How is the temperature measured and calculated?

The continuous change of temperature with time in a day is called the daily change of temperature. In a day, the temperature has a maximum and a minimum, and the difference between them is the daily temperature difference. Usually, the highest temperature appears at two o'clock in the afternoon, that is, from 14 to 15 local time, and the lowest temperature appears around sunrise (about 6 o'clock local time in two minutes).

Affected by seasons and weather, the occurrence time may be ahead of schedule or behind schedule. For example, the highest temperature in summer appears in14-15; Winter is in 13- 14. Because the sunrise time is different at different latitudes, the occurrence time of the lowest temperature will also be different with different latitudes.

The daily range of temperature is smaller than the daily range of surface soil temperature. The farther away from the ground, the smaller the daily range of temperature, and the later the highest and lowest temperatures appear. In agricultural production, sometimes a large daily temperature difference is needed, which is beneficial to the high yield of crops.

Because of the large diurnal range, it means that the temperature is higher during the day and lower at night, so that the leaves have strong photosynthesis during the day, produce more carbohydrates, consume less at night, accumulate more, and have high crop yield, high sugar content and good quality.

The temperature in a certain place changes periodically not only because of the change of solar radiation, but also because of the movement of the atmosphere rather than periodically. The change of actual temperature is the result of the interaction between these two aspects.

If the former plays a big role, the temperature changes periodically; On the contrary, it shows an aperiodic change. However, from the general trend and most cases, the periodicity of daily and annual temperature changes is still the main one. Various components in the heat balance, such as radiation difference, latent heat and sensible heat exchange, are affected by different control factors.

Astronomical factors such as latitude and season have obvious zonal and periodic characteristics. However, the nature, topography and weather conditions of the underlying surface, such as cloud cover and atmospheric humidity, all have non-zonal characteristics. At the same time, the influence of these factors is different in different places, so the temperature distribution caused by the change of heat budget is also uneven.

Human influence:

(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.