Variability and trends of Pacific Arctic atmospheric circulation according to an updated Alaska Blocking Index

Alaska’s climate has undergone rapid change during the last half century. This is supported by multiple lines of observational evidence that show, for instance, increased air temperatures and liquid precipitation across much of the state, with widespread environmental impacts on the terrestrial environment (e.g., tundra productivity and wildfire activity) and marine system (e.g., sea ice growth and seasonality). While physical and biological changes are increasingly well-monitored, the local-to-large-scale climate drivers of these changes remain poorly understood across space and time. Motivated by an effort to better understand how local atmospheric variability drives these statewide surface climatic changes, we present an updated analysis of the Alaska Blocking Index (ABI; McLeod et al., 2018) that spans 1948–2020. The ABI describes the mean 500 hPa geopotential height pattern from 55–75°N, 125–180°W and therefore the magnitude of ridging or troughing across the area with good qualitative agreement regarding directional windflow and heat and moisture advection along the boundaries of the circulation pattern. In addition to discussing index changes and improvements since its initial development, the monthly variability and linear trends of the ABI will be quantified for the full and sub-periods. An overlapping correlation analysis will be conducted to assess relationships between monthly ABI variability and changes and the occurrence of daily ABI extremes (i.e., ABI values at least one standard deviation above and below the 1981–2010 mean). Finally, a correlation analysis of the ABI against Alaska air temperature and precipitation patterns at the climate division scale will be undertaken to provide insights on spatiotemporal variability and linkages between the overlying circulation pattern and surface climate. The update to the ABI dataset and subsequent climatological evaluation will provide a framework for characterizing and quantifying Pacific Arctic atmospheric circulation conditions through the lens of a single regional circulation metric, setting the stage for future research aimed at quantifying the role of circulation-driven forcing on regional Arctic system components.