Radiative Effect of Clouds around Darwin

Posted by on Sep 1, 2015 in Abstracts, Abstracts 2014

Reconciling Ground-Based and Space-Based Estimates of the Frequency of Occurrence and Radiative Effect of Clouds around Darwin, Australia


The objective of this paper is to investigate whether estimates of the cloud frequency of occurrence and associated cloud radiative forcing as derived from ground-based and satellite active remote sensing and radiative transfer calculations can be reconciled over a well  instrumented active remote sensing site located in Darwin, Australia, despite the very different  viewing geometry and instrument characteristics. It is found that the ground-based radar-lidar  combination at Darwin does not detect most of the cirrus clouds above 10 km (due to limited  lidar detection capability and signal obscuration by low-level clouds) and that the CloudSat radar  – Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) combination underreports the 0 hydrometeor frequency of occurrence below 2 km height, due to instrument limitations at these  heights. The radiative impact associated with these differences in cloud frequency of occurrence  is large on the surface downwelling shortwave fluxes (ground and satellite) and the top-of atmosphere upwelling shortwave and longwave fluxes (ground). Good agreement is found for  other radiative fluxes. Large differences in radiative heating rate as derived from ground and  satellite radar-lidar instruments and RT calculations are also found above 10 km (up to 0.35 Kday-1 for the shortwave and 0.8 Kday-1  for the longwave). Given that the ground-based and  satellite estimates of cloud frequency of occurrence and radiative impact cannot be fully  reconciled over Darwin, caution should be exercised when evaluating the representation of  clouds and cloud-radiation interactions in large-scale models and limitations of each set of  instrumentation should be considered when interpreting model-observations differences.