Sea ice near-inertial response to atmospheric storms

Thesis (M.A.) University of Alaska Fairbanks, 2015A moored oceanographic array was deployed on the Beaufort Sea continental slope from August 2008-August 2009 to measure Arctic sea ice near-inertial motion in response to rapidly changing wind stress. Upward looking Acoustic Doppler Current Profilers detected sea ice and measured ice drift using a combination of bottom track and error velocity. An analysis of in-situ mooring data in conjunction with data from National Center for Environmental Prediction (NCEP) reanalysis suggest that many high and low pressure systems cross the Beaufort in winter, but not all of these create a near-inertial ice response. Two unusually strong low pressure systems that passed near the array in December 2008 and February/March 2009 were accompanied by elevated levels of near-inertial kinetic energy in the ice. The analysis suggests pressure systems which have a diameter to ground track velocity ratio close to 3/4 of the local inertial period can excite a large near-inertial response in the sea ice. It is conjectured that this results from the combined effect of resonance arising from similar intrinsic timescales of the storm and the local inertial period and from stresses that are able to overcome the damping of sea ice arising from ice-mechanics and damping in the ice-ocean boundary layer. Those systems whose intrinsic times scales do not approach resonance with the local inertial period did not excite a large near- inertial response in the sea ice. From an analysis of two storms in February 2009, and two in December 2008, it appears that wind stresses associated with previous low pressure systems preconditioned the ice pack, allowing for larger near-inertial response during subsequent events

Circulation and Thermohaline Variability of the Hanna Shoal Region on the Northeastern Chukchi Sea Shelf

We analyzed velocity and hydrographic data from 23 moorings in the northeast Chukchi Sea from 2011 to 2014. In most years the eastern side of Hanna Shoal was strongly stratified year-round, while weakly stratified regions prevailed on the shelf south and west of the Shoal. Stratification differences cause differential vertical mixing rates, which in conjunction with advection of different bottom water properties resulted in seasonally varying along-isobath density gradients. In agreement with numerical models, we find that bottom waters flow anticyclonically around the Shoal. Whereas most of the shelf responded barotropically to wind-forcing, there was a strong baroclinic component to the flow field northeast of Hanna Shoal, resulting in no net vertically integrated transport on average. In contrast there is a net eastward transport from west of the Shoal, which implies convergence north of the Shoal. Convergence and along-isobath density gradients may foster cross-shelf exchange north of Hanna Shoal. Modal analyses indicate that the shelf south of the Shoal and Barrow Canyon responded coherently to local and remote winds, whereas the wind-current response around Hanna Shoal was less coherent. Barotropic topographic waves, of ~3-day period, were generated episodically northeast of the Shoal and propagate clockwise around Hanna Shoal, but are blocked from entering Barrow Canyon and are possibly scattered by the horizontally sheared flow and converging isobaths on the western side of the Shoal. Analysis of water properties on the western side of Hanna Shoal suggests that these include contributions from the western and southern portions of the Chukchi Sea