Measuring Turbulent Dissipation Rates Beneath an Antarctic Ice Shelf

2014 ◽  
Vol 48 (5) ◽  
pp. 18-24 ◽  
Author(s):  
Emily Venables ◽  
Keith Nicholls ◽  
Fabian Wolk ◽  
Keith Makinson ◽  
Paul Anker
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Open Water ◽  
Ice Shelf ◽  
Turbulent Dissipation ◽  
Novel Technique ◽  
Dissipation Rates ◽  
Vertical Heat ◽  
Drilling Technique ◽  
Vertical Heat Flux

AbstractMicrostructure shear, temperature, and conductivity observations from a tethered profiler have been made beneath George VI Ice Shelf to examine processes driving vertical heat flux in the oceanic turbulent boundary layer. Such measurements at the ice-ocean interface within the cavity of an ice shelf are unprecedented, requiring the deployment of a profiler through 400-m deep access boreholes. We describe the drilling technique developed for this purpose, which involves using a brush to widen the deepest section of the borehole, and as evidence that this novel technique can be successful, we present shear and thermal variance spectra from the profiler. These spectra indicate that dissipation rates of turbulent kinetic energy, from which heat flux can be calculated, can be resolved beneath an ice shelf as well as they can be in open water.

scholarly journals Statistical Analysis of Sodium Doppler Wind–Temperature Lidar Measurements of Vertical Heat Flux

2008 ◽  
Vol 25 (3) ◽  
pp. 401-415 ◽  
Author(s):  
Liguo Su ◽  
Richard L. Collins ◽  
David A. Krueger ◽  
Chiao-Yao She
Keyword(s):  
Heat Flux ◽  
Photon Counting ◽  
Doppler Lidar ◽  
State University ◽  
Colorado State University ◽  
Lidar Measurements ◽  
Vertical Heat ◽  
Different Seasons ◽  
Flux Measurements ◽  
Vertical Heat Flux

Abstract A statistical study is presented of the errors in sodium Doppler lidar measurements of wind and temperature in the mesosphere that arise from the statistics of the photon-counting process that is inherent in the technique. The authors use data from the Colorado State University (CSU) sodium Doppler wind-temperature lidar, acquired at a midlatitude site, to define the statistics of the lidar measurements in different seasons under both daytime and nighttime conditions. The CSU lidar measurements are scaled, based on a 35-cm-diameter receiver telescope, to the use of large-aperture telescopes (i.e., 1-, 1.8-, and 3.5-m diameters). The expected biases in vertical heat flux measurements at a resolution of 480 m and 150 s are determined and compared to Gardner and Yang’s reported geophysical values of 2.3 K m s−1. A cross-correlation coefficient of 2%–7% between the lidar wind and temperature estimates is found. It is also found that the biases vary from −4 × 10−3 K m s−1 for wintertime measurements at night with a 3.5-m telescope to −61 K m s−1 for summertime measurements at midday with a 1-m telescope. During winter, at night, the three telescope systems yield biases in their heat flux measurements that are less than 10% of the reported value of the heat flux; and during summer, at night, the 1.8- and 3.5-m systems yield biases in their heat flux measurements that are less than 10% of the geophysical value. While during winter at midday the 3.5-m system yields biases in their heat flux measurements that are less than 10% of the geophysical value, during summer at midday all of the systems yield flux biases that are greater than the geophysical value of the heat flux. The results are discussed in terms of current lidar measurements and proposed measurements at high-latitude sites.

scholarly journals Vertical Redistribution of Oceanic Heat Content

2015 ◽  
Vol 28 (9) ◽  
pp. 3821-3833 ◽  
Author(s):  
Xinfeng Liang ◽  
Carl Wunsch ◽  
Patrick Heimbach ◽  
Gael Forget
Keyword(s):  
Heat Flux ◽  
Heat Exchange ◽  
Heat Transport ◽  
Heat Content ◽  
Deep Ocean ◽  
Temporal Variations ◽  
Near Surface ◽  
Carbon 14 ◽  
Vertical Heat ◽  
Vertical Heat Flux

Abstract Estimated values of recent oceanic heat uptake are on the order of a few tenths of a W m−2, and are a very small residual of air–sea exchanges, with annual average regional magnitudes of hundreds of W m−2. Using a dynamically consistent state estimate, the redistribution of heat within the ocean is calculated over a 20-yr period. The 20-yr mean vertical heat flux shows strong variations in both the lateral and vertical directions, consistent with the ocean being a dynamically active and spatially complex heat exchanger. Between mixing and advection, the two processes determining the vertical heat transport in the deep ocean, advection plays a more important role in setting the spatial patterns of vertical heat exchange and its temporal variations. The global integral of vertical heat flux shows an upward heat transport in the deep ocean, suggesting a cooling trend in the deep ocean. These results support an inference that the near-surface thermal properties of the ocean are a consequence, at least in part, of internal redistributions of heat, some of which must reflect water that has undergone long trajectories since last exposure to the atmosphere. The small residual heat exchange with the atmosphere today is unlikely to represent the interaction with an ocean that was in thermal equilibrium at the start of global warming. An analogy is drawn with carbon-14 “reservoir ages,” which range from over hundreds to a thousand years.

scholarly journals Observation and Parameterization of Ablation at the Base of Ronne Ice Shelf, Antarctica

2010 ◽  
Vol 40 (10) ◽  
pp. 2298-2312 ◽  
Author(s):  
Adrian Jenkins ◽  
Keith W. Nicholls ◽  
Hugh F. J. Corr
Keyword(s):  
Boundary Layer ◽  
Open Water ◽  
Ablation Rate ◽  
Ocean Currents ◽  
Turbulent Transfer ◽  
Transfer Coefficients ◽  
Ice Shelf ◽  
Direct Measurements ◽  
Oceanic Boundary Layer ◽  
The Impact

Abstract Parameterizations of turbulent transfer through the oceanic boundary layer beneath an ice shelf are tested using direct measurements of basal ablation. Observations were made in the southwestern part of Ronne Ice Shelf, about 500 km from open water. The mean basal ablation rate was measured over a month-long and a year-long period using phase-sensitive radar to record the thinning of the ice shelf. Ocean temperatures were observed within about 25 m of the ice shelf base over the period of the radar observations, while the tidally dominated ocean currents were estimated from tidal analysis of collocated current observations from an earlier period. Ablation rates derived using these ocean data and a number of bulk parameterizations of turbulent transfer within the boundary layer are compared with the direct measurements. The ablation rates derived using a parameterization that explicitly includes the impact of ocean currents on the turbulent transfer of heat and salt match the observations to within 40%; with suitable tuning of the drag coefficient, the mismatch can be reduced below the level of the observational errors. Equally good agreement can be obtained with two slightly simpler, current-dependent parameterizations that use constant turbulent transfer coefficients, and the optimal values for the coefficients at this particular location on Ronne Ice Shelf are given.

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