Formation Mechanism for Isopycnal Temperature–Salinity Anomalies Propagating from the Eastern South Pacific to the Equatorial Region

Abstract Equatorward propagation of temperature–salinity (or spiciness) anomalies on an isopycnal surface emanating from the eastern subtropical South Pacific and their formation mechanism are investigated based on a hindcast simulation with an eddy-resolving quasi-global ocean general circulation model. Because of density-compensating meridional distributions of temperature and salinity, the meridional density gradient is weak at the sea surface in the eastern subtropical South Pacific. With these mean fields, cool sea surface temperature anomalies (SSTAs) can make the outcrop line of an isopycnal surface migrate equatorward more than 5° and induce warm and salty anomalies on the isopycnal surface. Subducted warm, salty anomalies propagate to the equatorial region over approximately 5 yr and may influence equatorial isopycnal temperature–salinity anomalies. Although the associated effects are unclear, if these anomalies could further induce warm eastern equatorial SSTAs that are positively correlated wit...

[1]  Dongxiao Zhang,et al.  Slowdown of the meridional overturning circulation in the upper Pacific Ocean , 2002, Nature.

[2]  S. Xie,et al.  Propagation of North Pacific interdecadal subsurface temperature anomalies in an ocean GCM , 2000 .

[3]  J. S. Godfrey,et al.  A Model of Sea Level Rise Caused by Ocean Thermal Expansion , 1991 .

[4]  G. Johnson,et al.  Generation and Initial Evolution of a Mode Water (cid:1) – S Anomaly* , 2006 .

[5]  K. Hanawa,et al.  North Pacific Tropical Water: its climatology and temporal changes associated with the climate regime shift in the 1970s , 2000 .

[6]  M. Maltrud,et al.  Numerical simulation of the North Atlantic Ocean at 1/10 degrees , 2000 .

[7]  S. Philander,et al.  Interdecadal Climate Fluctuations That Depend on Exchanges Between the Tropics and Extratropics , 1997, Science.

[8]  Hitoshi Uehara,et al.  An Eddy-Resolving Hindcast Simulation of the Quasiglobal Ocean from 1950 to 2003 on the Earth Simulator , 2008 .

[9]  C. Deser,et al.  Upper-Ocean Thermal Variations in the North Pacific during 1970–1991 , 1996 .

[10]  N. Bindoff,et al.  Diagnosing Climate Change and Ocean Ventilation using Hydrographic Data , 1994 .

[11]  T. Yamagata,et al.  Long-term El Niño-Southern Oscillation (ENSO)-like variation with special emphasis on the South Pacific , 2001 .

[12]  B. Huang,et al.  Pacific subtropical‐tropical thermocline water exchange in the National Centers for Environmental Prediction ocean model , 1999 .

[13]  G. Johnson,et al.  South Pacific Eastern Subtropical Mode Water , 2003 .

[14]  N. Fučkar,et al.  Southern Hemisphere Origins of the 1976 Climate Shift , 2002 .

[15]  Kazutoshi Horiuchi,et al.  Improved estimates of the dynamical state of the North Pacific Ocean from a 4 dimensional variational data assimilation , 2003 .

[16]  W. Kessler.  Interannual Variability of the Subsurface High Salinity Tongue South of the Equator at 165°E* , 1999 .

[17]  W. Large,et al.  Oceanic vertical mixing: a review and a model with a nonlocal boundary layer parameterization , 1994 .

[18]  A. Busalacchi,et al.  On the connection between South Pacific subtropical spiciness anomalies and decadal equatorial variability in an ocean general circulation model , 2005 .

[19]  N. Schneider.  The Response of Tropical Climate to the Equatorial Emergence of Spiciness Anomalies , 2004 .

[20]  Hisashi Nakamura,et al.  Decadal Variability in the Kuroshio–Oyashio Extension Simulated in an Eddy-Resolving OGCM , 2006 .

[21]  S. Xie,et al.  Equatorward Spreading of a Passive Tracer with Application to North Pacific Interdecadal Temperature Variations , 2000 .

[22]  M. Mcphaden,et al.  Interior pycnocline flow from the subtropical to the Equatorial Pacific Ocean , 1999 .

[23]  W. Large,et al.  Late-winter generation of spiciness on subducted isopycnals , 2004 .

[24]  M. Nonaka,et al.  Tropical Subsurface Salinity and Tritium Distributions in the Pacific: Their Differences and Formation Mechanisms* , 2001 .

[25]  Y. Masumoto.  A fifty-year eddy-resolving simulation of the world ocean : Preliminary outcomes of OFES (OGCM for the Earth Simulator) , 2004 .

[26]  P. Delecluse,et al.  South Pacific origin of the decadal ENSO‐like variation as simulated by a coupled GCM , 2003 .

[27]  R. Reynolds,et al.  The NCEP/NCAR 40-Year Reanalysis Project , 1996, Renewable Energy.

[28]  P. Lu,et al.  Interaction between the Subtropical and Equatorial Ocean Circulations: The Subtropical Cell , 1994 .

[29]  N. Schneider,et al.  Salinity Variations in the Southern California Current , 2005 .

[30]  T. Barnett,et al.  Pacific thermocline bridge revisited , 1999 .

[31]  S. Xie,et al.  Decadal variations in the subtropical cells and equatorial pacific SST , 2002 .

[32]  N. Schneider.  A decadal spiciness mode in the tropics , 2000 .

[33]  R. Kleeman,et al.  A mechanism for generating ENSO decadal variability , 1999 .

[34]  W. Luo,et al.  Morphometric analysis of Martian valley network basins using a circularity function , 2005 .