photo #6590783

Storm Cloud Week: FridayPaul M Smith is a chaser of sprites. These are forms of transient luminous events (TLEs) that appear as fleeting streaks of red light up in the high atmosphere above thunderstorms. You could think of Paul as a nighttime, long-distance storm chaser, whose challenge is to photograph atmospheric displays that appear above distant storms for just a few milliseconds – far briefer than the blink of an eye.Sprites are electrical discharges triggered by very strong positively charged lightning bolts in the thundercloud way below, typically flowing from the cloud to the ground. So much energy is released in these strikes that they excite the gases in the mesosphere and ionosphere way above the storm, causing them to emit light. Sprites are enormous streaks and branches of red light stretching 30-55 miles (50-85 km) up that are so short lived as to be only just visible to the naked eye. Best spotted with high-speed cameras, they are cold plasma discharges that have more in common with auroras than the extremely hot lightning bolts that trigger them far below. Sprites come in all shapes and sizes – as Paul puts it, ‘from a tiny static spark to a city-sized flash of cold plasma like this one’, which he spotted over Oklahoma, US. It is the type that is known as a jellyfish sprite. The lightning bolt illuminating the storm cloud here is not, Paul explained, the ‘parent strike’ that caused this sprite to appear. That was actually a larger lightning strike happening in a storm hidden from view beyond