Interannual‑decadal variability of wintertime mixed layer depthsin the North Pacific detected by an ensemble of ocean syntheses
Takahiro Toyoda1, Yosuke Fujii2, Tsurane Kuragano2, Naohiro Kosugi3, Daisuke Sasano4, Masafumi Kamachi2, Yoichi Ishikawa5, Shuhei Masuda5, Kanako Sato6, Toshiyuki Awaji7, Fabrice Hernandez8, Nicolas Ferry9, Stephanie Guinehut10, Matthew Martin11, Andrew Peterson12, Simon A Good11, Maria Valdivieso13, Keith Haines14, Dr. Andrea Storto, PhD15, Simona Masina16, Armin Koehl17, Yonghong Yin18, Li Shi18, Oscar Alves19, Gregory C Smith20, You-Soon Chang21, Guillaume Vernieres22, Xiaochun Wang23, Gael Forget24, Patrick Heimbach25, Ou Wang23, Ichiro Fukumori23, Tong Lee23, Hao Zuo26 and Magdalena Balmaseda26, (1)Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Japan, (2)Meteorological Research Institute, Ibaraki, Japan, (3)Meteorological Research Institute, Tsukuba, Japan, (4)Meteorological Research Institute, Oceanography and Geochemistry Research Department, Tsukuba, Japan, (5)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan, (6)Ministry of Environment, Tokyo, Japan, (7)Kyoto University, Kyoto, Japan, (8)IRD/Mercator Ocean, Ramonville St Agne, France, (9)Mercator Ocean, Ramonville St Agne, France, (10)Collecte Localisation Satellites (CLS), Ramonville Saint‑Agne, France, (11)Met Office, Exeter, United Kingdom, (12)UK MetOffice, Exeter, United Kingdom, (13)University of Reading, Department of Meteorology, Reading, United Kingdom, (14)Reading University, Meteorology, Reading, United Kingdom, (15)Fondazione CMCC, Bolognia, Italy, (16)Euro-Mediterranean Center on Climate Change, Ocean Modeling and Data Assimilation Division, Bologna, Italy, (17)Universität Hamburg, Centrum für Erdsystemforschung und Nachhaltigkeit, Institute of Oceanography, Hamburg, Germany, (18)Centre for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne, Australia, (19)Australian Bureau of Meteorology, Research & Development, Melbourne, Australia, (20)Environment and Climate Change Canada, Meteorological Research Division, Quebec, QC, Canada, (21)Kongju National University, Gongju, Korea, Republic of (South), (22)NASA GSFC, Greenbelt, United States, (23)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (24)Massachusetts Institute of Technology, EAPS, Cambridge, United States, (25)University of Texas at Austin, Oden Institute for Computational Engineering and Sciences, Austin, TX, United States, (26)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.
