Suprathermal ions ahead of interplanetary shocks: New observations and critical instrumentation required for future space weather monitoring

We report new findings on the low-energy ion population associated with interplanetary (IP) shocks based on Wind/Suprathermal Ion Composition Spectrometer (STICS) observations. Suprathermal ions (6-200 keV) are present in the upstream region of most (86%) IP shocks at 1 AU. These foreshock ions are characterized by ( 1) median energy >25 keV, that is, higher than a thermal distribution; ( 2) spectra that increase in intensity with energy in the range 10-30 keV; ( 3) flow predominantly outward (antisunward). In the months surveyed, all forward shocks with speeds >30 km/s showed at least one of the above features. Because these characteristics are so often seen in foreshocks, 5 to 100 keV ions can be used to provide advance warning (similar to 5-72 hours) of disturbances that are drivers of the most hazardous geomagnetic storms. These characteristics of the preshock suprathermal ions could be readily monitored on future space weather missions in order to predict the arrival of the IP shocks that initiate space weather events; here we define these measurement requirements and describe the implementation of such an instrument.