How to get unity particles to move closer to a line over time, to create a flame effect?

How can I get particles to spawn in a sphere, then move closer to the Y origin line as they move? I want to get a flame effect.

Note how the flame in the middle goes higher. I want to replicate that. (Not replicate the image exactly, just achieve that 'air column' effect.

Solution

You could always just fake it, with a sizable density of particles travelling upwards, then you simply reduce the size over lifetime.

I know youtube videos are shunned on here. But this video is a good start.

If you wanted more control over the origin line, Unity still exposes the particlesystem through script.