Subdiem Oscillation in Sea Level and 

 Associated Variables in the Eastern and 

 Central Tropical Pacific 



rU . //. »unk, G. iV. Groves, and G. R. Miller) 



In this work, which is not complete, the 

 purpose is to use the very long series of 

 hourly values of sea level, atmospheric pres- 

 sure, and wind components that are available 

 from Balboa, Canal Zone, and Honolulu and 

 other stations in Hawaii, for an analysis of 

 oscillations with subdiem frequencies, i.e., 

 less than one cycle per day. 



Compilation of data in suitable punchcard 

 form for analysis has involved much labor 

 even with the assistance of error-catching 

 computer programs. The following time series 

 are now in suitable form: 



Balboa sea level 1907-57 

 Balboa pressure and wind 



components 1943-56 



Honolulu sea level 1905-57 

 Honolulu pressure and wind 



components 1941-56 



Hilo, Hawaii, sea level June 1947-57 



Kauai, Hawaii, sea level Dec. 1954-56 



Maui, Hawaii, sea level 1951-56 



Processing of the data will involve cross 

 spectral analyses between the oceanographic 

 and meteorological series to derive informa- 

 tion about the role of wind and pressure in 

 setting up the oscillations in sea level. Dif- 

 ferences bet\veen midocean (Hawaii) and the 

 continental margin (Balboa), and between sea- 

 sons, may have particular interest. 



Relation Between Wind Velocity and Surface 

 Temperature in the Gulf of Tehuantepec 



(G. I. Roden) 



In the Gulf of Tehuantepec, on the Pacific 

 coast of southern Mexico, an area of cold 

 surface water roughly coincides at certain 

 seasons with a belt of high wind; this is 

 discussed below. To study the statistical 

 relation between sea temperature and wind 

 velocity a spectral analysis was made of 

 anomalies of 10-day means during the period 

 January 1949 through June 1957, in four ad- 

 jacent 2-degree rectangles. The results showed 

 a good coherence of temperature anomalies 

 and wind anomalies in adjacent rectangles. 

 The coherence between wind and temperature 

 anomalies was less good and significant only 

 for frequencies between two and four cycles 

 per year, approximately. The highest coher- 

 ence was found near three cycles per year, 

 with about 50 percent of temperature anomaly 

 due to wind anomaly. 



The study was incomplete in June 1960, but 

 has since been completed and is in press, 



entitled "On the wind-driven circulation in 

 the Gulf of Tehuantepec and its effect upon 

 surface temperatures," in Geofisica Inter- 

 nacional. It has been supported in part (about 

 50 percent) by the California Marine Research 

 Committee. 



RECENT CHANGES IN THE OCEAN 



It is now common knowledge that 1955 was 

 a year of low surface tennperatures in the 

 eastern Pacific off the coasts of North 

 America and Peru, and 1957-58 the beginning 

 of a period of high temperatures in the same 

 waters (e.g., Rodewald, 1957 and 1959). Several 

 research agencies have been concerned with 

 the investigation of the warming as far as it 

 affected the waters off North America, which 

 was the subject of a symposium held in 1958 

 on "The changing Pacific Ocean in 1957 and 

 1958" (Sette and Isaacs, I960). The changes 

 have been less well documented in the rest of 

 the eastern Pacific, because of the smaller 

 number of investigations and observational 

 facilities, but some attention has been given 

 to thenn by the STOR program, as shown below, 

 and by the Inter-American Tropical Tuna 

 Commission. 



Surface Temperature Anomalies in Middle 

 American Coastal Waters fw. Blackburn) 



Figure 5 shows these changes as they 

 appeared in the fourth quarter (October- 

 December) of each year 1955 through 1959. 

 The fourth quarter was chosen because of ex- 

 peditions at that period in 1955 and 1956 

 (EASTROPIC and SCOPE, respectively) which, 

 together with charts issued monthly since 

 January 1957 by the Bureau of Connmercial 

 Fisheries, provided surface temperature data 

 over a comparable period in the 5 successive 

 years. The observations for each year, 

 averaged for the available 1 -degree rectangles 

 which are indicated by points in figure 5, 

 have been contoured in intervals of 5° F. 

 Similar contours based on long-term average 

 surface temperatures, adapted from published 

 monthly charts (U.S. Navy Hydrographic Office, 

 1944), are shown for comparison in the left- 

 hand panel. 



The comparisons show that surface tem- 

 peratures for the region as a whole were 

 lower than average in 1955, about average in 

 1956, above average in 1957 and 1958, and 

 reapproaching average off Central America, 

 but not off southern Mexico, in 1959. 



The information on tuna distribution in 

 figure 5 is discussed later in this paper, 

 under "Tuna ecology." 



The above-mentioned monthly tennperature 

 charts of the Bureau of Commercial Fisheries, 



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