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Global Patterns of Atmospheric Heating

1. Describe global patterns of atmospheric heating and circulation.  What mechanisms produce high precipitation in the tropics? What mechanisms produce high precipitation at temperate latitudes?  What mechanisms produce low precipitation in the tropics?
2. Use what you know about atmospheric circulation and seasonal changes in the sun’s orientation to earth to explain the highly seasonal rainfall in the tropical dry forest and tropical savanna biomes.

1. a) Describe global patterns of atmospheric heating and circulation.

The sun’s rays fall unevenly on the spherical earth surface, whereby some parts point directly to the sun. This shortens the distance between the sun and the earth surface that face each other and focuses over a small surface area. However, some divert from the sun hence lengthening the distance between the two, allowing more energy to hit atmospheric particles that deflect them back to space (Rubey et al., 2017).  In this case, the amount of solar energy received by an area over time is called insolation.  Resultantly, the tropics and equator receive more insolation as they are warmer, and the temperatures decrease as they approach the poles due to a decrease in insolation (Dexter et al., 2018). The difference in the solar input creates the global patterns of atmospheric heating and circulation. Notably, the distance from the equator and the tropics to the sun is shorter, and the air is highly heated, igniting its tendency to rise.

Additionally, the earth rotates around the sun on a tilted axis. This explains why some parts experience intense solar radiation while others receive low.  For instance, the tropical and equatorial regions tend to be hotter than the polar and mid-latitude regions. The resultant uneven heating creates global patterns of circulations hence influencing the precipitation patterns.  However, the global patterns of atmospheric circulation and heating are influenced by three cells – Polar, Ferrel, and Hadley cells whose function is regulated by the earth’s poles and the equator.  The polar cell is driven by cold air sinking and operates between the latitudes of 60 and 90 degrees (Hammond & Pierrehumbert, 2018). In this case, the warm is rises towards the higher altitudes as the cold are descends. As a result, the cold air moves slowly and increasingly become easterly. The Ferrel cell maneuvers between the Hadley and Polar cells whereby the warm air rises at higher latitudes near the polar cell and cools as it moves to lower latitudes and descends in high-pressure areas (Hammond & Pierrehumbert, 2018).  In other words, it depicts the resultant effect of air motions from the storms occurring in the mid-latitudes.

The Hadley cell is responsible for trade winds and operates between 0 and 30 degrees. It begins with warm air rising at the equator in low-pressure areas and descends to high-pressure regions. The rising of the air at the equator moves it to the poles while deflecting to become westerly. This circulation breaks down as the air moves to the ground (Hammond & Pierrehumbert, 2018). The descending air returns to the equator and is deflected to the east, becoming easterly trade winds.  Generally, although the earth experiences disruptions of storms and weather fronts, there is a consistent pattern of the air that moves around the atmosphere.

1. b) What mechanisms produce high precipitation in the tropics?

Precipitation refers to a situation whereby the ascending moist air masses cool by forming water droplets in the atmosphere. High precipitation is rampant in areas with the rapid and continual ascension of air masses. In the tropics, the trade winds converge in the Inter-Tropical Convergence Zone (ITCZ) and ascend due to low pressure (Tharammal, Bala & Noone, 2017). In other words, the humid and warm air from both hemispheres joins in the ITCZ, causing the low-pressure areas to move up until it descends in high-pressure areas. This causes atmospheric convection, which increases precipitation in the tropics. Besides, there is also a high evaporation rate in these areas that causes the air to rise as it cools. As a result, the warm air condenses and holds more water causing high precipitation.

1. c) What mechanisms produce high precipitation at temperate latitudes?

High precipitation is usually due to the cold air rising from the earth’s surface. In this case, it occurs at the temperate latitudes due to the convergence of moist subtropical air and cold polar air, which enforces condensation (Popov et al., 2019). Besides, at the temperate latitudes, a lot of solar radiation is received, increasing the evaporation rate, increasing the amount of moist air in the atmosphere. Further, the temperate latitudes are characterized by the low-pressure system, which increased air rising, hence creating precipitation as the clouds develop through the rising air that collects moisture from dry land.

1. d) What mechanisms produce low precipitation in the tropics?

In the tropics, low precipitations result from warm prevailing winds, which hold less moisture. Usually, the tropics experience warm weather, and as the moist air flows over the mountains, precipitation is caused by tropical cyclones, convective clouds, and frontal systems (González-M et al., 2018). However, as the mountainous terrain slows down the winds, low precipitation occurs. In other words, the mountains force the moisture engulfed in the blowing winds to fall on the side that blocks them, as rain. Resultantly, the warm air condenses on one side while leaving the other side with low precipitation.

1. Use what you know about atmospheric circulation and seasonal changes in the sun’s orientation to Earth to explain the highly seasonal rainfall in the tropical dry forest and tropical savanna biomes.

The distribution of the precipitation on the earth’s surface relies on the global pressure systems. The tropical dry forests and tropical savannas are found in the ITCZ, where high precipitation is experienced (Hammond & Pierrehumbert, 2018). This results in the variation of the climate than in the tropical rain forest. They experience both wet and dry seasons, although the rains are less than in the rainforest. A few scattered trees and grassland dominate the tropical savannas. On the other side, the tropical dry forests are characterized by more green trees during the rainy seasons that wither and lose leaves during the dry season.  Notably, the rotation of the earth around its axis and its spherical shape influence the intensity of the rays hitting the ground and the amount of thermal energy absorbed. In this case, the dry trees and grassland depict limited capability to release water droplets to the atmosphere responsible for forming clouds. Resultantly, this reduces the amount of rainfall released in these areas compared to the areas with more trees. As a result, the rays reach the equator perpendicularly to the surface, making the tropics remain warmer to the temperate regions (Rubey et al., 2017). Contrary, as the rays approach the poles, they strike at an angle, spreading the energy to a larger surface area, cooling the areas.  As the earth rotates around the sun, insolation changes for higher latitudes while remaining constant at the equator. In other words, the areas that receive direct sunlight cause the air to become unsteady and rise, causing low pressure. This is due to the migration of winds that cause the shifting of ITCZ. The overhead sun causes low equatorial pressure leading to moist and warm air to rise. This causes high precipitation, and as the ITCZ shifts between the southern and northern hemispheres, it causes seasonal variation in pressure, leading to precipitation (Dexter et al., 2018). Therefore, during the dry season, the ITCZ moves to the other side of the equator, which allows the dry and warm trade winds to flow to the equator.  The shortened distance between the sun and the earth’s surface decreases the precipitation causing a dry season.

References

Dexter, K. G., Pennington, R. T., Oliveira-Filho, A. T., Bueno, M. L., Silva de Miranda, P. L., & Neves, D. M. (2018). Inserting tropical dry forests into the discussion on biome transitions in the tropics. Frontiers in Ecology and Evolution, 6, 104.

González-M, R., García, H., Isaacs, P., Cuadros, H., López-Camacho, R., Rodríguez, N., & Pizano, C. (2018). Disentangling the environmental heterogeneity, floristic distinctiveness and current threats of tropical dry forests in Colombia. Environmental Research Letters, 13(4), 045007.

Hammond, M., & Pierrehumbert, R. T. (2018). Wave-mean Flow Interactions in the Atmospheric Circulation of Tidally Locked Planets. The Astrophysical Journal, 869(1), 65.

Popov, L. E., Álvaro, J. J., Holmer, L. E., Bauert, H., Pour, M. G., Dronov, A. V., … & Zhang, Z. (2019). Glendonite occurrences in the Tremadocian of Baltica: first Early Palaeozoic evidence of massive ikaite precipitation at temperate latitudes. Scientific reports, 9(1), 1-10.

Rubey, M., Brune, S., Heine, C., Davies, D. R., Williams, S. E., & Müller, R. D. (2017). Global patterns in Earth’s dynamic topography since the Jurassic: the role of subducted slabs. Solid Earth, 8(5), 899-919.

Tharammal, T., Bala, G., & Noone, D. (2017). Impact of deep convection on the isotopic amount effect in tropical precipitation. Journal of Geophysical Research: Atmospheres, 122(3), 1505-1523.