Cold fronts are a primary feature of the day-to-day variability of
weather in the midlatitudes, and feature in conceptual extratropical cyclone
models alongside the dry intrusion airstream. Here the climatological frequency
and spatial distribution of the co-occurrence of these two features are quantified, and the differences in ...
Cold fronts are a primary feature of the day-to-day variability of
weather in the midlatitudes, and feature in conceptual extratropical cyclone
models alongside the dry intrusion airstream. Here the climatological frequency
and spatial distribution of the co-occurrence of these two features are quantified, and the differences in cold front characteristics (intensity, size, and
precipitation) when a dry intrusion is present or not are calculated. Fronts
are objectively identified in the ECMWF ERA-Interim dataset for the winter
seasons in each hemisphere and split into 3 sub-types: central fronts (within a cyclone area); trailing fronts (outwith the cyclone area but connected to a
central front); and isolated fronts (not connected to a cyclone). These are then
associated with dry intrusions identified using Lagrangian trajectory analysis.
Trailing fronts are most likely to be associated with a DI in both hemispheres,
and this occurs more frequently in the western parts of the major storm track
regions. Isolated fronts are linked to DIs more frequently on the eastern ends
of the storm tracks, and in the subtropics. All front types, when co-occurring
with a DI, are stronger in terms of their temperature gradient, are much larger
in area, and typically have higher average precipitation. Therefore, climatologically the link with DIs increases the impact of cold fronts. There are some
differences in the statistics of the precipitation for trailing and isolated fronts
that are further investigated in Part II of this study.