NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

1. Record warming in the South Pacific & western Antarctica associated with the 2009-10 El Nino NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA Tong Lee, Will Hobbs, Josh Willis, Daria Halkides, Ichiro Fukumori, Ed Armstrong, Akiko Hayashi, Tim Liu, Bill Patzert, Ou Wang Tong.Lee@jpl.nasa.gov Synopsis We report an event with extreme oceanic & atmospheric anomalies in the S. Pacific & western Antarctica during late 2009-early 2010. A suite of satellite & in-situ data & reanalysis products are used to describe the evolution of the event, to examine the physical processes, and to investigate its relations to climate variability at low and high latitudes (Lee et al. 2010). Also see related work by Böning et al. (2011). Fig.1 SST anomaly in January 2010, showing large anomalous warming in the South-central Pacific (SCP) that is larger than Australia and stronger than the concurrent El Nino. Data: Reynolds ¼-deg. GHRSST. Image credit: PO.DAAC. • Main findings • Record (1982-2010) oceanic warming in the South-central Pacific (SCP) & western Antarctica during 2009-10 austral spring-summer (Fig.1, 2, 3). • The SCP warming is confined to the mixed layer (as revealed by Argo float data, not shown). • Associated with an extreme & persistent anticyclone (Fig. 2, 3, 4) • Wind changes related to the anticyclone are major causes of oceanic warming (Fig.4): • comparable roles of reduced oceanic surface heat loss & less advection of cold waters from the south. • Warm air & water are diverted towards western Antarctica (Fig. 4); a record austral-summer warming is found in the Bellingshausen Sea & around the Wilkins Ice Shelf (Fig. 5). • The strong central-Pacific El Nino in 2009-10 may have fueled the event via atmospheric teleconnection (Fig.6). • Implications: • Extreme events like this may adversely affect the Antarctic environment, esp. if they become more frequent in the future associated with the increasing frequency and amplitude of El Nino in the central equatorial Pacific (Lee & McPhaden (2010)) (Fig.6) Fig.4 Nov. 2009 anomalies of wind speed (a & b) and wind vector (c and d). Blue color in the SCP box indicates low wind speed & less oceanic heat loss. The anticyclone (1) caused easterly wind in the SCP box that inhibited northward flow of cold water, (2) diverted warmer air carried by the circumpolar westerly to Antarctica. Fig.2 Anomalies of SST (color & 500-hPa geopotential height (contour, NCEPII) in late 2009-early 2010, showing the evolution of the ocean warming & the associated atmospheric high-pressure system (anticyclone) in the SCP region (the square). 5 standard deviation Fig.5 SST anomaly near the Bellingshausen Sea (see box in upper panels) and time series of SST anomaly averaged within this sea (lower). References: [1] Lee, T., W. Hobbs, and J. Willis, et al., 2010: Record warming in the South Pacific and western Antarctica associated with the strong central-Pacific El Niño in 2009-10. Geophys. Res. Lett., 37, L19704, doi:10.1029/2010GL044865.  [2] Lee, T., and M. McPhaden, 2010: Increasing intensity of El Nino in the central-equatorial Pacific. Geophys. Res. Lett., L14603, doi:10.1029/2010GL044007. [3] Böning, C., T. Lee, and V. Zlotnicki, 2011: A record-high ocean bottom pressure in the South Pacific observed by GRACE. Geophys. Res. Lett., 38, L04602, doi:10.1029/2010GL046013. 4 standard deviation Fig.6 Correlation of SCP-averaged SST anomaly and SST anomalies in the tropical & South Pacific (left); amplitude of El Nino in the central Pacific as measured by peak Nino4 SST index (right). After Lee & McPhaden (2010). Fig.3 SCP-averaged anomalies of SST (upper) & 500-hPa geopotential height (lower).