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The role of clouds in reflecting solar radiation to space and thereby reducing surface heating is of critical importance to climate. Combustion processes that produce greenhouse gases also increase cloud condensation nuclei (CCN) concentrations which in turn increase cloud drop concentrations and thereby cloud albedo. A calculation of cloud susceptibility, defined in this work as the increase in albedo resulting from the addition of one cloud drop per cubic centimeter (as cloud liquid water content remains constant), is made through satellite remote sensing of cloud drop radius and optical thickness. The remote technique uses spectral channels of the Advanced Very High Resolution Radiometer (AVHRR) instrument on board the NOAA polar orbiting satellites. Radiative transfer calculations of reflectance and effective surface and cloud emissivities are made for applicable sun and satellite viewing angles, including azimuth, at various radii and optical thicknesses for each AVHRR channel. Emission in channel 3 (at 3.75 μm) is removed to give the reflected solar component. These calculations are used to infer the radius and optical thickness giving the best match to the satellite measurements. The effect of the atmosphere on the signal received by the satellite is included in the analysis. Marine stratus clouds are a focus of this work. As well as being important modifiers to climate, they are cleaner than continental clouds and so likely to be of higher susceptibility. Analysis of several stratus scenes, including some containing ship tracks, supports this expectation.

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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

Thesis (Ph. D.)--University of Oklahoma, 1997. / Includes bibliographical references (leaves 125-128).

Thesis (Ph. D.)--University of Oklahoma, 1997. / Includes bibliographical references (leaves 125-131).

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