Search Results

You are looking at 1 - 7 of 7 items for

  • Author or Editor: James H. Morison x
  • Refine by Access: All Content x
Clear All Modify Search
Michael Steele and James H. Morison

Abstract

SALARGOS buoys that measure upper-ocean temperature and salinity in ice-covered seas have been collecting data in the Arctic basin for several years. The buoys consist of a 300-m-long string of six temperature-conductivity sensors at fixed depths, with a pressure sensor at the bottom. The electronics housing, including an Argos transmitter, is frozen into the sea ice. The buoy drifts with the sea ice, sampling a region described by the Lagrangian drift of the surrounding ice pack. When the ice is moving slowly, the relative water velocity in the upper ocean is low and the buoy simply produces hydrographic time series at six depths. In periods of rapid drift the buoy cable is displaced upward and the sensors sample other depths. Collecting such data over time can produce plots with relatively high vertical resolution. But to use this information, one needs a reasonable curve fit to these data similar to a smoothed version of a CTD (conductivity-temperature-depth) cast. Two methods have been investigated parametric regression analysis and nonparametric smoothing routines. The quality of the parametric fits depends in part on the choice of analytical profile, as is demonstrated here by comparing the efficacy of a common three-parameter model with a more complete five-parameter model. Both share the advantage of containing explicit geophysical quantities (such as mixed-layer depth) as the free parameters of the system. The nonpammetric smoother, on the other hand, assumes no a priori knowledge of the underlying physics. The data are smoothed and interpolated onto a grid of depth values in a procedure that includes both median and mean running fitters, which results in a relatively small standard error. The standard error for the parametric routines is larger by a factor of 2 or 3, but these schemes produce better estimates of geophysical parameters such as mixed-layer depth. Either technique could also be used to gain enhanced vertical resolution with bottom-moored ocean buoys.

Full access
Daniel R. Hayes and James H. Morison

Abstract

The authors show that vertical turbulent fluxes in the upper ocean can be measured directly with an autonomous underwater vehicle (AUV). A horizontal profile of vertical water velocity is obtained by applying a Kalman smoother to AUV motion data. The smoother uses a linearized model for vehicle motion and vehicle data such as depth, pitch, and pitch rate to produce an optimal estimate of the state of the system, which includes other vehicle variables and the vertical water velocity. Vertical water velocity estimated by applying the smoother to data from the autonomous microconductivity temperature vehicle (AMTV) is accurate at horizontal scales from three to several hundred meters, encompassing the energy-containing scales of most oceanic turbulence. The zero-lag covariances between vertical water velocity and concurrent measurements of temperature or salinity represent the heat and salt fluxes, respectively. The authors have measured horizontal profiles of turbulent fluxes with two different AUVs in three separate polar ocean experiments using this technique. Flux magnitudes and directions are reasonable and in general agreement with fixed turbulence sensors. With this technique, one can gather boundary layer data in inaccessible regions without disturbing or affecting the surface.

Full access
Murray D. Levine, Clayton A. Paulson, and James H. Morison

Abstract

A thermistor chain was moored below the pack ice from 50–150 m in the Arctic Ocean for five days in 1981. Oscillations in temperature are attributed to the vertical dispalcement of internal waves. The spectral shape of isotherm dispalcement is consistent with the Garrett-Munk model and other internal wave observations, but the spectral level is significantly lower. Other observations from the Arctic Ocean also exhibit lower internal-wave energy when compared with historical data from lower latitudes. The lower energy may be related to the unique generation and dissipation mechanisms present in the ice-covered Arctic Ocean. Significant peaks in vertical coherence occur at 0.81 and 2.6 cph. The peak at 2.6 cph coincides approximately with the high-frequency spectral cutoff near the local buoyancy frequency; this feature has been observed in many other internal wave experiments. The coherent oscillations at 0.81 cph exhibit a node in vertical dispalcement at 75–100 m. This is consistent with either the second, third or fourth vertical mode calculated from the mean buoyancy frequency profile. Evidence is presented which suggests that, contrary to the Garrett-Munk model, the frequency spectrum does not scale with the Coriolis parameter.

Full access
Sarah R. Dewey, James H. Morison, and Jinlun Zhang

Abstract

To understand the factors causing the interannual variations in the summer retreat of the Beaufort Sea ice edge, Seasonal Ice Zone Reconnaissance Surveys (SIZRS) aboard U.S. Coast Guard Arctic Domain Awareness flights were made monthly from June to October in 2012, 2013, and 2014. The seasonal ice zone (SIZ) is where sea ice melts and reforms annually and encompasses the nominally narrower marginal ice zone (MIZ) where a mix of open-ocean and ice pack processes prevail. Thus, SIZRS provides a regional context for the smaller-scale MIZ processes. Observations with aircraft expendable conductivity–temperature–depth probes reveal a salinity pattern associated with large-scale gyre circulation and the seasonal formation of a shallow (~20 m) fresh layer moving with the ice edge position. Repeat occupations of the SIZRS lines from 72° to 76°N on 140° and 150°W allow a comparison of observed hydrography to atmospheric indices. Using this relationship, the basinwide salinity signals are separated from the fresh layer associated with the ice edge. While this layer extends northward under the ice edge as the melt season progresses, low salinities and warm temperatures appear south of the edge. Within this fresh layer, average salinity is correlated with distance from the ice edge. The salinity observations suggest that the upper-ocean freshening over the summer is dominated by local sea ice melt and vertical mixing. A Price–Weller–Pinkel model analysis reveals that observed changes in heat content and density structure are also consistent with a 1D mixing process.

Full access
Miles G. McPhee, Christoph Kottmeier, and James H. Morison

Abstract

Seasonal sea ice, which plays a pivotal role in air–sea interaction in the Weddell Sea (a region of large deep-water formation with potential impact on climate), depends critically on heat flux from the deep ocean. During the austral winter of 1994, an intensive process-oriented field program named the Antarctic Zone Flux Experiment measured upper-ocean turbulent fluxes during two short manned ice-drift station experiments near the Maud Rise seamount region of the Weddell Sea. Unmanned data buoys left at the site of the first manned drift provided a season-long time series of ice motion, mixed layer temperature and salinity, plus a (truncated) high-resolution record of temperature within the ice column. Direct turbulence flux measurements made in the ocean boundary layer during the manned drift stations were extended to the ice–ocean interface with a “mixing length” model and were used to evaluate parameters in bulk expressions for interfacial stress (a “Rossby similarity” drag law) and ocean-to-ice heat flux (proportional to the product of friction velocity and mixed layer temperature elevation above freezing). The Rossby parameters and dimensionless heat transfer coefficient agree closely with previous studies from perennial pack ice in the Arctic, despite a large disparity in undersurface roughness. For the manned drifts, ocean heat flux averaged 52 W m−2 west of Maud Rise and 23 W m−2 over Maud Rise. Unmanned buoy heat flux averaged 27 W m−2 over a 76-day drift. Although short-term differences were large, average conductive heat flux in the ice was nearly identical to ocean heat flux over the 44-day ice thermistor record.

Full access
Cecilia Peralta-Ferriz, James H. Morison, John M. Wallace, Jennifer A. Bonin, and Jinlun Zhang

Abstract

Measurements of ocean bottom pressure (OBP) anomalies from the satellite mission Gravity Recovery and Climate Experiment (GRACE), complemented by information from two ocean models, are used to investigate the variations and distribution of the Arctic Ocean mass from 2002 through 2011. The forcing and dynamics associated with the observed OBP changes are explored. Major findings are the identification of three primary temporal–spatial modes of OBP variability at monthly-to-interannual time scales with the following characteristics. Mode 1 (50% of the variance) is a wintertime basin-coherent Arctic mass change forced by southerly winds through Fram Strait, and to a lesser extent through Bering Strait. These winds generate northward geostrophic current anomalies that increase the mass in the Arctic Ocean. Mode 2 (20%) reveals a mass change along the Siberian shelves, driven by surface Ekman transport and associated with the Arctic Oscillation. Mode 3 (10%) reveals a mass dipole, with mass decreasing in the Chukchi, East Siberian, and Laptev Seas, and mass increasing in the Barents and Kara Seas. During the summer, the mass decrease on the East Siberian shelves is due to the basin-scale anticyclonic atmospheric circulation that removes mass from the shelves via Ekman transport. During the winter, the forcing mechanisms include a large-scale cyclonic atmospheric circulation in the eastern-central Arctic that produces mass divergence into the Canada Basin and the Barents Sea. In addition, strengthening of the Beaufort high tends to remove mass from the East Siberian and Chukchi Seas. Supporting previous modeling results, the month-to-month variability in OBP associated with each mode is predominantly of barotropic character.

Full access
Taneil Uttal, Judith A. Curry, Miles G. McPhee, Donald K. Perovich, Richard E. Moritz, James A. Maslanik, Peter S. Guest, Harry L. Stern, James A. Moore, Rene Turenne, Andreas Heiberg, Mark. C. Serreze, Donald P. Wylie, Ola G. Persson, Clayton A. Paulson, Christopher Halle, James H. Morison, Patricia A. Wheeler, Alexander Makshtas, Harold Welch, Matthew D. Shupe, Janet M. Intrieri, Knut Stamnes, Ronald W. Lindsey, Robert Pinkel, W. Scott Pegau, Timothy P. Stanton, and Thomas C. Grenfeld

A summary is presented of the Surface Heat Budget of the Arctic Ocean (SHEBA) project, with a focus on the field experiment that was conducted from October 1997 to October 1998. The primary objective of the field work was to collect ocean, ice, and atmospheric datasets over a full annual cycle that could be used to understand the processes controlling surface heat exchanges—in particular, the ice–albedo feedback and cloud–radiation feedback. This information is being used to improve formulations of arctic ice–ocean–atmosphere processes in climate models and thereby improve simulations of present and future arctic climate. The experiment was deployed from an ice breaker that was frozen into the ice pack and allowed to drift for the duration of the experiment. This research platform allowed the use of an extensive suite of instruments that directly measured ocean, atmosphere, and ice properties from both the ship and the ice pack in the immediate vicinity of the ship. This summary describes the project goals, experimental design, instrumentation, and the resulting datasets. Examples of various data products available from the SHEBA project are presented.

Full access