Nick Szapiro-March 12-School of Meteorology (Defense)

School of Meteorology (Defense)

Impacts of tropopause polar vortices on Arctic sea ice loss

Nick Szapiro

Tuesday, March 12^th

11:00am/NWC 1120

Towards furthering understanding and extending predictions of the polar environment, this thesis explores the variability in Arctic summer sea ice driven by coherent upper-level potential vorticity anomalies common in the Arctic termed tropopause polar vortices (TPVs). A novel restricted regional watershed segmentation and overlap tracking method more robustly defines the spatial shape and time history of TPVs relative to previous methods. Motivated by limitations in artificially limited area models and coarser general circulation models in representing couplings across latitudes, scales, and components, 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 hierarchy of model experiments illustrate sensitivities to local resolution of the representation of TPV structure, connections, and sea ice impacts. These motivate a global, Arctic-refined configuration for CESM-CAM-MPAS to better represent intensities of local interactions, evaluated with subseasonal forecasts. With simple mixed historical and analog initial conditions, summer simulations capture mean polar circulation anomalies and yield competitive sea ice forecasts. Artificial, localized tendencies directly modify TPVs and permit TPV-based sensitivity experiments. Using the formulation, sensitivity experiments with directly modified TPV intensity are conducted to quantify impacts of TPVs on Arctic sea ice. Strongly intensifying cyclonic TPVs in the Arctic can cause less sea ice loss. Coupled multi-scale, thermodynamic, dynamic, and intra-component mechanisms all contribute with coherent patterns. Extensions of the approach may provide qualitative depictions, quantitative sensitivities, and dynamical insights into relationships throughout the Earth system. The aggregated work motivates directions for future process and prediction studies