float y = 0; // change with time

void setup() {
  size(600, 400);
}

void draw() {
  background(255);
  float x = 0; // change with horizontal position
  for (int i = 0; i < width; i++) {
    point(i, 150 + noise(x, y) * 200);
    x += 0.01;
  }
  y += 0.003;
}