Internal Mixing Of The Chinese Pioneer Area Waters And Near The Bottom Of Low-frequency Fluctuations

The interior mixing and near-bottom low-frequecy currents of Chinese Pioneer Area (CPA) are analyzed based on the CTD and LADCP simultaneous observations and deep sea mooring observations.The general introduce and background are givn in chapter 1, basic theories and physical principle of ocean interior mixing are introduced in chapter 2 , and the instruments and observing methods used are discussed in chapter 3.In chapter 4 the distributions and annual variability characteristics of temperature, salinity and surface currents are statistically analyzed. In summer, the temperature of the south part of the area is higher than the north part. Both the main thermocline and the main halocline are thin and their depths range from 50 to 120m. (2) North Equatorial Current and North Equatorial Counter Current are the main currents most of the year in the upper sea of the area.In chapter 5, under the simply turbulent kinetic energy (TKE) equation, dissipation rate of TKE, dissipation rate of temperature variance, Richardson number(Ri) and mixing efficiency of both the east area and the west area are examined frommeasurements of both temperature gradient and velocity shears. The results of calculations show that (1) the dissipation rate of temperature variance of CPA is0.5×10-8~5×10-8 ℃2 /s , which high values are in the thermocline layer, and verylow values are in the range of 1200m to the bottom. (2) high horizontal velocity shears are found in the ranges of 0~500m, 1200~2000m and 60m above the bottom,but the low 16-m Ri,just dose not occur in the range of 0~500m. many lowRi numbers in the ranges of 1200~2000m and 60m above the bottom imply that theshear instabilities are main causes of the mixing. (3)No obvious bottom boundary layer structure is seen from temperature and salinity structure as that in the deepseain the Atlantic, but deep sea bottom boundary layers are obvious in the horizontal velocity shears and the particle concentration structures near the bottom. (4) Mixing by shear instability causes rapidly increase of suspended particular concentration in the bottom boundary layer.Data of two deep-sea moorings deployed respectively in the east area and the west area of CPA to monitor the regional deep-sea dynamics below 600 meters above bottom (mab) since July 1997 to Oct. 1999. are analyzed In chapter6. Results of statistics, spectral estimate and correlation analysis of the low-passed velocity data show that time scales of low-frequency components of the near-bottom currents are 25~120-day, in which 51-day period dominates the lower band of the frequency domain; Topographic features have obvious effect on low-frequency currents below 50mab: modulations of the bottom-intensified sheared mean flow to the low-frequency currents is the dynamic mechanism of the frequency shift that occurs both in the east-area and the west-area.