The signature of an auroral substorm on a riometer.

The onset is indicated by the sharp increase in absorption at 2105 UT.

You can also see the aurora and magnetometer records for this event.

A sudden storm commencement. The compression of the magnetosphere causes high-energy particles to precipitate from the radiation belts. The SSC is at 1231 UT.
You can also see the magnetometer record for this event.