新聘教師候選人演講公告 4月13日(五) 15：30 Upper Ocean Research using Subsurface EM-APEX Floats. Dr. Je-Yuan Hsu (Commonwealth Scientific and Industrial Organisation (CSIRO), Perth, Australia)
講者：Dr. Je-Yuan Hsu (Commonwealth Scientific and Industrial Organisation (CSIRO), Perth, Australia)
題目：Upper Ocean Research using Subsurface EM-APEX Floats.
EM-APEX floats as the autonomous and vertical-profiling floats, can measure the voltage induced by the seawater motion, temperature and salinity in the upper ocean. The voltage measurements are processed to estimate the ocean current velocity (< 0.02 Hz) and high-frequency velocity variance (> 0.02 Hz). Nineteen EM-APEX floats were deployed from the aircrafts at one day before the passage of five tropical cyclones’ eyes.
Strong tropical cyclone wind forced the upper ocean cooling by more than 1 °C on the right of tropical cyclones’ tracks due to the vertical mixing.
The storm-induced ocean current velocity was measured and used to estimate the surface wind stress under tropical cyclones, assuming the linear momentum balance. The downwind drag coefficient is about 1.2－3.0×10-3 at wind speed |U10|=25－40 m s-1, and 1.6×10-3 at |U10| > 40 m s-1. The angle between the wind U10 and surface wind stress can be up to 30°. The profiles of high-frequency velocity variance are least-squared fitted nonlinearly to estimate the significant wave height and peak frequency under tropical cyclones, assuming the JONSWAP surface wave spectrum. The comparison between the float estimates and simulations in the WAVEWATCH III surface wave model is in a good agreement with the previous studies. For the future research in the upper ocean physics and air-sea interaction, EM-APEX floats may be useful for studying the dynamics of internal waves, upper ocean response to the atmospheric forcing, and the role of surface waves in the momentum coupling between the atmosphere and ocean.