Low-Frequency Seiche in a Large Bay

Abstract

hort-term observations of sea surface elevations ? along the 10-m isobath and long-term observations inside and outside of a large bay (Monterey Bay, CA) were obtained to describe the nodal structure of the modes 0?3 seiches within the bay and the low-frequency (<346 cpd) seiche forcing mechanism. The measured nodal pattern validates previous numerical estimates associated with a northern amplitude bias, though variability exists across the modal frequency band, particularly for modes 0 and 1. Low-frequency oceanic ? white noise within seiche frequency bands (24?69 cpd) provides a continuous resonant forcing of the bay seiche with a ?2 (variance) amplification of 16?40 for the different modes. The temporal variation of the oceanic ? white noise is significantly correlated (R2 = 0.86) at the 95% confidence interval with the bay seiche ? that varies seasonally. The oceanic ? white noise is hypothesized as being from low-frequency, free, infragravity waves that are forced by short waves.