Abstract
Here, we analyze the inter-relationships between weather types (WTs) and
atmospheric rivers (ARs) around Aotearoa New Zealand (ANZ), their
respective properties, as well as their combined and separate influence
on daily precipitation amounts and extremes. Results show that ARs are
often associated with 3-4 WTs, but these WTs change depending on the
regions where ARs landfall. The WTs most frequently associated with ARs
generally correspond to those favoring anomalously strong westerly wind
in the mid-latitudes, especially for southern regions of ANZ, or
northwesterly anomalies favoring moisture export from the lower
latitudes, especially for the northern regions.
WTs and ARs show strong within-type and inter-event diversity. The
synoptic patterns of the WTs significantly differ when they are
associated with AR occurrences, with atmospheric centers of actions
being shifted so that moisture fluxes towards ANZ are enhanced.
Symmetrically, the location, angle, and persistence of ARs appear
strongly driven by the synoptic configurations of the WTs. Although
total moisture transport shows weaker WT-dependency, it appears strongly
related to zonal wind speed to the south of ANZ, or the moisture content
of the air mass to the north. Finally, WT influence on daily
precipitation may completely change depending on their association, or
lack thereof, with AR events. WTs traditionally considered as favorable
to wet conditions may conceal daily precipitation extremes occurring
during AR days, and anomalously dry days or near-climatological
conditions during non-AR days.