The evolution of a fully developed convective hydrogen-rich envelope on top of a C-O white dwarf, at a stage close to thermonuclear runaway, is investigated using a two-dimensional implicit hydrocode. We find that convection plays a crucial role in the burning process when multidimensional effects are taken into account. Temperature fluctuations caused by convective mixing give rise to local enhancement of nuclear burning. Nonsimultaneous eruptions of fast burning, lasting for a few seconds, occur locally at the base of the hydrogen envelope. The convection cells, bounded within the envelope, become violent near such eruption sites and induce further eruptions nearby. The burning process slows down only after enough energy is released and global expansion takes place. Since the flow stays subsonic all through the runaway, the pressure equalizes laterally and the expansion is almost spherically symmetric.
- Novae, cataclysmic variables