"Your hard drive lying unconnected in the sun, will feel like it's raining lots of very tiny magnets. It will respond with a tiny surface current, but that would be it. This should not erase the data."
I don't necessarily agree with this. There is a variety of radiation emitted during solar events. Most of the higher energy radiation that would cause corruption (above uvb) is protected against by the atmosphere and magnetic fields. However, even under normal conditions we see that solar radiation can cause corruption of data, particularly in aircraft. Large solar events that increase that radiation can see a higher number of that radiation reaching the surface of the earth (even if the overall amount is still low). So it's still unlikely to corrupt the data by flipping bits, but it is still a minor risk.