Tham khảo tài liệu 'kundu fluid mechanics 2 episode 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 3. Ei uatiim of Motion 559 with height is due to the absorption of solar radiation within the upper layer of the ocean. The density distribution in the ocean is also affected by the salinity. However there is no characteristic variation of salinity with depth and a decrease with depth is found to be as common as an increase with depth. In most cases however the vertical structure of density in the ocean is determined mainly by that of temperature the salinity effects being secondary. The upper 50-200 m of ocean is well-mixed due to the turbulence generated by the wind waves current shear and the convective overturn ing caused by surface cooling. The temperature gradients decrease with depth becoming quite small below a depth of 1500 m. There is usually a large temperature gradient in the depth range of 100-500 m. This layer of high stability is called the thermocline. Figure also shows the profile of buoyancy frequency N defined by A az where p of course stands for the potential density and Po is a constant reference density. The buoyancy frequency reaches a typical maximum value of Mnax s-1 period 10 min in the thermocline and decreases both upward and downward. 3. Equations of Motion. In this section we shall review the relevant equations of motion which are derived and discussed in Chapter 4. The equations of motion for a stratified medium observed in a system of coordinates rotating at an angular velocity Ỉ2 with respect to the fixed stars are V u 0 Du _ _ 1 _ go. 2Sixu -- Vp- k F il42 Dt Po Po where F is the friction force per unit mass. The diffusive effects in the density equation are omitted in set because they will not be considered here. Set makes the so-called Boussinesq approximation discussed in Chapter 4 Section 18 in which the density variations are neglected everywhere except in the gravity term. Along with other restrictions it assumes that the vertical scale of the motion is less than the scale height of the medium c2 g where c
