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Titel |
Diurnal cycle of mixed layer turbulence and stratification in the tropics |
VerfasserIn |
Marcus Dengler, Peter Brandt, Gerd Krahmann, Sören Thomsen, Tim Fischer |
Konferenz |
EGU General Assembly 2013
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 15 (2013) |
Datensatznummer |
250084274
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Zusammenfassung |
Gliders based microstructure measurements using a MicroRider turbulence package from
different locations in the tropical Atlantic are used to investigate the diurnal variability of
turbulence and stratification in the mixed layer. The autonomous platform enables us to
collect time series of turbulent dissipation rates along with stratification over several weeks in
undisturbed waters in the depth range between 2m and 1000m. Microstructure profile time
series from the equator, 5° and 8° North in the central and eastern regions show strongly
elevated turbulent dissipations rates in the upper mixed layer between 2-10 m depth occurring
during day time from about 9am to 5pm. Peak dissipation rates are above 1x10-6W/kg
close to the surface and occur at about 14:00 hours local time. Concurrently, strong
vertical gradients in temperature develop in the upper 10 meters of the water column
indicating the development of stratification due to differential solar heating. On
average, the diurnal cycle of temperature in the upper 10m shows an amplitude
of 0.4°C. A likely explanation of the enhanced mixing in the upper mixed layer
is that wind-induced vertical turbulent momentum transport is strongly inhibited
during the diurnal stratified period, leading to large shear in upper few meters of
the water column. Strongly enhanced day-time turbulence in the mixed layer is
evident in all turbulent dissipation rate time series indicating that the process is not
restricted to a specific location or season. Finally, the dataset impressively shows that
turbulence in the tropical upper mixed layer peaks during day time rather than at night. |
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