Browsing by Subject "Parameterization"
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Item Parameterization and Statistical Analysis of Hurricane Waves(2014-05-03) Mclaughlin, Patrick WilliamRecently, Gulf coast communities have experienced significant damage from landfalling hurricanes. While the effects of hurricane surge on coastal communities have been examined and better defined, risk of damage due to hurricane waves is less quantified. This thesis presents the Wave Response Function (WRF) methodology. Hurricanes are parameterized in the form of non-dimensional equations incorporating key physical hurricane parameters. The non-dimensional equations are then combined with a fully developed sea state cap (Young and Verhagan 1996) to form the open coast and bay methodologies. This approach yields root mean square errors (RMSE) ranging from 0.01-0.46 m, with the majority of points below 0.3 m. This approach yields small bias values. The WRF method was compared to Hurricane Ike data (Kennedy et al. 2011) and yielded RMSE of 0.67 meters despite the higher depths of the recording stations. The WRF method was also compared to Taylor?s (2012) parameterized wave equations, with mean RMSE improvements ranging from 0.13-0.32 m. Once WRF coefficients are adjust to minimize RMSE at each station under consideration, extreme value analysis via the Joint Probability Method with Optimal Sampling (JPM-OS) was conducted. When applied to Panama City, FL the JPM-OS methodology yielded extreme value statistics for 179 stations of interest. Maps detailing the spatial extents of the 100 and 1000 year maximum wave event were created using ArcGIS.Item Radiative Effects of Dust Aerosols, Natural Cirrus Clouds and Contrails: Broadband Optical Properties and Sensitivity Studies(2013-07-09) Yi, BingqiThis dissertation aims to study the broadband optical properties and radiative effects of dust aerosols and ice clouds. It covers three main topics: the uncertainty of dust optical properties and radiative effects from the dust particle shape and refractive index, the influence of ice particle surface roughening on the global cloud radiative effect, and the simulations of the global contrail radiative forcing. In the first part of this dissertation, the effects of dust non-spherical shape on radiative transfer simulations are investigated. We utilize a spectral database of the single-scattering properties of tri-axial ellipsoidal dust-like aerosols and determined a suitable dust shape model. The radiance and flux differences between the spherical and ellipsoidal models are quantified, and the non-spherical effect on the net flux and heating rate is obtained over the solar spectrum. The results indicate the particle shape effect is related to the dust optical depth and surface albedo. Under certain conditions, the dust particle shape effect contributes to 30% of the net flux at the top of the atmosphere. The second part discusses how the ice surface roughening can exert influence on the global cloud radiative effect. A new broadband parameterization for ice cloud bulk scattering properties is developed using severely roughened ice particles. The effect of ice particle surface roughness is derived through simulations with the Fu-Liou and RRTMG radiative transfer codes and the Community Atmospheric Model. The global averaged net cloud radiative effect due to surface roughness is around 1.46 Wm-2. Non-negligible increase in longwave cloud radiative effect is also found. The third part is about the simulation of global contrail radiative forcing and its sensitivity studies using both offline and online modeling frameworks. Global contrail distributions from the literature and Contrail Cirrus Prediction Tool are used. The 2006 global annual averaged contrail net radiative forcing from the offline model is estimated to be 11.3 mW m^(-2), with the regional contrail radiative forcing being more than ten times stronger. Sensitivity tests show that contrail effective size, contrail layer height, the model cloud overlap assumption, and contrail optical properties are among the most important factors.