PART IV — DYNAMICS OF THE ATMOSPHERE-OCEAN SYSTEM 



large-scale atmospheric evolutions of 

 the order of a week. These advances 

 give promise that, as known deficien- 

 cies are systematically removed, the 

 practical level of the large-scale pre- 

 dictability of the atmosphere can 

 converge on a theoretical determin- 

 istic limitation of several weeks. 



Models have also been used in 

 some, more limited applications. For 

 example, an attempt was made to 

 simulate the long-term, large-scale 

 dispersion of inert tracing material, 

 such as radioactive tungsten, which 

 had been released at an instantaneous 

 source in the lower equatorial tropos- 

 phere. The results were surprisingly 

 good. Only limited attempts have 

 been made to apply extant models to 

 test the sensitivity of climate to small 

 external influences. The reason is 

 that one normally seeks to detect 

 departures from fairly delicately bal- 

 anced states. It is often beyond the 

 current level of capability to simulate 

 an abnormal response that is com- 

 parable in magnitude to the natural 

 variability noise level. 



Observational Problems 



The present large-scale data base 

 is essentially dictated by the extent 

 of the operational networks created 

 by the weather forecast services of 

 the world. The existing network is 

 hardly adequate to define the north- 

 ern-hemisphere extratropical atmos- 

 phere; it is completely inadequate in 

 the southern hemisphere and in the 

 equatorial tropics. For example, there 

 are only 50 radiosonde stations in 

 the southern hemisphere in contrast 

 to approximately 500 in the northern. 

 The main difficulties arise from the 

 large expanses of open ocean which, 

 by conventional methods, impede de- 

 termination of the large-scale com- 

 ponents of atmospheric structure 

 responsible for the major energy 

 transformations. This critical defi- 

 ciency in the global observational data 

 store makes it difficult to define the 

 variability of the atmosphere in 

 enough detail to discern systematic 



theoretical deficiencies. Furthermore, 

 the data are inadequate for the spec- 

 ification of initial conditions in the 

 calculation of long-range forecasts. 



Recent dramatic advances in in- 

 frared spectroscopy from satellites 

 promise significant strides in defining 

 the state of the extratropical atmo- 

 sphere virtually independent of loca- 

 tion. (See Figure IV-6) However, the 

 motions of the equatorial tropical at- 

 mosphere lack strong rotational cou- 

 pling, making the observational prob- 

 lem there more acute. Independent 



wind determinations may be needed 

 as well as the information supplied by 

 a Nimbus 3 (SIRS sensor) type satel- 

 lite. It is not yet known to what ex- 

 tent balloon-borne instrumentation or 

 measurements from ocean buoys will 

 be needed to augment satellite obser- 

 vations, especially in the lower tropos- 

 phere. This will depend on just 

 how strongly the variable character- 

 istics of the atmosphere are coupled. 

 A more precise knowledge would per- 

 mit relaxing observational require- 

 ments for an adequate definition of 

 its structure. 



Figure IV-6 — SIRS SOUNDING 



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250 

 TEMPERATURE ( # K) 



(Illustration Courtesy ot the American Meteorological Society ) 

 This figure shows the broad similarities between simultaneous temperature sound- 

 ings obtained by radiosonde equipment and satellite-borne SIRS (Satellite Infrared 

 Spectrometer) and IRIS (Infrared Interferometer Spectrometer) systems. The latter 

 systems, however, are able to provide far broader and more continuous coverage 

 than conventional equipment. Further work is in progress to overcome the difficul- 

 ties of the present instruments in predominantly overcast areas. 



90 



