Bidlot
Jean-Raymond
Bidlot
Jean-Raymond
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ArticleEmerging trends in the sea state of the Beaufort and Chukchi seas(Elsevier, 2016-07-06) Thomson, James M. ; Fan, Yalin ; Stammerjohn, Sharon E. ; Stopa, Justin ; Rogers, W. Erick ; Girard-Ardhuin, Fanny ; Ardhuin, Fabrice ; Shen, Hayley ; Perrie, Will ; Shen, Hui ; Ackley, Stephen ; Babanin, Alexander ; Liu, Qingxiang ; Guest, Peter ; Maksym, Ted ; Wadhams, Peter ; Fairall, Christopher W. ; Persson, Ola ; Doble, Martin J. ; Graber, Hans C. ; Lund, Bjoern ; Squire, Vernon ; Gemmrich, Johannes ; Lehner, Susanne ; Holt, Benjamin ; Meylan, Michael ; Brozena, John ; Bidlot, Jean-RaymondThe sea state of the Beaufort and Chukchi seas is controlled by the wind forcing and the amount of ice-free water available to generate surface waves. Clear trends in the annual duration of the open water season and in the extent of the seasonal sea ice minimum suggest that the sea state should be increasing, independent of changes in the wind forcing. Wave model hindcasts from four selected years spanning recent conditions are consistent with this expectation. In particular, larger waves are more common in years with less summer sea ice and/or a longer open water season, and peak wave periods are generally longer. The increase in wave energy may affect both the coastal zones and the remaining summer ice pack, as well as delay the autumn ice-edge advance. However, trends in the amount of wave energy impinging on the ice-edge are inconclusive, and the associated processes, especially in the autumn period of new ice formation, have yet to be well-described by in situ observations. There is an implicit trend and evidence for increasing wave energy along the coast of northern Alaska, and this coastal signal is corroborated by satellite altimeter estimates of wave energy.
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ArticleWind 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.
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ArticleA deep ocean acoustic noise floor, 1–800 Hz(Acoustical Society of America, 2018-02-26) Berger, Jonathan ; Bidlot, Jean-Raymond ; Dzieciuch, Matthew A. ; Farrell, W. E. ; Worcester, Peter F. ; Stephen, Ralph A.The ocean acoustic noise floor (observed when the overhead wind is low, ships are distant, and marine life silent) has been measured on an array extending up 987 m from 5048 m depth in the eastern North Pacific, in what is one of only a few recent measurements of the vertical noise distribution near the seafloor in the deep ocean. The floor is roughly independent of depth for 1–6 Hz, and the slope (∼ f−7) is consistent with Longuet-Higgins radiation from oppositely-directed surface waves. Above 6 Hz, the acoustic floor increases with frequency due to distant shipping before falling as ∼ f−2 from 40 to 800 Hz. The noise floor just above the seafloor is only about 5 dB greater than during the 1975 CHURCH OPAL experiment (50–200 Hz), even though these measurements are not subject to the same bathymetric blockage. The floor increases up the array by roughly 15 dB for 40–500 Hz. Immediately above the seafloor, the acoustic energy is concentrated in a narrow, horizontal beam that narrows as f−1 and has a beam width at 75 Hz that is less than the array resolution. The power in the beam falls more steeply with frequency than the omnidirectional spectrum.
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ArticleRobust wavebuoys for the marginal ice zone : experiences from a large persistent array in the Beaufort Sea(University of California Press, 2017-08-21) Doble, Martin J. ; Wilkinson, Jeremy P. ; Valcic, Lovro ; Robst, Jeremy ; Tait, Andrew ; Preston, Mark ; Bidlot, Jean-Raymond ; Hwang, Byongjun ; Maksym, Ted ; Wadhams, PeterAn array of novel directional wavebuoys was designed and deployed into the Beaufort Sea ice cover in March 2014, as part of the Office of Naval Research Marginal Ice Zone experiment. The buoys were designed to drift with the ice throughout the year and monitor the expected breakup and retreat of the ice cover, forced by waves travelling into the ice from open water. Buoys were deployed from fast-and-light air-supported ice camps, based out of Sachs Harbour on Canada’s Banks Island, and drifted westwards with the sea ice over the course of spring, summer and autumn, as the ice melted, broke up and finally re-froze. The buoys transmitted heave, roll and pitch timeseries at 1 Hz sample frequency over the course of up to eight months, surviving both convergent ice dynamics and significant waves-in-ice events. Twelve of the 19 buoys survived until their batteries were finally exhausted during freeze-up in late October/November. Ice impact was found to have contaminated a significant proportion of the Kalman-filter-derived heave records, and these bad records were removed with reference to raw x/y/z accelerations. The quality of magnetometer-derived buoy headings at the very high magnetic field inclinations close to the magnetic pole was found to be generally acceptable, except in the case of four buoys which had probably suffered rough handling during transport to the ice. In general, these new buoys performed as expected, though vigilance as to the veracity of the output is required.