an interannual time scale [4] Another significant SST variation is the century-long accelerated warming (since 1900) in the western boundary region, at a rate that far exceeds the globally averaged surface ocean warming [29]. It is worth noting that as the main purpose of this paper is to assess the effect of SST warming in the Gulf Stream extension region on ARs, we focus on the increase of SST value in recent decades and its effect on atmosphere.
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