Date of Award

Summer 8-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Science

Committee Chair

Dr. Vladimir Kamenkovich

Committee Chair Department

Marine Science

Committee Member 2

Dr. Dmiri Nechaev

Committee Member 2 Department

Marine Science

Committee Member 3

Dr. Ralph Goodman

Committee Member 3 Department

Marine Science

Committee Member 4

Dr. John Kindle

Committee Member 5

Dr. Patrick Hogan

Abstract

This study describes the ocean circulation o f the Indonesian Seas based on results using a 3D regional model. The study is divided into 3 parts. In the first part, Chapter 2, the basic properties of a developed regional model of the circulation o f the Indonesian Seas are outlined. It is well known that the complex topography o f the region strongly influences temperature, salinity and current distributions there. One of the significant properties of this model is that all basic topographic features are resolved. The model has four open ports to simulate inflow o f North Pacific Water from the Mindanao Current, inflow of South Pacific Water from the New Guinea Coastal Current, outflow to the Pacific Ocean due to the North Equatorial Counter Current, and outflow to the Indian Ocean due to the Indonesian Throughflow. Total transports through the open ports and port normal velocities are specified from observations. Orlanski's conditions are employed at the open ports with port normal velocity nudged to observed values and temperature and salinity to climatology. Port channels are introduced so the effects of open boundary conditions do not impact the dynamics of the main region. An additional friction was included in the vicinity of some narrow passages and sills as a proxy for specific processes such as tides and internal waves that occur within these topographic features. Four experiments are discussed: seasonally varying and annual mean transports and port normal velocities both with and without local winds. All experiments are totally spun up after 10 years. This analysis uses data from the post spin up period only. The basic properties of simulated total transports through the main passages in the region, surface circulation, and sea surface heights are discussed. The portion o f North Pacific Water entering the Indonesian Seas relative to that leaving through the North Equatorial Counter Current port is fairly constant throughout the year. Most of this water takes the western route through the Makassar Strait. The portion of South Pacific Water entering the Halmahera Sea compared to that exiting in the North Equatorial Counter Current varies considerably with the seasons. Turning off the local winds does not substantially influence the transport through main passages in the model domain. Surface circulation patterns change substantially with the seasons. The role of different terms in the heat and salt equations were investigated by dividing the region into a number of boxes. For any given box, the sum of the horizontal advective fluxes of temperature (salinity) through all sides of the box is on the same order as the vertical heat (salt) flux at the surface, interior nudging term and the rate of time variation of the box integrated temperature (salinity). The comparison of the basic structure of the model surface circulation, sea-surface heights, and total transport values through the main passages with observations appears satisfactory. The main objective of the second part, Chapter 3, is to analyze the basic features of potential temperature and salinity distributions in the Indonesian Seas simulated by the model. The influence of bottom topography on the formation o f temperature and salinity distributions is considered by following the three major routes of flow of North Pacific and South Pacific Water through the Indonesian Seas. Major elevations o f bottom relief, such as the Sangihe Ridge; the topographic rise between the Sulawesi Sea and Makassar Strait; the Dewakang Sill; the ridge between the Flores and Banda Seas; the topographic rise between the Pacific Ocean and Morotai Basin; the Lifamatola Sill; and the northern and southern Flalmahera Sills; break the region down to separate basins having different temperature and salinity stratifications. The differences in stratification are caused by these topographic features that act to impede the advection o f cold and salty water from a basin (located upstream) to the neighboring basin (located downstream). Arguments are included to support this conclusion. In the upper ocean (500m), the Indonesian Throughflow is primarily shaped by North Pacific Water taking the route through the Makassar Strait. Deep Banda Sea water is formed by the overflow o f North Pacific Water across the Lifamatola Passage into the Banda Sea. Below 500m South Pacific Water is blocked by the Halmahera Sills and does not enter the Indonesian Seas. But in the upper ocean (0-500m) SPW can probably penetrate into the Seram and Maluku Seas to mix with NPW there.

There are no substantial structural changes o f potential temperature and salinity distributions between seasons, though values o f some parameters o f temperature and salinity distributions (e.g., magnitudes of maxima and minima) can change. It is shown that the main structure o f the observed distributions o f temperature and salinity are satisfactorily displayed throughout the entire model domain. The calculated transports o f internal energy (heat) and salt mass through the Lombok and Ombai Straits and Timor Passage in August and February are in reasonable agreement with published observed and simulated data.

In the last part, Chapter 4, aspects o f turbulence and mixing in the Indonesian Seas are presented and discussed. The results are based on the Mellor-Yamada 2.5 turbulence parameterization model. Though the importance o f mixing in the Indonesian Seas has been widely acknowledged, very few observations are available and there have been no model studies o f mixing or turbulent diffusion in the region. The study is focused on turbulent diffusion and turbulent kinetic energy in the upper mixed layer, the thermocline and in deep water near topographic features. Very large turbulent kinetic energies and vertical turbulent diffusivities are seen around topography and are important for the deep overflows found in the region. Large turbulent energies and diffusivities found in the thermocline are important for the diffusion o f temperature and salinity signatures found in the Indonesian Seas. Monsoon winds and local currents lead to large diffusivities in the upper mixed layer.

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