Aleutian Low-Beaufort Sea Anticyclone (ALBSA) index, 1940-2025

The Aleutian Low-Beaufort Sea Anticyclone, or "ALBSA", is a daily, 4-point index combining two orthogonal 850 hPa (hectopascal) differences (one meridional, one zonal). Collectively, this captures the variability in the North Pacific/Pacific Arctic tropospheric circulation. The purpose is to track the juxtaposition of the Aleutian Low and Beaufort High pressure centers, specifically the strength/position of the former and the meridional dipole associated with the latter. The utility of the index is its sensitivity to advection events from the North Pacific into the Arctic and how the pattern of circulation steers that advection. It represents the variability of the NPI, and also includes information specific to the advection across Alaska and up through the Bering Strait, and the East Siberian/Chukchi/Beaufort Seas. To date, the index has been used to evaluate interannual variability in the timing of seasonal cryospheric transitions and ecosystem phenology of the North Pacific and Pacific Arctic, as well as subseasonal variability in Bering Sea ice expansion/retreat and aerosol transport events. The first data set in this series was calculated using the ECMWF Reanalysis v5 (ERA5) (see methods) for January 1940 through May 2025. We intend to update the series periodically, approximately annually in June because the index is most useful September through May, to append the most recent year.