When do the highest and lowest temperatures appear in a day? Why?

In a day, the highest temperature is around 2 pm, and the lowest temperature is around sunrise.

1. The hot and cold weather mainly depends on the temperature, and the fundamental factor affecting the temperature is the intensity of solar radiation. Solar photothermal is not the main reason for the direct temperature rise. The direct absorption of solar heat energy by air is only about 14%, while 43% of the energy in the visible region is absorbed by the ground. When the ground absorbs solar radiation heat, it is conducted into the air through radiation, convection and other forms, which is the main reason for the temperature rise.

2. After noon, the solar radiation began to weaken, but the ground still absorbed more heat than it consumed. Until about 1 in the afternoon, the ground temperature reached the highest and the ground radiation reached the strongest. Because it takes a certain time for heat to transfer from the ground to the atmosphere, the temperature near the ground reaches the highest at about 2 pm, and the atmospheric reverse radiation also reaches the maximum in a day.

3. Similarly, the atmosphere mainly loses heat in the form of inverse radiation and atmospheric radiation, and there is no solar radiation to supplement heat before the next sunrise, so the temperature reaches the lowest value of the day before and after the next sunrise.

Extended data:

Man-made factors affecting temperature

(1) The influence of urban underlying surface (the interface between atmospheric bottom and surface)

A large number of artificial structures in the city, such as paving the ground and various building walls, have changed the thermal properties of the underlying surface. Urban surface water content is less, and more heat enters the air in the form of sensible heat, which leads to air warming. At the same time, the absorption rate of sunlight on the urban surface is higher than that on the natural surface, which can absorb more solar radiation, so that the air can get more heat and the temperature will rise.

(2) Urban air pollution

Motor vehicles, industrial production and a large number of people's activities in cities produce a lot of nitrogen oxides, carbon dioxide, dust and so on, which can absorb a lot of energy from the thermal radiation in the environment, produce a well-known greenhouse effect, and cause further warming of the atmosphere.

(3) the influence of artificial heat source

Factories, motor vehicles, residents' lives, etc. Burning all kinds of fuels consumes a lot of energy and countless stoves are burning and emitting heat.

(4) The urban natural underlying surface is reduced.

Buildings, squares, roads, etc. It has increased a lot in the city, and the natural factors such as green space and water body have decreased accordingly, releasing more heat and absorbing less heat, and the ability to alleviate the heat island effect has weakened.

References:

Baidu encyclopedia-temperature