Altimeter-derived surface circulation in the large–scale NE Pacific Gyres.: Part 1. seasonal variability

Abstract The seasonal variability of sea surface height (SSH) and currents are defined by analysis of altimeter data in the NE Pacific Ocean over the region from Central America to the Alaska Gyre. The results help to clarify questions about the timing of seasonal maxima in the boundary currents. As explained below, the long-term temporal mean of the SSH values must be removed at each spatial point to remove the temporally invariant (and large) signal caused by the marine geoid. We refer to the resulting SSH values, which contain all of the temporal variations, as the ‘residual’ SSH. Our main findings are: 1. The maximum surface velocities around the boundaries of the cyclonic Alaska Gyre (the Alaska Current and the Alaska Stream) occur in winter, at the same time that the equatorward California Current is weakest or reversed (forming the poleward Davidson Current); the maximum surface velocities in the California Current occur in summer. These seasonal maxima are coincident with the large-scale atmospheric wind forcing over each region. 2. Most of the seasonal variability occurs as strong residuals in alongshore surface currents around the boundaries of the NE Pacific basin, directly connecting the boundaries of the subpolar gyre, the subtropical gyre and the Equatorial Current System. 3. Seasonal variability in the surface velocities of the eastward North Pacific Current (West Wind Drift) is weak in comparison to seasonal changes in the surface currents along the boundaries. 4. There is an initial appearance next to the coast and offshore migration of seasonal highs and lows in SSH, alongshore velocity and eddy kinetic energy (EKE) in the Alaska Gyre, similar to the previously-described seasonal offshore migration in the California Current. 5. The seasonal development of high SSH and poleward current residuals next to the coast appear first off Central America and mainland Mexico in May–June, prior to their appearance in the southern part of the California Current in July–August and their eventual spread around the entire basin in November–December. Similarly, low SSH and equatorward transport residuals appear first off Central America and Mexico in January–February before spreading farther north in spring and summer. 6. The maximum values of EKE occur when each of the boundary currents are maximum.

[1]  P. Strub,et al.  Altimeter-derived variability of surface velocities in the California Current System: 2. Seasonal circulation and eddy statistics , 2000 .

[2]  R. Grimshaw,et al.  Low-Frequency Baroclinic Waves off Coastal Boundaries , 1988 .

[3]  M. Mcphaden,et al.  Genesis and evolution of the 1997-98 El Nino , 1999, Science.

[4]  A. Filonov,et al.  El Niño 1997–98 monitoring in mixed layer at the Pacific Ocean near mexico's West Coast , 2000 .

[5]  Franklin B. Schwing,et al.  Coastal upwelling indices, west coast of North America, 1946-1995 , 1996 .

[6]  S. Tabata.  The Anticyclonic, Baroclinic Eddy off Sitka, Alaska, in the Northeast Pacific Ocean , 1982 .

[7]  P. Strub,et al.  The 1997-1998 oceanic El Nino signal along the southeast and northeast Pacific boundaries—an altimetric view , 2002 .

[8]  M. Caruso,et al.  A view of the 1993-1994 California Current based on surface drifters, floats, and remotely sensed data , 2000 .

[9]  R. Davis,et al.  Techniques for statistical analysis and prediction of geophysical fluid systems , 1977 .

[10]  Robert L. Smith,et al.  Seasonal cycles of currents, temperatures, winds, and sea level over the northeast pacific continental shelf: 35°N to 48°N , 1987 .

[11]  Dale B. Haidvogel,et al.  Dynamical simulations of filament formation and evolution in the Coastal Transition Zone , 1991 .

[12]  Russ E. Davis,et al.  Predictability of Sea Surface Temperature and Sea Level Pressure Anomalies over the North Pacific Ocean , 1976 .

[13]  Arnold W. Mantyla,et al.  The State of the California Current, 1997-1998: Transition to El Niño Conditions , 1997 .

[14]  G. Halliwell,et al.  The large-scale coastal wind field along the west coast of North America , 1987 .

[15]  H. Hotelling.  Relations Between Two Sets of Variates , 1936 .

[16]  W. White,et al.  Annual Rossby Wave Characteristics in the California Current Region from the GEOSAT Exact Repeat Mission , 1990 .

[17]  M. Levine,et al.  Altimeter‐derived variability of surface velocities in the California Current System: 1. Evaluation of TOPEX altimeter velocity resolution , 1997 .

[18]  Andrew C. Thomas,et al.  Chlorophyll variability in eastern boundary currents , 2001 .

[19]  W. Emery,et al.  Atmospheric forcing of interannual variability in the northeast Pacific Ocean: Connections with El Niño , 1985 .

[20]  J. Blanco,et al.  Hydrographic Conditions Off Northern Chile During the 1996-1998 La Niña and El Niño Events , 2002 .

[21]  P. Fiedler.  The annual cycle and biological effects of the Costa Rica Dome , 2002 .

[22]  Dong-Ping Wang.  Effects of small‐scale wind on coastal upwelling with application to Point Conception , 1997 .

[23]  J. S. Godfrey,et al.  Regional Oceanography: An Introduction , 1994 .

[24]  Lee-Lueng Fu,et al.  Sea level variabilities in the Gulf Stream between Cape Hatteras and 50°W: A Geosat study , 1990 .

[25]  P. T. Strub,et al.  Altimeter-derived surface circulation in the large-scale NE Pacific Gyres. Part 2: 1997-1998 El Nino anomalies , 2002 .

[26]  Richard E. Thomson,et al.  A basin‐scale oceanic instability event in the Gulf of Alaska , 1998 .

[27]  A. J. Clarke,et al.  On ENSO Coastal Currents and Sea Levels , 1994 .

[28]  M. Richman,et al.  Rotation of principal components , 1986 .

[29]  Detlef Stammer,et al.  Steric and wind-induced changes in TOPEX/POSEIDON large-scale sea surface topography observations , 1997 .

[30]  J. McClean,et al.  Observations and modeling of the 1991–1992 El Niño signal off central California , 1997 .

[31]  S. Bograd,et al.  Near-surface circulation of the northeast Pacific Ocean derived from WOCE-SVP satellite-tracked drifters , 1999 .

[32]  S. Basu,et al.  Eddies in the eastern Gulf of Alaska from TOPEX/POSEIDON altimetry , 1999 .

[33]  Michael J. McPhaden,et al.  Equatorial waves and the 1997–98 El Niño , 1999 .

[34]  Robert L. Smith,et al.  The Peru Undercurrent: a study in variability , 1991 .

[35]  R. Davis,et al.  Predictability of Sea Level Pressure Anomalies Over the North Pacific Ocean , 1978 .

[36]  P. Fiedler.  Seasonal climatologies and variability of eastern tropical Pacific surface waters , 1992 .

[37]  James J. Simpson,et al.  El Nino‐induced onshore transport in the California Current during 1982‐1983 , 1984 .

[38]  Adriana Huyer,et al.  The coastal ocean off Oregon and northern California during the 1997–8 El Niño , 2002 .

[39]  W. Crawford,et al.  Mesoscale eddy aswirl with data in Gulf of Alaska , 1999 .

[40]  Kenneth H. Brink,et al.  The global coastal ocean : regional studies and syntheses , 1998 .

[41]  R. Samelson,et al.  Quasi-Geostrophic Topographically Generated Mean Flow over the Continental Margin , 1987 .

[42]  G. Mcnally.  Satellite‐tracked drift buoy observations of the near‐surface flow in the eastern mid‐latitude North Pacific , 1981 .

[43]  P. Kosro.  A poleward jet and an equatorward undercurrent observed off Oregon and northern California, during the 1997-98 El Nino , 2002 .

[44]  J. Paduan,et al.  Variability of the near‐surface eddy kinetic energy in the California Current based on altimetric, drifter, and moored current data , 1998 .

[45]  E. Hofmann,et al.  Wind Generation of the Costa Rica Dome , 1981, Science.

[46]  M. Batteen,et al.  Modeling studies of the effects of wind forcing and thermohaline gradients on the California Current System , 1998 .

[47]  W. Johnson,et al.  On the seasonal variability of the Alaska Coastal Current , 1988 .

[48]  A. Parés-Sierra,et al.  The seasonal and interannual variability of the California Current system: A numerical model , 1989 .

[49]  Robert L. Smith,et al.  A separating coastal upwelling jet at Cape Blanco, Oregon and its connection to the California Current System , 2000 .

[50]  Adriana Huyer,et al.  The nature of the cold filaments in the California Current system , 1991 .

[51]  R. Beamish,et al.  Effects of ocean variability on recruitment and an evaluation of parameters used in stock assessment models , 2004, Reviews in Fish Biology and Fisheries.

[52]  Sydney Levitus,et al.  NODC Inventory of Physical Oceanographic profiles , 1992 .

[53]  G. Holloway.  Systematic forcing of large-scale geophysical flows by eddy-topography interaction , 1987, Journal of Fluid Mechanics.

[54]  M. Tsuchiya.  Inshore circulation in the Southern California Bight, 1974–1977 , 1980 .

[55]  D. Chelton.  Seasonal variability of alongshore geostrophic velocity off central California , 1984 .

[56]  D. Chelton,et al.  Poleward flow off central California during the spring and summer of 1981 and 1984 , 1988 .

[57]  C. Mooers,et al.  A Summary of the Optoma Program's Mesoscale Ocean Prediction Studies in the California Current System. , 1989 .

[58]  Russ E. Davis,et al.  Monthly Mean Sea-Level Variability Along the West Coast of North America , 1982 .

[59]  J. Largier,et al.  Subtidal circulation over the northern California shelf , 1993 .

[60]  P. Strub,et al.  The large-scale summer circulation of the California current , 1995 .

[61]  Michael J. Caruso,et al.  Wind-forced Variations in Sea Surface Height in the Northeast Pacific Ocean , 1993 .

[62]  P. Stabeno,et al.  The Alaska Coastal Current: Continuity of transport and forcing , 1995 .

[63]  L. Oey.  A forcing mechanism for the poleward flow off the southern California coast , 1999 .

[64]  A. Bratseth.  Statistical interpolation by means of successive corrections , 1986 .

[65]  Francisco P. Chavez,et al.  Biological‐physical coupling in the Central Equatorial Pacific during the onset of the 1997–98 El Niño , 1998 .

[66]  M. Noble,et al.  Sea level response to ENSO along the central California coast: how the 1997–1998 event compares with the historic record , 2002 .

[67]  C. Mooers,et al.  Mean and variable flow over the central California continental margin, 1978 1980 , 1987 .

[68]  P. Leblond,et al.  Velocity and temperature fluctuations in a buoyancy‐driven current off Vancouver Island , 1991 .

[69]  K. Wyrtki.  UPWELLING IN THE COSTA RICA DOME , 1964 .

[70]  W. P. Wickett.  Ekman Transport and Zooplankton Concentration in the North Pacific Ocean , 1967 .

[71]  D. Enfield,et al.  On the Structure and Dynamics of Monthly Mean Sea Level Anomalies along the Pacific Coast of North and South America , 1980 .

[72]  Josef Y. Cherniawsky,et al.  Multi‐year meanders and eddies in the Alaskan Stream as observed by TOPEX/Poseidon altimeter , 2000 .

[73]  Barbara M. Hickey,et al.  The California current system—hypotheses and facts☆ , 1979 .

[74]  P. Strub,et al.  Seasonal and nonseasonal variability of satellite‐derived surface pigment concentration in the California Current , 1990 .

[75]  J. Riley.  Progress in Oceanography , 1964, Nature.

[76]  James J. Simpson,et al.  The California Current system: The seasonal variability of its physical characteristics , 1987 .

[77]  Variability in the Gulf of Alaska from Geosat altimetry data , 1993 .

[78]  T. C. Royer,et al.  Baroclinic transport in the Gulf of Alaska, Part II. Freshwater driven coastal current , 1981 .

[79]  J. Wahr,et al.  Coupled Pattern Analysis of Sea Surface Temperature and TOPEX/Poseidon Sea Surface Height , 1999 .

[80]  Robert L. Smith,et al.  The signature of El Niño off Oregon, 1982–1983 , 1985 .

[81]  Robert L. Smith,et al.  The structure of the transition zone between coastal waters and the open ocean off northern California, winter and spring 1987 , 1991 .

[82]  C. Winant,et al.  Characteristic patterns of the circulation in the Santa Barbara Channel , 1998 .