Characterizing Arctic Spring Onset

Abstract

he high-latitude atmosphere experiences a rapid state transition during Arctic spring onset (ASO) with distinct warming in surface 2-m air temperature (T2m) occurring over broad geographical regions. Three methods are tested to optimally isolate this transition: The first two, the time derivative and the radius of curvature (RoC) methods, identify periods of large T2m acceleration. The third technique, the two-phase linear regression model, identifies a transition from an approximately steady winter state to a warming spring state. Although all three methods are largely successful in isolating the state transition associated with ASO, the RoC method is most effective in capturing the most rapid temperature increases and is adopted to define ASO in the study.Statistical analyses indicate that the annual ASO timing is roughly bimodal with strong interannual variability but no significant long-term trends. Composite time evolution analyses of ASO uncover a critical warming region over northern Siberia common to most events. Several subcategories of ASO events are identified in which distinct warming signatures are also observed in the Greenland?North American, East Asian, and Alaskan sectors. The characteristic synoptic structures associated with these events are isolated via a parallel composite analysis of sea level pressure. These analyses provide initial evidence that, during ASO, the synoptic evolutions of semipermanent surface pressure systems (oceanic lows and continental highs) provide favorable conditions for rapid regional advective and diabatic warming in the lower troposphere.