A modelling investigation of sudden sodium layers

A time‐resolved model, incorporating both vertical diffusion and chemistry, indicates that the minimum source strength required to produce a typical sudden sodium layer (SSL) is about 3 Na atoms cm−3s−1. However, many of the mechanisms proposed to explain the formation of SSLs are not able realistically to provide this source strength, or the source strength of about 1 Na atom cm−3s−1 that is required to maintain an SSL over several hours. Furthermore, the sodium reservoirs do not appear to contain sufficient sodium to produce an SSL, although sodium ions (Na+), and meteoric dust coated with sodium compounds, cannot be ruled out. An additional mechanism is proposed, namely, the release of atomic Na by dissociative electron attachment to sodium‐containing silicate molecules (e.g. Na2SiO3 or NaAlSiO4) that are produced by meteoric ablation.