| Summary: | The Arctic and sea ice cover play fundamental roles in the environment of the Earth system. Improved causal understanding of their changes is needed for meaningful predictions and planning. Among the linkages composing our understanding and predictions, hypothesized mechanisms and historical cases suggest that potentially long-lived, (sub-)synoptic coherent circulation features termed tropopause polar vortices (TPVs) can impact the evolution of Arctic sea ice on daily to seasonal time scales. Diagnostics and causal dynamical experiments are developed to evaluate whether there are mechanisms sufficient for TPVs to significantly impact Arctic summer sea ice loss. A TPV's place, structure, and history are intimately related to its dynamics and associated impacts. A restricted regional watershed segmentation and major correspondence overlap TPV tracking method more robustly defines tracked TPVs' spatial structure (through restricted regional watershed basins with variable shapes and intensities) and time evolution (through similarity overlap with mergers and splits) relative to previous methods. Tracking with a more restrictive definition of lifetime and more robust, variable size, individual cyclonic TPVs can exceed radii of 1000~km, amplitudes of 40~K, and lifetimes of 2 months, coincide with multi-day extreme sea ice loss, and contribute seasonal-scale geographic anomalies. To represent the potential, integrated impacts of TPVs on Arctic sea ice, it is argued that a comprehensive model should resolve TPVs and feedbacks with the larger polar circulation, consistently couple and realistically evolve sea ice, and be computationally tractable. Motivated by limitations in limited-area and coarser general circulation models to satisfy these requirements, the Model for Predictions Across Scales non-hydrostatic atmospheric dynamical core is embedded within the Community Atmospheric Model of the Community Earth System Model (CESM-CAM-MPAS). A global, Arctic-refined atmospheric configuration efficiently provides needed ...
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