Feb 13, 2020
Lightning is not well understood.
Prevailing ideas see circulating water vapor moving up and down through clouds in a process of convection. The condensation theory presupposes that water is heated by the Sun until it evaporates, rising into the air where it collects into clouds, finally cooling enough to condense into liquid. Earth’s gravity then pulls it back to the surface where the cycle repeats.
Consensus opinions assert that water droplets collide during convection, knocking electrons off one another, thus creating charge separation. Electrons accumulate in the lower portion of a cloud, thereby imparting a negative charge. As droplets that have lost electrons rise, they carry positive charges into the top of the cloud. Charge separation is the key, causing clouds to act like a capacitor, storing electric charge.
Charges across the cloud capacitor cause an electric field to increase, stressing the atmospheric insulator’s ability to keep them separate. A high enough potential across the two conductive regions causes the atmospheric insulator to fail and the capacitor will short circuit, suddenly releasing its stored energy.
It is that phenomenon that most likely contributes to lightning discharges. Stored electrical energy in the clouds and in the ground overcome the atmosphere’s ability to keep the two charges separate, so they reach out to each other as “leader strokes.” When the two lightning leaders meet, a circuit between the clouds and the ground (or between one cloud and another) is completed and a burst of electric current flashes along the conductive pathway.
Human beings are not equipped to sense electric and magnetic fields. However, the feel of a breeze or the chill of a wind are readily detected. This can lead to an idea that all weather is convective in nature, depending only on the rise of hot air and the fall of its cold analog. In consensus viewpoints, lightning appears to be an aftereffect of that convection, so the electrical interactions between Earth and its surrounding charged plasma sheath are overlooked.
Electrical phenomena are scalable: they demonstrate characteristics that are alike whether the spark spans a millimeter or thousands of kilometers. Tiny electric arc scars are seen with a microscope on insulators and semiconductors. As previous Picture of the Day articles reveal, those arc scars can be seen on the faces of planets and moons, as well.
The Thunderbolts Picture of the Day is generously supported by the Mainwaring Archive Foundation.