| Summary: | 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
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