Physical OceanographyPhysical oceanography is a most fundamental and important scientific domain. It seeks to understand the basic nature and fluctuations of flows such as tidal streams and ocean currents generated by swells and wind waves as well as the distribution of water temperature salinity, etc. The Earth fluids comprise the oceans and the atmosphere, and have the following features.
- They are extremely thin films enveloping the Earth and are driven by thermic motors activated by solar energy. They carry the excess solar energy from low-to high-latitude regions and indicate the true nature of wind generation, which increases over hot oceans and decreases in cold sea regions.
- Remarkable Air-Sea interactions, such as atmospheric circulation (wind), are generation by the distribution of the sea surface temperature and ocean currents are driven by wind stress. There is thus a single system comprised of the atmosphere and oceans that represents the effects of atmospheric warming and oceanic cooling.
- Most wind and oceanic flows are turbulent, and from the characteristics of fluid mechanics, important nonlinear effects occur. Wind and ocean currents are therefore not simple flows that can be represented by arrows on maps, but instead are very complex streams.
- The Coriolis force, an apparent bending force caused by the rotation of the Earth, plays a key role in long-term, large-scale phenoma. The Coriolis force -- a very important force when studying the fluid mechanics of the Earth -- is a grateful force that equally deviate complex flows such as wind and ocean currents in perpendicular directions.
Wind stress from the atmospheric wind and density differences of the seawater generate ocean currents. Large oceanic circulations carry water along with heat, salinity, much dissolved matter, and plankton. There circulation thus contribute to the material cycle and formation of peculiar water mass, and have a huge impact on the Earth’s climate and environment. In addition, in the boundary region where they meet, the atmosphere and ocean continuously exchanging energy, momentum, and matter -- mainly water. As a result, multi scale disturbances are generated in the atmosphere above the oceans, along with very complex phenomena mixing turbulent flows, precipitation, water phase transitions, and dynamics that greatly influence the human life through daily weather modifications and climatic hazards. Global warming results from an increase of atmospheric carbon dioxide. The destruction of the ozone layer that protects life on Earth, acid rains that destroy vegetation, El Nino phenomenon, etc. are environmental changes on a global scale and have recently become serious issues. These phenomena, whose circulation and mutual interactions are driven by solar energy while many substances modify their appearance and shape, were generated as large-scale natural phenomena. Understanding, clarifying, and forecasting these phenomena are important issues in the future study of the relationships between the Earth environment and human activities. Considering the Earth as a single system, it is necessary to correct by understand on the many processes that the atmosphere, oceans, lands, and their interactions generate various timescales, and to clarify the structure of these variations. The influence on the Global Environment from the fluctuations in oceans, which cover 70% of the globe, is still unknown. Clarifying the fluctuations and dynamic processes in the large oceanic circulation and the mechanisms that generate and preserve water mass is essential for understanding the atmosphere-ocean interaction mechanisms, and represents the first step toward contributing to resolute the global environment issue.
A variety of satellite-borne sensors are being operated today to understand the physical phenomena within the oceans. These various types of sensors are used as follows.
1.Sensors for Sea Surface Temperature
The sea-surface temperature, an important index of the marine environment, is measured over large areas. Visualizing the temperature fluctuation allow detecting variations in the space-time distribution of water mass, oceanic fronts, and eddies. Oceanic fronts and eddies, called fishery resource treasures, are widely used as fishery data.
2.Sensors for Ocean Surface Topography
Because of the density contrast of the seawater, it is usually assumed that the higher the salinity the heavier the seawater, and the lower the salinity the lighter the seawater. When seawater mass with different characteristics come into contact, a difference of sea-surface elevation is generated of the sea- surface. By visualizing these differences of sea-surface elevation of, it is possible to clearly sample the distribution of water mass such as eddies or oceanic fronts. Combining the Sea-Surface Altimeter with other sensors is expected to help clarify the mechanisms of the oceanic circulation and mixing layer.
3.Sensors for Sea Surface Wind
The wind disturbs the sea surface and thus plays a key role in the circulation, vertical mixing, and heat budget of the oceans. Beside its contributions to weather observations, this sensor is expected to significant by facilitate role in the understanding of the water cycle and oceanic phenomena through analyses, using its argued data as well as AMSR and GLI data.
- Outline of Physical Oceanography (Yoshihiko Sekine, 1995)
- Ocean and Environment (Compilation of the Oceanographic Society of Japan, 2001)
Earth Obserbation Research Center