مدل‌سازی مدار الکتریکی جهانی جوّ با استفاده از داده‌های WWLLN

A model of the global atmospheric electric circuit has been presented that based on more realistic and up-to-date data and models for current generators and atmospheric conductivity. The World Wide Lightning Location Network data has been employed to estimate distribution of thunderstorms as the main sources of electric current in global electric circuit by means of the clustering approach. Thunderstorm clusters are combined with aircraft observations of electrified clouds to determine the contribution of thunderstorm and shower clouds in total conduction (Wilson) currents. The electrical conductivity of atmosphere results from the concentration of small ions and varies with height, because the ion sources, i.e. cosmic rays, radon isotopes and terrestrial radioactivity, and the primary sink, i.e. aerosol particles all have height profile. The CRAC:CRII, that is one of the most commonly used atmospheric ionization models, is employed to calculate the cosmic rays induced ionization rate, and radioactivity induced ionization rate is determined using an exponential vertical profile combined with an up-to-date data for surface Radon 222 ionization rate, as the main source of ionization agent in boundary layer. Considering the aerosol particles to be monodisperse, the variation with height be represented by an exponential vertical profile. Based on these models and considering simple and well-known models for ion-aerosol attachment coefficients and ions mobility, the 3-dimentioal distribution of the atmospheric conductivity is calculated. It is found that near the earth the conductivity profile resembles radioactivity induced ionization rate, while at higher altitudes it looks like the cosmic rays counterpart. From the air conductivity profile, the columnar resistance, namely the resistance of a unit area column of atmosphere from the orographic surface to the ionosphere, is found and shown that the major contribution to the columnar resistance is the resistance of the boundary layer, where the ion production rate is relatively small and the loss rate is large. Total atmospheric resistance is the total resistance of all the column resistances summed in parallel over the world, taking into account the change with latitude of the area of each grid element. Production of total resistance and total conduction current gives us ionosphere’s electric potential, while electric potential at the surface of the earth is assumed to be zero. The global distribution of the downward air-earth current density that is independent of altitude, while affected by the orography and geographical coordinates via columnar resistance is calculated and it is found that current density above land is larger than above sea. As the columnar resistance on high mountains is smaller, more air–earth current flows over those areas of the earth than others, in general. Atmospheric electric field, as one of the most studied elements of the global electric circuit, related to the local electrical conductivity and current density is evaluated using Ohm’s law and its global distribution at different altitudes is shown. The model described in the present research is validated by comparing the global diurnal variations of the electric field with the well-known Carnegie Curve, which represents the mean diurnal variability of the global electric circuit. The model confirms that the global atmospheric electric activity peaks daily ~20 UTC and it is found that overall variation of electric fields at 3 positions are same and similar to that of the Carnegie curve.