Ruddick
Barry R.
Ruddick
Barry R.
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ArticleToward quantifying the increasing role oceanic heat in sea ice loss in the new Arctic(American Meteorological Society, 201512) Carmack, Eddy C. ; Polyakov, Igor V. ; Padman, Laurie ; Fer, Ilker ; Hunke, Elizabeth C. ; Hutchings, Jennifer K. ; Jackson, Jennifer M. ; Kelley, Daniel E. ; Kwok, Ron ; Layton, Chantelle ; Melling, Humfrey ; Perovich, Donald K. ; Persson, Ola ; Ruddick, Barry R. ; Timmermans, MaryLouise ; Toole, John M. ; Ross, Tetjana ; Vavrus, Steve ; Winsor, PeterThe loss of Arctic sea ice has emerged as a leading signal of global warming. This, together with acknowledged impacts on other components of the Earth system, has led to the term “the new Arctic.” Global coupled climate models predict that ice loss will continue through the twentyfirst century, with implications for governance, economics, security, and global weather. A wide range in model projections reflects the complex, highly coupled interactions between the polar atmosphere, ocean, and cryosphere, including teleconnections to lower latitudes. This paper summarizes our present understanding of how heat reaches the ice base from the original sources—inflows of Atlantic and Pacific Water, river discharge, and summer sensible heat and shortwave radiative fluxes at the ocean/ice surface—and speculates on how such processes may change in the new Arctic. The complexity of the coupled Arctic system, and the logistic and technological challenges of working in the Arctic Ocean, require a coordinated interdisciplinary and international program that will not only improve understanding of this critical component of global climate but will also provide opportunities to develop human resources with the skills required to tackle related problems in complex climate systems. We propose a research strategy with components that include 1) improved mapping of the upper and middepth Arctic Ocean, 2) enhanced quantification of important process, 3) expanded longterm monitoring at key heatflux locations, and 4) development of numerical capabilities that focus on parameterization of heatflux mechanisms and their interactions.

Technical ReportObservations of interaction between the internal wavefield and lowfrequency flows in the North Atlantic(Woods Hole Oceanographic Institution, 197910) Ruddick, Barry R. ; Joyce, Terrence M.A total of four moorings from POLYMODE array I and II were analyzed in an investigation of the interaction of wavefields and mean flow. In particular, evidence for internal wavemean flow interaction was sought by searching for time correlations between the vertically acting Reynolds stress of the wavefield (estimated using the temperature and velocity records), and the mean shear. No significant stressshear correlations were found at the less energetic moorings (u¯≲10 cm s−1), indicating that the magnitude of the eddy viscosity was under 200 cm2 s−1, with the sign of the energy transfer uncertain. This is considerably below the O(4500 cm2 s−1) predicted by Müller (1976). An extensive error analysis indicates that the large wave stress predicted by the theory should have been observable clearly under the conditions of measurement. At moorings typified by a higher mean velocity (u¯≈25 cm s−1), statistically significant stressshear correlations were found, and the wavefield energy level was observed to modulate with the strength of the mean shear. The observations were consistent with generation of short (∼1 km horizontal wavelength) internal waves by the mean shear near the thermocline, resulting in an effective eddy viscosity of ∼100 cm2 s−1. Theoretical computations indicate that the wavefield “basic state” may not be independent of the mean flow as assumed by Müller (1976) but can actually be modified by largescale vertical shear and still remain in equilibrium. In that case, the wavefield does not exchange momentum with a largescale vertical shear flow and, excepting criticallayer effects, a small vertical eddy viscosity is to be expected. Using the GarrettMunk (1975) model internal wave spectrum, estimates were made of the maximum momentum flux (stress) expected to be lost to criticallayer absorption. This stress was found to increase almost linearly with the velocity difference across the shear zone, corresponding to a vertical eddy viscosity of −100 cm2 s−1. Stresses indicative of this effect were not observed in the data.

Technical ReportCritical layers and the GarrettMunk spectrum(Woods Hole Oceanographic Institution, 198011) Ruddick, Barry R.The effects of critical level absorption of oceanic internal waves by a mean flow are estimated using the Garrett and Munk (1975) model spectrum. The horizontal currents of the wave field are found to be more intense perpendicular to the mean flow than parallel to it. The cause of this anisotropy is preferential absorption of waves travelling with the mean flow. However, the current anisotropy is only half as large as would be necessary to explain Frankignoul's (1974) observations. The wave momentum flux lost to critical level absorption is found to be nearly proportional to the mean velocity. When the momentum flux is deposited throughout a 400 m thick shear zone, typical of the main thermocline in the Northwest Atlantic, the observed stressshear relationship would correspond to a waveinduced eddy viscosity of 200 cm2 s1. The effect of the absorbed momentum on the mean flow is to cause a slow (5 m/day) downward phase propagation and slow broadening of the shear profile.

ThesisObservations of interaction between the internal wavefield and low frequency flows in the North Atlantic(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 197704) Ruddick, Barry R.A total of four moorings from POLYMODE Array I and II were analyzed in an investigation of internal wavefieldmean flow interactions. In particular, evidence for wavemean flow interaction was sought by searching for time correlations between the wavefield verticallyacting Reynolds stress (estimated using the temperature and velocity records), and the mean shear. No significant stressshear correlations were found at the less energetic moorings, indicating that the magnitude of the eddy viscosity was under 200 cm2/sec, with the sign of the energy transfer uncertain. This is considerably below the 0(4500 cm2/sec) predicted by Müller (1976). An extensive error analysis indicates that the large wave stress predicted by the theory should have been clearly observable under the conditions of measurement. Theoretical computations indicate that the wavefield "basic state" may not be independent of the mean flow as assumed by Müller, but can actually be modified by largescale vertical shear and still remain in equilibrium. In that case, the wavefield does not exchange momentum with a largescale vertical shear flow, and, excepting critical layer effects, a small vertical eddy viscosity is to be expected. Using the GarrettMunk (1975) model internal wave spectrum, estimates were made of the maximum momentum flux (stress) expected to be lost to critical layer absorption. Stress was found to increase almost linearly with the velocity difference across the shear zone, corresponding to a vertical eddy viscosity of 100 cm2 s 1. Stresses indicative of this effect were not observed in the data. The only significantly nonzero stress correlations were found at the more energetic moorings. Associated with the 600 m mean velocity and the shear at the thermocline were a positively correlated stress at 600 m, and a negatively correlated stress at 1000 m. These stress correlations were most clearly observable in the frequency range corresponding to 1 to 8 hour wave periods. The internal wavefield kinetic and potential energy were modulated by the mean flow at both levels, increasing by a factor of two with a factor of ten in the mean flow. The observed stress correlations and energy level changes were found to be inconsistent with ideas of a strictly local eddy viscosity, in which the spectrum of waves is only slightly modified by the shear. When Doppler effects in the temperature equation used to estimate vertical velocity were considered, the observations of stress and energy changes were found to be consistent with generation of short (0.4 to 3 km) internal waves at the level of maximum shear, about 800 m. The intensity of the generated waves increases with the shear, resulting in an effective vertical eddy viscosity (based on the main thermocline shear) of about +100 cm2 s1 The stresses were not observable at the 1500 m level, indicating that the waves were absorbed within 500 m of vertical travel. The tendency for internal wave currents to be horizontally anisotropic in the presence of a mean current was investigated. Using the Garrett Munk (1975) model internal wave spectrum, it was found that critical layer absorption cannot induce anisotropies as large as observed. A mechanical noise problem was found to be the cause of large anisotropies measured with Geodyne 850 current meters. It could not be decided, however, whether or not the A.M.F. Vector Averaging Current Meter is able to satisfactorily remove the noise with its averaging scheme.