title: Persistence of pressure patterns over North America and the North Pacific since AD 1500.
abstract: Changes in moisture delivery to western North America are largely controlled by interrelated, synoptic-scale atmospheric pressure patterns. Long-term records of upper-atmosphere pressure and related circulation patterns are needed to assess potential drivers of past severe droughts and evaluate how future climate changes may impact hydroclimatic systems. Here we develop a tree-ring-based climate field reconstruction of cool-season 500 hPa geopotential height on a 2° × 2° grid over North America and the North Pacific to AD 1500 and examine the frequency and persistence of preinstrumental atmospheric pressure patterns using Self-Organizing Maps. Our results show extended time periods dominated by a set of persistent upper-air pressure patterns, providing insight into the atmospheric conditions leading to periods of sustained drought and pluvial periods in the preinstrumental past. A striking shift from meridional to zonal flow occurred at the end of the Little Ice Age and was sustained for several decades.
authors.affiliation: Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
authors.forename: Erika K
authors.initials: EK
authors.lastname: Wise
authors.affiliation: Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Dannenberg