Hydrostatic and non-hydrostatic simulations of dense waters cascading off a shelf: The East Greenland case. (February 2015)

• Record Type: Journal Article
• Authors: Magaldi, Marcello G.; Haine, Thomas W.N.
• Is Part Of: Deep sea research. Volume 96(2015)
• Page Start: 89
• Page End: 104
• Publication Date: 2015-02
• Subjects: Dense water cascading -- Non-hydrostatic model -- Irminger Sea; Oceanography -- Periodicals; Océanographie -- Périodiques; 551.4605
• DOI: 10.1016/j.dsr.2014.10.008
• Languages: English
• ISSNs: 0967-0637

Abstract

Abstract: The cascade of dense waters of the Southeast Greenland shelf during summer 2003 is investigated with two very high-resolution (0.5-km) simulations. The first simulation is non-hydrostatic. The second simulation is hydrostatic and about 3.75 times less expensive. Both simulations are compared to a 2-km hydrostatic run, about 31 times less expensive than the 0.5 km non-hydrostatic case. Time-averaged volume transport values for deep waters are insensitive to the changes in horizontal resolution and vertical momentum dynamics. By this metric, both lateral stirring and vertical shear instabilities associated with the cascading process are accurately parameterized by the turbulent schemes used at 2-km horizontal resolution. All runs compare well with observations and confirm that the cascade is mainly driven by cyclones which are linked to dense overflow boluses at depth. The passage of the cyclones is also associated with the generation of internal gravity waves (IGWs) near the shelf. Surface fields and kinetic energy spectra do not differ significantly between the runs for horizontal scales L > 30 km . Complex structures emerge and the spectra flatten at scales L < 30 km in the 0.5-km runs. In the non-hydrostatic case, additional energy is found in the vertical kinetic energy spectra at depth in the 2 km < L < 10 km range and with frequencies around 7 times the inertial frequency. This enhancement is missing in both hydrostatic runs and is here argued to be due to the different IGW evolution and propagation offshore. The different IGW behavior in the non-hydrostatic case has strong implications for the energetics: compared to the 2-km case, the baroclinic conversion term and vertical kinetic energy are about 1.4 and at least 34 times larger, respectively. This indicates that the energy transfer from the geostrophic eddy field to IGWs and their propagation away from the continental slope is not properly represented in the hydrostatic runs. Abstract : Highlights: Dense water cascading off the East Greenland shelf is modeled with two 0.5-km runs. The two runs, one hydrostatic and one non-hydrostatic, are compared to a 2-km run. Volume fluxes are insensitive to changes in resolution and momentum dynamics. Eddies in the cascade are associated with internal gravity waves (IGWs). IGWs have larger amplitudes and propagate farther in the non-hydrostatic run.