Characterising the seasonal cycle of wind forcing, surface circulation and temperature around the sub-Antarctic Prince Edward Islands

Long-Term Trends and Interannual Variability of Wind Forcing, Surface Circulation, and Temperature around the Sub-Antarctic Prince Edward Islands

“…For V wind , the differences between the seasonal cycles for the longer and shorter periods were less obvious (Figure 2b-d). While previous studies observed the strongest negative wind stress curl (WSC) at the PEIs in August (−2.30 × 10 −8 N m −3 ), with the weakest during December (0 N m −3 ) [29,30], our study showed the 2 • × 2 • area averaged WSC for a longer period (1979-2020) was weakest in November (0.31 × 10 −8 N m −3 ) and December (0.29 × 10 −8 N m −3 ), and strongest in June (−2.05 × 10 −8 N m −3 ), August (−2.00 × 10 −8 N m −3 ), and September (−2.01 × 10 −8 N m −3 ) (Figure S3a). These differences in the WSC climatology likely resulted from the differing time series lengths used, as illustrated in Figure S3a.…”

“…The seasonal SST cycle for a shorter period showed no significant differences compared to the seasonal cycle derived over the full time period (1982-2020) (Figure 2a). Given the dominance of strong west-northwesterly winds in the PEI region [29,30], the zonal component of wind speed (U wind ) and the resultant wind speed (R wind ) showed very similar patterns (Figure 2b,c). Highest wind speed was observed in July (R wind , 9.96 m s −1 ; U wind , 9.62 m s −1 ) and lowest wind speed occurred in February (R wind , 8.19 m s −1 ; U wind , 7.55 m s −1 ).…”

“…Given the relatively short length of the GlobCurrent dataset, we also examined the DUACS DT2018 geostrophic current speeds [38] from the Copernicus Marine Environment Monitoring Service (CMEMS; http://marine.copernicus.eu, accessed on 1 September 2021). These data are available over a longer period between 1 January 1993 and 31 December 2020 and were used to derive the long-term mean positions of the branches of the SAF and APF, from optimized sea surface height contours, similar to [28][29][30].…”

“…The seasonal cycle of SST, winds, and currents has been described in detail by [29], for a wider area around the PEIs, and thus here we only provide a brief description of the patterns observed within the averaged 2 • × 2 • area (Figure 1). The monthly climatology of SST showed a clear seasonality with a peak of 7.24 • C in February and a minimum of 4.67 • C in September (Figure 2a).…”

“…In contrast, satellite and reanalysis products provide a more consistent and long-term data record with a broader spatial coverage that can be used to compare climate variability at the PEIs with that across the rest of the Southern Ocean. A recent investigation used satellite and reanalysis data to characterize the local scale seasonal variations in surface hydrography around the islands, providing a useful baseline against which interannual and long-term changes can be assessed [29]. Here, following on from the study by [30], we expand upon previous research [29] by using satellite and reanalysis data to investigate the long-term trends and interannual variability of the surface temperature, wind forcing, and circulation at the PEIs.…”