CHARACTERISTICS OF SEA-SURFACE TEMPERATURE ANOMALIES 



L. E. Eber' 



ABSTRACT 



Sea-surface temperature anomalies in the North Pacific Ocean, constructed from a 14-year series (1949- 

 62) of monthly mean charts, exhibit numerous instances of quasi-stationary behavior. Selected exam- 

 ples from this series reveal a recurring pattern in which the principal feature is a positive or negative 

 cell in the anomaly field, located approximately between lat 30° N and 50° N. The cell in this pat- 

 tern is partially encircled by anomalies of opposite sign to the north, east, and south in a zone contig- 

 uous with the North American coast. This anomaly configuration, viewed with consideration of the 

 associated sea-temperature field, suggests the existence of a standing wave in the current structure. 

 Such a wave could affect the partitioning of the West Wind Drift Current as it approaches the coast 

 and splits into northward and southward flowing branches. Physical data for verification of a stand- 

 ing wave are not available, but dimensional attributes inferred from the sea-temperature anomaly 

 structure conform loosely to theoretical constraints. 



The temperatures in the upj^er mixed layer of 

 the ocean undergo annual cycles, induced by 

 seasonal heating and cooling, which vary from 

 year to year. This variation can be expressed 

 in terms of departures from the mean annual 

 temperature cycle obtained by averaging over 

 a number of years. The magnitudes, area) dis- 

 tributions, and time changes of such departures 

 define anomalous conditions in the surface layer 

 of the sea. 



The 14-year series, 1949-62, of monthly sea- 

 surface temperature charts, published by Eber, 

 Saur, and Sette (1968), provides a base for 

 studying temperature variations in the North 

 Pacific Ocean. Monthly anomaly charts were 

 constructed from this series by taking the dif- 

 ference between the sea-surface temperature 

 fields for each month and year and the corres- 

 ]3onding monthly normal fields. The latter were 

 obtained by computing the 14-year averages, by 

 month, at grid points. A number of selected 

 examples are presented here to show the char- 

 acter of some of the prominent and long-lasting 

 anomalies that occurred in the North Pacific 

 Ocean between 1949 and 1962. 



Many of the features to be discussed are in 

 the vicinity of the transition zone between the 

 subarctic and subtropic oceanographic regions 

 as described by Tully (1964). Through this 



' National Marine Fisheries Service Fishery-Ocean- 

 ography Center, La Jolla, Calif. 92037. 



zone, which is located approximately at lat 35° N 

 to 45° N between long 160° E and 140° W, 

 the surface current flows eastward as the West 

 Wind Drift. The mean surface temperature 

 distribution in this region is essentially zonal 

 with isotherms oriented along the circles of lat- 

 itude. The chart of the 14-year average for 

 October (Figure 1) illustrates these charac- 

 teristics. As the West Wind Drift approaches 



IZO" 130* 140* aO- 160* 170* WO* ITO* WO* OO* I40* 130* 120* IW* 100* 90* 90* 



Figure 1. — Average sea-surface temperatures of the 

 North Pacific Ocean in October, based on data from the 

 14-year period 1949-62. 



the North American coast, it splits. One part 

 turns north and moves in a counterclockwise 

 trajectory around the Alaska Gyre and the other 

 part turns south to become the California 



Manuscript received January 1971. 



FISHERY BULLETIN: VOL. 69. NO. 2. 1971. 



345 



