The relationship between precipitation and its spatial pattern in the
trades observed during EUREC4A
Abstract
Trade wind convection organises into a rich spectrum of spatial
patterns, often in conjunction with precipitation development. Which
role spatial organisation plays for precipitation and vice versa is not
well understood. We analyse scenes of trade wind convection scanned by
the C-band radar Poldirad during the EUREC4A field campaign to
investigate how trade wind precipitation fields are spatially organised,
quantified by the cells’ number, mean size and spatial arrangement, and
how this matters for precipitation characteristics. We find that the
mean rain rate, i.e. the amount of precipitation in a scene, and the
intensity of precipitation (mean conditional rain rate) relate
differently to the spatial pattern of precipitation. While the amount of
precipitation increases with mean cell size or number, as it scales well
with the precipitation fraction, the intensity increases predominantly
with mean cell size. In dry scenes, the increase of precipitation
intensity with mean cell size is stronger than in moist scenes. Dry
scenes usually contain fewer cells with a higher degree of clustering
than moist scenes. High precipitation intensities hence typically occur
in dry scenes with rather large, few and strongly clustered cells, while
high precipitation amounts typically occur in moist scenes with rather
large, numerous and weakly clustered cells. As cell size influences both
the intensity and amount of precipitation, its importance is
highlighted. Our analyses suggest that the cells’ spatial arrangement,
correlating mainly weakly with precipitation characteristics, is of
second order importance for precipitation across all regimes, but could
be important for high precipitation intensities and to maintain
precipitation amounts in dry environments.