  Rapid bursts at optical wavelengths have been reported for several accreting
white dwarfs, where the optical luminosity can increase by up to a factor 30 in
less than an hour fading on timescales of several hours, and where the energy
release can reach $\approx10^{39}$ erg ("micronovae"). Several systems have
also shown these bursts to be semi-recurrent on timescales of days to months
and the temporal profiles of these bursts strongly resemble those observed in
Type-I X-ray bursts in accreting neutron stars. It has been suggested that the
observed micronovae may be the result of localised thermonuclear runaways on
the surface layers of accreting white dwarfs. Here we propose a model where
magnetic confinement of the accretion stream on to accreting magnetic white
dwarfs may trigger localised thermonuclear runaways. The proposed model to
trigger micronovae appears to favour magnetic systems with both high white
dwarf masses and high mass-transfer rates.
