Thor is the son of Odin and Jord. In other words, in nineteenth century
literature it would be explained as follows: thunder is created in the
eternal tensionfield between heaven and earth, when Odin as skygod
impregnates Jord the Earth, Tunder is generated. This thunder is
generally followed by rain, thus fertilising the land.
In this
picture I was inspired by 2 completly different sources. On the one hand
ther was Benjamin Thorpe and on the other an egyphtian representation
of the skygodess and the earth meeting each other..
Also you should
notice that the midgard serpent, Thors future enemy encircles his
conception, the lighting departing from Odins loins to those of Jord?
Finaly, the form of the "thunder area" suggests a THors Hammer