Increased negative ion content in the air
On rainy days, the temperature of the air will be slightly higher than usual, and the negative ion content in the air will also increase. This is because the friction between rain and air will produce negative ions; if it is accompanied by lightning, the negative ions in the air will increase greatly. .
Negative ions can significantly improve the human nervous system, cardiovascular system, blood system and respiratory system, making people feel more comfortable, plus negative ions also have a sedative and hypnotic effect, so people who come into contact with negative ions are prone to drowsiness.
Decreased oxygen content in the air
When it rains, the amount of water vapor in the air is greatly increased compared with the weekdays, resulting in a decrease in the average number of air molecules, a decrease in the gas pressure, and a decrease in the oxygen content.
Oxygen is an indispensable resource for the brain. It stimulates the brain and makes people feel refreshed. In an oxygen-deficient environment, the brain’s ability to respond will be greatly reduced. Therefore, in the rainy days when the oxygen content in the air is lower than usual, the human brain will slack off, and the sympathetic nerve excitability is reduced, which makes it easier to sleep.
Rain sounds are lullaby
Ticking and ticking, the sound of raindrops falling on the eaves sounds pleasant and full of rhythm, but it is precisely this constant rhythm of dripping rain, but it can promote our sleep like a lullaby.
The study found that when rain sounds into the brain, the brain unconsciously relaxes and produces alpha waves, which are very close to the state of the brain when the body sleeps. The sound of raining rustling is generally between 0 and 20 kHz, commonly known as “white noise.” People are often very sensitive to this range of frequencies, but this noise is not annoying, but rather very harmonious.
This is because “white noise” presents an evenly distributed state in the power spectrum, which weakens the irritating sounds, makes the listener’s mood soothing, and the whole person presents a relaxed state.
Increased secretion of melatonin
There is a part of the human brain called the pineal gland, which secretes a sleep-related hormone, melatonin. When the night or the light is dark, the pineal gland secretes melatonin. Generate the urge to sleep.
In addition, our eyes also produce a sleep-related protein. The brighter the light, the less the protein will be synthesized; the darker the light, the more the protein will be synthesized.
The rainy sun is covered by dark clouds, causing the sky to become dim. At this time, the pineal gland secretes melatonin, and the sleep-related protein synthesized by the human eye is increased, and the dual effect makes people sleepy.