ISSN:
1573-1472
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
,
Physics
Notes:
Abstract A numerical model is developed to simulate convective stratus cloud formation over the sea. The model is based on quasi-steady state moist plumes advecting over an area of increasing sea-surface temperature with the sea warmer than the air, but it is also a good approximation for non-steady states whenever the model is matched to air-sea temperature differences. Combining the effects of upward transfer of heat and moisture fluxes as well as adiabatic cooling, stratus cloud forms and spreads downward in this field. The depth of the convective field, the sea surface temperature gradient, the liquid water content at cloud top, and the horizontal pressure gradient are the four controlling parameters for the convective field. Alternatively, the wind speed, air-sea temperature difference, and the mixing ratio of the air, derived variables in this treatment, can be taken, with the depth, as the basic parameters. The entity type of convective model used here has the advantage that it models the transport and modification of air parcels and hence provides a method for studying drop size development in stratus clouds. It also uses relationships derived from water tank experiments with plumes and tested in dry convection and so needs no parameters specific to each situation. Its most important feature, however, is that the mean motion of plumes, rather than turbulent diffusion, transports the moisture. The upward growth and erosion of a temperature step increase to produce an inversion can be attributed to liquid water present in haze drops or cloud drops, rather than to turbulent diffusion. Radiative transfer is not a necessary requirement, but may either enhance or slow down the process.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00164329
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