The discharging current in the atmosphere due to small conductivity of air is known to be 1800A on an average over the globe. Why then does the atmosphere discharge itself completely in due course and become electrically neutral ? In other words, what keeps the atmosphere charged ?

The Earth's surface has a negative surface charge density of 10^(-9)C//m^2 . The potential difference of 400kV between the top of the atmosphere and the surface, results (due to low conductivity of the lower atmosphere) in a current of only 1800 A over the entire globe. If there is no mechanism of sustaining atmospheric electric field, how much time (roughly) would be required to neutralise the Earth’s surface?

The earth's surface has a negative surface charge density of 10^-9C.m^-2 . The potential difference of 400kV between the top of the atmosphere and the surface results (due to the low conductivity of the lower atmosphere) in a current of only 1800 A over the entire globe. If there wre no mechanism of sustaining atmospheric,electric field, how much time (roughly) would be required to neutralise earth's surface? [Radius of earth = 6.37 times 10^6m ]