Response to Question One
Atmospheric heating and circulation are processes that result in global air movement patterns, thus the concept of global patterns of atmospheric heating and circulation. When heat imbalance occurs on the earth’s surface, atmospheric heating and circulation patterns occur in the form of air circulation over the earth. As a result, the global circulation of both the winds and the pressure occurs in an effort to regulate the heat imbalances of the earth. The heating and circulation patterns, as a result, influence the creation of ocean currents. In order to describe global patterns of atmospheric heating and circulation, it is important to establish what to base it on, thus facilitating its description. As a result, global patterns of atmospheric heating and circulation are based on the three-cell model. There are three cells that exist between the earth’s poles and the equator that influence global patterns of atmospheric heating and circulation ( Bharatdwaj, 2006 ) . The first cell is the polar cell, which is operational between the latitudes of 60 degrees and 90 degrees. The second cell is the Ferrel cell, which is operational between the latitudes of 30 degrees and 60 degrees. The third and final cell is the Hadley cell, which operates between the latitudes of 0 degrees and 30 degrees ( Bharatdwaj, 2006 ) .
Each cell is responsible for certain different global patterns of atmospheric heating and circulation. For instance, the polar cell is responsible for the polar easterlies, where at lower latitudes warm air rises moving to higher altitudes, whereas cold air descends owing to the high pressure ( Bharatdwaj, 2006 ) . In the case of the Hadley cell, which is associated with the trade winds, warm air rises at the equator from low-pressure areas moving up to the 30 degrees latitude, where it eventually descends into high-pressure areas ( Bharatdwaj, 2006 ) . Lastly, the Ferrel cell, which s typically deemed a rather complicated zone, consists of warm air rising at higher latitudes close to the polar cell, which it cools as the warm air moves to lower latitudes and descends in high-pressure areas in the lower latitudes close to the Hadley cell ( Bharatdwaj, 2006 ) . Therefore, global patterns of atmospheric heating and circulation can be established by observations of the three-cell model. This hence facilitates an understanding of the differences in the climatic condition in different regions of the globe depending on their locations with regard to the three cells.
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On the one hand, the mechanism attributed to high precipitation in the tropics can be described as follows; warm and humid air from both hemispheres brought in by trade wind patterns as well as subsequent air convection, converge in the Inter-Tropical Convergence Zone owing to low pressure, resulting in convection in the atmosphere. Such occurrence is what is referred to as the Hadley cell as it results from cloudy and rainy weather close to the equator ( Bharatdwaj, 2006 ). On the other hand, the mechanism that is attributed to high precipitation in the temperate zones can be caused by many factors including low-pressure systems, stationary fronts, warm fronts as well as cold fronts.
High precipitation in the temperate zones is caused by the rising of air which picks up moisture from dry regions in lower latitudes causing the building up of clouds, thus resulting in high amounts of precipitation. Lastly, low precipitation in the tropical zone is attributed to the impeding of warm prevailing winds by mountain ranges owing to the fact that the mountains cause the moisture in the winds to fall as rain on the side of the mountain that is blocking the winds ( Bharatdwaj, 2006 ) . This results in low precipitation on the other side of the mountain. Precipitation is dependent on temperature, which means that when temperatures are low air cannot hold much moisture. At the tropics, the air is very warm, such air needs to interact with cold weather in order to lose its moisture in order for precipitation to remain low.
Response to Question Two
One way of explaining why the tropical dry forests and savanna biomes are located in the Inter-Tropical Convergence Zone which receives a lot of precipitation is through the concept of atmospheric circulation. The occurrence of such precipitation, which causes the high seasonal rainfall in the tropical dry forest and tropical savanna biomes can be attributed to atmospheric circulation, which causes changes in air pressure leading to condensation and the formation of clouds, hence high precipitation. Near the equator, the amount of sunlight received causes the Inter-Tropical Convergence Zone to receive a lot of precipitation (Chang, 1977) . This is because the sunlight causes a rise in the temperature of the air, which in turn causes pressure to drop and then causes the low-pressure air to rise. The low-pressure air which rises then reaches higher latitudes and its temperature drops resulting in its condensation and formation of clouds as a result. In the event that the clouds condense in a timely fashion, then they cause high amounts of precipitation, thus one of the ways of explaining why there occurs high seasonal rainfall in the tropical dry forest and tropical savanna biomes.
Another way of explaining why the tropical dry forests and savanna biomes, which are located in the Inter-Tropical Convergence Zone, receive a lot of precipitation is through the establishment of global pressure systems, caused by seasonal changes in the sun’s orientation to earth (Chang, 1977) . The geographical distribution of precipitation is highly dependent on the global pressure systems this is because global pressure systems have the ability to influence and affect the relationship between pressure patterns across regions and the distribution of precipitation in those regions. For instance, the biomes of tropical dry forests and tropical savannas show correspondence with regards to their climatic zones. The tropical dry forest is geographically located on the opposite sides of the equator, which is typically up north and down south of the equator. This causes the tropical dry forests to experience climatic variations that are more compared to those experienced by the tropical rainforest. Owing to the seasonal changes in the sun’s orientation to earth, the tropical dry forest is typically characterized by dry and wet seasons (Chang, 1977) . However, the tropical dry forest experiences less rain than the tropical rainforest. Similarly, just like the tropical dry forest has alternating wet and dry seasons, so does the tropical savannas, which are also attributed to the sun’s orientation to the earth. However, dry forests are dominated by grassland, which is not the case for the tropical dry forest.
The Inter-Tropical Convergence Zone, commonly abbreviated ITCZ receives most of the direct daylight, which explains why the tropical dry forests and savanna biomes receive a lot of precipitation since they are located in the ITCZ (Chang, 1977) . When the ITCZ receives direct sunlight depending on the sun’s orientation to earth, the air becomes unsteady and is caused to rise. Once the air has been caused to rise, the pressure drops making the ITCZ a low-pressure area. The high temperatures in the area that are attributed to the sun’s orientation to earth cause the area to experience direct sunlight to the area, which then causes the rise of unsteady air, which eventually cools, condenses and forms clouds, which in turn causes precipitation. This then explains why the tropical dry forests and savanna biomes receive a lot of precipitation.
Seasonal precipitation patterns are influenced by the moving of the Inter-Tropical Convergence Zone since it is an area that is influenced by the sun’s orientation on earth, such that the sun passes directly overhead (Chang, 1977) . Therefore, in the summertime, the sun passes directly overhead the tropic. Similarly, the moving of the Inter-Tropical Convergence Zone affects seasonal precipitation patterns in tropical climate areas where the sun is not directly overhead high-pressure areas, hence the advantage of cloud formation hence precipitation is not present. Areas where the sun is not overhead, typically known as doldrums, constitute the north and the south of the Inter-Tropical Convergence Zone. As a result of their seasonal parallel movement, doldrums are associated with the dry season in the tropics (Chang, 1977) . However, the same phenomenon explains why tropical rainforests experience excessive rain, which is also the case in the tropical monsoon in Africa since they re near the equator hence close to the ITCZ most of the year where cloud formation, hence precipitation are favorable. The savannas, located in the northern hemisphere, which is north of the dry forest and in the southern hemisphere, which is south of the dry forests, are not under the ITCZ for longer periods compared to wet and dry forests on either side of the rainforest. As a result, the savanna climate is the opposite of that of the monsoon and rainforest, which is the tropical wet/dry climate. Rain in the savanna climate is seasonal but is not as much, and during the low-sun season, the savanna climate experiences dry conditions.
References
Bharatdwaj, K. (2006). Physical geography (atmosphere) . New Delhi: Discovery Publishing House.
Chang, J. C. (1977). General circulation models of the atmosphere . New York: Academic Press.
