Seasonal resonance of diurnal coastal trapped waves in the southern Weddell Sea, Antarctica
The summer enhancement of diurnal tidal currents at the shelf break in the southern Weddell Sea is studied using velocity measurements from 29 moorings during the period 1968 to 2014. Kinetic energy associated with diurnal tidal frequencies is largest at the shelf break and decreases rapidly with di...
Main Authors: | , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-01-01
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Series: | Ocean Science |
Online Access: | http://www.ocean-sci.net/13/77/2017/os-13-77-2017.pdf |
Summary: | The summer enhancement of diurnal tidal currents at the shelf
break in the southern Weddell Sea is studied using velocity measurements from
29 moorings during the period 1968 to 2014. Kinetic energy associated with
diurnal tidal frequencies is largest at the shelf break and decreases rapidly
with distance from it. The diurnal tidal energy increases from austral winter
to summer by, on average, 50 %. The austral summer enhancement is observed
in all deployments. The observations are compared to results from an
idealised numerical solution of the properties of coastal trapped waves
(CTWs) for a given bathymetry, stratification and an along-slope current. The
frequency at which the dispersion curve for mode 1 CTWs displays a maximum
(i.e. where the group velocity is zero and resonance is possible) is found
within or near the diurnal frequency band, and it is sensitive to the
stratification in the upper part of the water column and to the background
current. The maximum of the dispersion curve is shifted towards higher
frequencies, above the diurnal band, for weak stratification and a strong
background current (i.e. austral winter-like conditions) and towards lower
frequencies for strong upper-layer stratification and a weak background
current (austral summer). The seasonal evolution of hydrography and currents
in the region is inferred from available mooring data and
conductivity–temperature–depth profiles. Near-resonance of diurnal tidal CTWs
during austral summer can explain the observed seasonality in tidal currents. |
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ISSN: | 1812-0784 1812-0792 |