When is the first day of this year's hot summer?

July this year (2023) 1 1, the first day of the summer heat.

Summer generally refers to the dog days, appearing between light summer and great summer. It is the time when the temperature is the highest and it is humid and sultry in a year. Three volts can be divided into initial, middle and final volts, and its date is determined by the coordination of 24 solar terms and the dates of dry and branch. After "entering the volt", many places in the country will enter the continuous high temperature mode.

The traditional almanac stipulates that "counting from the third Geng day of the summer solstice", that is to say, "counting down from the summer solstice until the third Geng day" began to crouch. The "Geng Day" here refers to the days prefixed with "Geng" in the ancient "Ganzhi Jiri Law". "crouching" means being forced to hide underground; This also means that it is too hot to move.

The length of dog days mainly lies in the difference between middle and next days. Because the third Geng day (the first autumn) after the summer solstice solar terms occurs at different times every year, the number of days of the Mid-Autumn Festival is also different. The incubation time is long or short, which may be 10 day or 20 days. So there are two situations: some years are 30 days in dog days, and some years are 40 days.

The reason why the air humidity is high in dog days is that the southeast wind blows in dog days, while the southeast is the ocean and the air is humid. The humidity of the sea breeze leads to the high humidity in dog days. In dog days, "high temperature and high humidity" are the climatic characteristics of most parts of north and south China. The inland areas in the north are far from the ocean, and the climate is characterized by "high temperature and dryness".

Climate and temperature analysis in rainy days;

Because the surface humidity becomes higher after the fall, the surface absorbs more heat every day, emits less heat and accumulates heat, so it gets hotter every day. When entering the alto, the heat accumulated on the ground reaches the highest value, and the weather is the hottest.

In addition, there is much rain in summer, the air humidity is high, and the heat capacity of water is much larger than that of dry air, which is also an important reason for the sultry weather in dog days. The subtropical high intensified in July and August. Under the control of the subtropical high, the descending airflow inside the high makes the weather clear and cloudy, which is beneficial to the sunshine, the ground radiation heats up and the weather is hotter.

After entering the last day, the weather is getting colder, it is cooler in the morning and evening, and it is still hot at noon, and each region will be different. Because the last stage is after beginning of autumn, even the so-called "autumn tiger" is hot during the day and cool in the morning and evening.