نوع مقاله : مقاله پژوهشی
نویسنده
گروه فیزیک، دانشکده علوم، دانشگاه محقق اردبیلی، اردبیل، ایران.
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسنده [English]
The atmospheric conductivity, the most important parameter in atmospheric electricity, is modeled using up to date data and models for ionization agents. Then the space charge production in clouds layer is investigated based on this conductivity model. In the troposphere and the lower stratosphere, cosmic rays and radioactive materials are primarily sources of ionization and ions production in the Earth’s atmosphere. Here, the ionization rate induced by cosmic rays is calculated based on the Monte Carlo CRAC: CRII model that is able to compute it in the atmosphere at any given location and time, provided the energy spectrum of incoming cosmic rays is known. The ionization rate caused by radioactive materials, mainly in atmospheric boundary layer, is determined in virtue of a semi-empirical model which is based on more recent data presented in literature. The profile of ionization rate induced by cosmic rays as well as total ionization rate are provided and their dependence on latitude is thoroughly investigated. In order to calculate the atmospheric conductivity, the data was obtained for ionization rate is utilized alongside the existing models for ion-ion recombination coefficient, ion attachment coefficients to aerosols and droplets, and ions mobility. Dependence of atmospheric conductivity on various parameters is inspected. It is shown that, close to the Earth’s surface, conductivity decreases when the altitude increases, but at higher altitudes its behavior is different; conductivity increases with altitude and reaches a maximum at top of the troposphere. One of the main goals of this paper is to investigate the space charge production at the boundaries of clouds layer (strati-form). To do so, the charge continuity and Poisson equations are employed to obtain an equation that relates space charge to vertical derivative of atmospheric conductivity. Then, it is shown that the flow of global electric current through the cloud causes space charges to be created at the upper and lower boundaries of clouds layer. This occurs because cloud commutativity is about an order of magnitude greater than the conductivity of clear air. Then, when global current flows through the boundaries, according to Gauss’s law, space charge accumulation takes place because of existence of a gradient in electric field inside and outside of cloud boundaries. Calculations show that the upper cloud edge acquires positive charge and the lower cloud edge obtains negative charge, with the upper layer charge density being slightly larger. It is also shown that the amount of space charge in both boundaries depends on latitude as well as to cloud altitude and to its thickness. The different charge accumulation at upper and lower boundaries of cloud layer bears a resemblance to an electric dipole moment that can be defined using standard definition. The values of these dipole moments depend on the characteristics of the cloud and the dipole moments per square meter of various clouds that are calculated for various clouds. Finally, a brief discussion is presented based on the findings. The presence of space charge at cloud layer boundaries is equivalent to charging of droplets there. Charging of droplets can affect cloud microphysics, i.e. it can affect droplet activation, droplet evaporation, and droplet-droplet collision which usually results in collection efficiency enhancement. Enhancing the collection efficiency can also shorten the droplet growth time scale. Moreover, the acquired electrical structure of clouds layer reinforces the fact that they should be considered as an important element in modeling global electric circuit.
کلیدواژهها [English]
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