The underwater sounds produced by impacting snowflakes
In 1985, Scrimger [Nature 318, 647 (1985)] reported measurements of noise levels significantly above the ambient level for snow falling on a quiet freshwater lake. He examined only the time-averaged sound levels and did not report measurements of individual snowflake impacts. Subsequently, the noise produced by individual and multiple snowflake impacts was examined for a number of different snowfalls. The radiated acoustic signals generated by the impact of individual snowflakes upon a body of water have a remarkable similarity to each other and differ principally in the frequency of the emitted sound wave. The acoustic signal of a snowflake impact thus generates a characteristic signature for snowfall that is clearly distinct from other forms of precipitation noise. Various aspects of this signature suggest that the radiated acoustic waveform from a snowflake impacting with water is due to the entrainment of a gas bubble into the liquid, and the subsequent oscillation of this bubble as it establishes its equilibrium state. Various scenarios are presented for bubble entrainment and approximations to the amplitude of the radiated signal and the acoustic waveform are obtained.