Two relatively stationary molecules travel 30 meters (wind) from west to east, and the next molecule suddenly hits upwards at a speed of 344 meters per second. Obviously, the molecules above will move northeast to hit the molecules directly above at the moment, so the information will spread northeast. The topic is about the speed of propagation to the north, so from a microscopic point of view, the direction of the molecules involved in the impact (more reasonable) is biased towards the northwest. Therefore, 344 is the hypotenuse.