Characterizing precipitation and improving radar rainfall estimates over
the Southern Ocean using ship-borne disdrometer and dual-polarimetric
C-band radar
Abstract
Large satellite discrepancies and model biases in representing
precipitation over the Southern Ocean (SO) are related directly to the
region’s limited surface observations of precipitation. To help address
this knowledge gap, the study investigated the precipitation
characteristics and rain rate retrievals over the remote SO using
ship-borne data of the Ocean Rainfall And Ice-phase precipitation
measurement Network disdrometer (OceanRAIN) and dual-polarimetric C-band
radar (OceanPOL) aboard the Research Vessel (RV) Investigator in the
Austral warm seasons of 2016 to 2018. Seven distinct synoptic types over
the SO were analyzed based on their radar polarimetric signatures,
surface precipitation phase, and rain microphysical properties.
OceanRAIN observations revealed that the SO precipitation was dominated
by drizzle and light rain, with small-sized raindrops (diameter
< 1 mm) constituting up to 47 % of total accumulation.
Precipitation occurred most frequently over the warm sector of
extratropical cyclones, while concentrations of large-sized raindrops
(diameter > 3 mm) were prominent over synoptic types with
colder and more convectively unstable environments. OceanPOL
observations complement and extend the surface precipitation properties
sampled by OceanRAIN, providing unique information to help characterize
the variety of potential precipitation types and associated mechanisms
under different synoptic conditions. Raindrop size distributions (DSD)
measured with OceanRAIN over the SO were better characterized by
analytical DSD forms with two-shape parameters than single-shape
parameters currently implemented in satellite retrieval algorithms. This
study also revised a rainfall retrieval algorithm for C-band radars to
reflect the large amount of small drops and provide improved radar
rainfall estimates over the SO.