A numerical study of near-inertial motions in the Mid-Atlantic Bight area induced by Hurricane Irene (2011)

Abstract

Abstract. Hurricane Irene generated strong near-inertial currents (NICs) in ocean waters when passing over the Mid-Atlantic Bight (MAB) of the US East Coast in late August 2011. It is demonstrated that a combination of valuable field data and detailed model results can be taken advantage of to study the development and decay mechanism of this event. Numerical results obtained with the Regional Oceanic Modeling System (ROMS) are shown to agree well with the field data. Both computed and observed results show that the NICs were significant in most areas of the MAB region except in the nearshore area where the stratification was totally destroyed by the hurricane-induced strong mixing. Based on the energy budget, it is clarified that the near-inertial kinetic energy (NIKE) was mainly gained from the wind power during the hurricane event. In the deepwater region, NIKE was basically balanced by the vertical turbulence diffusion (40 %) and downward divergence (33 %), while in the continental shelf region, NIKE was mainly dissipated by the vertical turbulence diffusion (67 %) and partially by the bottom friction (24 %). Local dissipation of NIKE due to turbulence diffusion is much more closely related to the rate of the vertical shear rather than the intensity of turbulence. The strong vertical shear at the offshore side of the continental shelf led to a rapid dissipation of NIKE in this region.