Identifying and Characterizing Southern California’s Atmospheric Rivers



02/05/2016 - 12:45pm


Sarah Harris

On synoptic timescales, atmospheric rivers (ARs) are channels of high
water vapor flux within the low atmospheric that move moisture towards
midlatitudes. These features are important to coastal mountainous areas,
such as North America’s west coast, due to orographic forcing that often
leads to high intensity rainfall. Several North American studies on ARs
focus on the Pacific Northwest, as this is where the highest frequency
of ARs occurs, whereas areas such as southern California (SCA) that
experience relatively few AR landfalls per year are overlooked. However,
in SCA ARs are responsible for a large proportion of the region’s annual
precipitation total as well as some of the area’s highest intensity
rainfall. As SCA is prone to both drought as well as
precipitation-induced hazards and is dependent on few rainfall events to
provide much of the annual precipitation total, any modification of
storm frequency and/or intensity may dramatic affect the region.
Understanding the characteristics and mechanisms of high-impact AR
events affecting SCA is crucial for proper forecasting and hazard

Daily total precipitable water (TPW) fields from reanalysis are used to
identify ARs affecting North America’s west coast using an AR
identification algorithm. ARs are then categorized according to landfall
region. Composites of atmospheric variables during AR events and
according to region of landfall are created using additional reanalysis
fields. Composites are created for the days prior to, on the day of, and
after AR landfall and help to determine spatial characteristics and
features of ARs impacting varying regions. This allows us to determine
the atmospheric makeup behind ARs affecting SCA, including possible
indications as to the mechanisms behind their initiation as well as