Generate a vector that has a random value for the X and Z axes, and multiply that value by the size and the speed. Add that vector the the particle’s position.
The big particles will wobble more than the small ones, and all particles will wobble progressively more as they gain speed.
Hopefully that gives you enough info to get started. Ive attached a compound as well which has this setup, get an empty point cloud, creat a simulated ice tree, attach this compound, then just attach a torpedo emitting object and hopefully should work