PD Effects MET

One of the stranger questions on the Met exam. As the ionosphere is charged (ionosphere = sphere of ions, which are charged particles) there is a potential difference (or voltage) between it and the surface of the earth, which is (quite literally) "earthed". Suffice to say that powerful electrical charges, like the lightning that comes from thunderstorms, affect the charge of the surface of the earth and hence the distribution of this electrical field.