OCEANIC CIRCULATION AND OCEAN-ATMOSPHL 



tern, which in November 1965 was 

 displaced toward northern Europe 

 and, consequently, on the Alaskan 

 side of the pole left room for the 

 moving low-pressure systems from 

 the Pacific to penetrate farther north 

 than normal. 



So much for a description of the 

 air-sea rhythms. Supporting evidence 

 is available from a few other case 

 histories. The motivation for con- 

 tinued research on the equatorial air- 

 sea rhythms is the desire to develop 

 skill in forecasting climatic anomalies. 



Current Scientific Knowledge 



The data base is, unfortunately, 

 scanty. As mentioned earlier, Canton 

 Island is the only place where a 

 continuous record of the near-equa- 

 torial air-sea interaction was main- 

 tained; even there, scientific knowl- 

 edge of the air-sea rhythms, extending 

 vertically to great heights in the 

 atmosphere, must be based mainly 

 on a study of the years from 1950 

 through 1967. 



Oceanographic cruises in the equa- 

 torial belt have been few and far 

 between in space and time. The 

 EASTROPAC Program, a series of 

 internationally coordinated cruises in 

 the eastern tropical Pacific and trans- 

 equatorial cruises in the mid-Pacific, 

 sponsored by the U.S. National Ma- 

 rine Fisheries Service (NMFS), Hono- 

 lulu, has been the best oceanographic 

 effort to date to explore air-sea in- 

 teraction in the critical area where 

 the air-sea rhythms originate. Eess 

 sophisticated, widely scattered ob- 

 servations are available from com- 

 mercial ships. Those collected by the 

 NMFS in Honolulu from commercial 

 ships that ply the route from Hawaii 

 to Samoa have provided a time-series 

 of equatorial sea temperature at 

 165°W., together with the corre- 

 sponding sea-temperature series at 

 Canton Island. The two records agree 

 rather well as far as the long rhythms 

 are concerned. 



Organized reporting of sea and 

 air temperatures from commercial 

 ships crossing the east and central 

 part of the Pacific tropical zone is in 

 good hands with the NMFS in La 

 Jolla, California; the monthly maps 

 issued by that institution are at 

 present the best source of informa- 

 tion on tropical air-sea rhythms. 



The Status of Instrumentation ■ — 

 An important technical improvement 

 in the ocean data reported from 

 commercial ships will come soon. 

 Selected ships will be equipped with 

 Expendable Bathy-Thermographs 

 (XBT) to enable them to monitor the 

 varying heat storage in the ocean 

 down to the thermocline. 



Anchored buoys can provide the 

 same information as XBT-equipped 

 commercial ships and will have the 

 advantage of delivery data for long 

 time-series at fixed locations. The 

 buoys that can be permanently fi- 

 nanced should preferably be placed 

 to fill the big gaps between fre- 

 quented shipping lanes. Also, their 

 locations should be selected where 

 ocean temperatures are likely to vary 

 significantly, for instance along the 

 equator. 



Infrared radiometers on satellites 

 can be adjusted to record sea tem- 

 perature in cloud-free areas, but the 

 accuracy of such measurements can- 

 not quite compare with careful ship- 

 or buoy-based observations. The 

 great contributions of the satellites 

 to tropical studies are — presently 

 and in the future — the TV-mapping 

 of cloud distribution, the temperature 

 measurements of the top surface of 

 cloud, and, under favorable condi- 

 tions, the movement of individual 

 clouds and cloud clusters. 



Fixed installations on tropical is- 

 lands will continue to be important 

 for research on ocean-atmosphere in- 

 teraction. Aerological soundings, in- 

 cluding upper wind measurements, 

 are best done from islands; moreover, 

 fundamental measurements like the 

 time variations of the topography of 



ocean level can only be done with 

 a network of island-based tide 

 gauges. The latter job does not call 

 for very expensive equipment, and 

 the tide gauges can be serviced as 

 part-time work by trained islanders; 

 the aerological work, on the other 

 hand, calls for a technologically 

 skilled staff on permanent duty. 



Replacements for Canton Island as 

 an aerological observatory would be 

 relatively expensive, but yet cheaper 

 than was Canton, if islands with 

 stable native population were selected 

 for observatory sites. The two British 

 islands of Tarawa (l°2l'N. 172°56'E.) 

 and Christmas (1°59'N. 157°29'W.) 

 would be ideal choices. 



Mathematical Modeling — A crude 

 modeling of an asymptotically ap- 

 proached "steady state" of an equa- 

 torial ocean exposed to the stress of 

 constant easterly winds has been pro- 

 duced by Bryan, of the Geophysical 

 Fluid Dynamics Laboratory, NOAA. 

 A corresponding, quickly adjusting 

 atmospheric model of the equatorial 

 circulation, such as observed over the 

 Pacific, was described in 1969 by 

 Manabe, also of the Princeton NOAA 

 team. 



Presumably, the ocean and atmos- 

 pheric models can soon be joined for 

 a simulation of the equatorial air- 

 sea rhythms. Even without mathe- 

 matical formulation, the rhythm can 

 be crudely visualized to operate as 

 follows: 



The cooling phase of the rhythm 

 begins when the equatorial easterlies 

 of the eastern Pacific start increasing 

 and thereby start intensifying the 

 upwelling. This increases the tem- 

 perature deficit of the eastern end 

 of the oceanic equatorial belt com- 

 pared to its western end. The asso- 

 ciated feedback upon the atmosphere 

 shows up in an increased east-west 

 temperature contrast, which produces 

 an increment of kinetic energy in 

 the equatorial atmospheric circula- 

 tion. This, in turn, feeds back into 



87 



