Abstract
The influence of the Madden-Julian oscillation (MJO) on Antarctic sea ice extent has not been extensively explored. This study investigates intraseasonal variability of the sea ice extent induced by the MJO and its physical mechanism. During austral winter, the sea ice extent anomaly exhibits considerable melting and freezing as the MJO evolves. Numerical experiments and the Rossby wave theory show that the high-latitude circulation anomalies in response to the MJO are responsible for the sea ice change. The MJO-induced Rossby waves propagate into the Southern Hemisphere through the northerly ducts over the western Indian Ocean–central Africa and the Maritime Continent. The MJO-induced circulation anomalies reach high latitudes and lead to anomalous meridional temperature advection, causing changes in the sea ice extent. The time difference between the meridional wind and sea ice anomalies is ~5 days. As the MJO moves, the sea ice extent anomaly also exhibits eastward-migrating behavior. Strong sea ice melting in the total anomaly is synchronous to the evolution of the MJO, suggesting the practical usefulness of the location of the MJO for the prediction of the sea ice decrease.
Highlights
To investigate the circulation response to the MJO, a numerical experiment is performed using an atmospheric linear baroclinic model (LBM) with T42 horizontal resolution and 20 vertical levels in sigma coordinates
This study shows that the variation in Antarctic sea ice extent is driven by the austral winter MJO
The 25 × 25 km gridded ice concentration data provided in the National Snow and Ice Data Center (NSIDC) are used
Summary
To investigate the circulation response to the MJO, a numerical experiment is performed using an atmospheric linear baroclinic model (LBM) with T42 horizontal resolution and 20 vertical levels in sigma coordinates. To imitate the MJO convection in the experiment, the areas where the OLR is greater (lesser) than 10 (−10) W m−2 in the composite map are chosen as diabatic cooling (heating). Since the MJO convection is not spatially stationary, the diabatic forcing is given for the first 7 days and turned off. Note that the simulated circulation fields have weaker intensity than that observed due to the switching-off of the forcing. If the forcing is persistently applied, the intensity is similar to that of the observation, the circulation pattern in the subtropics is somewhat different than that indicated from the observatio
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