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CR prepress abstract   -  DOI: https://doi.org/10.3354/cr01592

Reconstructing summer upper-level flow in the northern Rocky Mountains using an Alpine larch (Larix lyallii Parl.) tree-ring chronology

Evan E. Montpellier*, Peter T. Soulé, Paul A. Knapp, L. Baker Perry

*Corresponding author:

ABSTRACT: Mid-latitude mesoscale weather during climatological summer is strongly influenced by fluctuations in synoptic-scale circulation patterns. Previous research has linked Arctic amplification to alterations in summer synoptic climatology, leading to more extreme weather events in the mid-latitudes. In this study, seasonal (JJA) upper-level (500 hPa) atmospheric flow is reconstructed in the mid-latitudes using an alpine larch (Larix lyallii Parl.) tree-ring chronology sampled from western Montana. Significant relationships were found between alpine larch radial growth and upper-level flow patterns derived from the North American Regional Reanalysis Dataset (1979–2015). Meridional and zonal flow that manifest in ridging is associated with enhanced radial growth of alpine larch (i.e. meridional flow west (r = 0.504, p = 0.001) and zonal flow north (r = 0.642, p < 0.001) of the study site). Meridional and zonal flow associated with troughing results in decreased radial growth (i.e. meridional flow east (r = –0.497, p = 0.001) and zonal flow south (r = –0.584, p < 0.001) of the study site). Using the leave-one-out method, a linear regression model was calibrated and verified between a Principal Components Analysis score derived from measurements of upper-level flow in western North America and alpine larch tree growth. The 444-year climate reconstruction of summer 500 hPa flow suggest that ridging is becoming more intense over the western United States and Canada since the 1980s.