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tokens: Additional details of our numerical set-up are described in Appendix A . Mass-loss is a key ingredient in novae, which plays an important role in setting the time-scale of the eruption by removing mass from the white dwarf envelope (Livio et al. 1990 ; Kato Hachisu 1994 ). However, the exact mechanisms giving rise to the unbound outflows, as needed to produce variable internal shocks, are uncertain and not addressed in this work. Relatively slow outflows, of up to several hundreds of km s −1 , may be launched from near the binary L 2 Lagrange point. These could be driven for instance by frictional drag (e.g. Livio et al. 1990 ; Shankar, Livio Truran 1991 ; Lloyd, O’Brien Bode 1997 ; however, see Kato Hachisu 1991 ), non-axisymmetric gravitational torques from the binary (Pejcha, Metzger Tomida 2016a ), or in the outflow of a circumbinary disc formed from matter ejected from L 2 that initially remains gravitationally bound (Pejcha, Metzger Tomida 2016b ). These slow outflows, with velocities of order the binary escape speed, would plausibly be concentrated in the binary equatorial plane. Outflows can also occur from the white dwarf directly, with little or no influence from the binary. These could be driven by radiation pressure acting on the iron opacity bump (e.g. Kato Hachisu 1994 ), or by any large (near- or super-Eddington) localized energy deposition in the white dwarf envelope, e.g. from radioactive heating or damping of convectively excited waves (e.g. Quataert et al. 2016 ). Outflows launched from deeper locations in the potential well of the white dwarf would be expected to possess higher velocities ∼2000–5000 km s −1 and a more spherical geometry than the slower outflows from L 2 . Lacking a first principles model, we are motivated on phenomenological grounds to consider two outflow modes characterized by distinct mass-loss rates, , and asymptotic velocities, v w . Somewhat arbitrarily (as the precise values will vary between novae), we assume a ‘fast’ mode outflow with and a ‘slow’ outflow mode with These are spherically equivalent mass-loss rates. To obtain the true value, must be multiplied by the fraction of the total solid angle covered by each outflow component, f Ω . For instance, f Ω ≈ 1 for the fast spherical outflow, while f Ω ≈ 0.3 for the slow equatorially focused outflow. 1 The top panel of Fig. 2 shows the chosen time evolution of and v w for our two fiducial models (‘single transition’ and ‘multiple transition’). In the single-transition model (red lines in Fig. 2 ), the outflow velocity is increased from slow ( v w = v s ) to fast ( v w = v f ) only once at t ≈ 0, while in the multiple-transition model (blue lines in Fig. 2 ) the outflow velocity fluctuates between slow and fast modes several times. Local maxima (‘flares’) are observed in classical nova light curves on time-scales ranging from hours to weeks (e.g. Strope et al. 2010 ; Walter et al. 2012 ; Henze et al. 2018 ; Aydi et al. 2019 ). To generate