Asymmetric Ocean Response to Atmospheric Forcing in an Island Wake: A 35-Year High-Resolution Study

José M R Alves,Pedro M A Miranda,Rui M A Caldeira,Ricardo Tomé

doi:10.3389/fmars.2021.624392

José M R Alves, Pedro M A Miranda + Show 2 more

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https://doi.org/10.3389/fmars.2021.624392

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Abstract

The present study assesses the thermal variability of the regional ocean around Madeira Island, in intraseasonal and interdecadal time scales, using a 35-year (1983–2017), 3-km horizontal resolution ocean simulation forced by a co-located atmospheric simulation, with SODA and ERA5 boundary and initial conditions, respectively. Atmosphere–ocean interactions in this region are found to be driven by the variability of two quasi-permanent tip-jets, located at the island west and east tips, especially during the summer months. The ocean response is found to be larger in the regions of higher jets speed variability, but its thermal response is highly asymmetrical. On the interdecadal time scale, a significant intensification of both jets during the analyzed period is more prominent in the east tip, but the thermal signature is mostly associated with a much reduced sea surface temperature trend near the west tip.

Highlights

Isolated islands with steep orography and bathymetry constitute major obstacles to the flow, significantly modifying the regional atmospheric and ocean circulations, with an impact that may extend downstream for hundreds or even thousands of kilometers (Xie et al, 2001)
The presence of Madeira Island is especially clear in the perturbation it imposes to the wind
The establishment of the summer tip-jets was discussed in some detail by Miranda et al (2021), and both its intraseasonal and decadal variability were found to be controlled by the regional planetary boundary layer (PBL) height, defined as the height of maximum stability in the low troposphere

Summary

Introduction

Isolated islands with steep orography and bathymetry constitute major obstacles to the flow, significantly modifying the regional atmospheric and ocean circulations, with an impact that may extend downstream for hundreds or even thousands of kilometers (Xie et al, 2001). Alves et al (2020) looked at the regional atmosphere and ocean circulations around Madeira Island during the 2017 summer, using a high-resolution (1 km) fully coupled atmosphere–ocean simulation with the Coupled Ocean-Atmosphere-Wave–Sediment Transport (COAWST) model (Warner et al, 2010), validated against remote sensing sea surface temperature (SST) and wind observations, besides in situ observations in coastal weather stations and in an oceanographic field experiment. That study showed a remarkably steady summer flow during that year, with northeasterly trade winds impinging on the island and leading to the establishment of two low-level jets in the wake, emerging from the east and west tips of the island. That study showed a remarkably steady summer flow during that year, with northeasterly trade winds impinging on the island and leading to the establishment of two low-level jets in the wake, emerging from the east and west tips of the island. Alves et al (2020) argued that those tip-jets are similar to those simulated by Ólafsson and Bougeault (1997) and observed in Greenland (Doyle and Shapiro, 1999), with a much stronger constancy of the flow compensating for its reduced wind speed and that the variability of those jets is a dominant factor in the dynamics of the Madeira wake

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