Abstract. We show that if the dwarf-nova disc instability model includes the effects of heating by stream impact and tidal torque dissipation in the outer disc, the calculated properties of dwarf-nova outbursts change considerably, and several notorious deficiencies of this model are repaired. In particular: (1) outside-in outbursts occur for mass transfer rates lower than in the standard model as required by observations; (2) the presence of long (wide) and short (narrow) outbursts with similar peak luminosities is a natural property of the model. Mass-transfer fluctuations by factors ∼2 can explain the occurrence of both long and short outbursts above the cataclysmic variable period gap, whereas below 2 hr only short normal outbursts are expected (in addition to superoutbursts which are not dealt with in this article). With additional heating by the stream and tidal torques, such fluctuations can also explain the occurrence of both outside-in and inside-out outbursts in SS Cyg and similar systems. The occurrence of outside-in outbursts in short orbital-period, low mass-transfer-rate systems requires the disc to be much smaller than the tidal-truncation radius. In this case the recurrence time of both inside-out and outside-in outbursts have a similar dependence on the mass-transfer rateṀ2.

Abstract. We show that the disc instability model can reproduce all the observed properties of Z Cam stars if the energy equation includes heating of the outer disc by the mass-transfer stream impact and by tidal torques and if the mass-transfer rate from the secondary varies by about 30% around the value critical for stability. In particular the magnitude difference between outburst maxima and standstills corresponds to observations, all outbursts are of the inside-out type and can be divided into two classes: long (wide) and short (narrow) outbursts, as observed. Mass transfer rate fluctuations should occur in other dwarf novae but one can exclude variations similar to those observed in magnetic systems (AM Her's and some DQ Her's) and some nova-like systems (VY Scl's), in whicḣ M become very small during low states; these would produce mini-outbursts which, although detectable, have never been observed.

Abstract. We include the tidal instability due to the 3:1 resonance in the disc instability model developed by Hameury et al. (1998) and modified by Buat-Ménard et al. (2001). We confirm earlier results by Osaki (1989) that the tidal instability can account for the SU UMa light curves. We show that in ultra-low mass ratio systems such as ER UMa stars and WZ Sge stars, the superoutburst ends while the disc is still eccentric, as proposed by Hellier (2001). However, since the disc shrinks rapidly once a cooling wave has started, the eccentricity should stop shortly after the end of a superoutburst. This result disagrees with the suggestion by Hellier that decoupling the thermal and tidal instability in the TTI model can account for late superhumps and echo outbursts in ultra-low mass ratio systems. We propose instead that ER UMa short supercycles can be explained either by the alternation of narrow and wide outbursts similar to those occurring in SS Cyg, or by the effects of irradiation (Hameury et al. 2000). In both cases, we predict that superhumps should be permanent, which is suggested by observations (Gao et al. 1999). We can also reproduce light curves similar to those of EG Cnc, varying the mass transfer rate in a TTI model including both irradiation and the presence of an inner hole in the disc.