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Isotherms Meaning, Lines, Adsorption Isotherms, Map


The term isotherm is frequently used in meteorology. Isotherms are a line connecting points on a map that are the same temperature at a certain time or on average over a certain period of time. The study of the Earth’s atmosphere and the patterns of temperature and moisture that produce different weather situations is known as meteorology. The main areas of study include rainfall, thunderstorms, tornadoes, hurricanes, and typhoons, to name just a few.

Isotherms Features

  • The Isotherms are generally parallel to the equator. They show successive temperature decreases towards the poles.
  • The spacing between isotherms indicates the rate of change in temperature. Closely drawn isotherms indicate a rapid change in temperature and vice-versa.
  • The Isotherms diverge in January, moving to the north over the sea and to the south over land. The difference in temperature between the land and the water, as well as warm and cold ocean currents, are the two causes. For instance, the Gulf Stream, North Atlantic Drift, and other warm ocean currents warm the Northern Atlantic Ocean and cause the isotherms to bend towards the north. In Europe, the Isotherms lean southward as the temperature drops precipitously across the terrain.
  • The average January temperature along the 60° E longitude is minus 20° C at latitudes 80° N and 50° N. Because there is less land mass in the southern hemisphere, the isotherms are more or less parallel to the latitudes.
  • Compared to the northern hemisphere, there is a more gradual change in temperature. The latitudes at which the isotherms of 20°C, 10°C, and 0°C are parallel are 35°S, 45°S, and 60°S, respectively.
  • The isotherms typically follow the latitude in July.

Isotherms Temperature Distribution

The distribution of global temperatures can best be understood by studying the Isotherms. Isotherms are lines that cover areas of equal temperature. As already mentioned, latitudes significantly affect temperature, and isotherms are often associated with latitude. Deviation from this common trend is more pronounced in January than in July. In the northern hemisphere, the surface area is much large than in the southern hemisphere. Therefore, the effects of land and sea currents are visible.

Isotherms Lines

By examining the temperature distribution in January and July, it is possible to comprehend the global distribution of temperature. Isotherms are typically used to depict the temperature distribution on a map. The lines connecting locations with the same temperature are known as isotherms. Since the isotherms are typically parallel to the latitude, the effect of the latitude on temperature is frequently well-pronounced on the map. Particularly in the northern hemisphere, the departure from this overall pattern is more pronounced in January than in July.

The land surface area of the northern hemisphere is significantly larger than that of the southern hemisphere. As a result, the impacts of landmass and ocean currents are rather noticeable.

Seasonal Temperature Distribution – January

In January, the northern hemisphere experiences winter, while the southern hemisphere experiences summer. Because Westerlies can carry high temperatures into landmasses, the western margins of continents are warmer than their eastern counterparts.

The temperature gradient is close to the continents’ eastern margins. In the southern hemisphere, isotherms behave more consistently.

Northern Hemisphere

The isotherms deviate north over the ocean and south over the continent. This is visible in the North Atlantic Ocean. Warm ocean currents, such as the Gulf Stream and North Atlantic drift, warm the Northern Atlantic Ocean, and isotherms show a poleward shift, indicating that the oceans are warmer and capable of carrying high temperatures poleward.

An equatorward bend in the isotherms over the northern continents indicates that the landmasses have been overcooled and that polar cold winds can penetrate southwards, even into the interiors. It is especially noticeable in the Siberian plain. Northern Siberia and Greenland have the coldest temperatures.

Southern Hemisphere

The ocean has a strong influence in the southern hemisphere. The isotherms are more or less parallel to the latitudes here, and the temperature variation is more gradual than in the northern hemisphere. The high-temperature belt runs along 30°S latitude in the southern hemisphere.

The thermal equator runs parallel to the geographical equator (because the Intertropical Convergence Zone or ITCZ has shifted southwards with the apparent southward movement of the sun).

Below is the diagram for the Average January sea-level temperature through Isotherms Lines:

Average January sea-level temperature
Average January Sea-Level Temperature

Seasonal Temperature Distribution – July

In July, the northern hemisphere experiences summer, while the southern hemisphere experiences winter. The isothermal behaviour is inverse to that of January.

Isotherms in July generally run parallel to latitudes. The equatorial oceans experience temperatures of more than 27°C. More than 30°C is observed over land in Asia’s subtropical continental region, along the 30° N latitude.

North Hemisphere

The temperature range is more than 60° C in the northeastern part of the Eurasian continent. This is because of the continent. The smallest temperature range, 3°C, is found between 20° S and 15° N. A poleward bend of the isotherms over the northern continents indicates that the landmasses are overheated, and hot tropical winds can penetrate deep into the northern interiors.

The northern ocean isotherms show an equatorward shift, indicating that the oceans are cooler and can carry the moderating effect into tropical interiors. Greenland experiences the coldest temperatures. Northern Africa, West Asia, northwest India, and the southeastern United States have the highest temperature belts. The temperature gradient is irregular and zigzags across the northern hemisphere.

Southern Hemisphere 

Over the southern hemisphere, the gradient becomes regular, with a slight bend towards the equator at the edges of continents. The thermal equator has moved north of the geographical equator.

Below is the diagram for the Average July Sea-level Temperatures through Isotherms Lines:

Average July Sea-level Temperatures
Average July Sea-level Temperatures

Vertical Distribution of Temperature

The normal lapse rate is uniform at any given altitude in the troposphere. The lapse rate stops at zero at the Tropopause, implying that there is no temperature change there. The lapse rate remains constant for some height in the lower stratosphere, while higher temperatures exist over the poles because this layer is closer to Earth at the poles.

Adsorption Isotherm

An Adsorption Isotherm is a graph that shows how, with constant temperature and pressure, the amount of adsorbate(x) adsorbed on the surface of the adsorbent varies.

As we know from Le Chatelier’s principle, the direction of equilibrium in response varies in the direction that stress is relieved. As a result, we can see that when the system is subjected to an excessive amount of pressure, the equilibrium shifts in a way that causes the pressure inside the system to drop as the number of molecules within the system drops.

The graph also shows that the fluctuation in the amount of adsorbent adhering to the adsorbate is zero after reaching a pressure Ps or saturation pressure. This occurs because there is a finite amount of surface area available for adsorption, and since every site is already occupied, an increase in pressure makes no impact.

Adsorption Isotherm Types

Various scientists have proposed various types of Adsorption Isotherms, including:

  • Langmuir Isotherm
  • Freundlich Isotherm
  • BET Theory

Since this topic (adsorption Isotherm)  is related to organic Chemistry part so to avoid any kind of confusion we won’t be getting into the detail.

Other Indian Geography Topics

Seasons of India Mountains of India
Mangrove Forests in India Important Mountain Passes in India
Monsoon in India
Indus River System
Climate of India
Rivers of India
Tributaries of Ganga
National Parks in India
Important Dams in India
Wildlife Sanctuaries of India
Tiger Reserves in India
Northern Plains of India
Physiography of India
Important Lakes of India
Wetlands in India
Biodiversity in India
Natural Vegetation in India Earthquakes in India
Types of Soil in India
Ramsar Sites in India
Brahmaputra River System
Hydropower Plants in India
Nuclear Power Plants in India
Major Ports in India
Biosphere Reserves in India
Waterfalls in India

Other Fundamental Geography Topics

Solar System Types of Clouds
Structure of the Atmosphere Himalayan Ranges
Component of Environment
El Nino and La Nina
Coral Reef
Continental Drift Theory
Endogenic and Exogenic Forces
Indian Ocean Region
Pacific Ocean
Indian Ocean Dipole
Air Pollution
Environmental Impact Assessment
Tropical Cyclone
Western Disturbances
Types of Rocks

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Why do isotherms bend towards the equator?

As they alter their temperature considerably more than the sea, large landmasses in the Northern hemisphere cause isotherms to bend toward the equator in the winter and the poles in the summer. Because land changes its temperature far more quickly than ocean water does, air temperatures over land fluctuate more.

In which hemisphere are the isotherms widely spaced?

Southern Hemisphere, When they cross land masses, they bend toward the poles, and when they cross oceans, they bend toward the equator. There is a sizable body of water in the southern hemisphere. As a result, isotherms in the southern hemisphere are regular and widely separated.

Why isotherms are parallel to latitude?

Follow the parallels generally: Isotherms are closely related to the latitude parallels since all sites on the same latitude receive an equal amount of insolation. Rapid temperature changes are indicated by the close spacing between isotherms (high thermal gradient).

What is an example of an isotherm?

Isothermal operation governs a refrigerator. The refrigerator's mechanism undergoes a number of alterations, yet the inside temperature doesn't vary. The heat energy is dissipated and delivered to the environment here. The heat pump is another illustration of an isothermal process.

Where is the isotherm located?

The line linking sites with a constant temperature on a map is called an isotherm. The field of meteorology or weather forecasting uses isotherms the most.


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