Comparing satellite and ground-based observations of cloud occurrence
over high southern latitudes
Abstract
The 2B-CLDCLASS-LIDAR R05 (2BCL5) and the raDAR/liDAR (DARDAR) satellite
retrievals of cloud occurrence are compared as a function of altitude
and latitude. The largest disparities are observed at low altitudes over
high southern latitudes. These datasets are cross referenced to
ground–based measurements from the Atmospheric Radiation Measurement
(ARM) West Antarctic Radiation Experiment (AWARE) campaign at McMurdo
Station, Antarctica. Compared to AWARE observations, both 2BCL5 and
DARDAR underestimate cloud occurrence below 1.5 km, with 2BCL5 and
DARDAR distinguishing roughly one third of cloud occurrences observed by
AWARE at 0.5 km. While DARDAR identifies greater cloud occurrences than
2BCL5 below 1.5 km, cloud occurrence values for the two datasets have
similar differences relative to ground-based measurements. Therefore,
the DARDAR retrievals of greater cloud occurrence at low altitudes are
likely due to a larger quantity of false positives associated with radar
ground clutter or attenuated lidar retrievals. DARDAR cloud occurrences
match better with AWARE than 2BCL5 above 5 km. However, the likely
underestimation of ground-based measurements at higher altitudes
suggests DARDAR may underestimate high level cloud occurrence. Finally,
both datasets indicate the presence of liquid containing clouds at
temperatures within the homogeneous freezing regime, despite the fact
that the ECMWF-AUX dataset implemented in their processing clearly
indicates temperatures below -38 °C. Using AWARE radiosonde (ECMWF-AUX)
temperature data, we find that 2BCL5 detects 13.3% (13.8%) of mixed
phase clouds below -38 °C, while DARDAR detects 5.7% (6.6%) of mixed
phase and 1.1% (1.3%) of liquid phase clouds below -38 °C.