Rapid Arctic Sea Ice Loss on the Synoptic Time Scale and Related Atmospheric Circulation Anomalies

Large sea ice loss on the synoptic time scale is examined in various subregions in the Arctic as well as the pan-Arctic scale using daily sea ice extent data. It is found that the frequency of large daily sea ice loss (LDSIL) days is significantly correlated with the September sea ice extent over the Beaufort-Chukchi-Siberian Seas, the Laptev-Kara Seas, the Central Arctic and the All-Arctic regions, indicating a link between the synoptic sea ice variability and the interannual variability of the annual minimum sea ice extent. Composite analysis reveals dipoles of anomalous cyclone and anticyclone associated with LDSIL days. Contrary to the well-known Arctic dipole pattern, the dipoles are oriented east-west over the corresponding regions of LDSIL in the Arctic marginal seas, associated with the increasing frequency of occurrence of Rossby wave breaking and atmospheric rivers. The anticyclones of the dipoles are persistent and nearly quasi-stationary, reminiscent of blocking. The anomalous poleward flow between the cyclone and the anticyclone enhances the poleward transport of heat and water vapor in the lower troposphere. Although enhanced downward shortwave radiation, associated with reduced cloud fraction, is found in some regions, the more robust and pronounced signal is the enhanced downward longwave radiation in the regions of increasing column water vapor, indicating the importance of atmospheric rivers in LDSIL events. Lead/lag composites with respect to the onset of LDSIL episodes reveal precursor wavetrains spanning the midlatitude. The wavetrains have predominantly zonal energy propagation in the mid-latitude and do not show a clear link to tropical or subtropical forcing.