Abstract

Low-level winds over Antarctica are overwhelmingly controlled by the local orography. They, in turn, exert a large control on sea ice formation and transport.

In this work, we investigate the relationship between Antarctic sea ice and the parameterized Orographic Gravity Wave Drag (OGWD) in the UK Earth System Model (UKESM). We present results from sensitivity tests performed using the UKESM -CMIP6 historical runs.

In these simulations, the partition between the “flow-blocking” component and the “gravity wave” component of the OGWD parameterization was altered to simulate “flow-over” and “flow-blocking” regimes. These experiments show that sea ice strongly responds to changes in the orographic gravity wave drag. The strong sea ice decline simulated by the control run from 1980 to 2015 is delayed by 15-20 years (across the ensemble members) in our flow-blocking regime simulation. Conversely, in the flow-over regime simulation, sea ice begins declining about 10 years earlier than in the control run.

The systematic response of the coupled system suggests the existence of a dynamical relationship between sea ice and OGWD . To explain this, we investigate changes in surface circulation and total ocean surface stress across the different flow regimes.