| The dynamic and thermodynamic processes in the mixed layer provide the means for the exchange of mass, momentum and energy between the atmosphere and the underlying ocean. The thermal structure of the upper ocean has been well understood, however, some dynamic processes in the mixed layer, as well as the coupled thermodynamic processes, are not so clear. Additionally, some problems are neglected for a long time, e.g., the effects of penetration radiation (PR) and salinity on mixed layer dynamics and thermodynamics. The lack of knowledge about these problems will result in some errors in the simulation models.The major task of this dissertation is to investigate the effects of PR and salinity on mixed layer depth (MLD), using the Kraus-Turner one-dimensional mixed layer model. The main structure of this dissertation is as follows. First, the PR effects on MLD will be studied using the parameterization method of Murtugudde et al.(1996). And then, the salinity effects will be considered by adding a mixed layer salinity conservation equation. In the last part, the surface temperature inversion induced by salinity effects will be discussed.?The PR effects on MLDThe PR parameterization method of Murtugudde et al.(1996) is used to study its effects on MLD, with the aid of some numerical experiments. The results indicate that the PR effects, which are influenced by both the wind speed and the net solar short-wave radiation (NSSR), lead to deeper mixed layer. Neglecting the PR effects will cause significant errors on the determination of MLD, when the wind speed is weaker than l0m/s and the NSSR is in the range of 40-200 W/m2.The variations of the PR effects with wind speed and NSSR are also studied. The results indicate that the effects of PR on MLD increase with NSSR when the wind speed is stronger than lOm/s, and decrease with it when the wind speed is weak and the NSSR is larger than 200 W/m2. The results also show that the PR effects decreasewith wind speed when NSSR is small, while PR effects increase with wind speed initially, and then decrease when NSSR is large enough.The MLD at 2?N,95 ?W is calculated with and without PR, using the one-dimensional mixed layer model. The results indicate that PR can significantly influence the short time-scale variations of the MLD. And compare to the observations, the calculated MLD results considering PR are more accurate than those results neglecting PR.?The salinity effects on MLDBased on the one-dimensional mixed layer model considering PR effects, a salinity conservation equation is added and its effects on MLD variations are analyzed. If the evaporation and precipitation on the ocean surface are neglected, the salinity effects on MLD will be very significant in the m ixed 1 ayer entrainment processes. Additionally, the salinity effects on MLD are related to the vertical salinity structure of the upper ocean. If the salinity in the mixed layer is lower than salinity under the mixed layer, the salinity effects will lead to a shallower mixed layer and vice versa. The results also show that the salinity effects increase with wind speed and decrease with the NSSR.Salinity changes due to evaporation and precipitation processes can also influence the MLD variations. Both the observations and numerical experiment results show that the strong precipitation can result in a significant shallower mixed layer.The surface temperature inversion can not occur if the salinity effects are neglected. In the last part of this dissertation, the subsurface temperature and salinity equations are added to investigate the development of the inversion process. The effects of the temperature inversion on MLD and thermal structure of the upper ocean are also discussed. The r esults indicate that the temperature inversion increases the likelihood of the mixed layer entrainment. Given a temperature inversion occuring, the mixed layer temperature increases more rapidly when the ocean is heated, and, on the other hand, decreases more slowly when the ocean is cooled.
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