ATMOSPHERIC \TION 



There is some controversy as to 

 the inherent deterministic limitations 

 of the predictability of the atmos- 

 phere — say, for scales corresponding 

 to individual extratropical cyclones. 

 The span of controversy ranges from 

 about one to several weeks. More- 

 over, it is not known at all whether 

 longer-term characteristics of atmos- 

 pheric variability are determinate. 

 For example, is it inherently possible 

 to distinguish the mean conditions 

 over eastern United States from one 

 January to another in some deter- 

 ministic sense? In the equatorial 

 tropics there is very little insight as 

 to the spectrum of predictability. 



Needs for Future Improvements 



Broadly, there are three areas that 

 require intensive upgrading, the first 

 two of which are essentially tech- 

 nological: 



Technological Requirements — The 

 need for establishment of an adequate 

 global observing system has already 

 been discussed. In addition, com- 

 puters two orders of magnitude faster 

 than those currently available are 

 needed to permit the positive reduc- 

 tion of mathematical errors incurred 

 by inadequate computational resolu- 

 tion. Faster computers will also per- 

 mit more exhaustive tests of model 

 performance over a much larger 

 range of parameter-space to assess 

 the sensitivity of simulations to 

 parameterizations of physical process 

 elements of the model. Faster com- 

 puters will also provide an ability 

 to undertake the broad range of ap- 

 plications implied by a more sophisti- 

 cated modeling capability. 



Scientific Requirements — The sci- 

 entific requirements stem from the 

 necessity of refining the formulation 

 of process elements in the models. 

 To cite a few: boundary-layer inter- 

 actions — to determine the depend- 



ence of the heat, momentum, and 

 water-vapor exchange within the 

 lower kilometer of the atmosphere 

 as a function of the large-scale struc- 

 tural characteristics; internal turbu- 

 lence — to determine the structure 

 and mechanisms responsible for in- 

 termittent turbulence in the "free" 

 atmosphere, which is apparently re- 

 sponsible for the removal of signifi- 

 cant amounts of energy from the 

 large scale and may also play a role 

 in the diffusion of heat, momentum, 

 and water vapor; and convection — 

 to determine how cumulus overturn- 

 ing gives rise to the deep vertical 

 transport of heat, water vapor, and, 

 possibly, momentum. 



We still do not know the con- 

 sequences of particulates, man-made 

 or natural, either directly on the 

 radiative balance or ultimately on 

 the dynamics. 



In the tropics, we have yet to com- 

 pletely understand the instability 

 mechanisms responsible for the for- 

 mation of weak disturbances or the 

 nature of an apparent second level 

 of instability which transforms some 

 of these disturbances into intense 

 vortices, manifested as hurricanes 

 and typhoons. Without an under- 

 standing of the intricacies of the 

 tropics, it is impossible to deal com- 

 prehensively or coherently with the 

 global circulation, particularly with 

 the interactions of the circulation of 

 one atmosphere with that of the 

 other. 



Most of these critical scientific 

 areas of uncertainty require intensive 

 phenomenological or regional obser- 

 vational studies. These will provide 

 the basic data as foundations for a 

 better theoretical understanding. 



Any one of the general scientific 

 and technological categories listed 

 above may at any one time provide 

 the weakest link in the complex 



required to advance a modeling and 

 simulation capability. Obviously, 

 then, they must be upgraded at com- 

 patible rates. 



Prospects 



A comprehensive look at the status, 

 needs, and implications of an under- 

 standing and simulation capability of 

 the global circulation is embodied in 

 the Global Atmospheric Research 

 Program (GARP), which was estab- 

 lished several years ago as an inter- 

 national venture under the joint 

 auspices of the World Meteorological 

 Organization and the International 

 Council of Scientific Unions. In the 

 United States, GARP is overseen by 

 a National Academy of Sciences 

 committee that has produced a plan- 

 ning document for U.S. national par- 

 ticipation. Almost all the problem 

 areas discussed above have come to 

 the attention of the U.S. Committee 

 for GARP. The international time- 

 scale for major field experiments ex- 

 tends into the late 1970's. Concomi- 

 tantly, national and international 

 research programs to support and 

 derive results from the field programs 

 will be established. The time-scales 

 governing GARP planning imply that 

 one can expect the necessary elements 

 to be systematically undertaken over 

 about a ten-year period. The first 

 GARP tropical experiment will take 

 place in 1974 in the eastern equatorial 

 Atlantic and the first GARP global 

 data-gathering experiment is sched- 

 uled for 1976 or later. GARP is the 

 research part of the World Weather 

 Program (WWP). The other part of 

 the WWP is the World Weather 

 Watch (WWW), whose objective is 

 to bring the global atmosphere under 

 surveillance and provide for the 

 rapid collection and exchange of 

 weather data as well as the dissemi- 

 nation of weather products from cen- 

 tralized processing centers. GARP 

 will rely heavily on data obtained 

 from the WWW. (See Figure IV-7) 



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