// Attach this script to an existing particle emitter.

function LateUpdate () {
    // extract the particles
    var particles = particleEmitter.particles;
    for (var i = 0; i < particles.Length; i++) {
        // Move the particles up and down on a sinus curve
        var yPosition = Mathf.Sin (Time.time) * Time.deltaTime;
        particles[i].position += Vector3 (0, yPosition, 0);
        // make the particles red
        particles[i].color = Color.red;
        // modify the size on a sinus curve
        particles[i].size = Mathf.Sin (Time.time) * 0.2;
    }
    // copy them back to the particle emitter
    particleEmitter.particles = particles;
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void LateUpdate() {
        Particle[] particles = particleEmitter.particles;
        int i = 0;
        while (i < particles.Length) {
            float yPosition = Mathf.Sin(Time.time) * Time.deltaTime;
            particles[i].position += new Vector3(0, yPosition, 0);
            particles[i].color = Color.red;
            particles[i].size = Mathf.Sin(Time.time) * 0.2F;
            i++;
        }
        particleEmitter.particles = particles;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def LateUpdate():
        particles as (Particle) = particleEmitter.particles
        i as int = 0
        while i < particles.Length:
            yPosition as single = (Mathf.Sin(Time.time) * Time.deltaTime)
            particles[i].position += Vector3(0, yPosition, 0)
            particles[i].color = Color.red
            particles[i].size = (Mathf.Sin(Time.time) * 0.2F)
            i++
        particleEmitter.particles = particles