What is Atmospheric Temperature?
Atmospheric temperature is the temperature of the earths atmosphere measured at different levels. This is dependent on many factors such as clouds, latitude, incoming radiation, land surface, air, altitude, ocean currents, and water surface, etc.
The reason for the warmth and the coldness of the atmosphere is due to air temperature. The suns rays or solar energy is the main reason why the atmosphere experiences coldness and warmness at the same time. The temperature of a place varies in different locations within a day and also brings about seasonal differences.
Range of temperature
The range of temperature is the difference between the maximum and minimum temperatures. There are two terms that are used to consider temperature ranges.
- Diurnal range of temperature: this is the daily pattern of temperature change that we normally experience, it shows energy changes on a small time scale. On a calm day with little cloud cover, air temperatures usually reach their minimum just before the sun rises, this is because the ground has been giving off long-wave radiation all through the night, it gradually becomes colder and cools the air above by conduction. When it is sunrise, the temperature of the ground begins to rise. Maximum insolation receives at midday, however, at the peak of air temperature is usually about 2:00 PM. After sun-set, the air initially remains slightly warm as it is still being heated by long-wave radiation from the ground, but this gradually fades away. Desert areas for example typically have the greatest diurnal temperature variations while Low lying humid areas typically have the least range.
- The annual average range of temperature: this is the monthly range of temperature or the difference between the average temperature of the hottest month and the average temperature of the coldest month of the year. The annual range of temperature is always lower in low latitudes but higher in high latitudes. However, in the same latitudes, it is higher over the continents and lowers over the oceans and coastal regions. The highest annual range of temperature is more than 60C over the north-eastern part of the Eurasian continent. This is due to continentality. The least range of temperature, 3C and is seen between latitudes 20S and 15N.
The interaction of insolation with the atmosphere and the earths surface creates the places located on the coast where the warm ocean currents flow record higher temperatures than the places located on the coast where the cold currents flow.
Generally, as you go higher the temperature decreases with a normal lapse rate. It is 6.5C per 1,000 m. Contrary to this normal rule sometimes, instead of the temperature to decrease, it may rise as you move higher. The cooler air is closer to the earth and the warmer air is above it. This rise of temperature with height is referred to as Temperature inversion. There are certain conditions that allow temperature inversion to take place, these are explained below:
- Long winter nights: during winter seasons, the sky appears clear during long nights and the terrestrial radiation is accelerated. The reason is that the land surface gets cooled fairly quickly. The bottom layer of the atmosphere that is in contact with the ground is also cooled and the upper layer remains relatively warm.
- Calm atmosphere: the blowing of winds bring warm and cold air into contact. Under conditions of calm atmosphere, the cold air stays put near the ground.
- Cloudless clear sky: the clouds obstruct the terrestrial radiation. But this radiation does not face any obstacles for being reflected into space when the sky is clear. Therefore the ground is cooled quickly and so is the air in contact with it cooled.
- Ice-covered surface: in ice-covered areas due to high albedo less insolation is received. During night due to terrestrial radiation, most of the heat is lost to the atmosphere and the surface is cooled. The air in contact with it is also cooled but the upper layer remains warm
- Dry air: humid air absorbs the terrestrial radiation but dry air is no obstruction to terrestrial radiation and allows the radiation to escape into space.
The stability of the night time temperature inversion is usually destroyed soon after sunrise as the sun’s energy warms the ground, which warms the air in the inversion layer. The warmer, less dense air then rises, destroying the stability that characterizes the nightly inversion. The phenomenon of inversion of temperature is especially observed in valleys. During winters the mountain slopes cool very rapidly due to the quick radiation of heat. The air resting above them also becomes cold and its density increases. It then moves down the slopes and settles down in the valleys. This air pushes the comparatively warmer air of valleys upwards and leads to the phenomenon of inversion of temperature.
Distribution of Temperature
A better way to understand the global distribution of temperature is by studying the temperature distribution on the map. This temperature distribution is generally shown on the map with the help of isotherms. The Isotherms are defined as imaginary lines joining places of equal temperature, they show the temperature of all points or the average for many days or several months of a year for any particular time.
Generally, the effect of the latitude on temperature is well prominent on the map, as the isotherms are generally parallel to the latitude. The deviation from this general trend is more pronounced in January than in July, especially in the northern hemisphere. In the northern hemisphere, the land surface area is much larger than in the southern hemisphere. Hence, the effects of landmass andocean currentsare well pronounced. In January the isotherms deviate to the north over the ocean and to the south over the continent. This can be seen in the North Atlantic Ocean. The presence of warm ocean currents, Gulf Stream and North Atlantic drift, make the Northern\ Atlantic Ocean warmer and the isotherms bend towards the north. Over the land, the temperature decreases sharply and the isotherms bend towards the south in Europe. It is much prominent in the Siberian plain. The mean January temperature along 60 E longitude is minus 20 C both at 80 N and 50 N latitudes. The mean monthly temperature for January is over 27 C, in equatorial oceans over 24 C in the tropics and 2 C – 0 C in the middle latitudes and 18 C to 48 C in the Eurasian continental interior.
Factors that determinethe temperature distribution
- Latitude of the place: Latitude determines the intensity of insolation. However, the amount of insolation depends on the incidence of the suns rays, which further depends on the latitude of the place. At the equator suns rays fall directly overhead throughout the year, when one moves away from the equator and towards poles, the inclination of the Suns rays increases. If all things remain equal, the temperature of the air will keep on decreasing from the equator towards the poles. In a similar way, the temperature of surface water decreases from the equator towards the poles because the amount of insolation decreases towards the pole.
- Distance from the sea: Another factor that influences the temperature is the location of a place with respect to the sea. The sea when compared to land, gets heated slowly and loses heat slowly. While the land heats up and cools down quickly. Therefore, the variation in temperature over the sea is less compared to land. The places situated near the sea come under the moderating influence of the sea and land breezes which moderate the temperature.
- The altitude: The atmosphere is indirectly heated by terrestrial radiation from below. Therefore, the places near the sea-level record a higher temperature than areas of higher elevations. In other words, the higher you go the cooler it becomes hence, the temperature generally decreases with increasing height. The rate of decrease of temperature with height is termed as the normal lapse rate. The value is 6.5C per 1,000m.
- Ocean currents: Just like the land and sea breezes, the passage of air masses also influences the temperature. The places that fall under the influence of warm air-masses experience higher temperature and the places that are under the influence of cold air masses experience low temperatures. Warm ocean currents raise the temperature in cold areas while the cold currents decrease the temperature in warm ocean areas. For example, Gulfstream (warm current) raises the temperature near the eastern coast of North America and the West Coast of Europe while the Labrador current (cold current) lowers the temperature near the north-east coast of North America. The enclosed seas in the low latitudes record relatively higher temperatures than the open seas; whereas the enclosed seas in the high latitudes have a lower temperature than the open seas.
- The slope of the Land, Shelter, and Aspect: the slopes of a mountain facing the sun experience high temperature than the slopes on the leeward side due to more insolation, A steep slope experiences a more rapid change in temperature than a gentle one. Similarly, the air and the land become heated where the suns rays fall directly on the slopes of the high lands. But to the opposite side of the slope, the air remains cold due to the inclined or feeble suns rays. The mountain ranges at certain places stop the cold winds and prevent the temperature from going down. This is found in areas where mountains lie in the direction facing the winds as in the case of Himalayas.
- Nature of ground surface: The nature of the surface in terms of color, vegetation, soil, land use, snow cover, etc. affects the temperature of a place. The structure of soil or its texture plays a vital role in the preservation of temperature. In tropical and subtropical deserts, for instance, the sandy surface records high temperatures because they receive most of the solar radiation. Snow has a very high albedo and thus, reflects much of the insolation without absorption. Thick vegetation like Amazon forest, for instance, cuts off much of the in-coming insolation and in many places sunlight never reaches the ground. It is cool in the jungle and its shade temperature is a few degrees lower than that of open spaces in corresponding latitudes. Light soils reflect more heat than darker soils. Dry soils like sands are very sensitive to temperature changes, whereas wet soils, like clay, retain much moisture and warm up more slowly. Urban areas have a relatively higher temperature than the surrounding.
The above factors are what influence the temperature of the ocean currents locally also. The enclosed seas in the low latitudes record relatively higher temperatures than the open seas; whereas the enclosed seas in the high latitudes have a lower temperature than the open seas.