Why is it easy to fall asleep when it rains late at night? Second-hand is easy to get sleepy. What is the principle?

Several factors are mixed together, and it is easier to fall asleep on rainy nights. First of all, the sound of rain belongs to white noise and is a natural lullaby. The so-called white noise refers to some relatively uniform sounds, and the sound of rain is similar to this white noise. And the sound of air conditioning, tap water and so on that we often hear is white noise. Because of the white noise in rainy days, other noises can be shielded. Moreover, the noise generated by the rain is relatively small, which will give you a false sense of peace, gradually adjust your mood to a peaceful state, and let you enter a good sleep with high quality. Secondly, in rainy weather, dark clouds block sunlight from entering the ground, and the light intensity is weakened, while dim light will stimulate the secretion of melatonin, which dominates sleep. When melatonin accumulates, we will feel sleepy, which shows that our body has begun to enter sleep mode. Thirdly, in rainy weather, the air pressure is relatively low, the oxygen content in the air drops, the brain and body tissues are prone to hypoxia, and the sympathetic nerve excitability decreases, resulting in drowsiness. In addition, when it rains, the air humidity increases, and the friction between lightning and rain and air will produce a large number of negative ions. Because the human body inhales negative oxygen ions, it can relax nerves, relieve nervous mood and get closer to the state of sleep.