A comparison of coastal trapped wave model with velocity observations in Norske Trough, Northeast Greenland
Date
2021
Authors
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Publisher
University of Delaware
Abstract
Bottom-intensified flow of warm ocean water leads to basal melting of many Greenland glaciers. I here focus on Norske Trough, a topographic depression that transects the generally 150-m shallow continental shelf of Northeast Greenland where I analyze velocity, temperature, and salinity measured from 2016 to 2017. A year-long mooring record indicates mean currents of about 6 cm/s towards the glaciers. Empirical Orthogonal Functions (EOF) reveal that about 80% of the variance is in the same direction as the mean flow. Currents thus move along the sloping bottom towards the glaciers and are modulated by temporal fluctuations. I identify monthly oscillations that are especially pronounced in winter. A more persistent oscillation at 24 days has an amplitude of about 1 cm/s that I diagnose for topographic Rossby wave dynamics. Horizontal motions at this frequency are almost uniform with depth, however, density stratification is not negligible. Observed Burger numbers B are Ο(1) with B={L_d}^2/L^2, L_d the internal Rossby radius, and L the width of the Norske Trough slope region. Ocean physics thus contain both barotropic and baroclinic elements of Rossby wave theory. Predicted and observed velocity profiles across the slope region agree well enough for a 16 km wide channel, however, the dispersion relation for such channels does not allow for baroclinic Rossby waves with the small vertical current shear I observe at monthly periods. I thus conclude that observations and theory are not entirely consistent and do not support the hypothesis that linear topographic Rossby waves explain velocity variations in Norske Trough unambiguously.
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Keywords
Coastal trapped wave model, Velocity observation, Norske Trough