  Stellar radio emission can measure a star's magnetic field strength and
structure, plasma density and dynamics, and the stellar wind pressure impinging
on exoplanet atmospheres. However, properly interpreting the radio data often
requires temporal baselines that cover the rotation of the stars, orbits of
their planets and any longer-term stellar activity cycles. Here we present our
monitoring campaign on the young, active M dwarf AU Microscopii with the
Australia Telescope Compact Array between 1.1 and 3.1 GHz. With over 250 hours
of observations, these data represent the longest radio monitoring campaign on
a single main-sequence star to date. We find that AU Mic produces a wide
variety of radio emission, for which we introduce a phenomenological
classification scheme predicated on the polarisation fraction and
time-frequency structure of the emission. The radio emission detected on AU Mic
can be broadly categorised into five distinct types of bursts, and broadband
quiescent emission. The radio bursts are highly circularly polarised and
periodic with the rotation period of the star, implying that the emission is
beamed. It is therefore most likely produced by the electron cyclotron maser
instability. We present a model to show that the observed emission can be
explained with auroral rings on the magnetic poles. The total intensity of the
broadband emission is stochastic, but we show that its circular polarisation
fraction is also periodic with the rotation of the star. We present a
qualitative model to describe the periodicity in the polarisation fraction of
the broadband emission using gyromagnetic emission, and infer a magnetic
obliquity of at least 20 degrees from the observed variation in polarisation
fraction. Finally, we show that the radio emission might be evolving on long
timescales, hinting at a potential stellar magnetic activity cycle.
