Thermodynamic and dynamic drivers underlying extreme central Arctic sea ice loss

Abstract. Variability of sea ice in the central Arctic is pivotal to the entire Arctic region, yet in-depth understanding of its characteristics and underlying mechanisms remains elusive. We investigate the characteristics and mechanisms of extremely low sea ice concentration (SIC) events (ELSEs) in the central Arctic by analysing the reanalysis data. First, we define the area where climatological SIC exceeds 90 % as the central Arctic. Moreover, this paper primarily investigates the relative variations in sea ice, i.e., the standardized sea ice anomalies, which highlight common characteristics of sea ice variations. Based on the Empirical Orthogonal Function method, we identify the first two dominant modes of relative variations of ELSEs within the central Arctic: the East–West Seesaw Mode (EWSM) and the Pacific–Atlantic Seesaw Mode (PASM). By using the sea ice budget diagnostic method for comparison, it is found that the thermodynamic (dynamic) contributions of EWSM and PASM account for 68 % (32 %) and 72 % (28 %), respectively. Thermodynamically, both the EWSM and the PASM are dominated by local diabatic heating, with their maintenance and intensification facilitated by water vapor and cloud feedbacks. Dynamically, sea ice advection plays an important role in the formation of the two modes. In particular, the upper tropospheric divergence anomalies over the North Pacific induce Rossby wave train that modulate the EWSM. Overall, this study elucidates the key drivers of ELSEs in the central Arctic, which enriches our knowledge of the complex cryosphere processes.