Moisture transport axes and their relation to atmospheric rivers and
warm moist intrusions
Abstract
The water vapor transport in the extratropics is mainly organized in
narrow elongated filaments. These filaments are referred to with a
variety of names depending on the contexts. When making landfall on a
coastline, they are generally referred to as atmospheric rivers; when
occurring at high latitudes, many authors regard them as warm moist
intrusions; when occurring along a cold front and near a cyclone core,
the most commonly used term is warm conveyor belt. Here, we propose an
algorithm that detects these various lines of moisture transport in
instantaneous maps of the vertically integrated water vapor transport.
The detection algorithm extracts well-defined maxima in the water vapor
transport and connects them to lines that we refer to as moisture
transport axes. By only requiring a well-defined maximum in the vapor
transport, we avoid imposing a threshold in the absolute magnitude of
this transport (or the total column water vapor). Consequently, the
algorithm is able to pick up moisture transport axes at all latitudes
without requiring region-specific tuning or normalization. We
demonstrate that the algorithm can detect both atmospheric rivers and
warm moist intrusions. Atmospheric rivers sometimes consist of several
distinct moisture transport axes, indicating the merging of several
moisture filaments into one atmospheric river. Finally, we showcase the
synoptic situations and precipitation patterns associated with the
occurrence of the identified moisture transport axes in example regions
in the low, mid, and high latitudes.