Quasi-periodic oscillations in convective evaporation

Quasi-periodic oscillations of air temperature are observed above water in open cylindrical Dewar flasks with non-cylindrical boundary conditions. The amplitude vary from 0.1 to almost 1 °C and the period vary from 10 to 45 minutes, depending on the position and room conditions. The fluctuations of period suggest the behaviour of a forced Van der Pol relaxation oscillator, which may effectively represent the interaction of two coexisting configurations of turbulent convection. These instabilities bear some similarities, albeit with significant differences, with the oscillations of the mean wind in Rayleigh Bénard convection, or with the inversions of the Earth magnetic field.