Air University Review, November-December 1969

The Space Forecasting System:
Confluence of Military and Scientific Interests

Colonel Dale J. Flinders

A large Air Force environmental support capability is being assembled—quietly and with little attention by the military and scientific communities--to be placed in operation on 1 March 1970. The system is designed to predict hours, days, or weeks in advance bursts of radiation and energetic particles from the sun and their effects on the earth’s atmosphere.

The system draws on most of the environmental sciences, the product of which forms a complex matrix of causal interrelationships involving radio and optical solar astronomy, astrophysics, radio propagation physics, and the physics and chemistry of the upper atmosphere. The observational phenomena with which these scientific studies deal have a direct and sometimes profound influence on a range of Air Force electronic and optical systems. Radars, delicate satellite sensors, radio communication, and navigation systems are all subject to changes in performance due to the occurrence of astrogeophysical events. The events of interest are absorption of radio waves in the polar regions, geomagnetic disturbances, auroral activity, enhanced airglow levels, variations in atmospheric density, and ionospheric fluctuations and inhomogeneities. It is of obvious concern to the Air Force to know well in advance any predictable degradation of its electromagnetic operational systems. All these environmental effects are triggered by one or both of two possible causes: bursts of electromagnetic (EM) radiation and energetic particles from the sun; (2) the "dumping" of particles from the earth’s radiation belts into lower levels of the near-earth space environment, A particularly devastating phenomenon is the impinging of high-energy solar protons into the polar cap regions.

If we can predict the magnitude of bursts of particles and EM radiation from the sun, then we can in theory predict some ultimate effects on Air Force operations. This pre-supposes that we understand the relationship between a particular solar event and a particular terrestrial effect. At present we do not know these relationships except coarsely and qualitatively. Nor do we know with any degree of precision the precursor solar features that trigger the solar burst. The latter calls for a more thorough knowledge of the dynamic processes on the sun; the former calls for an understanding of solar-terrestrial relationships in greater depth. As our knowledge and understanding increase, so will the accuracy of our predictions.

The system that will both accelerate the acquisition of such knowledge and make the predictions is being developed by the Air Force Cambridge Research Laboratories (AFCRL) and the Air Weather Service (AWS). The heart of the system, after it becomes operational, will be the Air Force Global Weather Central complex of Univac 1108 computers at Offutt Air Force Base, Omaha, Nebraska. Linked to these computers is a worldwide net of optical and radio observatories, which will provide real-time inputs from the radio and optically observed sun. Every observable feature of the sun will be monitored by the system, together with changes in these features and their rate of change. In addition, observations from riometers, neutron monitors, magnetometers, and satellites will be fed directly into the network. From these observations the AWS-AFCRL system designers hope to define the conditions that precede a burst of solar energy and the terrestrial effects that follow it.

In the future the system observational net will be expanded to include a more comprehensive array of both solar and terrestrial monitoring stations. But right now, the problems of standardizing data inputs, calibrating the sensing instrumentation, and developing the basic system software are about all that the system designers can cope with. The requirement for precise standardized reporting and the need for uniformly calibrated instrumentation have been the foremost difficulties in bringing the system to fruition; when achieved, they may prove to be the system’ major legacy to science.

Technical planning and systems evaluation are done through the Working Group on Space Forecasting, which meets monthly to plan, review schedules, assign priorities, and look into special problems. The Working Group is composed of about twelve AFCRL and about six AWS representatives plus many interested representatives from other government organizations, the composition and number varying from meeting to meeting.

The Working Group was set up early in 1966, but much work on the system had already been completed, and the AWS was already doing routine forecasting. Many of the effects of solar eruptions on the terrestrial environment were known in a general, qualitative sort of way. Since the 1950s the Central Radio Propagation Laboratory, formerly under the National Bureau of Standards but now part of the Environment Science Services Administration (ESSA), has made regular predictions of geomagnetic disturbances based on bursts of radio energy and optical and magnetic features observed on the sun. In 1964 the Air Weather Service established its Solar Forecast Center, which is now located in the NORAD Cheyenne Mountain complex near Colorado Springs, to provide forecasts relating to Air Force operations based on similar observations. Also, in the early 1960s, several major optical observatories were predicting periods when there would be an absence of solar proton showers. Foremost among the observatories working on the problem was the AFCRL Sacramento Peak Observatory in Sunspot, New Mexico. NASA relied heavily on these predictions in connection with the early Mercury flights.

Many of us first learned of high-energy solar protons in connection with these Mercury flights. We learned that high-energy solar protons were an ionizing hazard to man in space and to electronic systems aboard aircraft. True, but perhaps overdramatized. (The mental picture of an astronaut being bombarded by radiation has an emotional impact and thus is easily remembered.) Air Force interest encompasses this man-in-space problem, but the priority interest is the effects of these protons and associated solar emissions on the terrestrial environment.

The forecasts that the AWS Solar Forecast Center provides its customers—NORAD, SAMSO, and others—are a normal extension of the AWS weather forecasting mission. The center receives regular daily transmissions on the status of the sun from almost a dozen radio and optical telescopes around the world. A primary source of radio data is AFCRL's Sagamore Hill Radio Observatory in Hamilton, Massachusetts, where AFCRL and AWS have for many years continuously monitored the radio spectrum of the sun. The Solar Forecast Center manually inspects the data for any pattern that might foretell eventual terrestrial effects.

In late 1963 AFCRL undertook a large new endeavor, designated the Space Forecasting Program. This program, in which AWS people work side-by-side with AFCRL scientists, can  be viewed as a special research effort in support of the AWS Solar Forecast Center. Before this program got under way at AFCRL, no one had taken a broad look at all aspects of the forecasting problem in an attempt to tie them together as an entity. Solar, radio, and atmospheric physicists were all doing much research related to forecasting and were contributing useful solutions, but each was considering the problem from the narrow perspective of his own discipline.

By 1966, work was in progress at three loosely coordinated levels. There was the operational AWS Solar Forecast Center, providing daily predictions to its Air Force customers. There was the Space Forecasting Program at AFCRL, doing studies and research directly related to the work of the center. And there were the scientists conducting generalized research on environmental phenomena. It became apparent that work at these three levels had to be brought together in a closer working relationship. One reason making this need immediate was that the AWS Solar Forecast Center had embarked on a program for markedly upgrading its observational network and required a closer working relationship with those involved in the Space Forecasting Program at AFCRL. And the Space Forecasting Program people had come to realize the need for closer participation by specialists in a diversity of fields—energetic particles, ionospheric variability, the earth’s magnetosphere, atmospheric density and so on.

Through the Space Forecasting Working Group, an interface among the three levels was effected. The Working Group had two primary tasks, the first immediate and specific, the other more general. The first was to review, advise, and work out problems associated with the updating of the observational network of stations and the basic reduction of these data for the AWS Solar Forecast Center.  These particular problems have occupied most of the attention of the Working Group to date. The other task was to examine all available scientific knowledge that might be applied to improve the accuracy of predictions and extend the warning time.

Considerations of accuracy and warning time lead to the physics of the problem. This background will help make a description of the system and some of the problems of bringing it into being more meaningful. All bursts of electromagnetic energy and high-energy particles from the sun are associated with solar flares, and solar flares (with a few rare exceptions) are associated with sunspots. But not all sunspots produce flares, and not all flares produce disruptive solar bursts. Of three basic prediction problems, the first is that of predicting whether a given flare, once it has been observed optically and by radio, will emit an intense flux of radiation and/or particles.

The second problem is that of predicting effects on the earth’s environment--magnetic storms, auroras, ionospheric disturbances, and so on. The effects and their onset vary because the ratios of intensities of the different emissions in the solar burst vary markedly from flare to flare. High-energy protons reach the earth from a few minutes to a few hours after the flare peak. Other protons are strung out in time (and space), and the maximum flux of protons is usually observed several hours after the first measurable terrestrial effect. Low energy particles emitted at the same time travel much slower. Their effects are observed two or three days later in the form of magnetic storms and ionospheric disturbances worldwide. These electrons modulate the earth’s magnetosphere, causing magnetic storms. The problem is that of predicting not only whether a solar flare will produce a terrestrial effect but also the kind of effect, its onset, and its duration.

The first two prediction problems are concerned only with effects, if any, once a flare is observed. This means that predictions are limited to about two days in advance. The third problem, that of forecasting the occurrence of the flares, can only be solved by monitoring the visible features of the sun and associated magnetic configurations. However, this would yield longer-range forecasts. We do not yet know, except in a general way, the characteristics on the visible surface which portend a flare that will produce disruptive energy. What we can predict at the present time is that under certain limited conditions no disruptive event is likely to occur during the next three to five days.

Long-term prediction has been primarily the concern of the optical astronomer, while short-term prediction has been largely in the province of the radio astronomer. Radio astronomers in 1968 reported some extremely favorable results in making forecasts up to about two hours, based on solar radio emissions in the centimeter range. AFCRL radio astronomers can now say with about 80 percent assurance that, if a certain characteristic radio spectral pattern is observed, it heralds the arrival of high-energy protons in the earth’s atmosphere.

In addition to optical observations and centimeter radio observations, there is another promising instrument that may provide a key parameter for prediction. This instrument is a radio telescope that observes solar emissions in the millimeter range (35 GHz). AFCRL operates such a telescope at its site in Waltham, Massachusetts. From millimeter wave emissions it is possible to map temperature profiles just above the visible surface of the sun in the chromosphere. Activity centers on these radio maps of the sun seem to be highly correlated with bursts of radio, X-ray, and particle emissions from the sun.

Future plans call for observing the ultraviolet (UV) and soft x-radiation (XUV) emissions from the sun with satellite sensors. Almost no work has been done to date in correlating UV data with proton events, but such observations may prove most valuable. The ultimate system—but not the initial system that will become operational in 1970—will observe all solar emissions across a broad spectrum of radio and optical wavelengths.

The forecasting task appeared to be rather straightforward to those who planned the Space Forecasting Program at AFCRL in 1963. AFCRL decided to concentrate its initial attention on optical rather than radio observations because there appeared to be fewer problems demanding attention in the radio area. Whatever the radio astronomers learned could be melded into the overall system later.

To start, AFCRL scientists opened what they believed to be a treasure chest of avail-able data. Daily records of the visible sun extending back three decades had been accumulated by observatories all over the world. These daily records of sunspot groups and flares, when properly analyzed and subjected to a range of statistical processing techniques, would quickly reveal prediction correlates, so it was believed. There was no corresponding record of solar energy bursts—at least no direct record; but past solar events could be deduced from the recorded history of terrestrial effects such as geomagnetic disturbances, auroral activity, and so on.

Within a year after work with these historical records began, the AFCRL space forecasting team faced a problem that was to alter drastically the course of its planning. Past solar records were almost useless from the standpoint of systems planning. Examination revealed gross imprecision, inconsistencies, and multitudinous errors throughout. To solar scientists, the AFCRL analysis proved particularly traumatic, since it revealed gross fallacies in the international historical record and thus placed in question all scientific studies making use of these records.

The reasons for the inconsistencies were not hard to identify. Because each observatory tends to be an isolated scientific island unto itself, reporting procedures and interpretations of observations varied widely. Although the International Astronomical Union sets reporting standards which all members should follow, these standards have undergone frequent revisions over the years. There was often a lag before all observatories adopted them, and some never did. The mathematical conversion of data from one standard to another in order to achieve a common data base was a monumental task. Those working on the space forecasting problem, however, were willing to undertake it.

But in the process of examining the records from all the observatories, another and even more critical source of error was uncovered. This had a serious implication which in 1967 forced the Air Weather Service to reconfigure the entire network structure of the Space Environmental Support System. The optical inputs for the system, as originally conceived, were to come from established solar observatories. But two observatories, both looking at the sun at the same time and both reporting according to the latest international standards, often reported disparate data. Why was this? It was because each tended to calibrate its instruments in its own way or to use distinctive filters that it believed provided the best view of the sun.

As a result, AWS in 1967 decided that its Space Environmental Support System could not rely on data from existing observatories. AWS at that time concluded plans to establish new observatories whose exclusive function would be to provide data for the Space Environmental Support System. These observatories would be located worldwide so as to give continuous coverage of the sun. Sites were selected in Tehran, Puerto Rico, Hawaii, and the Philippines, and others are planned whose locations are not yet determined. Radio telescopes will also be located at three of these sites. The relatively small optical telescopes presently used, with a five- or ten-inch refractor, do not yield consistent data. Therefore, in order to eliminate the last major deficiency in the optical network, a complete re-equipment with identical solar telescopes is planned for the early 1970s. A test program is now under way in which the first pair of identical solar patrol telescopes will be set up side-by-side for thorough calibration in order to ensure uniformity.

Another revision in system design occurred in 1965. Initial planning called for the manual analysis and interpretation of the solar and radio telescope observations of the sun. But clues for prediction are often intricate and subtle, requiring careful subjective assignment of weighting factors. More important, the system as it evolved was seen to generate massive amounts of data, the interpretation of which would exceed the capabilities of the most skilled analyst. When all this became apparent, the decision was made to automate the system. Data from the observational network would be transmitted as a direct input to the AWS Univac 1108 computers in the Air Force Global Weather Central complex at Offutt AFB.

In developing the system, its designers drew from the huge reservoir of knowledge accrued over the years by solar astronomers, environmental physicists, and astrophysicists in both the East and West. Once the system is in operation, it will more than repay its debt to science. The system will be capable of processing masses of data on a real-time basis from a worldwide network of radio and optical observatories, all carefully calibrated and providing uniform reports. Military purposes aside, the system will give us a powerful tool for exploring our environment, providing researchers with a unique facility for studying not only solar-terrestrial relationships but many of the basic processes of the sun itself.

The simple prediction that a solar event will or will not occur is only the first task of the system. Later tasks will be to predict not only that a disruptive solar event will occur but its magnitude as well. There are large events and small events, with a continuum of sizes between. While the system concerns itself with all emissions contained in a solar burst, most of the attention of system planners to date has been focused on high-energy proton emissions.

The AFCRL-AWS Working Group is presently looking into the complex task of predicting not just the occurrence of a proton shower but its magnitude as well. The first problem the group encountered was the unsystematic reporting of the magnitude of solar proton events. Descriptions in terms of "major," "intense," "moderate," and "minor" are not very useful as parameters for a computer program. Discussion of this problem and its effect on other parts of the system led two AFCRL scientists in the group to develop a classification scheme, which they presented to the Inter-Union Commission on Solar Terrestrial Physics in London on 26 January 1969. The method classifies proton events in five categories of intensity. The scheme was favorably accepted by members of the commission and is likely to receive international standardized use by solar astrophysicists.

Solar protons are measured directly only by sensors in satellites above the earth’s atmosphere. The first direct measurement was made by AFCRL in 1962 when photographic emulsion plates aboard Discoverer 17 were completely saturated by a dense flux of high-energy protons. The variety of sensors used since then has presented system designers with the problem they had faced from the beginning--lack of a common data reference base. With AFCRL’S proton classification scheme, however, a fresh start can be made. The fresh start could consist of specially designed satellites for continuous monitoring of proton events. But specially designed satellites may not be necessary because ones adequate to do the task are already in orbit. These are the Vela satellites designed to monitor nuclear detonations in space.

The satellites will have several roles, some well defined, some uncertain. One possible operational role is that of acquiring data for predicting the intensity, duration, and extent of a terrestrial effect once disruptive solar emissions have reached the vicinity of the atmosphere. But system planners are at present interested in satellites as research instrumentation for discerning system parameters. For example, after the satellite has detected a critical solar emission and its magnitude, we can look back to the combination of solar features that existed prior to the emission in an effort to uncover prediction criteria. Assuming such prediction criteria are perfected, then it may be possible to predict the magnitude of an event days or weeks in advance.

Satellites can also provide bench-mark data for ground instruments. Because intensity and duration of the terrestrial effect are correlated with the magnitude of the shower, we should be able to determine the magnitude of the proton shower indirectly by ground-based monitors. Riometers for measuring the opacity of the ionosphere constitute one such class of instruments. Another is the neutron counter. The solar proton classification method, noted earlier, takes into account these two instruments, showing that a proton event of a given magnitude can be correlated with the magnitude of a measurable effect detected by these ground instruments.

The Space Environmental Support System, then, is one that traces through an exceedingly intricate web of causal relationships among a diversity of environmental phenomena. The system has the curious feature of being a major system development in which the technology is available before there is a full scientific understanding of the problem. The technology is solved in the sense that most instruments presently thought to be needed for observations and for processing data are either in place or can be readily assembled. Reversal of the normal sequence, in which science precedes technology, dictated the unconventional Working Group systems-management approach. A centralized systems project office, with the function of setting specifications and schedules, would not have worked simply because you cannot direct a scientist to make a key discovery in order to meet schedules and maintain specifications. Even if solar and environmental physicists make no future discoveries, the Space Environmental Support System will fill an important need based solely on present knowledge.

Outside of a small group at AFCRL and AWS directly involved in the system, no scientific team was assembled for specific research on the system. The Working Group had to and will continue to rely on scientific discoveries as they become available. Because the problems are scientific and not technical, it is not altogether unlikely that some essential relationship that will greatly increase the capability of this Air Force system could result from a paper published by a Russian solar astronomer working, for example, at the Crimean Astrophysical Observatory. More likely, however, scientists at AFCRL will make many of the discoveries that will advance the capabilities of the system.

AFCRL is the Air Force center for environmental research--research that includes the dynamics and chemistry of the upper atmosphere, solar and radio astronomy, studies of the earth’s magnetic field, the aurora, cosmic rays, charged particles in space and in the earth’s upper atmosphere, astrophysics, and so on. The 250 or so scientists at AFCRL engaged in research that is in one way or another related to the space forecasting problem have available to them facilities that no other research laboratory in the world can match. In addition to its large solar and radio observatories, AFCRL each year instruments scores of rockets and satellites for upper-air and space research, and its five flying laboratories give AFCLR scientists the mobility to make measurements all over the world.

A further advantage, one that tends to be overlooked, is that because of their special skills and talents AFCRL scientists are called upon whenever the government or the DOD mounts large experimental programs involving the upper atmosphere. From the experiments there is often an abundant fallout of experimental data that are directly applicable to the Space Environmental Support System. Two examples of experiments that may seem far afield will show the kinship that exists:

· During the last series of nuclear tests in the atmosphere in 1962, about 150 AFCRL scientists with a vast array of rockets, aircraft, and ground instrumentation were on hand to participate. The data on atmospheric and near-space effects of nuclear detonations collected by AFCRL scientists have been essential to weapons and strategic planning by the DOD. After a lapse of seven years, in the summer of 1969, AFCRL, the Army Ballistic Research Laboratory, and the Defense Atomic Support Agency undertook a huge program in the arctic involving the launch of some 39 rockets, two of AFCRL’S instrumented KC-135 flying laboratories, a satellite, and a range of ground instrumentation. These vehicles and instrumentation had been assembled to measure all phenomena associated with a polar cap absorption (PCA) event.  PCA events—radio black-out in the arctic—are caused by high-energy solar protons. The same kinds of scientific specialties and the same general types of instrumentation were involved in both the 1962 and 1969 experiments because the environmental effects of high-energy charged particles from a nuclear explosion are much the same as those from energetic solar protons.  A PCA event provides a kind of simulated nuclear explosion in the atmosphere. The studies conducted in the summer of 1969 were in no way a part of the Space Environmental Support System, yet the results are directly applicable, adding a further refinement to the computer program for correlating and analyzing environmental information.

· Some 30 to 40 AFCRL scientists participated in the Ft. Churchill, Canada, PCA experiments. Were they motivated in this work primarily by the desire to understand more of the environment we live in, or were they motivated primarily by the desire to improve Air Force operational capabilities? The question is meaningless, of course, and could not be answered even by those directly engaged in the experiments; their motivations are inextricably mixed. I would hope that tire scientific component assays high in the mixture, however, because it is only through good science that such Air Force programs as the Space Environmental Support System will evolve to fulfill all the prediction tasks envisioned for it.