The objective of this project is to utilize the extensive atmospheric boundary layer measurements obtained over the Arctic sea ice during the MOSAiC year combined with available modeling resources to further evaluate, develop, and understand the proposed Arctic Inversion conceptual model, or paradigm, of the lower troposphere over Arctic regions covered by sea ice, including its substructures and a few key processes. Previous studies suggest that the atmospheric boundary layer over Arctic sea ice can conceptually be described as an ubiquitous Arctic inversion (AI) separating the free troposphere above from the sea-ice boundary below and extending to heights of 1000-1500 m. This typically stable AI inhibits vertical mixing, but is modified by the Arctic boundary layer (ABL) nearest the surface through local frictional or buoyant processes and the cloud-forced mixed layer (CML) aloft forced by cloud-top radiative cooling. When the forcing of the ABL is sufficiently strong, the ABL becomes a surface-based mixed layer (SML). While the CML and SML are generally distinct, they at times appear to couple with each other, producing a near-neutral layer from the surface to cloud top. This coupled SML-CML may allow significant transport of heat, moisture, momentum, aerosols, and trace gases. The formation of low-level wind jets (LLJs) within the AI also modifies the turbulent structure within the AI, possibly enhancing the vertical transport. An automatic technique for identifying mixed-layers, inversions, and AI tops using sounding data from MOSAiC has been devised, and is being used to deduce the characteristics and temporal variability of these Arctic boundary-layer features. Statistical analyses show the seasonal variability of these features, and their variability with other features, such as Arctic cyclones. For instance, a significant lowering of the AI appears to occur in the warm sector of transient cyclones, while SMLs are at times forced by enhanced downwelling LW radiation associated with warm sector clouds in cyclones without any solar radiation. Cold-air advection over a previously-warmed snow cover can destabilize the lower troposphere, producing SMLs and even horizontal roll vortices when occurring in conjunction with LLJs. The MOSAiC data has been classified as being under a cyclone or an anticyclone, and the cyclone time periods are further classified as to the cyclone developmental stage and the cyclone mesoscale sector passing over the MOSAiC Central Observatory. These classifications are being used to provide composite boundary-layer structure for each cyclone stage/sector and for the anticyclones, including cloud macro and microphysical structure and coupled/decoupled status.