A two-dimensional numerical mesoscale model, which ic1udes radiative and turbulent transfers, has been constructed to study the formation, development and dissipation of coastal stratus cloud under an inversion. In the model, the delta-Eddington and emissivity approximations are used for the solar and thermal radiative transfers, respectively. K-theory parameterization is adopted for the turbulent transfer. Ground surface temperature and moisture are predicted using the methods of Deardorff (1977, 1978). This model is applied to a domain which extends 180 km into sea and 240 km inland horizontally and about 2 km from the earth1s surface vertically. A bare, flat soil surface is assumed. As a prelude to the study of the stratus cloud, sea breeze circulations with and without a temperature inversion have been investigated. The model without an inversion yields speeds of the sea breeze front which are close to the values that have been observed under insolation and other meteorological conditions similar to those used in the model. The presence of an inversion causes the depth of sea breeze circulation to be shallower and its inland penetration during the evening hours to be weaker compared to the case without inversion; however, the basic structure of the sea breeze circulation is unaffected by the inversion. The model has been used to study the growth, development and dissipation of stratus cloud under an inversion in the west coast region of the United States. The effects of large scale motions on these processes have also been examined. Cloud parameters such as the times of initial formation and of dissipation inland, the maximum distance of inland penetration, the maximum liquid water path and the cloud-top height are affected in the presence of such large scale motions; for example, both the maximum liquid water path and the cloud-top height are appreciably enhanced - by about a factor of two - when large scale westerly winds (U[subscript g]=5mfs, V[subscript g]=0) are present compared to the case when U[subscript g]=V[subscript g]=0. The cloud parameters predicted by the model are in close correspondence with existing observations in southern California. It is found that the sea breeze circulation is not appreciably affected by the presence of moderate amounts of stratus cloud. While advection plays a dominant role in the horizontal development of the stratus cloud inland, radiative processes (cooling and heating) are observed to govern the vertical growth and dissipation of the cloud layer. Vertical growth is influenced by the rate of radiative cooling at cloud-top. Because of the combined effects of solar and surface heating, the stratus inland is observed to dissipate more rapidly during the morning hours than the cloud over the ocean where surface heating is minimal. / Graduation date: 1984

Typescript. / Theses (Ph. D.)--University of Hawaii at Manoa, 1978. / Bibliography: leaves 85-89. / Microfiche. / viii, 89 leaves ill

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Microfiche copy available in Archives and Science. / Bibliography : leaves 99-101. / M.S.

No description available.

Cloud-wind interactions play an important role in long-lived multiphase flows in various galaxy-related contexts (e.g., galactic fountains and winds, cosmological cold-mode accretion, or multiphase tails of satellites). These interactions occur when a volume-filling hot phase, the wind, moves relative to a cool pressure-confined body of gas, the cloud. The conditions necessary for clouds to survive the destructive effects of mixing and become entrained within the wind (i.e. for the relative velocity to be removed), has been a long-standing problem. This problem has received particular attention in the context of galactic winds: cloud entrainment is expected to play a critical role in explaining observed multiphase structure in these outflows. This thesis investigates a mechanism for facilitating cloud survival in the context of rapid cooling, which we hereafter term TRML (turbulent radiative mixing layer) entrainment. Our investigation leverages numerical (magneto)hydrodynamic ENZO-E simulations of a cool (≲10⁴𝐊) clouds that encounter a hot (≳10⁶𝐊), supersonic winds. We begin by introducing a simple entropy-based formalism to characterize the role of mixing in cloud-wind interactions, and demonstrate example applications using simulations. Under this formalism, the high-dimensional description of the interaction's state at a given time is simplified to the joint distribution of mass over pressure (𝑃 ) and entropy (𝐾=𝑃𝞀^-𝜸). As a result, this approach provides a way for (empirically and analytically) quantifying the impact of different initial conditions and sets of physics on the interaction's evolution. We find that mixing predominantly alters the distribution along the 𝐾 direction and illustrate how the formalism can be used to model mixing and cooling for fluid elements originating in the cloud. We further confirm and generalize a previously suggested survival criterion for clouds undergoing TRML entrainment, and demonstrate that the shape of the cooling curve, particularly at the low temperature end, can play an important role in controlling condensation. Moreover, we discuss the capacity of our approach to generalize such a criterion to apply to additional sets of physics, and to build intuition for the impact of subtle higher order effects not directly addressed by the criterion. Despite the fact that the competition the between turbulent mixing and radiative cooling dictate the outcome of the cloud-wind interaction (as well as many observable properties), turbulence in these interactions remains poorly understood. Thus, we next investigate the turbulence that arises for clouds undergoing TRML entrainment. To obtain robust results, we employ multiple metrics to characterize the turbulent velocity, 𝝂_turb. We find four primary results. First, 𝝂_turb manifests clear temperature dependence. Initially, 𝝂_turb roughly matches the scaling of sound speed on temperature. In gas hotter than the temperature where cooling peaks, this dependence weakens with time until 𝝂_turb is constant. Second, the relative velocity between the cloud and wind initially drives rapid growth of 𝝂_turb. As it drops (from entrainment), 𝝂_turb starts to decay before it stabilizes at roughly half its maximum. At late times cooling flows appear to support turbulence. Third, the magnitude of 𝝂_turb scales with the ratio between the hot phase sound crossing time and the minimum cooling time. Finally, we find tentative evidence for a length-scale associated with resolving turbulence. Under-resolving this scale may cause violent shattering and affect the cloud's large-scale morphological properties. Finally, we propose a new criterion for clouds to survive interactions with the wind in the via TRML entrainment, and validate it with simulations. Properties of TRML entrainment are generally understood to be controlled by ratio between the relevant dynamical and cooling timescales 𝝉_dyn / 𝝉_cool. Previously proposed survival criteria disagree about the size of the smallest surviving cloud by factors of up to ∼100. These criteria primarily differ in their choice of 𝝉_{\rm cool}$; perplexingly, the choices most consistent with the well-modeled micro-scale physics observed in shear-layer studies are associated with less-accurate criteria. We present a new criterion which agrees with previous fitting formulae but is based on a set of simple physical principles. Whereas prior criteria link 𝝉_dyn with the cloud destruction timescale, our new criterion links it to the characteristic cloud-crossing timescale of a hot-phase fluid element. This choice leads to scaling relations that are more physically consistent with shear-layer studies. Additionally, we illustrate that discrepancies among previous criteria primarily emerged due to the choices of simulation conditions, rather than commonly-cited differences in the definition of cloud destruction.

The atmospheres of exoplanets are being characterised in increasing detail by observational facilities and will be examined with even greater clarity with upcoming space based missions such as the James Webb Space Telescope (JWST) and the Wide Field InfraRed Survey Telescope (WFIRST). A major component of exoplanet atmospheres is the presence of cloud particles which produce characteristic observational signatures in transit spectra and influence the geometric albedo of exoplanets. Despite a decade of observational evidence, the formation, dynamics and radiative-transport of exoplanet atmospheric cloud particles remains an open question in the exoplanet community. In this thesis, we investigate the kinetic chemistry of cloud formation in hot Jupiter exoplanets, their effect on the atmospheric dynamics and observable properties. We use a static 1D cloud formation code to investigate the cloud formation properties of the hot Jupiter HD 189733b. We couple a time-dependent kinetic cloud formation to a 3D radiative-hydrodynamic simulation of the atmosphere of HD 189733b and investigate the dynamical properties of cloud particles in the atmosphere. We develop a 3D multiple-scattering Monte Carlo radiative-transfer code to post-process the results of the cloudy HD 189733b RHD simulation and compare the results to observational results. We find that the cloud structures of the hot Jupiter HD 189733b are likely to be highly inhomogeneous, with differences in cloud particle sizes, number density and composition with longitude, latitude and depth. Cloud structures are most divergent between the dayside and nightside faces of the planet due to the instability of silicate materials on the hotter dayside. We find that the HD 189733b simulation in post-processing is consistent with geometric albedo observations of the planet. Due to the scattering properties of the cloud particles we predict that HD 189733b will be brighter in the upcoming space missions CHaracterising ExOPlanet Satellite (CHEOPS) bandpass compared to the Transiting Exoplanet Space Survey (TESS) bandpass.