Munk Walter H.

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Munk
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Walter H.
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  • Article
    Tales of the venerable Honolulu tide gauge
    (American Meteorological Society, 2006-06) Colosi, John A. ; Munk, Walter H.
    Surface expressions of internal tides constitute a significant component of the total recorded tide. The internal component is strongly modulated by the time-variable density structure, and the resulting perturbation of the recorded tide gives a welcome look at twentieth-century interannual and secular variability. Time series of mean sea level hSL(t) and total recorded M2 vector aTT(t) are extracted from the Honolulu 1905–2000 and Hilo 1947–2000 (Hawaii) tide records. Internal tide parameters are derived from the intertidal continuum surrounding the M2 frequency line and from a Cartesian display of aTT(t), yielding aST = 16.6 and 22.1 cm, aIT = 1.8 and 1.0 cm for surface and internal tides at Honolulu and Hilo, respectively. The proposed model aTT(t) = aST + aIT cosθIT(t) is of a phase-modulated internal tide generated by the surface tide at some remote point and traveling to the tide gauge with velocity modulated by the underlying variable density structure. Mean sea level hSL(t) [a surrogate for the density structure and hence for θIT(t)] is coherent with aIT(t) within the decadal band 0.2–0.5 cycles per year. For both the decadal band and the century drift the recorded M2 amplitude is high when sea level is high, according to δaTT = O(0.1δhSL). The authors attribute the recorded secular increase in the Honolulu M2 amplitude from aTT = 16.1 to 16.9 cm between 1915 and 2000 to a 28° rotation of the internal tide vector in response to ocean warming.
  • Article
    Multipurpose acoustic networks in the integrated Arctic Ocean observing system
    (Arctic Institute of North America, 2015) Mikhalevsky, Peter N. ; Sagen, Hanne ; Worcester, Peter F. ; Baggeroer, Arthur B. ; Orcutt, John A. ; Moore, Sue E. ; Lee, Craig M. ; Vigness-Raposa, Kathleen J. ; Freitag, Lee E. ; Arrott, Matthew ; Atakan, Kuvvet ; Beszczynska-Möller, Agnieszka ; Duda, Timothy F. ; Dushaw, Brian D. ; Gascard, Jean-Claude ; Gavrilov, Alexander N. ; Keers, Henk ; Morozov, Andrey K. ; Munk, Walter H. ; Rixen, Michel ; Sandven, Stein ; Skarsoulis, Emmanuel ; Stafford, Kathleen M. ; Vernon, Frank L. ; Yuen, Mo Yan
    The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This activity will be driven by increased demand for energy and the marine resources of an Arctic Ocean accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism, and search and rescue will increase the pressure on the vulnerable Arctic environment. Technologies that allow synoptic in situ observations year-round are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual, and decadal scales. These data can inform and enable both sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. In this paper, we discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic, and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings, and vehicles. We support the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary in situ Arctic Ocean observatory.
  • Article
    Wind sea behind a cold front and deep ocean acoustics
    (American Meteorological Society, 2016-05-10) Farrell, W. E. ; Berger, Jonathan ; Bidlot, Jean-Raymond ; Dzieciuch, Monika ; Munk, Walter H. ; Stephen, Ralph A. ; Worcester, Peter F.
    A rapid and broadband (1 h, 1 < f < 400 Hz) increase in pressure and vertical velocity on the deep ocean floor was observed on seven instruments comprising a 20-km array in the northeastern subtropical Pacific. The authors associate the jump with the passage of a cold front and focus on the 4- and 400-Hz spectra. At every station, the time of the jump is consistent with the front coming from the northwest. The apparent rate of progress, 10–20 km h−1 (2.8–5.6 m s−1), agrees with meteorological observations. The acoustic radiation below the front is modeled as arising from a moving half-plane of uncorrelated acoustic dipoles. The half-plane is preceded by a 10-km transition zone, over which the radiator strength increases linearly from zero. With this model, the time derivative of the jump at a station yields a second and independent estimate of the front’s speed, 8.5 km h−1 (2.4 m s−1). For the 4-Hz spectra, the source physics is taken to be Longuet-Higgins radiation. Its strength depends on the quantity , where Fζ is the wave amplitude power spectrum and I the overlap integral. Thus, the 1-h time constant observed in the bottom data implies a similar time constant for the growth of the wave field quantity behind the front. The spectra at 400 Hz have a similar time constant, but the jump occurs 25 min later. The implications of this difference for the source physics are uncertain.
  • Article
    A test of basin-scale acoustic thermometry using a large-aperture vertical array at 3250-km range in the eastern North Pacific Ocean
    (Acoustical Society of America, 1999-06) Worcester, Peter F. ; Cornuelle, Bruce D. ; Dzieciuch, Matthew A. ; Munk, Walter H. ; Howe, Bruce M. ; Mercer, James A. ; Spindel, Robert C. ; Colosi, John A. ; Metzger, Kurt ; Birdsall, Theodore G. ; Baggeroer, Arthur B.
    Broadband acoustic signals were transmitted during November 1994 from a 75-Hz source suspended near the depth of the sound-channel axis to a 700-m long vertical receiving array approximately 3250 km distant in the eastern North Pacific Ocean. The early part of the arrival pattern consists of raylike wave fronts that are resolvable, identifiable, and stable. The later part of the arrival pattern does not contain identifiable raylike arrivals, due to scattering from internal-wave-induced sound-speed fluctuations. The observed ray travel times differ from ray predictions based on the sound-speed field constructed using nearly concurrent temperature and salinity measurements by more than a priori variability estimates, suggesting that the equation used to compute sound speed requires refinement. The range-averaged oceansound speed can be determined with an uncertainty of about 0.05 m/s from the observed ray travel times together with the time at which the near-axial acoustic reception ends, used as a surrogate for the group delay of adiabatic mode 1. The change in temperature over six days can be estimated with an uncertainty of about 0.006 °C. The sensitivity of the travel times to ocean variability is concentrated near the ocean surface and at the corresponding conjugate depths, because all of the resolved ray arrivals have upper turning depths within a few hundred meters of the surface.