  We present simulations of dwarf nova outbursts taking into account realistic
variations of the mass loss rate from the secondary. The mass transfer
variation has been derived from 20 years of visual monitoring and from X-ray
observations covering various accretion states of the discless cataclysmic
variable AM Herculis. We find that the outburst behaviour of a fictitious dwarf
nova with the same system parameters as AM Her is strongly influenced by these
variations of the mass loss rate. Depending on the mass loss rate, the disc
produces either long outbursts, a cycle of one long outburst followed by two
short outbursts, or only short outbursts. The course of the transfer rate
dominates the shape of the outbursts because the mass accreted during an
outburst cycle roughly equals the mass transferred from the secondary over the
outburst interval. Only for less than 10% of the simulated time, when the mass
transfer rate is nearly constant, the disc is in a quasi-stationary state
during which it periodically repeats the same cycle of outbursts. Consequently,
assuming that the secondary stars in non-magnetic CV's do not differ from those
in magnetic ones, our simulation indicates that probably all dwarf novae are
rarely in a stationary state and are constantly adjusting to the prevailing
value of the mass transfer rate from the secondary.

Astrophysics