Haven't read it but this sounds like the original: Phillips, O. (1970) On flows induced by diffusion in a stably stratified fluid. Deep-Sea Res. 17, 435-443. And you might find this useful: IMBERGER J, HAMBLIN PF DYNAMICS OF LAKES, RESERVOIRS, AND COOLING PONDS ANNU REV FLUID MECH 14: 153-187 1982 A.