In Meteorology, What Are Isotherms?

Isotherm, that is, the line connecting the points with the same temperature value on the graph, is called an isotherm.

The temperature data measured at the same time are filled in a special map called a temperature distribution map. On the temperature distribution chart, connecting the points with the same temperature value into a smooth curve is called an isotherm, and a map with an isotherm is called an isotherm map. Observe the isotherm map first by looking at the numerical height and interval, and then by looking at the density of the isotherm to analyze the small or large temperature difference; then you can combine the topographic map and other analysis to analyze the reasons that affect the isotherm distribution. If the isotherm is parallel to the coast, it will be significantly affected by the ocean. If the isotherm is parallel to the direction of the mountains, the topographical influence needs to be considered. Therefore, the extension of the isotherm can provide information for studying the temperature distribution and cause in an area. The map is the basis for studying the spatial distribution of surface heat conditions. ^[1]

(1) If the isotherm protrudes to low latitudes, the temperature of the area is lower than that of the same latitudes; if the area is on land: winter continent, the terrain is higher; if the area is on the ocean: summer The ocean passes the cold current.

(2) If the isotherm protrudes to high latitudes, the temperature of the area is higher than the area of the same latitude; if the area is on land: summer land, lower terrain; if the area is on the ocean: winter Ocean, warm current passes.

(3) If the isotherm is straight, it indicates that the underlying surface is of a single nature (such as the 400-600 isotherm in the southern hemisphere is relatively straight, indicating that the area of the area is large and the nature is uniform).

(4) Areas where the isotherm is a closed curve are affected by the terrain and form warm or cold centers.

A straight isotherm indicates that there are only one factor that affects the temperature. For example, if the isotherm is parallel to the parallel, it means that the factors that affect the temperature are

I. Latitude Factor

Latitude position determines gain

Judging the North and South Hemispheres

The value of the isotherm is used to judge the northern and southern hemispheres, that is, the value of the northward isotherm decreases to the northern hemisphere, and the value of the southward isotherm decreases to the southern hemisphere.

Determining seasonal and land-sea distribution

Judging the seasonal or sea-land distribution using the convexity of the same-latitude sea-land isotherm. In the northern hemisphere, the isotherm on the continent in January (winter) protrudes to the south (low latitudes), and the ocean is to the north (high latitude); in July (summer) the isotherm on the continent protrudes north (high latitudes) , The ocean is convex southward (low latitude). The opposite is true of the southern hemisphere.

Judging the nature and direction of ocean currents

Isotherm

(1) The isotherm is curved to a low value: the ocean current flows from a high water temperature to a low water temperature, that is, from a low latitude to a high latitude is a warm current.

(2) The isotherm is bent to a high value: the ocean current flows from a low water temperature to a higher water temperature, that is, a high current to a low latitude is a cold current.

(3) The direction of the isotherm curve is the direction of the ocean current.

Analyze the trend of the isotherm and its influencing factors

(1) The direction of the isotherm and the latitude is basically the same, extending east-west, indicating that the main factor affecting the temperature of the area is solar radiation. The isotherm protrudes to low latitudes, and the temperature in the area is lower than in the same latitudes; the isotherm protrudes to high latitudes, and the temperature in the area is higher than in the same latitudes.

(2) The isotherm is generally parallel to the coastline, indicating that the main factor affecting the temperature of the area is the land and sea distribution.

(3) The isotherm is parallel to the contour line or parallel to the direction of the mountains and the edge of the plateau, indicating that the temperature of the area is affected by the topographic fluctuations.

5. Calculate the altitude of a place according to the distribution of the isotherm. In the troposphere, the temperature decreases with increasing altitude, with a coefficient of variation of 0.6oC / 100 meters.

6. Determine the size of the temperature difference: In general, regardless of time and space, the isotherms are dense, the temperature difference is large, otherwise, the temperature difference is small. From the characteristics of the temperature distribution in the world and in China, we can know that: Winter isotherms are dense, and summer isotherms are thin. Because the temperature difference in winter is greater than in summer. Temperature isotherms are dense, and tropical isotherms are thin. Because the temperature difference in temperate regions is greater than tropical regions with high annual temperatures. The land isotherms are dense, and the ocean isotherms are thin. Because the land surface is complex in shape and the heat capacity of the ocean is large, the temperature difference between the land is greater than the sea surface. ^[1]