TERRESTRIAL EFFECTS OF SOLA 



ried out in the relatively less compli- 

 cated mesosphere may produce sig- 

 nificant insights into these practical 

 problems of the lower atmosphere. 



Research Needs in the Upper At- 

 mosphere — The greatest single need 

 in this area of geophysics is for a 

 systematic exploration of the prop- 

 erties of the upper atmosphere using 

 rocket and satellite techniques. At 

 present we have only tantalizing 



glimpses of many of the important 

 features, and little or no information 

 on how they change with time of 

 day, season, solar activity, and al- 

 titude. The techniques exist, and 

 all that is required is a sustained 

 synoptic program aimed at studying 

 a variety of upper-atmosphere param- 

 eters simultaneously under a wide 

 range of conditions. Such a program 

 would add immensely to our knowl- 

 edge of the upper reaches of the 



atmosphere, and of the mechanisms 

 occurring there that may be important 

 to our existence. Because of the 

 complexity of the region, single prob- 

 lems cannot be handled in isolation, 

 and there is a real need for a thor- 

 ough exploration of the entire region. 

 Some scientists believe, however, that 

 we now have enough general knowl- 

 edge of what goes on in space that 

 future studies should be limited and 

 carefully aimed at specific goals. 



TERRESTRIAL EFFECTS OF SOLAR ACTIVITY 



The sun and the motions of the 

 of the earth about it essentially de- 

 termine the earth's climate. The time 

 of day and the season are associated 

 with well-known, normal variations 

 in the weather. Superimposed on 

 these regular patterns, however, are 

 extremely large deviations from cli- 

 matology. Some of these can be ex- 

 plained (and, hence, forecast with 

 some success) on the basis of physical 

 equations; some are so irregular or 

 little understood as to require a 

 statistical and probabilistic approach 

 to prediction. 



Advances in Forecasting Technique 



For many decades, atmospheric sci- 

 entists attempted to relate solar 

 perturbations to terrestrial weather 

 features, with no significant success. 

 Until recently, the only data avail- 

 able to them were those collected 

 from ground-based observatories and 

 weather stations. When radio arrived 

 on the scene, scientists began to re- 

 late variations in radio propagation 

 to observed changes in the character 

 of the sun. 



The Space Age produced a revolu- 

 tion in understanding and procedure. 

 It became clear that, in general, the 

 farther one moves away from the 

 troposphere, the more one's environ- 

 ment is influenced by solar perturba- 

 tions. In the region above the meso- 



pause, at about 80 kilometers from 

 the earth, variations in temperature 

 and density result almost entirely 

 from irregular solar emissions and 

 hardly at all from the moving pattern 

 of low-level cyclones and anticyclones. 



These new insights — together with 

 the realization that men, equipment, 

 and their activities above the lower, 

 protective atmosphere are vulnerable 

 to (and may benefit from) environ- 

 mental changes — gave impetus to a 

 rush of new, very-high-altitude scien- 

 tific missions and related activities. 

 These include observations from rock- 

 ets, satellites, and improved ground- 

 based platforms; computerized data- 

 processing techniques; and prediction. 



Solar Forecasting Services — At- 

 mospheric scientists, ionospheric and 

 solar physicists, and even astrono- 

 mers have shared in these new activi- 

 ties. But the atmospheric scientist, in 

 becoming involved with the expanded 

 environment, brings with him a spe- 

 cial point of view: he is vitally con- 

 cerned with data standardization, real- 

 time use and rapid transmission of 

 data, and the tailoring of his products 

 to operational needs. He brings added 

 emphasis with regard to synoptic cov- 

 erage. He uses meteorological tech- 

 niques in studying high-altitude vari- 

 ations such as anomalous variations 

 in neutral density. He even applies 

 Rossby's concepts to circulation fea- 

 tures on the "surface" of the sun. 



A combination of the viewpoints 

 and methods of various kinds of sci- 

 entists has now brought a new and 

 important scientific service into being 

 — the solar forecast center. The first 

 such center was established by the 

 U.S. Air Force with a nucleus of 

 highly trained and cross-disciplined 

 scientists from the Air Weather Serv- 

 ice and the Air Force Cambridge Re- 

 search Laboratories; their mission was 

 to provide tailored, real-time support 

 to military operations affected by 

 the environment above the "classical 

 atmosphere." The ionospheric-pre- 

 diction activity of the National Oce- 

 anic and Atmospheric Administration 

 (NOAA) has been enlarged to pro- 

 vide a complementary service for the 

 civilian community. 



Major Problem Areas 



Solar forecasting centers and other 

 such forecasting services undertake 

 to meet the needs of a variety of cus- 

 tomers, including radio communica- 

 tors, astronauts, and scientific re- 

 searchers. The most important areas 

 of interest for such customers are as 

 follows: 



Tlie Ionosphere — High frequency 

 (HF) (3-30 mHz) radio communica- 

 tions are widely used as an inexpen- 

 sive, fairly reliable means of trans- 

 mitting signals over long distances. 



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