The heat wave in the south has cooked all the eggs on the ground, but why does the weather forecast tell me that it will be 37℃ today?

Recently, friends in the north have fully felt the coolness of autumn, but in the south, the summer heat has not completely dissipated, and the temperature in some places in the south is still relatively high. According to the weather conditions released by the Central Meteorological Observatory at 08:00 on September 10: parts of eastern Sichuan, most of Chongqing, most of Hubei, central and northern Hunan, central and northern Jiangxi, central and western Zhejiang, southern Anhui, and southern Henan have experienced high temperatures of 35 to 39 degrees Celsius, and Wuxi, Kaizhou, Fengjie, Yunyang and Wanzhou in Chongqing, Yichang in Hubei, and Chizhou in Anhui have experienced local temperatures of 40 to 41.8 degrees Celsius.

You may have this question: In hot weather, the hot asphalt road can even cook eggs, but the highest temperature predicted by the Meteorological Bureau is only 37 degrees Celsius? In meteorology, what are the concepts of temperature? This article will help you figure it out at once.

Figure 1 National high temperature forecast map (08:00-20:00, September 10) (Source: Central Meteorological Observatory)

01 Who is wrong? Actually, no one is wrong!

Although under the same sun, the temperature under the shade of a tree is lower than that under direct sunlight, and indoors is cooler than outdoors. Even if the air temperature is exactly the same, the south with high humidity feels like a sauna, while this is less common in the north. Similarly, at the same air temperature, it is hotter when there is no wind and cooler when there is wind. Of course, people who wear more clothes and less clothes feel different temperatures; the elderly and the young also feel different temperatures...

Temperature is a very complex concept. In our daily life, it can be divided into many situations. So, how many kinds of temperature are there in meteorology? Let's figure it out all at once.

01Surface atmospheric temperature

The air temperature referred to in meteorology is the air temperature at a certain height (usually 1.5 meters) from the ground. It is the most basic temperature parameter in meteorological observation and is measured using a thermometer in a louvered box to avoid interference from external factors such as solar radiation, rain, snow, and wind.

Meteorological observations are based on the temperature inside a louvered box 1.5 meters above the ground (Image source: provided by the author)

Thermometer in the louvered box. (Image source: provided by the author)

Automatic recording instrument for temperature and humidity in the louvered box (Image source: provided by the author)

Real-time temperature: refers to the actual temperature of the weather at that time, that is, the temperature at this moment , which is a clear and immediate temperature report. It is of great significance to our daily life, work and decision-making. It can help us understand the current weather conditions and provide reference for travel, clothing, agricultural production and other activities.

Daily maximum temperature : refers to the highest temperature in a day (usually from 20:00 to 20:00 the next day, the same below), reflecting the highest degree of heat received by the surface in a day. It usually occurs between 14:00 and 15:00 a.m. , because solar radiation reaches its strongest point at this time, and the surface absorbs the most heat, causing the temperature to reach its peak. By continuously observing the changes in the daily maximum temperature, we can understand the local climate characteristics, seasonal changes , and extreme weather events . High temperature warnings are mainly based on this data.

Daily minimum temperature : refers to the lowest value of air temperature observed in a day, reflecting the time when the surface heat dissipation reaches the maximum, that is, the temperature drops to the lowest point. The daily minimum temperature generally occurs around sunrise in the early morning . This is because during this period of time, the surface temperature drops to the lowest point after a night of radiation heat dissipation. The size and changing trend of the daily minimum temperature are of great significance for understanding local climate characteristics, formulating agricultural production plans , and preventing extreme weather events . Cold wave warnings are mainly based on changes in this data.

Daily average temperature : Daily average temperature refers to the average of the temperature values ​​at different times of the day. It comprehensively considers the temperature changes during the day and at night. It is an important parameter for assessing the climate conditions within a day. It is of great significance in many fields such as meteorology, agricultural production, and human health .

02Upper atmosphere temperature

The upper air temperature refers to the temperature change in the atmosphere that changes with increasing altitude. It is of great significance in meteorological and climatological research because it directly affects the movement of air currents, cloud formation and precipitation in the atmosphere . It is also closely related to the changes in the ionosphere in the atmosphere. The air temperature in the troposphere gradually decreases with increasing altitude. On average, the temperature decreases by about 6.5℃ for every kilometer increase (this value may vary depending on the region and season). The upper air temperature in meteorological detection is mainly obtained through balloon detection, rocket detection and satellite remote sensing .

The radiosonde is released twice a day, at 7:15 and 19:15 respectively. All observation stations across the country release it at these two times. (Image source: provided by the author)

Temperature of the 850 hPa pressure layer : refers to the temperature of the air layer at an altitude of about 1,500 meters in the atmosphere (this altitude may vary due to geographical location, season, etc.). This is an important indicator in meteorological observation, reflecting the temperature conditions of the lower atmosphere (i.e., the layer close to the ground), and has important reference value for predicting ground weather, such as rainfall, snowfall, strong winds , etc.

The temperature of the 700 hPa pressure layer : refers to the atmospheric temperature corresponding to the specific layer where the air pressure reaches 700 hPa . Since the 700 hPa pressure layer is close to the ground, its temperature changes are often affected by factors such as ground heat sources, topography, and oceans. The atmosphere is relatively active, and the temperature changes relatively quickly, which can quickly reflect changes in the ground weather system. By analyzing the temperature changes at this level, future weather conditions, such as precipitation, wind direction and speed , can be predicted.

The temperature of the 500 hPa pressure layer refers to the atmospheric temperature corresponding to the air pressure of 500 hPa in the middle troposphere (about 5,000 meters above sea level). When analyzing the middle atmosphere, the meteorological department will pay special attention to the meteorological conditions on the 500 hPa isobaric surface. The changes in the pressure, temperature, humidity and other parameters of this layer are of great reference value for predicting the movement, development and intensity of weather systems .

The temperature of the 100 hPa pressure layer refers to the atmospheric temperature at this altitude when the atmospheric pressure is 100 hPa. It is a relatively high altitude layer, belonging to the mesosphere or higher in the Earth's atmosphere. At this altitude, changes in temperature may be affected by a variety of complex factors, including atmospheric dynamics, radiation processes, chemical reactions, etc.

03Surface temperature

The surface temperature refers to the temperature at the junction of the earth's surface and the air. When measuring, the ground thermometer is usually placed horizontally on the ground surface, with half of the ball buried in the soil and the other half exposed to the air. Therefore, the measured temperature is actually the average of the surface temperature and the air temperature close to the ground . The temperature obtained by this measurement method is different from the surface temperature of cement ground and road ground that we often talk about, which is often higher under direct sunlight.

As the most intuitive description of the thermal conditions of the earth's surface, the surface temperature is the result of the energy balance of the earth's surface. It indicates the difference in the absorption of solar radiation energy by the earth's surface in different regions and is an important factor in the physical and ecological processes of the earth's surface at regional and global scales. It is of great significance for understanding the energy balance of the earth's surface, climate change , and changes in the ecological environment .

04Shallow ground temperature

Shallow ground temperature refers to the soil temperature within a certain depth range below the ground surface. This depth range is usually shallow and is used to reflect the thermal conditions of the soil near the ground surface, including different layers such as 5 cm, 10 cm, 15 cm, and 20 cm from the ground. It is usually measured using a special thermometer, such as a curved tube ground temperature meter, a platinum resistance sensor, etc., which is buried in the soil according to the soil depth.

Shallow ground temperature changes are affected by many factors, including solar radiation, surface cover, soil moisture, topography, etc. Solar radiation is one of the main factors affecting shallow ground temperature changes. Shallow ground temperature is one of the important indicators for assessing climate systems, predicting weather changes , and assessing environmental conditions . It is one of the meteorological factors that need to be closely monitored in agricultural production . It has important reference value for projects such as railway construction in plateau permafrost zones , underground mineral and geothermal resource mining , etc.

05Deep geothermal temperature

Deep geothermal refers to the temperature in the deeper soil layer below the surface, usually including the temperature in the middle of the ground at a depth of 40 cm, 80 cm, 160 cm, 320 cm, etc. Deep geothermal is usually observed using automated equipment such as platinum resistance sensors. These sensors are installed at a specified soil depth and can measure and record changes in soil temperature in real time.

They can measure the ground temperature at depths of 5 cm, 10 cm, 15 cm, 20 cm, 40 cm, 80 cm, 160 cm and 320 cm. Recording these temperatures is of great value for studying temperature changes. (Image source: provided by the author)

Deep geothermal data is an important basis for studying the temperature distribution and thermodynamic cycle inside the Earth, and helps to reveal the thermal evolution history and thermodynamic properties of the Earth's interior. Deep geothermal data is closely related to the exploitation of geothermal resources , and also plays an important role in the prediction of natural disasters such as earthquakes and volcanic activities.

summary

The meteorological temperatures introduced above are not all, but the most important temperature concepts. If you understand these concepts clearly, you will have a relatively comprehensive understanding of the concept of temperature in meteorology, and you will be able to accurately distinguish and identify the concept of temperature when faced with it.

Author: Wang Yuanhong, Senior Weather and Climate Engineer

Produced by: Science Popularization China