| Summary: | 碩士 === 國立中興大學 === 環境工程學系所 === 98 === On the research ship, air-sea fluxes were observed by the eddy covariance system (ECS) over the ocean. Four problems in the experiments should be considered:(1) ocean wave and the movement of the ship would caused the error of the measured wind velocity;(2) high measured CO2 concentrations would be emitted from the stack on the ship rather than from the ocean;(3) the ECS set up at different positions would affect the measurement of wind fields and cause the error of flux results;(4) the open path analyzer would be interfered with environmental factors, such as rain, sea spray and sea salt, and the usability and accuracy of the data would be reduced. In this study, three cruises of flux and meteorological observations were carried out in western Pacific Ocean (September 2009), South China Sea (March 2010) and Taiwan Straits (April 2010). The fluxes observed from ECS set up at different positions and different elevations were discussed to find out the possible interferences while doing flux measurements. Finally, the most suitable position to set up the ECS was recommended in this study.
The results show that the albedo over the sea is 0.04-0.08 at noon. Being positively correlated with solar radiation, the diurnal variations of air temperatures and water temperatures are obvious. The relative humidity is negatively correlated with solar radiation, and is about 70%-100% over the sea. In every cruise, the ECS were set up at two different positions at the same time to discuss the influence of the ship on wind fields. In three cruises, the ECS were set up at 25 m and 17 m above sea level, at left and right decks, at stem and stern, respectively. The results show that the horizontal wind directions at two ECS positions are similar, and the wind velocities are slightly different. However, the vertical wind velocity (w) is obviously affected by the hull and by the situation where the ship is heading wind or following wind.After the ship motion correction and the WPL correction, the CO2 flux sinks more obviously at 17 m above sea level than at 25 m above sea level. The CO2 flux measured by the underway pCO2 system and ECS were quite different, and were even up to 10 to 100 times the difference. In fourier spectral analysis, vertical wind velocities, CO2 concentrations and potential temperatures measured at different positions show different results and different diurnal trends. The signals of eddy vortex at stem were strongest. There are many obvious signals for the gyroscope; however, the signals are inconsistent in three axes (pitch, yaw and roll).
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