Global Patterns of Atmospheric Heating and Circulation
Global Patterns of Atmospheric Heating and Circulation
Atmospheric circulation is defined as the large-scale movement of air as well as the means by which thermal energy or heat is dispersed on the surface of globe. This paper is set to describe and clearly explain the influences of global patterns of atmospheric heating and circulation on weather patterns around the world.
The extensive structure of the atmospheric circulation differs from time to time, however the elementary climatological structure remains virtually stable. From this explanation it is clear to assert that due to this stability it is much easier to forecast certain individual weather structures as their climatic averages of these structures and patterns. This paper proves this hypothesis by explaining the following questions. What mechanisms produce high precipitation in the tropics? What mechanisms produce high precipitation at temperate latitudes? What mechanisms produce low precipitation in the tropics? Similarly the information gathered by the end of this study will also be used to explain the highly seasonal rainfall in the tropical dry forest and tropical savannah biomes.
Heating of the earth surface as well as atmospheric circulations influences patterns of precipitation, different regions around the world have different rainfall levels due to this factor. This phenomenon is well explained by the ‘Hadley cell mechanism’ as to why the tropics have higher precipitations. This atmospheric circulation pattern is described by George Hadley as the movement of trade winds from low pressure zones to high pressure zones through a closed circulation loop over the equator. In his explanation George stated that sun heats the air at the equator it causes it to expand and rise (Miller, & Spoolman, 2009). Consequently as this moist air rises it cools forming clouds. This is because cool air retains less moisture than warm air, as the warm air rises the water vapour is cooled to a temperature which forces it to condense and subsequently it accumulates and forms clouds which come back down to earth as the heavy rain fall associated with the tropical environment.
Due to the reduction of vapour, equatorial air mass eventually stops to rise and is blown north and south. It should be noted that by then this once warm moisture filled air is now high in altitude and has become colder in turn after reaching this point it plummets replacing warmer air spreading towards the poles roam the equator. This mass air flow causes another climatic change through this process as it draws moisture from the lands over which it flows and creates deserts in the process.
Image 1: Hadley cell mechanism’
The image above illustrates the loop that Hadley described happening in the Inter-tropical convergence zone at the equator.
From Hadley’s theory one might believe that only the tropics receive high rainfall and not the temperate regions further away from the equator. This hypothesis is not true, it should be noted that the tropics receive high rainfall almost throughout the year. However, the temperate regions do receive high rainfall but only seasonally and is explained by the Ferrel cell theory. William Ferrel created a secondary atmospheric circulations theory that reliant on mass air movements caused by both the Hadley cell and the Polar cell. It works much as an atmospheric circuit held between the Hadley cell and the Polar cell, giving rise to mid-latitudes rainfall (Miller, & Spoolman, 2009). From his explanation William stated that while the Hadley and Polar cells are truly closed loops, the Ferrel cell is not, as it is a result of the two cells converging. Due to their high powered air movement when the Hadley and Polar cells collide they form high and low pressure zones that tend to push warmer tropical air back to the equator direction, this warmer air quickly condenses due to the temperatures from the poles hence creating mid-latitude rainfall over the temperate region. From image 1, the Ferrel cell is clearly depicted as the mid latitude region that hold high and low pressure zones causing temperate rains.
Despite the fact as explained above that the tropical zones receive high rainfall some of this high precipitation regions have low rains. Differences in temperature similarly drive a set of longitudinal circulation cells; hence the overall atmospheric motion is termed as the zonal overturning circulation zones. Mostly found in coastal regions cooler air from the sea blows over the land with warmer and moist air and due to the topography of the increasing altitude the vapour might be blown towards the sea. As it cools it forms clouds that pour back to the sea and not the land, this causes the Diurnal wind change in coastal area. This hence means that the mainland tropics receive higher rainfall than the coastal regions.
Several ecological surveys have indicated that tropical rain forests mostly lie along the equator. The reason behind this is due to the fact that the equator climatically is the band that holds the range of the inter-tropical convergence zone, which for all or most of the year experiences heavy rainfall. From the equator there is a significant decrease in rainfall hence the existence of several tropical dry forest as well as tropical savannahs(Oliver, 2005). The occurrence of these two regions is based on the rainfall amount experienced by each region. Tropical forests such as the Congo forest are fed with almost round the year rainfall, however the further the movement north as well as south the lesser the rain. This in turn gives rise to the dry forests which only receive rainfall seasonally and in lesser amounts than the tropics as the moisturised air blown from the equator only brings limited rain. Further south from this region we find the savannah region which has much lesser rainfall. Unlike the lush green vegetation experienced in longer periods in the tropical and dry forests, the savannah is made up of plains, which have scattered trees mostly Acacia and tall brown grass. This is due to limited rainfall that may be attributed to with rain shadows and ocean currents that are unfavourable to these regions.
Rain shadows are created by landmarks such as hills and mountains that force moist air upwards creating a windward and leeward side which in many cases find the leeward side being savannahs that are brushed by dry winds (Oliver, 2005). Dry Ocean currents also play a major part as they may go against the warmer and vapour filled air that will consequently rise and condense, falling as rainfall further away from the savannah.
In conclusion, atmospheric circulation caused by disparities in both heat and air movements make up weather patterns all over the world. Theories like the Hadley, Polar and Ferrel, cells offer a major explanation in terms global heat transport and consequently rainfall.
Miller, G. T., & Spoolman, S. (2009). Living in the environment: Concepts, connections, and solutions. Belmont, CA: Thomson Brooks/Cole.
Oliver, J. E. (2005). Encyclopedia of world climatology. Dordrecht: