Harmonic Analysis of Currents Within Humboldt Bay*

Tidal currents can shape the structure of estuarine environments and interpreting them is essential to maritime travel in dynamic bays. Multiyear time series of current data measured by two Acoustic Doppler Current Profilers (ADCPs) in Humboldt Bay, CA were analyzed to determine the contributions of the different harmonic frequencies of the tide within the bay. The ADCPs, which are part of the National Oceanic Atmospheric Administration’s (NOAA’s) Physical Oceanographic Real-Time Systems (PORTSⓇ) program, have been deployed at various locations within the bay to improve maritime safety by providing mariners accurate real-time oceanographic data used to navigate Humboldt Bay’s changing currents and seafloor topography. Spectral analysis, using Fourier transforms of the time series data, revealed that the flow is dominated by tidal currents. The three dominant harmonic frequencies include M2, K1, and O1, but their contribution varies spatially between the two stations. Additional frequencies in the data indicate interference with seafloor topography as well as the more variable wind-induced currents.