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

Authors: Evan Montpellier*, , Peter T. Soulé, Appalachian State University, Paul A. Knapp, University of North Carolina at Greensboro, Baker Perry, Appalachian State University
Topics: Climatology and Meteorology
Keywords: climate reconstruction, upper-level flow, synoptic climatology, Montana, alpine larch
Session Type: Poster
Day: 4/13/2018
Start / End Time: 10:00 AM / 11:40 AM
Room: Napoleon Foyer/Common St. Corridor, Sheraton, 3rd Floor
Presentation File: No File Uploaded


Variability in synoptic-scale circulation patterns plays an important role in modulating mesoscale meteorology during the climatological summer in the mid-latitudes. 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 we reconstruct seasonal (JJA) upper-level (500 hPa) atmospheric flow for four geographic locations in the mid-latitudes using an alpine larch (Larix lyallii Parl.) tree ring chronology derived from the Selway-Bitterroot Wilderness of western Montana. Our goal is to assess the long term (~400 year) stability of upper-level flow in order to place the observed trends in a historical context. We found significant relationships between alpine larch tree growth and upper level flow patterns derived from the North American Reanalysis Dataset. Spatial pattern correlations indicate that tree growth increases when meridional flow and zonal flow are strong west (r = 0.504, p = 0.001, n = 37) and north (r = 0.642, p < 0.001, n = 37) of the study site, respectively. Tree growth declines when meridional flow and zonal flow are strong east (r = -0.497, p = 0.001, n = 37) and south (r = -0.584, p < 0.001, n = 37) of the study site, respectively. Using the leave-one-out method, we calibrated and verified our linear regression models between upper-level flow and tree growth. Our 445 year climate reconstructions of 500 hPa flow show that ridging is becoming more intense over time while troughs are declining in intensity.

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