Jamie Priest
Jamie Priest is a science journalist at Cosmos. She has a Bachelor of Science in Marine Biology from the University of Adelaide.
Skies above Western Australia were ablaze over the weekend, lit with the electric crackle of an unusually intense lightning display. By the time the storms had passed, more than two million lightning strikes had been recorded.
But who’s counting?
Turns out it’s not a fanatic storm chaser with a clipboard and a keen eye – it’s a series of strategically placed antennas that channel data to the Bureau of Meteorology in real time.
The BoM draws on data from a privately operated national lightning detection network to help track the location and intensity of thunderstorm activity, in turn helping to build more accurate forecasts.
The detection network relies on picking up parts of each lightning strike that we don’t see. The dazzling flash of a bolt from the blue is only part of the picture – each strike also emits other forms of electromagnetic radiation, including radio waves.
Dotted across the country, finely tuned antennas are waiting to catch these waves that carry the very characteristic signal of lightning strikes. With each individual strike picked up and logged by a number of these antennas, the signal can be triangulated and accurately mapped onto a central database.
Just how sensitive are these antennas? Certainly they can’t pick up everything – lightning strikes are extremely variable, ranging in intensity from barely noticeable to bone-rattling. Indeed, the pressure blast wave of a behemoth bolt, caused by the superheating of air as it rips through the atmosphere, can be strong enough to rupture eardrums and tear clothing.
The weakest signals, generally generated by cloud-to-cloud strikes, are often missed by the detection array. But given each antenna has a detection range of approximately 10km, the vast majority of the much stronger cloud-to-ground strikes are picked up and mapped in fine resolution.
Each antenna is also fitted with a GPS receiver with which it communicates with satellites, acting as an extremely accurate clock that records the time each bolt is detected. Together, this package of location and time data that is sent to the BoM paints a vivid real-time picture of the lightning activity across the country.
Beyond giving us some jaw-dropping figures on the number of strikes in a particularly flashy storm, this lightning map plays an important role in weather forecasting.
The BoM relies heavily on radar to monitor storms, particularly by looking at the intensity of rain in their clouds. But this isn’t an infallible method. There are large dead-zones in the data set: regions that fall outside the range of radars. The lightning map can help to fill these voids, picking up storm activity that would otherwise be missed.
The map also helps to refine estimates of storm intensity. Together with assessments of the state of the atmospheric conditions as storms develop, lightning frequency can help meteorologists to decide whether Severe Thunderstorm Advice is warranted.
Because the map is updated in real time, it also allows meteorologists to track the progression of a storm from start to finish. Each lightning strike is colour-coded by time, allowing storm-trackers to plot how many strikes occur within each ten-minute interval – a simple framework to determine whether a storm is intensifying or dissipating.
It was this metric that caught the eye of storm watchers over the weekend. Two million strikes over Western Australia in two days seems a staggering figure – but is it really?
For Western Australia it sure is: the Gascoyne, Kimberley and Pilbara regions that experienced the most cracking lightshow usually have air that’s too dry to encourage plenty of lightning. A strong trough dragging down moisture from the north is responsible for the storms that brought the lightning belt, mimicking far more tropical conditions where lightning-heavy thunderstorms are more common.
In Australia, Darwin holds the title for thunderstorm capital – its hot and humid skies host an average of 80 thunderstorms per year, and many of these would be on par with Western Australia’s recent lightshow.
Looking globally, Darwin is quickly dethroned – Lake Maracaibo in Venezuela experiences nearly 300 thunderstorms each year.
And the planet as a whole is positively humming with electrical sparks beneath its atmospheric cloud – Earth experiences as many as 8 million lightning strikes per day, with around 44 strikes per second recorded at any one time.