ALOHA Cabled Observatory bottom pressure spectra

Date 2007
Temporal extent 2007-02-17 -2008-10-22
Author(s) Duennebier Fred1, Howe BruceORCID1
Affiliation(s) 1 : University of Hawaii
DOI 10.17882/92104
Publisher SEANOE
Keyword(s) ocean waves, acoustics, wind
Abstract

Frequency spectra from deep-ocean near-bottom acoustic measurements obtained contemporaneously with wind, wave, and seismic data are described and used to determine

the correlations among these data and to discuss possible causal relationships. Microseism energy appears to originate in four distinct regions relative to the hydrophone: wind waves above the sensors contribute microseism energy observed on the ocean floor; a fraction of this local wave energy propagates as seismic waves laterally, and provides a spatially integrated contribution to microseisms observed both in the ocean and on land; waves in storms generate microseism energy in deep water that travels as seismic waves to the sensor; and waves reflected from shorelines provide opposing waves that add to the microseism energy. Correlations of local wind speed with acoustic and seismic spectral time series suggest that the local Longuet-Higgins mechanism is visible in the acoustic spectrum from about 0.4 Hz to 80 Hz. Wind speed and acoustic levels at the hydrophone are poorly correlated below 0.4 Hz, implying that the microseism energy below 0.4 Hz is not typically generated by local winds. Correlation of ocean floor acoustic energy with seismic spectra from Oahu and with wave spectra near Oahu imply that wave reflections from Hawaiian coasts, wave interactions in the deep ocean near Hawaii, and storms far from Hawaii contribute energy to the seismic and acoustic spectra below 0.4 Hz. Wavefield directionality strongly influences the acoustic spectrum at frequencies below about 2 Hz, above which the acoustic levels imply near-isotropic surface wave directionality.

Licence CC0
Acknowledgements The authors thank William Farrell, Peter Bromirski, Ralph Stephen, Christine Pequignet and two anonymous reviewers for valuable discussions, and Charles McCreery for valuable discussions and permission to use a figure from his dissertation. Funding for the ALOHA Cabled Observatory was provided by the National Science Foundation and the State of Hawaii through the School of Ocean and Earth Sciences and Technology at the University of Hawaii-Manoa (F. Duennebier, PI). Donations from AT&T and TYCOM and the cooperation of the U.S. Navy made this project possible. The WHOI-Hawaii Ocean Time series Station (WHOTS) mooring is maintained by Woods Hole Oceanographic Institution (PIs R. Weller and A. Plueddemann) with funding from the NOAA Climate Program Office/Climate Observation Division. NSF grant OCE0926766 supported R. Lukas (co-PI) to augment and collaborate on the maintenance of WHOTS. Lukas was also supported during this analysis by The National Ocean Partnership Program “Advanced Coupled Atmosphere-Wave-Ocean Modeling for Improving Tropical Cyclone Prediction Models” under contract N00014-10-1-0154 to the University of Rhode Island (I. Ginis, PI). The Waimea wave buoy is operated by the University of Hawaii Sea Level Center; buoy data were obtained from the Coastal Data Information Center at the Scripps Institution of Oceanography. The facilities of the IRIS Data Management System, and specifically the IRIS Data Management Center, were used for access to waveform and metadata required in this study. SOEST contribution 8560.
Sensor metadata

broadband hydrophone (OAS Model E-2PD) was suspended 10 m above the ocean floor in 4720 m of water as part of a proof-of-concept package when the ACO was emplaced at Station ALOHA in February 2007

Data
File Size Format Processing Access
Hourly median PSD of bottom pressure after instrument correction (see figure A1 in Duennebier et al. 2012) 26 MB NC, NetCDF Processed data Open access
This is the data archive with the original 5 minute resolution spectrograms in *.mat format, together with all the matlab scripts neede to make figures for the paper. 708 MB matlab files Processed data Open access
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