float a = 0;
float b = PI;

void setup(){
  size(600,600); 
  frameRate(5);
  smooth(); 
  strokeWeight(1);
}

void draw() {
  background(0);
  stroke (255);
  fill(250,250,200);
  for(int i=0; i<height; i++) {
  line(6* random(i), 600, 6, 50+cos(a)*90);
  a = a + b;
  }
}