Low-frequency seiche in a large bay

Abstract

Short-term observations of sea surface elevations η 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 η white noise within seiche frequency bands (24-69 cpd) provides a continuous resonant forcing of the bay seiche with a η2 (variance) amplification of 16-40 for the different modes. The temporal variation of the oceanic η white noise is significantly correlated (R2=0.86) at the 95% confidence interval with the bay seiche η that varies seasonally. The oceanic η white noise is hypothesized as being from low-frequency, free, infragravity waves that are forced by short waves.