Particle system. Defining the front.

I assume the arrow denotes what direction this will face by default. How do I change its default facing. I want to change this because I have some code that will spawn this based on the facing direction of the character. Right now it spawns horizontally I would like it to spawn vertically. I know I could do this by just setting one of the parameters to 90 or -90 but I would like to know how to change its default facing.