Half-century perspectives on North American spring snowline and snow cover associations with the Pacific-North American teleconnection pattern

摘要

Spring (MAM) snow coverage across North America (NA) has significantly declined during the last half-century (1967-2016), with possible linkages to changing behaviors in large-scale atmospheric circulation. In this study, we investigated relationships between intraseasonal, sub-continental NA snow cover characteristics and the Pacific-North American (PNA) teleconnection pattern, which quantifies longwave, ridge-trough fluctuations in the 500 hPa geopotential height (GPH) field over the Northern Hemisphere. Correlation and composite techniques were applied to analyze NA spring and intra-spring snow cover extent (SCE) and snowline (SL) associations with PNA index variations. Results show the PNA pattern to be significantly correlated to interannual SL and SCE during April and climatological spring, particularly over western NA. Anomalous PNA values (i.e. exceeding +/- 1 SD from the index mean) particularly influence transient snow in early/mid-spring. Composites of 500 hPa GPH and low-level air temperature fields suggest that both positive and negative March PNA index anomalies are linked with expansion of western and NA-wide snow cover, while positive (negative) April PNA anomalies yield retreat (advance) to varying magnitudes across sub-continental NA. Seasonal persistence of the PNA pattern is also an important factor in determining regional snow conditions, as negative PNA values in March-April favors above-normal total spring snow coverage, while positive PNA values in these months evoke a slight retreat (advance) that is dependent on negative (positive) phase persistence through May. This study provides additional insight into mid-tropospheric circulation connections to NA springtime snow cover during an era of rapid climate and environmental change.