Seminar: Friday, 25 April, 3:10 pm, EN6085
The Southern Ocean region is an important but often-overlooked part of the earth's climate system that is associated with significant uncertainties in models. It is amongst the cloudiest locations on the planet, with frequent cyclone activity and a high fraction of relatively low clouds containing significant amounts of supercooled water. Clouds in this region are often poorly represented in climate models; in particular, modeled shortwave albedos are typically lower than what is observed such that too much radiation reaches the ocean surface. As a step toward addressing this issue, we seek to quantify the organization, vertical structure, and radiative characteristics of clouds over the Southern Ocean using a combination of active and passive satellite sensors.
This study uses geostationary and polar orbiter satellite data (ISCCP) to classify clouds into large-scale, recurring cloud regimes (sometimes referred to as weather states) using a statistical clustering method. Radar and lidar observations from CloudSat and CALIPSO are then used to examine the vertical structure, microphysics, precipitation characteristics, and radiative heating of these large-scale regimes. It is found that the regimes associated with ascent in cyclones have the highest shortwave cloud radiative effect at the top-of-atmosphere, but the low-cloud regimes, by virtue of their high frequency of occurrence, dominate both top-of-atmosphere and surface shortwave effects. Finally, radiation errors in one particular CMIP5 model (the Australian Community Climate and Earth System Simulator) are assessed using a hybrid model-observation clustering method.