PART I — THE SOLAR-TERRESTRIAL ENVIRONMENT 



Up to a year or two ago, processing 

 of the data was done by hand. Sys- 

 tems to process the data by machine 

 have now begun to come into use, 

 and the future will see more and more 

 use of computers in operational space- 

 environment support. 



Forecasts of Significant Solar Ac- 

 tivity and Geophysical Responses ■ — 

 Geophysically significant solar events 

 must be forecast several hours, days, 

 weeks, or even years in advance. Sig- 

 nificant factors of the earth's environ- 

 ment, such as density at satellite alti- 

 tudes and the state of the ionosphere, 

 must also be forecast. In general, the 

 shorter the forecast period, the more 

 stringent the accuracy requirement. 



Research on forecasting techniques 

 has been under way for many years. 

 The approaches have been many and 

 varied, and no single technique has 

 yet stood up under the test of con- 

 tinued operational use. Since knowl- 

 edge of the physics of solar processes 

 is lacking, present techniques are 

 based on statistical correlations and 

 relationships, observed solar features, 

 even the influence of planetary con- 

 figurations. By a combination of 

 many techniques and subjective skills, 

 operational forecasters have now de- 

 veloped a limited ability to forecast 

 solar activity. 



How well can solar activity be fore- 

 cast? It is fairly safe to say that fore- 

 casting cannot be done well enough 

 for the operator to place full reliance 

 on it. Predictions can be used to ad- 

 vantage, but the operator knows he 

 must have alternatives available to 

 compensate for an incorrect forecast. 

 As a rough approximation (doubtless 

 open to challenge), no better than one 

 out of every two major, geophysically 

 significant solar events can be fore- 

 cast 24 hours in advance. Addition- 

 ally, at least three forecasts of events 

 that do not occur are issued for every 

 forecast that proves accurate. The 

 most valuable forecasting tool has 

 proved to be persistence. If a region 

 of solar activity hasn't produced a 



major event, it probably won't. If a 

 major event has occurred, another is 

 likely to follow. Such factors as re- 

 gion size and radio-brightness tem- 

 perature, magnetic structures, and 

 flare history have also proved of some 

 value. 



One factor that complicates the 

 forecast problem is that most research 

 schemes attempt to predict large "so- 

 lar flares." In reality, what the system 

 operator or mission controller is in- 

 terested in is the geophysically sig- 

 nificant solar event, whether large or 

 small. Experience has shown that 

 most large solar flares are geophysi- 

 cally significant, but some are not. 

 Most small flares are of no conse- 

 quence, but a disturbing percentage 

 are. 



Forecasting of terrestrial proton 

 events after a flare has occurred has 

 been more successful, although it is 

 not without limitations due to uncer- 

 tainties and unavailability of relevant 

 data. The storm of particles emitted 

 by a flare takes a day or two to prop- 

 agate from the sun to the earth, and 

 this time interval permits a forecaster 

 to analyze the diagnostic information 

 contained in the electromagnetic 

 emissions that accompanied the solar 

 event. Analysis of radio-burst signa- 

 tures and X-ray enhancements indi- 

 cates whether the particles have been 

 accelerated. Quantitative forecasts of 

 the course and magnitude of the event 

 are often possible. 



Other aspects of the space environ- 

 ment are being forecast with varying 

 degrees of success. The mean 10.7- 

 centimeter radio flux from the sun is 

 an input into high-altitude-density 

 models; efforts to forecast it have 

 been reasonably successful, in part 

 because the parameter varies rather 

 slowly. In contrast, practically no 

 capability exists for forecasting vari- 

 ability in the geomagnetic field, an- 

 other important input; short-term 

 prediction of geomagnetic storms is 

 particularly difficult. 



Forecasts of ionospheric parameters 

 for radio communicators have been 

 made for many years. The field is 

 quite extensive and complex. The 

 Space Environment Laboratory, of 

 NOAA, issues monthly, and some- 

 times more frequent, outlooks on ra- 

 dio propagation conditions. Monthly 

 median predictions are generally ade- 

 quate for most frequency-manage- 

 ment applications, though significant 

 improvements could be made by more 

 frequent modification of the median 

 predictions. Ability to forecast iono- 

 spheric disturbances is closely tied to 

 the ability, discussed earlier, to fore- 

 cast geophysically significant solar 

 activity. 



Understanding of Operational 

 Needs 



Effective application of space en- 

 vironment observations and forecasts 

 requires, first, physical knowledge of 

 the interaction between the environ- 

 ment and the specific activity being 

 supported. Equally important, the 

 forecaster and the operator must de- 

 velop an effective rapport, based on a 

 thorough knowledge by the former of 

 the latter's system or mission. All 

 parties must recognize that many 

 things can happen to man's space- 

 related activities which are significant 

 but which cannot be explained. 



The Direction of Future 

 Scientific Effort 



There is a clear, continuing need to 

 advance the state of the art of opera- 

 tional solar and space-environmental 

 support. Capabilities are already far 

 from adequate, and the increasing 

 sophistication of the activities that are 

 affected requires a matching growth 

 in capabilities. 



Future scientific efforts need to fo- 

 cus on the following: 



1. Techniques to provide accurate 

 long-range and short-term fore- 

 casts of geophysically signifi- 



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