A possible explanation for the dominant effect of South American thunderstorms on the Carnegie curve

Abstract

The Carnegie curve shows the variation of the vertical electric field near the Earth's surface with Universal Time. The largest of the three maxima in this variation occurs at the time of maximum thunderstorm activity over the Americas, although this is weaker than that over Africa. This paradoxical effect may be explained by the fact that South American thunderstorms are close to the magnetic dip equator, whereas most African thunderstorms occur over the Congo at a higher (Southern) dip latitude. Kartalev et al. [2004. A quantitative model of the effect of global thunderstorms on the global distribution of ionospheric electrostatic potential. Journal of Atmospheric and Solar-Terrestrial Physics 66, 1233–1240.] modeled the global distribution of ionospheric electrostatic potential where the equatorial (within 11 ∘ magnetic latitude of the equator) lower ionosphere accumulates all upward thunderstorm currents into one line—the dip equator. Currents flow on a spherical shell of the magnetic coordinates model, and so change the distribution of the ionospheric potential on a global scale. That global distribution of ionospheric potential determines the vertical electric field near the Earth's surface everywhere. Thus, the Carnegie curve reflects preferentially the longitudinal distribution of thunderstorms within 11 ∘ of the magnetic dip equator.