Characteristics of Arctic Spring Onset

Abstract:

Each year the Arctic atmosphere experiences a dramatic transition to spring (Arctic spring onset or ASO) that is characterized by a rapid increase in surface air temperature (T2m). The annual timing of ASO, defined in terms of the acceleration of T2m, exhibits strong interannual variability with a bi-modal distribution of onset dates. The horizontal and vertical structure of the atmospheric changes occurring during ASO is investigated through a composite analysis. The associated warming signature is roughly zonally symmetric over Arctic latitudes and extends from the surface upward to the mid-troposphere. Further to the south, ASO is associated with zonally asymmetric warming patterns over the high-latitude continental regions with a common warming signature observed over Northern Siberia (denoted the “critical” warming region). In addition, sub-categories of ASO events exhibit regional warming signatures over Greenland-North American, East Asia, and/or Alaska, respectively. Composite analyses of sea level pressure indicate that the evolution of the surface circulation provides favorable synoptic conditions for producing the observed regional temperature increases. The related advective, diabatic, and adiabatic contributions to the regional warming signatures are assessed via a heat budget analysis.