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Browsing by Author "Dodson, Jason B., author"

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    Comparison of convective clouds observed by spaceborne W-band radar and simulated by cloud-resolving atmospheric models
    (Colorado State University. Libraries, 2014) Dodson, Jason B., author; Randall, David, advisor; Birner, Thomas, committee member; Maloney, Eric, committee member; Chandrasekar, V., committee member
    Deep convective clouds (DCCs) play an important role in regulating global climate through vertical mass flux, vertical water transport, and radiation. For general circulation models (GCMs) to simulate the global climate realistically, they must simulate DCCs realistically. GCMs have traditionally used cumulus parameterizations (CPs). Much recent research has shown that multiple persistent unrealistic behaviors in GCMs are related to limitations of CPs. Two alternatives to CPs exist: the global cloud-resolving model (GCRM), and the multiscale modeling framework (MMF). Both can directly simulate the coarser features of DCCs because of their multi-kilometer horizontal resolutions, and can simulate large-scale meteorological processes more realistically than GCMs. However, the question of realistic behavior of simulated DCCs remains. How closely do simulated DCCs resemble observed DCCs? In this study I examine the behavior of DCCs in the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) and Superparameterized Community Atmospheric Model (SP-CAM), the latter with both single-moment and double-moment microphysics. I place particular emphasis on the relationship between cloud vertical structure and convective environment. I also emphasize the transition between shallow clouds and mature DCCs. The spatial domains used are the tropical oceans and the contiguous United States (CONUS), the latter of which produces frequent vigorous convection during the summer. CloudSat is used to observe DCCs, and A-Train and reanalysis data are used to represent the large-scale environment in which the clouds form. The CloudSat cloud mask and radar reflectivity profiles for CONUS cumuliform clouds (defined as clouds with a base within the planetary boundary layer) during boreal summer are first averaged and compared. Both NICAM and SP-CAM greatly underestimate the vertical growth of cumuliform clouds. Then they are sorted by three large-scale environmental variables: total preciptable water (TPW), surface air temperature (SAT), and 500hPa vertical velocity (W500), representing the dynamical and thermodynamical environment in which the clouds form. The sorted CloudSat profiles are then compared with NICAM and SP-CAM profiles simulated with the Quickbeam CloudSat simulator. Both models have considerable difficulty representing the relationship of SAT and clouds over CONUS. For TPW and W500, shallow clouds transition to DCCs at higher values than observed. This may be an indication of the models' inability to represent the formation of DCCs in marginal convective environments. NICAM develops tall DCCs in highly favorable environments, but SP-CAM appears to be incapable of developing tall DCCs in almost any environment. The use of double moment microphysics in SP-CAM improves the frequency of deep clouds and their relationship with TPW, but not SAT. Both models underpredict radar reflectivity in the upper cloud of mature DCCs. SP-CAM with single moment microphysics has a particularly unrealistic DCC reflectivity profile, but with double moment microphysics it improves substantially. SP-CAM with double-moment microphysics unexpectedly appears to weaken DCC updraft strength as TPW increases, but otherwise both NICAM and SP-CAM represent the environment-versus-DCC relationships fairly realistically.
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    Observations of atmospheric rivers with CloudSat CPR and Aqua AMSR-E
    (Colorado State University. Libraries, 2008) Dodson, Jason B., author; Vonder Haar, Thomas H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
    "Atmospheric rivers" are filamentary water vapor structures, occurring primarily over oceans, thousands of kilometers long that form along the leading edge of cold fronts. These "rivers" are an important link between weather and climate by transporting large amounts of moisture (on the order of 108kgs-1) through the middle latitude regions and causing heavy precipitation events along coastal regions. The CloudSat satellite, launched 28 April 2006, is designed to measure vertical cloud structure and fill a long-existing gap in satellite observations. CloudSat and Aqua observed 22 river events (with multiple overpasses for each river) over a period from November 2006 to April 2007. In this project, CloudSat CPR observations of cloud location and cloud type are used along with moisture observations from Aqua AMSR-E to create a preliminary average profile of vertical cloud structure within atmospheric rivers. The CloudSat observations (using Aqua moisture and precipitation measurements as references) are first presented for case studies of four river events out of the total 22 events. The observations show deep convective (vertical extent more than 7km) and nimbostratus cloud (vertical extent more than 4km) bands more than 100km in horizontal width occurring in three of the four cases, and shallow convection (vertical extent less than 4km) occurring in the fourth case. Deep layer clouds occur most frequently during the river's early and middle stages, and these deep clouds usually erode into low and (sometimes) high cloud bands in the river's later life. The CloudSat measurements are then combined into composite frequency plots to show the typical cloud locations within and near the river with respect to the river's water vapor structure. Frequency plots are presented for all 92 overpasses along with categories of overpasses based on time of occurrence within the rivers' life spans to give a preliminary time evolution of cloud structure. Then, scatter plots comparing moisture structure properties with cloud structure properties are displayed to show any possible relationship between moisture and clouds. Finally, some statistics about the frequency of occurrence of different cloud types within the rivers are presented.