Constraining and Characterizing the size of Atmospheric Rivers: A
perspective independent from the detection algorithm.
Abstract
Atmospheric rivers (AR) are large and narrow filaments of poleward
horizontal water vapor transport. Because of its direct relationship
with horizontal vapor transport, extreme precipitation, and overall AR
impacts over land, the AR size is an important characteristic that needs
to be better understood. Current AR detection and tracking algorithms
have resulted in large uncertainty in estimating AR sizes, with areas
varying over several orders of magnitude among different detection
methods. We develop and implement five independent size estimation
methods to characterize the size of ARs that make landfall over the west
coast of North America in the 1980-2017 period and reduce the range of
size estimation from ARTMIP. ARs that originate in the Northwest Pacific
(WP) (100$^\circ$E-180$^\circ$E)
have larger sizes and are more zonally oriented than those from the
Northeast Pacific (EP)
(180$^\circ$E-240$^\circ$E). ARs
become smaller through their life cycle, mainly due to reductions in
their width. They also become more meridionally oriented towards the end
of their life cycle. Overall, the size estimation methods proposed in
this work provide a range of AR areas (between
7x10$^{11}$m$^2$ and 10$^{13}$ m$^2$) that is
several orders of magnitude narrower than current methods estimation.
This methodology can provide statistical constraints in size and
geometry for the AR detection and tracking algorithms; and an objective
insight for future studies about AR size changes under different climate
scenarios.