Happy #WeatherWednesday weather heads! Today we bring positivity, despite a rather potent weather system in place in the Deep South part of the country. Positive lightning that is!
Lightning is the discharge of charged droplets and ice crystals in clouds, most often cumulonimbus (conventional thunderstorms). Most lightning occurs between clouds, and a good amount of lightning occurs between the ground and parts of the storm cloud closest to the ground (CG – cloud to ground). These occur with negative charge buildup near the bottom of the cumulonimbus discharging with positive particles at the surface.
A less common type of lightning bolt is the positive lightning bolt! These are CG bolts, but can be ten times more powerful than the typical “negative” CG discharge. While the negatively charged particles from particle collisions and electron handoffs build up in the BOTTOM of the storm, the particles that lost electrons build up in the TOP of the storm due to mass loss. The discharge happening from the positive rich part of the storm to the ground is the “positive” bolt.
Given that the top of the storm is tens of thousands of feet above the ground, multiple times higher than the negative rich part of the storm, the positive lightning channel can be discharged from the surface farther away from the storm (see this type of arc in photo). This is what’s colloquially known as a “bolt from the blue” when the discharge arc is many miles from the core of the storm on a clear day with isolated to scattered storms. This along with higher voltage values is what makes positive lightning so much more dangerous, even if less common.
Theory is that since the top of the storm is so much higher than the bottom, it is harder to discharge. A massive amount of positive charge buildup is required to force discharge with the ground because of the gap distance. The energy of the positive discharge is much more in comparison to the typical negative discharge, making the channel more powerful and deadly.
The probability of ever being struck by lightning is 1/3,000 and can cause cardiac arrest, possibly death (National Geographic 2005, web). But lightning sure is pretty to watch, especially the positive bolts that are much taller and strike outside of the storm core.
More about lightning in general can be found at National Geographic.