The Interannual to Decadal Pacific Arctic Climate Regime Interpreted By a New, Mobile Alaskan Arctic Front Index

The orientation and strength of the large-scale atmospheric pressure gradient between the Pacific Arctic and subarctic is a key control of energy, mass, and momentum exchange between these regions. Such sustained pressure variations and changes in space and time affect the region’s climate with corresponding marine and terrestrial biogeochemical implications.

The Alaskan Arctic Front (AAF) index has previously been used to describe the strength of the meridional sea-level pressure (SLP) gradient between the northern Bering, Chukchi, and Beaufort seas and southern Bering Sea and north Pacific Ocean. This index represented the difference between a stationary gridpoint in the climatological center of the winter mean Beaufort High and Aleutian Low, respectively. To build upon this index by capturing the spatial variations in the surface pressure gradient through time, we apply an objective approach to ERA5 SLP fields, allowing northern node maximum SLP and southern node minimum SLP gridpoint extrema to migrate, respectively, across the Pacific Arctic seas and Bering Sea and adjacent landmasses.

Analysis of this new AAF index from 1959-2021 reveals distinct periods of variability. For example, during 1998-2010, a positive AAF was associated with an enhanced Beaufort High and suppressed Aleutian Low yielding weakened Bering Strait poleward ocean transport and more Siberian Arctic coastal sea ice. The more recent 2011-2021 decade saw an intensity reversal in these pressure features (i.e., suppressed Beaufort High and enhanced Aleutian Low), leading to a negative AAF tendency. It is noted that fluctuations in the Northern Hemisphere modes of atmospheric variability tend to modulate AAF strength. For example, when the Arctic Oscillation (Pacific North American pattern) was predominantly in positive phase as in 1998-2010 (2011-2021) the AAF was stronger (weaker) further signaling periodic forcing by synoptic-scale Arctic or Pacific atmospheric processes. Implications of AAF variability on both the region’s upper mixed layer conditions and marine biophysical environment will also be discussed.