Interannual‑decadal variability of wintertime mixed layer depthsin the North Pacific detected by an ensemble of ocean syntheses
Takahiro Toyoda1, Yosuke Fujii2, Tsurane Kuragano3, Naohiro Kosugi4, Daisuke Sasano5, Masafumi Kamachi3, Yoichi Ishikawa6, Shuhei Masuda6, Kanako Sato7, Toshiyuki Awaji8, Fabrice Hernandez9, Nicolas Ferry10, Stéphanie Guinehut11, Matthew Martin12, Andrew Peterson13, Simon A Good12, Maria Valdivieso14, Keith Haines15, Andrea Storto16, Simona Masina17, Armin Koehl18, Yonghong Yin19, Li Shi19, Oscar Alves20, Gregory C Smith21, You-Soon Chang22, Guillaume Vernieres23, Xiaochun Wang24, Gaël Forget25, Patrick Heimbach26, Ou Wang27, Ichiro Fukumori24, Tong Lee24, Hao Zuo28 and Balmaseda Magdalena29, (1)Meteorological Research Institute, Japan Meteorological Agency, Oceanography and Geochemistry Research Department, Tsukuba, Japan, (2)Meteorological Research Institute, Tsukuba, Ibaraki, Japan, (3)Meteorological Research Institute, Ibaraki, Japan, (4)Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Japan, (5)Meteorological Research Institute, Oceanography and Geochemistry Research Department, Tsukuba, Japan, (6)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan, (7)Ministry of Environment, Tokyo, Japan, (8)Kyoto University, Kyoto, Japan, (9)IRD/Mercator Ocean, Ramonville St Agne, France, (10)Mercator Ocean, Ramonville St Agne, France, (11)Collecte Localisation Satellites (CLS), Ramonville Saint‑Agne, France, (12)Met Office, Exeter, United Kingdom, (13)UK MetOffice, Exeter, United Kingdom, (14)University of Reading, Department of Meteorology, Reading, United Kingdom, (15)Reading University, Meteorology, Reading, United Kingdom, (16)Fondazione CMCC, Bolognia, Italy, (17)Istituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy, (18)Universität Hamburg, Hamburg, Germany, (19)Centre for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne, Australia, (20)Australian Bureau of Meteorology, Research & Development, Melbourne, Australia, (21)Environment Canada, Meteorological Research Division, Quebec, QC, Canada, (22)Kongju National University, Gongju, South Korea, (23)NASA GSFC, Greenbelt, United States, (24)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (25)Massachusetts Institute of Technology, Cambridge, MA, United States, (26)University of Texas at Austin, Austin, TX, United States, (27)Jet Propulsion Laboratory, Pasadena, CA, United States, (28)ECMWF, Reading, United Kingdom, (29)European Centre for Medium-Range Weather Forecasts, Reading, United Kingdom
Abstract:
The interannual-decadal variability of the wintertime mixed layer depths (MLDs) over the North Pacific is investigated from an empirical orthogonal function (EOF) analysis of an ensemble of global ocean reanalyses. The first leading EOF mode represents the interannual MLD anomalies centered in the eastern part of the central mode water formation region in phase opposition with those in the eastern subtropics and the central Alaskan Gyre. This first EOF mode is highly correlated with the Pacific decadal oscillation index on both the interannual and decadal time scales. The second leading EOF mode represents the MLD variability in the subtropical mode water (STMW) formation region and has a good correlation with the wintertime West Pacific (WP) index with time lag of 3 years, suggesting the importance of the oceanic dynamical response to the change in the surface wind field associated with the meridional shifts of the Aleutian Low. The above MLD variabilities are in basic agreement with previous observational and modeling findings. Moreover the reanalysis ensemble provides uncertainty estimates. The interannual MLD anomalies in the first and second EOF modes are consistently represented by the individual reanalyses and the amplitudes of the variabilities generally exceed the ensemble spread of the reanalyses. Besides, the resulting MLD variability indices, spanning the 1948–2012 period, should be helpful for characterizing the North Pacific climate variability. In particular, a 6-year oscillation including the WP teleconnection pattern in the atmosphere and the oceanic MLD variability in the STMW formation region is first detected.
