© Charles Chandler
A number of the geophysical hypotheses on this site assert the significance of electric currents. Tornadoes, volcanoes, earthquakes, and the Seneca Guns are all said to have powerful EM components. But due to the capricious nature of such phenomena, they are tough to study. Getting EM instrumentation into place in time to collect the relevant data has previously been prohibitively expensive. But that might change soon.
iPhones have built-in magnetometers, which they use to establish the orientation of the device. The sensitivity appears to be within a few micro-teslas, and the magnetic field is registered in 3 axes. And iPhones can be programmed to store this information for later retrieval. This means that there are a lot of magnetometers in the field, and we just need to develop the proper apps to collect and upload the data.
In addition to the theoretical value, there might also be a practical value. For example, the magnetic field generated by a tornado was measured at 1.50 × 10−8 teslas from a distance of 9.6 km away using a magnetometer. The iPhone, which displays whole-number values of micro-teslas, doesn't appear to be sensitive enough to register 1/100 of a micro-tesla, so detecting a tornado from 9.6 km away might not be possible. How much closer would the iPhone have to be, in order to detect a tornado? Only one way to find out, and that's to try it. But if it works, iPhones might be useful in confirming the presence of a tornado. Radar can only determine if a thunderstorm is present that might be capable of producing a tornado, but cannot actually see the twister itself. Radar-based tornado warnings are therefore somewhat unreliable (with a 75% false alarm rate), and for that reason, the warnings aren't always taken seriously. But a confirmed report of a tornado on the ground is taken very seriously. The problem there is that somebody has to be out there to visually observe it. If it is rain-wrapped, or if it occurs during the night, there isn't going to be any verification, and that's where magnetometers might be able to make a difference.
It's interesting to consider the possibility of getting real-time data from large numbers of iPhones, fed into a central server, and determining the location and direction of travel. The server software might then be able to issue extremely accurate forecasts of the damage path, and perhaps even warn those in harm's way.