From a communication vulnerability perspective, space weather influence derives from two classes of data: (a) ionospheric (or downstream)

data, and (b) exoionospheric (or upstream) data. The upstream space weather information can have a significant operational impact on terrestrial HF and SATCOM systems only if accurate forecasting algorithms relating the upstream data to pertinent ionospheric disturbances (i.e., the downstream data) can be developed. Such information will aid in top-level resource management decisions.

In the context of short-term forecasting and nowcasting, near realtime assimilation of ionospheric data (e.g., GAIM technology) is preferred over methods based upon purely upstream data assimilation. However neither approach should proceed in a vacuum. Without meticulous assimilation of the upstream and downstream data, a real solution to the forecasting problem will not be obtained. This solution is in fact a primary goal of the National Space Weather Program. It is encouraging to see that in the priority list showing the key physical parameters for the ionosphere and the thermosphere, the Space Weather Program Implementation Plan has the following listed as among the 1st priorities: Ne and its intrinsic variability and SNe/Ne (NSWP, 2000).

For certain communication systems, an accurate specification or forecast of the geoplasma distribution is a key ingredient to the improvement of performance. Robust systems have been developed, based upon the gloomy prospect that this "key ingredient" will never be available in a timely or with sufficient accuracy. But these robust approaches are more limited than should be necessary.

Some basic needs include the development of new and/or improved physical relationships between space weather parameters (e.g., IMF characteristics) and the global distribution of Ne in the ionosphere and plasmasphere. In addition we need further development of sensors and/or techniques for the timely delivery of space weather parameters.

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