  As a result of their important role in weather and the global hydrological
cycle, understanding atmospheric rivers' (ARs) connection to synoptic-scale
climate patterns and atmospheric dynamics has become increasingly important. In
addition to case studies of two extreme AR events, we produce a December
climatology of the three-dimensional structure of water vapor and O3 (ozone)
distributions associated with ARs in the northeastern Pacific from 2004-2014
using MERRA-2 reanalysis products. Results show that positive O3 anomalies
reside in dry intrusions of stratospheric air due to
stratosphere-to-troposphere transport (STT) behind the intense water vapor
transport of the AR. In composites, we find increased excesses of O3
concentration, as well as in the total O3 flux within the dry intrusions, with
increased AR strength. We find that STT O3 flux associated with ARs over the NE
Pacific accounts for up to 13 percent of total Northern Hemisphere STT O3 flux
in December, and extrapolation indicates that AR-associated dry intrusions may
account for as much as 32 percent of total NH STT O3 flux. This study
quantifies STT of O3 in connection with ARs for the first time and improves
estimates of tropospheric ozone concentration due to STT in the identification
of this correlation. In light of predictions that ARs will become more intense
and/or frequent with climate change, quantifying AR-related STT O3 flux is
especially valuable for future radiative forcing calculations.
