Abstract
Abstract. It is commonly accepted, that cloud formation is caused by the humidity flux directed from the warm bottom atmospheric layers towards the cold dry heights, and the transportation mechanism in stable stratification is due to development of so-called turbulent boundary layer. The transportation of vapor can be described by buoyancy profile, and requires two significant characteristics of the atmosphere. The first is the heat and water vapor fluxes from the underlying surface which has been investigated by Smith (1988). The second is the temperature profile in the atmosphere, which is usually approximated and parameterized in various ways, because the exact solution is complicated and difficult to use. In this paper we construct a theory of three-component gas mixture, containing air, vapor, and water droplets. This model can be applied for the internal cloud region. Later we use buoyancy to investigate the dynamics of cloud formation, taking into account condensation of the water vapor inside the cloud. The obtained results suggest a typical time of 10 h required for development of intense cloud layer over a sea surface.
Highlights
Troposphere is the lowest atmospheric layer up to approximately 15 km height, which is responsible for climate formation, which in turn affects all sides of human life
Accounting intensive turbulent stirring inside the convective layer, the value of buoyancy is transforming towards a constant b=b0 profile, while in the initial stable dry atmosphere the profile was following a linear function b=N 2z, where the frequency N was introduced earlier
The released heat in the cloud results in remarkable increase of the buoyancy flux above the condensation point. Such behaviour of buoyancy flux was observed by Bretherton (1997), and it is responsible for the cloud formation
Summary
Since the relative densities of the main atmospheric gases (N2, O2, Ar, CO2, and some others) are invariable within the troposphere, the dry component of the air is usually taken as a gas with atomic mass 29 a.m.u. In this work we use thermodynamics of a three-component gas mixture with phase transitions, and apply this model for dynamics of cloud formation and vapor transport in presence of gravity. Significant temperature drop between these to parts leads to intensive local stirring on the top of the layer, which is the main mechanism of the layer growth This model requires continuous flux of water vapor and heat from the underlying surface. The buoyancy model can describe the boundary layer growth below the dew point, phase transitions inside the cloud make the model more complicated Such model in the cloud requires thermodynamical description, where the temperature profile and the water vapor content affect each other. 4. Section 4 introduces the buoyancy model with vapor condensation and investigates dynamics of the cloud formation, i.e. the growth of the upper cloud boundary with time. The last section will summarize the results and briefly describe limitations of the model
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