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.
Sample Answer
Sample Answer
Global Patterns of Atmospheric Heating and Circulation
The global patterns of atmospheric heating and circulation play a crucial role in determining the distribution of precipitation across different regions of the Earth. These patterns are driven by the uneven distribution of solar radiation on the planet’s surface. The primary mechanisms that influence precipitation patterns are the Hadley Cell circulation in the tropics and mid-latitude weather systems at temperate latitudes.
Tropics
In the tropics, the primary mechanism that produces high precipitation is the Intertropical Convergence Zone (ITCZ). The ITCZ is a band of low pressure that encircles the Earth near the equator. It is characterized by the convergence of trade winds from both hemispheres, resulting in upward motion and the formation of thunderstorms. As warm, moist air rises in this region, it cools and condenses, leading to heavy precipitation.
Additionally, the high temperatures in the tropics contribute to increased evaporation rates, which further enhance atmospheric moisture content. The combination of these factors results in high precipitation levels in tropical regions.
On the other hand, the mechanisms that lead to low precipitation in the tropics can be attributed to two main factors. Firstly, regions that lie in the rainshadow of mountain ranges experience reduced precipitation due to the blocking effect of mountains on moisture-laden winds. Secondly, areas that are located in the subsidence zones of the Hadley Cell experience sinking air, which inhibits cloud formation and leads to drier conditions.
Temperate Latitudes
At temperate latitudes, high precipitation is primarily caused by mid-latitude weather systems, such as extratropical cyclones and fronts. These systems result from the interaction between cold polar air masses and warm tropical air masses. As these air masses converge, they create a boundary known as a front, which acts as a trigger for precipitation. The cyclonic circulation associated with these systems brings moist air into contact with cooler air, leading to condensation and the formation of precipitation.
The seasonal changes in the sun’s orientation to Earth also play a significant role in influencing precipitation patterns at temperate latitudes. During summer, when the sun is at a higher angle, there is increased heating and evaporation, leading to more convective activity and higher precipitation levels. In contrast, during winter, when the sun is at a lower angle, there is reduced heating and evaporation, resulting in lower precipitation levels.
Seasonal Rainfall in Tropical Dry Forest and Tropical Savanna Biomes
The highly seasonal rainfall in tropical dry forest and tropical savanna biomes can be explained by a combination of factors related to atmospheric circulation and seasonal changes in the sun’s orientation to Earth.
In these biomes, the dominant mechanism responsible for rainfall is the migration of the ITCZ. During the summer months, when the ITCZ shifts toward the poleward side of its normal position, it brings heavy rainfall to these regions. This is because as warm, moist air rises near the equator, it creates a low-pressure area that draws in moisture from the surrounding areas. This results in abundant rainfall during this period.
However, during the winter months, when the ITCZ migrates back toward its normal position near the equator, these regions experience a dry season. This is because the shift of the ITCZ takes away the main source of moist air and rainfall. As a result, these biomes undergo a period of drought and reduced precipitation.
The seasonal changes in the sun’s orientation also contribute to the highly seasonal rainfall in these biomes. During summer, when the sun is at a higher angle, there is increased heating and evaporation, leading to higher moisture content in the atmosphere. This enhances convective activity and increases the likelihood of rainfall. In contrast, during winter, when the sun is at a lower angle, there is reduced heating and evaporation, resulting in decreased moisture availability and lower chances of rainfall.
In conclusion, global patterns of atmospheric heating and circulation determine the distribution of precipitation on Earth. The mechanisms producing high precipitation include the Intertropical Convergence Zone (ITCZ) in the tropics and mid-latitude weather systems at temperate latitudes. The ITCZ brings heavy rainfall to tropical regions through convergence of trade winds, while mid-latitude weather systems trigger precipitation through interactions between air masses. The highly seasonal rainfall in tropical dry forest and tropical savanna biomes can be attributed to the migration of the ITCZ and seasonal changes in solar orientation.
