| In an effort to investigate the late-time electrical properties of the atmosphere, a computer model was developed that provided time-dependent numerical solutions to the continuity equation of electric current as a function of an impressed current source. This computer model was used to examine the electrical behavior of the atmosphere in the vicinity of a bipolar thunderstorm, and the results revealed that there are numerous similarities between the time-averaged electrical properties and the steady-state properties of an active thunderstorm. From the Maxwell continuity equation of electric current, a simple analytical equation was derived that expresses a thunderstorm's average current contribution to the global electric circuit in terms of the generator current within the thundercloud, the intracloud lightning current, the cloud-to-ground lightning current, the altitudes of the charge centers, and the conductivity profile of the atmosphere. This equation was found to be nearly as accurate as the more computationally intensive numerical model, even when it is applied to a thunderstorm with a reduced conductivity thundercloud, a time-varying generator current, a varying flash rate, and a changing lightning mix. This equation is then applied to data obtained beneath a thunderstorm, and an estimate of this thunderstorm's contribution to the global electric circuit is presented. In addition, data from measurements taken above several thunderstorms is analyzed using this analytical equation, and a relationship is shown for the time-averaged cloud-to-ground lightning current and the net upward current produced by each of the thunderstorms. |
