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double-diffusive convection

همبز ِ دوپخشی

hambaz-e do paxši

Fr.:

An instability involving two layers of fluid with opposite gradients of
properties. Same as → fingering instability. See also
→ salt finger.
Double-diffusive instabilities commonly occur in any astrophysical fluid that is
stable according to the → Ledoux criterion,
as long as the entropy and chemical
stratifications have opposing contributions to the dynamical stability of the system.
They drive weak forms of convection, and can cause substantial
heat and compositional → mixing.
Two cases can be distinguished. In fingering convection,
entropy is stably stratified (∇ - ∇ad < 0), but chemical
composition is unstably stratified (∇μ < 0); it is often
referred to as
→ thermohaline convection
by analogy with the oceanographic
context in which the instability was first discovered. In oscillatory double-diffusive
convection, entropy is unstably stratified (∇ - ∇ad > 0), but chemical
composition is stably stratified (∇μ > 0); it is related to semiconvection, but can
occur even when the → opacity
is independent of composition (P. Garaud, 2014, arXiv:1401.0928).