Near 5-Day Nonisostatic Response to Atmospheric Surface Pressure and Coastal-Trapped Waves Observed in the Northern South China Sea

Abstract

AbstractOceanic, nonisostatic responses to near 5-day Rossby–Haurwitz atmospheric pressure waves have been observed in open oceans; however, such responses based on observations in marginal seas such as the South China Sea have not been reported, owing to the limited ocean bottom pressure Pbot records. The Pbot measurements from pressure recording inverted echo sounders (PIESs) at sites in the northern South China Sea revealed a nonisostatic-like response near 5 days, although the coastal-trapped waves (CTWs) appeared to obscure it because their broadband periods include the near 5-day band. Cross-spectral analysis revealed that the PIES Pbot records and the sea level (SL) records of Hong Kong all correlate strongly with the atmospheric pressure and winds over the East China Sea. This is indicative of remotely forced CTWs. The PIES Pbot records showed higher coherence near 5 days with the zonal low-pass wavelength filters applied to the atmospheric pressure, and the phase analysis results strongly suggest nonisostatic oceanic responses to the westward-propagating Rossby–Haurwitz waves. Effective separation of CTWs and the nonisostatic responses from the Pbot records at the near 5-day period was achieved. The oceanic responses to the Rossby–Haurwitz waves in the northern South China Sea were nonisostatic; a 1-mbar change in air pressure resulted in a 1.58-mbar change in Pbot with a phase lag of 14.8°. The mean phase speed of CTWs from Hong Kong to station P3 was estimated to be 9.9 m s−1.