200
6 Internal Waves
finite depth and the approximate location of the surface rip, as observed in the
Andaman Sea by Osborne and Burch (1980).
6.4.4 Microstructure
Microstructure or fine-structure is the term used to describe the departure of
the values of temperature, salinity, or density from the mean value. Occasionally in the thermocline, a complex series of layers of approximately homogeneous regions separated by thinner sheets of high static stability have
been observed (Osborn and Cox, 1972; Gregg, 1973; Phillips, 1977; Monin and
Ozmidov, 1985; Druet, 1994). The typical layers of 10 to 20 metres thick can
often be traced horizontally for as far as 15 kilometres, while the layers of only
20-30 centimetres thick extend laterally for several hundred metres. Simultaneous, vertical measurements showed intense fluctuations of temperature and
salinity over a range of a few millimetres or centimetres. The microstructure
can be the result of several quite distinct mechanisms, such as the influence of
small scale internal waves, turbulent mixing and double-diffusive phenomena
(for more details see Chap. 8).