Integrating model simulations, paleoclimate proxy simulations, and reanalysis data to delineate synoptic climate patterns at the end of the Little Ice Age

Abstract:

Previous climate reconstructions have shown a marked change in atmospheric circulation patterns following the end of the Little Ice Age (LIA; ~1450-1850 AD). Shifts in these circulation patterns are resulted in a transition from meridional flow during the LIA to more zonal flow following the LIA. This study aims to better understand atmospheric circulation patterns and moisture transport at the end LIA for western North America during the cool season months using newly available climate data from the Coupled Model Intercomparison Project phase 6 (CMIP6) model simulations, Paleoclimate Model Intercomparison Project phase 4 (PMIP4) model simulations, Twentieth Century Reanalysis version 3 reanalysis products, and tree ring paleoclimate reconstructions. Three model outputs from CMIP6 historical experiment and PMIP4 past 1000 experiment were concatenated and averaged across all model runs to produce a continuous climate record spanning the end of the LIA (1840-1869 AD). The climate models were then projected to a 2°x2° grid for statistical analyses. None of the climate models display apparent atmospheric trends from meridional flow to zonal flow during the end of the LIA. However, there were statistically significant correlations between tree ring reconstructed geopotential height and several climate variables including temperature and precipitation rate. Variances and correlations between variances within the tree ring geopotential height reconstructions and CMIP6 climate variables suggest the strength and position of the Aleutian low is responsible for changes in moisture transport and precipitation rates for western North America. Results from this study highlight synoptic atmospheric process responsible for driving moisture transport at the end of the LIA. Understanding the role that synoptic atmospheric processes play in extreme climate events is vital for interpreting both paleoclimate reconstructions and future climate projections.