Contrasting trends in short-lived and long-lived mesoscale eddies in the
Southern Ocean since the 1990s
Abstract
Mesoscale eddies play an important role in both momentum and heat
balances in the Southern Ocean. Previous studies have documented an
increasing intensity of the Southern Ocean eddy field during recent
decades; however, it is still unclear whether the mesoscale eddies with
different lifetimes have different temporal variations. Using satellite
altimeter observations from 1993 to 2020, we find that the increasing
trend in the intensity of eddies is dominated by long-lived eddies (with
lifetimes ≥ 90 days), whose amplitude has increased at a rate of
~2.8% per decade; the increase is concentrated
downstream of topography. In contrast, short-lived eddies (with
lifetimes < 90 days) do not appear to have a significant trend
in their amplitudes since the early 1990s. An energy conversion analysis
indicates that the increased baroclinic instabilities of the mean flows
associated with topography are responsible for the amplitude increase of
the long-lived eddies.