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Browsing by Author "Marinescu, Peter James, author"

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    Latent heating and aerosol-precipitation interactions within mesoscale convective systems
    (Colorado State University. Libraries, 2016) Marinescu, Peter James, author; van den Heever, Susan C., advisor; Kreidenweis, Sonia M., advisor; Eykholt, Richard, committee member; Schumacher, Russ S., committee member
    Two studies are presented in this thesis that focus on understanding cloud processes within simulations of two mesoscale convective system (MCS) events that occurred during the Midlatitude Continental Convective Clouds Experiment (MC3E). Simulations are conducted with the Regional Atmospheric Modeling System (RAMS) and are compared with a suite of observations obtained during MC3E. It is concluded that the simulations reasonably reproduce the two MCS events of interest. Both studies provide information that can assist in the advancement of cloud process parameterizations in atmospheric models. The first study details the microphysical process contributions to latent heating profiles within MCS convective and stratiform regions and the evolution of these profiles throughout the MCS lifetime. Properly representing the distinctions between the latent heating profiles of MCS convective and stratiform regions has significant implications for the atmospheric responses to latent heating on various scales. The simulations show that throughout the MCSs, condensation and deposition are the primary contributors to latent warming, as compared to riming and nucleation processes. In terms of latent cooling, sublimation, melting, and evaporation all play significant roles. Furthermore, it is evident that throughout the MCS lifecycle, convective regions demonstrate an approximately linear decrease in the magnitudes of latent heating rates, while the evolution of latent heating within stratiform regions is associated with transitions between MCS flow regimes. The second study addresses the relative roles of middle-tropospheric and lower-tropospheric aerosol particles on MCS precipitation during the mature stage. A suite of sensitivity simulations for each MCS event is conducted, where the simulations are initialized with different aerosol profiles that vary in the vertical location of the peak aerosol particle number concentrations. Importantly, the total integrated aerosol mass remains constant between the different initialization aerosol profiles, and therefore, differences between the simulated MCS precipitation characteristics can be more directly attributed to the varied vertical location of the aerosol particles. The simulations from both MCS events demonstrate that during the mature stage, the concentrations of lower-tropospheric aerosol particles are the primary factor in determining the intensity of precipitation near the cold pool leading edge, while middle-tropospheric aerosol particles were entrained within convective updrafts, thus altering the cloud droplet properties. However, the aerosol effects on total surface precipitation is not consistent between the two simulated MCS events, suggesting that the MCS structure and environmental conditions play important roles in regulating the impacts of middle-tropospheric and lower-tropospheric aerosol particles on MCS precipitation. Lastly, changes in precipitation processes can result in dynamical feedbacks that further modify, and hence complicate, the net effect of aerosol particles on MCS precipitation. One such feedback process involving the MCS cold pool intensity and updraft tilt is discussed.
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    Observations of aerosol particles and deep convective updrafts and the modeling of their interactions
    (Colorado State University. Libraries, 2020) Marinescu, Peter James, author; van den Heever, Susan C., advisor; Kreidenweis, Sonia M., advisor; Bell, Michael M., committee member; Eykholt, Richard, committee member
    Within cloud updrafts, cloud droplets form on aerosol particles that serve as cloud condensation nuclei (CCN). Varying the concentrations of CCN alters the concentrations of cloud droplets, which in turn modifies subsequent microphysical processes within clouds. In this dissertation, both observational and modeling studies are presented that reduce the uncertainties associated with these aerosol-induced feedback processes in deep convective clouds. In the first study, five years of observations of aerosol particle size distributions from central Oklahoma are compared, and useful metrics are provided for implementing aerosol size distributions into models. Using these unique, long-term observations, power spectra analyses are also completed to determine the most relevant cycles (from hours to weeks) for different aerosol particle sizes. Diurnal cycles produce the strongest signals in every season, most consistently in the accumulation mode and the smallest (diameters < 30 nm) particles. The latter result suggests that these smallest particles may play a more important role in the CCN budget than previously thought. Ultimately, in understanding which, when and why different aerosol particles are present in the atmosphere, we can better assess the impacts that they have on clouds. The types and number of aerosol particles that can serve as CCN depend on the amount of supersaturation, and thus the magnitude of the cloud updraft vertical velocities. However, in situ updraft observations in deep convective clouds are scarce, and other vertical velocity estimates often have uncertainties that are difficult to characterize. In the next study, novel, in situ observations of deep convective updraft vertical velocities from targeted radiosonde launches during the CSU Convective Cloud Outflows and Updrafts Experiment (C3LOUD-Ex) are presented. Vertical velocities of over 50 m s-1 are estimated from radiosonde observations taken in Colorado. Radar data are used to contextualize the radiosonde measurements and to provide an independent estimate of the updraft magnitudes for comparison. These observations are valuable in that they: 1) contribute novel estimates of the vertical velocities within deep convective clouds, 2) demonstrate that in situ observations of vertical velocities complement estimates from other platforms and 3) will allow for better assessments of the supersaturation magnitudes, and thus the amount of CCN that are present within deep convective clouds. While the first two studies focus on observing aerosol particles and updrafts separately, the third study within this dissertation presents simulations of their interactions from an international model intercomparison project. Seven models from different institutions simulated the same case study of isolated deep convective clouds with both high and low CCN concentrations. The range of the responses in updrafts to varying CCN concentrations are calculated for this model suite. Despite the various physical parameterizations that these models utilize, all the models simulate stronger updrafts in the High-CCN simulations from near cloud base through ~8 km AGL, with diverging results above this altitude. The vertical velocity tendency equation is analyzed to explain which processes are causing the consistent and inconsistent updraft responses to varying CCN concentrations amongst the models. The three studies in this dissertation each reduce the uncertainties related to aerosol effects on deep convective cloud updrafts. This work also assisted in motivating the DOE Tracking Aerosol Convection Interactions Experiment (TRACER), which will further connect observational and modeling research to reduce the uncertainties in aerosol-cloud interactions.