Latitude determines how much solar radiation you get. The solar radiation obtained at the same latitude is the same, and the lower the latitude, the more solar radiation is obtained. Affected by this, in the northern and southern hemispheres, whether in July or 65438+ 10, the isotherm is roughly parallel to the latitude, and the temperature decreases from low latitude to high latitude. Therefore, according to the north-south gradual change of isotherm in the isotherm map, the northern and southern hemispheres where the illustrated area is located can be determined. Isothermal values decrease from south to north to the northern hemisphere, and vice versa. That is, "North increases and South decreases, South increases and North increases".
Second, land and sea factors.
The land is heated quickly and dissipated quickly; The ocean is slowly heated and dissipated. Affected by it, in summer, the land temperature is higher than the ocean temperature at the same latitude; In winter, the land temperature is lower than that of the ocean at the same latitude. Therefore, the isotherm changes seasonally in the coastal zone, as shown in figure 1 and figure 2 (the dotted line in the figure is the isotherm, T 1 and T2 are located in the northern hemisphere, t1>: T2; T3 and T4 are located in the southern hemisphere, T3 >；; T4). It is suggested that in July, the direct sunlight point is in the northern hemisphere, and it is summer in the northern hemisphere. The land temperature in the same latitude area is higher than that in the ocean, and the land isotherm protrudes northward to the high latitude (low temperature area). This season is winter in the southern hemisphere, the land temperature at the same latitude is lower than SST, and the land isotherm protrudes northward to the low latitude (high temperature area). As can be seen from the figure, in July, regardless of the northern and southern hemispheres, the land isotherm bulged northward near the coastal zone, which can be simply called "point north and land north" (that is, when the direct sunlight point is in the northern hemisphere, the global land isotherm bulged northward). In June+10/October, 5438, the direct sunlight point was in the southern hemisphere, with the northern winter and southern summer, and the global land isotherm protruded to the south near the coastal zone (the northern hemisphere protruded to the high temperature area at low latitude and the southern hemisphere protruded to the low temperature area at high latitude), which can be simply called "point south, land south". Whether in July or 65438+ 10, the bending direction of ocean isotherm is opposite to that of land. By remembering these eight-character formulas, we can quickly answer the question of interpreting the distribution of land, sea and season from the bending state of isotherm.
Third, the terrain factor.
On land, the curve of isotherm is deeply influenced by topography and landforms, which are as follows:
1. The higher the terrain, the lower the temperature. On the non-closed isotherm map, the isotherm degree of high terrain is lower than that of other areas at the same latitude, and that of low terrain is higher than that of other areas at the same latitude.
2. The terrain is steep, the vertical temperature difference is large, and the isotherms are dense; Flat and wide area, small vertical temperature difference and sparse isotherm.
3. The temperature in the hilly or peak area is lower than that in the surrounding area, and the isotherm is a set of closed curves with small inside and large outside. The closer to the center, the smaller the isotherm value. The temperature in the basin or depression is higher than that in the surrounding area, and the isotherm is a set of closed curves with large inside and small outside. The closer to the center, the greater the isotherm value. The closed isotherm in mountainous area is sparse, indicating that the hillside is slow; Dense isotherms in mountainous areas indicate steep slopes.
4. The terrain on both sides of the ridge belt is relatively high, the temperature is low, and the isotherm protrudes in the direction of high temperature (low altitude). The terrain along the valley or river (valley) is relatively low on both sides, the temperature is relatively high, and the isotherm protrudes in the direction of low temperature (high altitude).
5. Long mountains obviously affect the extension of isotherm. On both sides of the mountain range, the isotherms show several continuous isotherms extending roughly parallel to the contour line. In the north-south mountain belt (such as the Andes), due to the high altitude of the mountain and the low temperature on both sides of the same latitude, the isotherms protrude to the low-latitude high-temperature belt in several continuous isotherms, and the connecting line of the curved part is the mountain trend. In the east-west mountain belt (such as Qinling), the isotherm also extends from east to west, and the isotherm at higher altitude is a flat closed curve.
Fourth, the ocean current factor.
The influence of ocean currents on coastal climate is obvious. Warm current flows from low latitudes to high latitudes, increasing temperature and humidity; The cold current flows from high latitude to low latitude, cooling and dehumidifying. Therefore, the isotherm of the sea area where the warm current passes protrudes to the high latitude (low-value isotherm), and the isotherm of the sea area where the cold current passes protrudes to the low latitude (high-value isotherm). The flow direction of the cold and warm current is generally consistent with the convex direction of the isotherm.
Verb (abbreviation for verb) airflow movement
Cold wave, dry hot wind and other cold and warm air currents have little effect on the horizontal distribution of annual average temperature or monthly average temperature isotherm, but obviously affect the spatial distribution of daily average temperature isotherm. In the daily average temperature isotherm diagram, the cold air flows through the area, the air temperature is low, and the isotherm is convex to the high value isotherm; Hot air flows through this area, the air temperature is high, and the isotherm is convex to the low-value isotherm. The direction of airflow (wind direction) is consistent with the convex direction of isotherm. In the front area where cold and warm air masses meet, the temperature changes greatly and the isotherms are dense; In the area controlled by a single cold air mass or warm air mass, the temperature is relatively stable and the isotherm is relatively sparse.
Intransitive verbs human activities
The changes of human activities (such as the construction of the Three-North Shelterbelt and the Three Gorges Reservoir Area) on the underlying surface properties also affect the local temperature changes, and then affect the isotherm distribution in local small areas. In these local areas, isotherms are mostly closed curves, which are local cold or warm centers. For example, the temperature in the reservoir area is lower in summer than in the surrounding area and higher in winter; The "heat island effect" in big cities is obvious, and the temperature is higher than that in surrounding suburbs.
The general law of isotherms:
① Dense isotherms and large temperature difference; The isotherm is sparse and the temperature difference is small.
(2) Isotherms protrude to high latitudes, indicating that the high temperature zone is wide; The isotherm protrudes to the low latitude, indicating that the low temperature zone is wide.
③ The isotherm is parallel to latitude, indicating that it is strongly influenced by latitude.
④ The isotherm is parallel to the coast, indicating that it is significantly influenced by the ocean.
⑤ The isotherm is parallel to the strike of the mountain range or the edge of the plateau, which indicates that it is obviously influenced by the terrain, or the vertical variation is great.
⑥ The isotherm is a closed curve. If the temperature in the line is high, it can be judged as a basin. If the temperature in the line is low, it can be judged as a mountain.
Isothermal distribution law
(1) If the isotherm protrudes to the low latitude, the temperature there is lower than that in the same latitude area; If the area is on land, it is: ① mainland in winter, ② higher terrain; If the area is on the ocean, it is: ① summer ocean, ② cold current passing by.
(2) If the isotherm protrudes to the high latitude, the temperature in this area is higher than that in the same latitude area; If the area is on land, it is: ① land in summer, ② low terrain; If the area is on the ocean, it is: ① winter ocean, ② warm current passing through.
(3) If the isotherm is straight, it means that the underlying surface is single (for example, the isotherm of 400-600 in the southern hemisphere is flat, which means that the ocean area in this area is large and uniform).
(4) The closed area of isotherm is affected by topography, forming a warm center or a cold center.