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Department of Estuarine and Ocean Sciences Seminar Announcement-Dr. Valentina Giunta

When: Wednesday, September 15, 2021
12:30 PM - 1:30 PM
Where: > See description for location
Description: The School for Marine Science and Technology
Department of Estuarine and Ocean Sciences
Seminar Announcement

"Oceanic Mixing and Mixed Layer Depths"

Dr. Valentina Giunta
Department of Estuarine and Ocean Sciences
SMAST at UMass Dartmouth

Wednesday, September 15, 2021
12:30 pm to 1:30 pm
SMAST East Rooms 101/102
And Via Zoom

The ocean surface boundary layer (OSBL) is one of the largest global
regulators of climate. There are two definitions associated with its
depth: the mixed layer depth (MLD) and the mixing layer depth (XLD).
The former is estimated using vertical profiles of temperature and
density, and the latter using measurements of the dissipation rate of
turbulent kinetic energy. The relationship between the XLD and MLD has
not been extensively studied in the past, since this requires
specialized instruments which allow simultaneous measurements of ocean
state variables and turbulence across the full depth of the OSBL.
The overarching objective of this presentation is to show the variability of the XLD and MLD under different conditions. To achieve this,
different estimates of the MLD and XLD are applied to vertical
profiles derived from an autonomous vertical profiler (ASIP) deployed
in two different cruises in the North Atlantic. It was found that the
MLD criteria differ between themselves when the stratification is
weaker and the transition between the mixed layer and the pycnocline
is not well defined. On the contrary, the XLD criteria had a better
agreement between themselves, and a new method was proposed to improve
its estimation.
The action of the wind, waves, and buoyancy fluxes impact the
variability of the OSBL. To study the effect of each source of
turbulence in the OSBL, different parameters related to each forcing
were estimated and compared with the MLD and XLD. Given the close link
found between the XLD and each source of turbulence, a scaling for the
XLD was tested by dividing the ocean into different mixing regimes
according to the ratio between the Monin-Obukhov length, the MLD, and
the surface net heat flux. Under periods of convection, the XLD
shows a significant correlation with the MLD.
The results found using ASIP data were extrapolated to build a
climatology of the upper mixing using reanalysis data from ERA5 and
ARGO profiles during a period of 10 years (2009-2018). Significant
differences between the MLD and the XLD climatology were found during
this process.
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Contact: > See Description for contact information
Topical Areas: School for Marine Sciences and Technology, SMAST Seminar Series