Isothermal contour normal vectors

Hi All,

Background:
I am mapping the temperature gradients at the solidification front of a laser generated melt pool. However the gradients need to be measured in the direction normal to the solidification front (given by an isothermal contour in the results) - this is easy, I just need to map the magnitude of the temperature gradient as this is already in the normal direction.

Question:
I also need to map the angle that the normal (to the solidification front) makes to the direction of motion of the beam (in this case, the x-axis) in order to calculate the solidification rate vs=vb(dot)n. Any ideas on how to get this information in plotted form in the results section?

Many many thanks

Dan