The Disturbance Impact Assessment System (DIAS) is a computer software package designed to assess and predict the impact of solar flares on high-latitude HF radio communications. The analysis spans the period between the flare onset (TO hours) and the expected subsiding of its effects 5 days later (T120 hours). DIAS supports a HF communications system and when integrated into it, its operation will be entirely transparent to the user. A stand-alone PC version was designed for tutorial purposes. Key features combine the capabilities of the algorithmic PROPHET HF signal assessment system with expert system technology. The initial system provides qualitative advice and warnings. The rule sets in DIAS cover the following types of disturbances: (1) sudden ionospheric disturbances, (2) polar cap absorption, (3) ionospheric storm, (4) auroral zone absorption, and (5) auroral sporadic E and auroral E.

An experiment has been established to determine the range of environmentally induced fluctuations in the propagation of HF radio signals. Data are collected with a fully digitized system that is stablized with a cesium beam standard. Initial efforts have been directed toward monitoring at San Diego, California, the time of arrival of WWV transmissions from Fort Collins, Colorado, for the frequencies 5, 10, 15, and 20 MHz. Variations in these arrival times from 25 to 175 μs have been observed depending upon frequency, mode of propagation, time of day, and solar activity.

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Develop the MIN IMUF-3 model to provide a simplified predicti on of hf Maximum Usable Frequency (MUF) suitable for use on small mobile propagation fo recast (PROPH E T) terminals. With this tool , develop a variety of new forecast applications to serve the hi ' surveillance and communications community where the use of large-scale propagation programs in the operational environment is not practical. (The flexibility of these new applications to serve a variety of users depends to a large extent on the confidence of the internal prediction al gorithms. Because MINIMUF-3 represents such a significant degre e of simplification , a primary concern is the accuracy of the MUF estimates.) This report presents: (I) the M INIMUF model ; (2) results of verification tests ; (3) a specification on its capabilities and limitations ; and (4) app lications. RESULTS The MINIMUF-3 hf prediction model produces a consistent product with a nominal accuracy between 3 and 5 MHz rms residual error. This compare s favorabl y with the abilities of large-scale hi ' prediction programs which require sizable computer facilities. RECOMMENDATIONS Continue work to further re fine the MIN IMUF-3 model to include F and Spo radic I region propagation. Consider small-scale propagation forecast (PROPHET) capabilities for inclusion into new hf system development. Further continue new application development to exploit the capabilities of simple fo recast models like MIN IMUF-3 .

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