The PNA pattern across the Boreal region of North America and its implication for global ocean-atmospheric teleconnection patterns during the past 2,000 years

English Abstract:

The hydroclimate changes during the last 2,000 years are interpreted after spatially filtering the pollen-based paleoclimate reconstructions of total annual precipitation (ANNP). The use of a spatial filter based on the local Moran’s I statistic allows for better interpretation of regional atmospheric circulation patterns responsible for past hydroclimate variability across North America.

Minimum solar and high volcanic activity may have contributed to more complex regional hydroclimate patterns during the LIA with an opposing pattern of wet/dry conditions in the western and eastern boreal region suggestive of a positive phase of the Pacific North American (+PNA) pattern associated with a dominant El Nino state-like circulation, a negative North Atlantic Oscillation (-NAO) and a negative Atlantic Multidecadal Oscillation (–AMO), patterns which are also present during the Dark Ages Cold Period (DAC).

Conversely, the two warm periods, the Medieval Warm Period (MWP) and Roman Warm Period (RWP) are more similar hydro-climatically than the two cold periods (DAC and LIA). There is evidence for a La Nina state-like circulation, a positive North Atlantic Oscillation (+NAO) and a positive Atlantic Multidecadal Oscillation (+AMO) state that likely dominated both periods, although the MWP was generally drier than the RWP. The western and eastern boreal regions show similar wet/dry conditions suggesting a more zonal Pacific North American (-PNA) pattern during both the RWP and MWP as compared to the DAC and LIA.