Kyle R. Clem

South Pacific circulation changes and their connection to the tropics and regional Antarctic warming in austral spring, 1979–2012

After 1979, statistically significant warming in Antarctica is only observed in austral spring (September–November, SON) across West Antarctica and the Antarctic Peninsula. While previous work has linked this warming to reductions in sea ice cover, we note that a substantial (30–60%) portion of the warming is related to changes in the SON atmospheric circulation. In particular, western Antarctic Peninsula warming is consistent with increasing pressure in the South Atlantic, while western West Antarctica warming is tied to a deepening of the Amundsen Sea low near the eastern Ross Sea. While both of these circulation changes are associated with increased warm, northerly flow toward the Antarctic continent, they are connected with different aspects of tropical variability. The increase in pressure in the South Atlantic is associated with a trend toward more La Nina-like conditions in the tropical Pacific, and an associated Rossby wave train. In contrast, the deepening of the Amundsen Sea low is more strongly tied to a shift in the Pacific Decadal Oscillation (PDO) toward its negative phase since the 1990s. Compared to typical La Nina events, the recent negative PDO events display a different tropical forcing, which drives a Rossby wave train that propagates more meridionally across the South Pacific, culminating in the eastern Ross Sea, rather than in the South Atlantic. The results suggest multiple independent forcing mechanisms governing the SON pressure trends and associated Antarctic Peninsula and West Antarctica warming after 1979, which partially cancel each other out in the Amundsen Sea and portions of eastern West Antarctica.

Austral Spring Southern Hemisphere Circulation and Temperature Changes and Links to the SPCZ

AbstractSignificant austral spring trends have previously been observed in West Antarctica and Antarctic Peninsula temperatures and in atmospheric circulation across the southern Pacific and Atlantic. Here, physical mechanisms for the observed trends are investigated through analysis of monthly circulation and temperatures from the ERA-Interim dataset and outgoing longwave radiation (OLR) data. The negative pressure trend over the South Pacific during spring is strongest in September, while the positive pressure trend over the South Atlantic is strongest in October. Pressure trends in November are generally nonsignificant. The authors demonstrate that a significant September trend toward increased convection (reduced OLR) in the poleward portion of the South Pacific convergence zone (SPCZ) is statistically related to Rossby wave–like circulation changes across the southern oceans. The wave response is strongest over the South Pacific in September and propagates eastward to the South Atlantic in October. O...

The relative influence of ENSO and SAM on Antarctic Peninsula climate

Recent warming of the Antarctic Peninsula during austral autumn, winter, and spring has been linked to sea surface temperature (SST) trends in the tropical Pacific and tropical Atlantic, while warming of the northeast Peninsula during summer has been linked to a strengthening of westerly winds traversing the Peninsula associated with a positive trend in the Southern Annular Mode (SAM). Here we demonstrate that circulation changes associated with the SAM dominate interannual temperature variability across the entire Antarctic Peninsula during both summer and autumn, while relationships with tropical Pacific SST variability associated with the El Nino-Southern Oscillation (ENSO) are strongest and statistically significant primarily during winter and spring only. We find the ENSO-Peninsula temperature relationship during autumn to be weak on interannual timescales, and regional circulation anomalies associated with the SAM more important for interannual temperature variability across the Peninsula during autumn. Consistent with previous studies, western Peninsula temperatures during autumn, winter, and spring are closely tied to changes in the Amundsen Sea Low (ASL) and associated meridional wind anomalies. The interannual variability of ASL depth is most strongly correlated with the SAM index during autumn, while the ENSO relationship is strongest during winter and spring. Investigation of western and northeast Peninsula temperatures separately reveals that interannual variability of northeast Peninsula temperatures is primarily sensitive to zonal wind anomalies crossing the Peninsula and resultant lee-side adiabatic warming rather than to meridional wind anomalies, which is closely tied to variability in the zonal portion of the SAM pattern.

Large-Scale Forcing of the Amundsen Sea Low and Its Influence on Sea Ice and West Antarctic Temperature

AbstractUsing empirical orthogonal function (EOF) analysis and atmospheric reanalyses, the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea low (ASL) are examined. During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40%–50% of the variability) consists of an east–west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the southern annular mode (SAM) and in-phase El Nino–Southern Oscillation (ENSO)/SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15%–20% of the vari...

Community-based adaptation to climate variability and change: mapping and assessment of water resource management challenges in the North Pare highlands, Tanzania

In contrast to the technocentric emphasis on new irrigation infrastructure that has been the hallmark of Tanzania’s climate change adaptation policy, this paper examines challenges for local management of existing ‘traditional’ small-scale water resources through community-engaged research that is grounded in the emerging methods of community-based adaptation. We examine the shifting local institutional arrangements during the colonial and postcolonial periods that have shaped the social dynamics of climate risk and water resources management in the North Pare highlands. Secondly, we examine contemporary water use and management and perceptions of change in the North Pare highlands, where smallholder farmers manage water resources to fulfill domestic and other requirements of an intensively cultivated landscape. Last, we draw on community mapping and assessment of small-scale water resources to identify options for future action at community level. Our findings highlight a set of embedded institutional concerns that confront communities evaluating future trajectories of climate change adaptation.

The Springtime Influence of Natural Tropical Pacific Variability on the Surface Climate of the Ross Ice Shelf, West Antarctica: Implications for Ice Shelf Thinning

Observational records starting in the 1950s show West Antarctica is amongst the most rapidly warming regions on the planet. Together with increased intrusions of warm circumpolar deep water (CDW) onto the continental shelf due to local wind forcing (the primary mechanism in recent decades), this has resulted in enhanced surface and basal melting of floating ice shelves and an associated acceleration and thinning of West Antarctic outlet glaciers, increasing the rate of global sea level rise. In this study, it is shown that during the austral spring season, significant surface warming across West Antarctica has shifted westward to the Ross Ice Shelf in recent decades in response to enhanced cyclonic circulation over the Ross Sea. These circulation changes are caused by a Rossby wave train forced by increasing sea surface temperatures in the western tropical Pacific, which is tied to the springtime shift of the Interdecadal Pacific Oscillation (IPO) to its negative phase after 1992. While the local wind trends enhance warm air advection and surface warming across the Ross Ice Shelf, the strong easterly component of the wind trends reduces the likelihood for intrusions of CDW onto the continental shelf in this region. This suggests that during spring there are competing mechanisms of surface and basal melting of the Ross Ice Shelf, both of which are closely tied to natural tropical Pacific decadal variability. Moreover, that the projected transition of the IPO back to its positive phase in the coming decade, though likely to reduce surface warming on the Ross Ice Shelf, could increase the risk of disintegration of Ross Sea ice shelves due to increased intrusions of CDW and enhanced basal melting.