Mid-latitude clouds and precipitation are strongly modulated by synoptic scale circulations and in particular by extratropical cyclones. In these systems, they tend to be concentrated along frontal…

The National Aeronautics and Space Administration (NASA) awarded a $315,074 grant to the University of Wisconsin System to study the 3D structure and frequency of occluded extratropical cyclones and their impact on cloud and precipitation patterns. The research aims to use observations from the CloudSat and CALIPSO satellites to analyze how cloud and precipitation distributions evolve during the occlusion process and how they are influenced by large-scale environmental factors. The findings will provide an observational reference to evaluate how well climate models represent these processes. This work supports NASA's CloudSat and CALIPSO Science Team recompete requirements to enhance atmospheric and climate science through utilization of these satellite datasets.

Mid-latitude clouds and precipitation are strongly modulated by synoptic scale circulations and in particular by extratropical cyclones. In these systems, they tend to be concentrated along frontal boundaries. As cyclones evolve, frontal boundaries also evolve and eventually a thermal ridge connecting the peak of the warm sector to the cyclone center develops and grows, a process known as occlusion. Occlusions can have a devastating impact over land as they are associated with heavy snowfall, and often strong winds. Although there exists an extensive literature on the subject of occlusions, little is known about how their 3D structure and frequency might change in a changing climate. Present understanding suggests that the 3D structure associated with occlusion is fundamentally dependent upon latent heat release, i.e. clouds and precipitation play an important role in this process, and yet general circulation models still have difficulties representing them adequately. By using a newly developed automated occlusion detection technique, which we will apply to NASA merra-2 reanalysis, we propose to construct transects of clouds and precipitation across the occluded quadrant of cyclones, using cloudsat precipitation and combined cloudsat-calipso cloud detection profile observations. This will be achieved using a proven compositing technique that helps alleviate the sample size limitation issues. Over the past decade or so, cloudsat-calipso observations have provided a wealth of information on how clouds and precipitation are distributed across warm and cold fronts and their sensitivity to the synoptic scale conditions. We propose to add occluded structures to this climatology of frontal clouds and precipitation. This 10+ years global climatology will then be used to explore the sensitivity of cloud and precipitation distributions in occlusions to large scale conditions, such as the environmental moisture in the warm sector, close to the surface and aloft, the cyclone intensity, and the properties of the thermal ridge, its length and thermodynamic characteristics. These results will provide an observational reference for global numerical models evaluation. In particular, we will explore whether NASA merra-2 and giss-modele represent the evolution of cloud and precipitation during the occlusion, and their sensitivity to the large scale environment. This evaluation will in turn help US determine the future frequency and strength of occluded extratropical cyclones in a changing climate. To summarize, the proposal will address the following questions: 1) what is the horizontal and vertical distribution of clouds and precipitation in and around occluded thermal structures, and how do clouds and precipitation vary as a function of changes in occlusion properties and environment? 2) can gcms reproduce the formation of a canonical occluded structure given that such formation depends upon latent heating that occurs at scales that are not resolved at current model resolution? Can they represent clouds and precipitation in occluded quadrants and their sensitivity to the large scale environment? This proposal will address the NRA a.30 cloudsat and calipso science team RE-compete requirement that the work greatly enhances the state of atmospheric and climate science through the substantive utilization of cloudsat and calipso by conducting a phenomenological study of fundamental cloud and precipitation processes and evolution and more specifically focus on hydrologic processes in the context of weather and climate variability .