Sea Surface Temperature Variability along the Path of the Antarctic Circumpolar Current

Abstract

The spatial and temporal distributions of sea surface temperature (SST) anomalies in the Antarctic Circumpolar Current (ACC) are investigated, using monthly data from the NCEP-NCAR reanalysis for the period 1980-2004. Patterns of atmospheric forcing are identified in observations of sea level pressure and air-sea heat fluxes. It is found that a significant fraction of SST variability in the ACC can be understood as a linear response to surface forcing by the Southern Annular Mode (SAM) and remote forcing by ENSO. The physical mechanisms rely on the interplay between atmospheric variability and mean advection by the ACC. SAM and ENSO drive a low-level anomalous circulation pattern localized over the South Pacific Ocean, inducing surface heat fluxes and Ekman heat advection anomalies. A simple model of SST propagating in the ACC, forced with heat fluxes estimated from the reanalysis, suggests that surface heat fluxes and Ekman heat advection are equally important in driving the observed SST variability. Further diagnostics indicate that SST anomalies, generated mainly upstream of Drake Passage, are subsequently advected by the ACC and damped after a couple of years. It is suggested that SST variability along the path of the ACC is largely a passive response of the oceanic mixed layer to atmospheric forcing.

Inter-annual variability of the carbon dioxide oceanic sink south of Tasmania

“…Such patterns have been previously reported at mid-latitudes of the Southern Ocean in conjunction with changes in SAM (Hall and Visbeck, 2002;Lovenduski and Gruber, 2005;Morrow et al, 2007). Figure 7 shows that low wind speed years are in general associated with positive phases of SAM, although not as clear during the 1993-1998 period, possibly related to ENSO and SAM interactions (Verdy et al, 2006(Verdy et al, , 2007.…”

“…6), suggesting a similar driver of these anomalies in the three water masses. Large-scale coupled atmosphere-ocean oscillations likely to drive large SST anomalies in the mid-latitude band of the Southern Ocean are ENSO through atmospheric bridges (Li, 2000;Verdy et al, 2006;Morrow et al, 2007), the subtropical dipole pattern (Behera and Yamagata, 2001), or SAM (Hall and Visbeck, 2002;Lovenduski and Gruber, 2005;Morrow et al, 2007).…”

Estimates of Air–Sea Feedbacks on Sea Surface Temperature Anomalies in the Southern Ocean

“…With a grid scale of 0.758, the ERA-I data used here are likely to capture some remnants of ocean mesoscale variability (;100 km) and certainly adequately resolve the spatial scales of atmospheric synoptic disturbances (;1000 km). Given this information, what can we say about how strongly the overlying atmosphere damps dipolar, tripolar, or quadrupolar SST perturbations along the ACC, which are typically associated to SAM forcing (e.g., Verdy et al 2006;Ciasto and Thompson 2008)? Previous studies reported a reduced damping on basin compared to synoptic scales in the NH (e.g., FK02), and we theoretically expect (Bretherton 1982;Frankignoul 1985) such a weakening of the air-sea feedback as spatial scales expand.…”

“…Moreover, in addition to weather systems, SO SST variability is largely driven by the southern annular mode (SAM), the primary mode of atmospheric variability in the middle-to-high-latitude Southern Hemisphere (SH). The SAM induces SST anomalies on larger-than-synoptic spatial scales, typically characterized by a few poles along the circumpolar channel (e.g., Verdy et al 2006;Ciasto and Thompson 2008). Given the possible link between observed trends in the SAM and anthropogenic perturbations of climate, by greenhouse gases and stratospheric ozone (e.g., Thompson et al 2011), the fate of these large-scale SAM-induced SST anomalies is of particular interest, as it determines their potential influence on recent observed SH climate trends.…”

Interannual Variability of Summer Chlorophyll in the Southern Ocean: ENSO Effects

“…바람장 변화 이외에 남극 해양 환경에 주요한 변화를 유발하는 대기 경년변동성 중 하나는 적도 남태평양의 해 양/대기 변화를 나타내는 엔소(El Niño Southern Oscillation, ENSO)이다 (White and Peterson 1996;Yuan 2004;Verdy et al 2006;Sallée et al 2008;Stammerjohn et al 2008;Vivier et al 2010;Ding et al 2011;Kim and Orsi 2014). 적도 태평양 표층해수가 평년에 비하여 따뜻해지는 엘리 뇨 시기에 적도에서 시작된 로스비 파열(Rossby wave train)의 일부로 고기압 어노말리가 남태평양 상에 생성된 다 (Turner 2004;Fogt et al 2011).…”