Invisible Gorilla

Greetings friends, I have a question about the factors that might account for the continuous variation that can occur in the earth's magnetic field ? How might solar flares induce changes in the magnetic field that covers the earth ? Furthermore, is it possible to detect certain repeated patterns of variation in different geographical locations ? Please do excuse me if the questions might come across as strange, I'm sort of new to this topic. Also, it would be greatly appreciated if you could provide me with the names of a few websites or books that give a general overview or some introductory information about the earth's electromagnetic field.