Intrusions: What Drives Them?

Abstract

The driving mechanism for the observed interleaving of water masses is generally assumed to be double-diffusive mixing. However, some observations of intrusions have been made in regions where the mean stratification is stable to double-diffusive mixing. It has been hypothesized that a finite amplitude disturbance must occur to produce regions where the stratification allows double-diffusive mixing or that an instability due to differences in the molecular diffusivity of salinity and temperature produces the desired stratification for double-diffusive mixing to start. There is also the possibility of a differential vertical flux of salt and heat due to incomplete mixing by turbulence. The basis of this idea is described in this paper. Growth rates, vertical scales, and cross-frontal slopes of intrusions predicted by this process are compared to those predicted by double-diffusive mixing.