  We report the discovery of bright, fast, radio flashes lasting tens of
seconds with the AARTFAAC high-cadence all-sky survey at 60 MHz. The vast
majority of these coincide with known, bright radio sources that brighten by
factors of up to 100 during such an event. We attribute them to magnification
events induced by plasma near the Earth, most likely in the densest parts of
the ionosphere. They can occur both in relative isolation, during otherwise
quiescent ionospheric conditions, and in large clusters during more turbulent
ionospheric conditions. Using a toy model, we show that the likely origin of
the more extreme (up to a factor of 100 or so) magnification events likely
originate in the region of peak electron density in the ionosphere, at an
altitude of 300-400 km. Distinguishing these events from genuine astrophysical
transients is imperative for future surveys searching for low frequency radio
transient at timescales below a minute.

Instrumentation and Methods for Astrophysics;Earth and Planetary Astrophysics;High Energy Astrophysical Phenomena