Temporal variations of the conduction current density during fair weather days in Israel

Abstract

Ground-based measurements of the atmospheric conduction current density were conducted on Mount Hermon in northern Israel (33°18′N 35°47.2′E, 2050 m a.s.l). The aim was to measure the conduction current diurnal behavior during days that are defined meteorologically as fair weather days. Results from 86 selected fair weather days show an average value of 0.9 pA/m2 downward, and a double oscillation behavior of the conduction current density with two maxima – a morning peak due to local effect and an evening peak due to global effect, with lower values in between. Fourier transform analysis applied to the continuous data shows the two maxima peaks under the daily background level. The conduction current density, together with the fair weather vertical electric field was used to calculate the fair weather mean conductivity behavior (based on Ohm's law). The conductivity shows minimum values during local noon hours when the station is assumed to be within the boundary layer and high conductivity values during the night hours when the station is above the boundary layer. This is likely due to the respective diurnal changes in concentrations of aerosol particles. A WRF simulation of a single fair weather day was conducted in order to determine the meteorological regime and the boundary layer height and is presented to support the hypothesis that conductivity values depend, at least in part, on the height of the boundary layer relative to the station.