Atmosphere
The atmosphere is primarily composed of gases and vapors. It receives incoming solar energy from the sun, which gives rise to various climatic conditions. The lowest layer of the atmosphere, known as the troposphere, extends up to a height of 6 miles and is where weather phenomena are confined. Within the troposphere, temperature generally decreases with increasing altitude. The climatic elements of temperature, precipitation, clouds, pressure, and humidity in the troposphere account for significant variations in local climate, making them essential for our daily lives.
Origin of the Atmosphere
The atmosphere is an integral part of Earth, encompassing both the land and water bodies. It supports life through processes such as respiration and photosynthesis. Additionally, the atmosphere acts as a protective layer against harmful radiation and meteorite impacts. It also plays a vital role in physical processes like weathering.
Ist Stage: Nebular Accretion Process
The atmosphere is thought to have originated during the nebular accretion process. Gases like hydrogen and helium were segregated during the density stratification of the nebula, resulting in the formation of the first atmosphere.
IInd Stage: Volcanism and Outgassing
The next stage of atmospheric formation occurred due to volcanic activity and outgassing. The most abundant gas released was water vapor, which condensed and rained down, eventually forming the Earth’s oceans. Carbon dioxide, another significant gas, was washed off and dissolved in the oceans. Thus, the second atmosphere underwent modifications during this stage.
IIIrd Stage: Biological Processes
The third atmosphere began forming due to biological processes such as respiration and photosynthesis. These processes introduced oxygen into the atmosphere, along with the formation of ozone. Unlike the earlier atmospheres, the third atmosphere was a product of physical and biological processes rather than catastrophic events. The presence of anaerobic respiration in the early atmosphere played a crucial role in sustaining the first oxygen levels.
Components of the Atmosphere
The major components of the atmosphere include nitrogen (78%), oxygen (21%), argon (0.93%), carbon dioxide (0.03%), and water vapor. Minor components consist of helium, hydrogen, xenon, rare gases, and ozone. The atmosphere can be categorized into permanent gases, such as nitrogen, oxygen, and argon, which have relatively stable concentrations, and variable gases, mainly water vapor, which fluctuate in their amounts.
Structure of the Atmosphere
The organization of the atmosphere is based on density stratification, relative mixing, and temperature patterns. The atmosphere can be divided into lower and upper layers, with the lower layer being denser and having more molecules. The upper layer becomes progressively rarefied and lighter due to a lower concentration of molecules. Within the lower atmosphere, called the homosphere, major permanent gases are well mixed. Beyond 80 km, in the heterosphere, there is a segregation of molecular and atomic gases, and the atmosphere is no longer uniformly mixed. Temperature patterns in different layers of the atmosphere depend on greenhouse gases like carbon dioxide, water vapor, ozone, and dust particles, which absorb solar radiations and affect the rate of cooling and warming.
Extension of Atmospheric Boundaries
The atmospheric boundaries extend up to approximately 800-1000 km from the Earth’s surface. However, the perceptible atmosphere is mostly confined within about 30 km, although this can vary.
Features of the Atmosphere
The atmosphere possesses several noteworthy features that contribute to its unique properties.
A. Transparency to the Visible Spectrum
The atmosphere is transparent to the visible spectrum of light, allowing sunlight to reach the Earth’s surface. This transparency enables the existence of life on our planet as it enables photosynthesis, the process by which plants convert sunlight into energy.
B. Selective Absorption of Radiation
The atmosphere exhibits selective absorption properties, which refers to its ability to absorb certain types of radiation. Various gases present in the atmosphere have the capacity to absorb specific wavelengths of energy.
- Ability to Absorb Radiation
Different gases in the atmosphere possess the capability to absorb specific wavelengths of radiation. This selective absorption plays a crucial role in determining the distribution of energy in the atmosphere.
All Parts of the Atmosphere
The entire atmosphere, including all its gases, cannot absorb all types of radiation. The interactions between radiation and the different components of the atmosphere are essential in shaping its overall behavior.
A. Earth as a Heat Engine
The Earth can be considered as a heat engine due to its ability to transform and distribute energy. It operates similar to a black body, which absorbs and emits radiation based on its temperature.
B. Energy Radiated from the Sun
The energy emitted by the Sun covers a wide electromagnetic spectrum. However, the bulk of the energy that enters the Earth’s atmosphere consists of high radiation energy, primarily in the form of UV and visible spectrum energy.
Layers of the Atmosphere
The atmosphere is divided into distinct layers, each with unique characteristics and functions. Understanding these layers is crucial for comprehending atmospheric processes and phenomena.
A. Troposphere
The troposphere is the lowest layer of the atmosphere and is often referred to as the weather layer. It is heated from below, primarily through energy transfer from the Earth’s surface. Key features of the troposphere include:
- Cooling with Height
As altitude increases, the temperature decreases. The rate of cooling in the troposphere is approximately 6.4 degrees Celsius per kilometer, which is known as the Normal Lapse Rate (NLR). This rate varies considerably based on surface conditions, seasonal variations, and atmospheric composition.
- Influence on Weather Processes
The troposphere’s atmospheric lapse rate is responsible for driving various weather processes and phenomena, such as cloud formation, precipitation, and wind patterns.
B. Stratosphere
The stratosphere is situated above the troposphere and is heated from above. This heating is primarily caused by the presence of ozone, which is capable of absorbing harmful UV radiation. Key characteristics of the stratosphere include:
- Calm and Non-Mixing Layer
The stratosphere is a relatively stable and non-mixing layer due to the presence of ozone. This stability leads to the formation of scattered clouds known as nacreous clouds.
C. Thermosphere
The thermosphere is situated above the stratosphere and contains ions and dissociated molecules capable of absorbing radiation. Key features of the thermosphere include:
- Heating from Above
The thermosphere is primarily heated by the absorption of high-energy radiation from the Sun. As a result, it becomes warmer with increasing altitude.
- High Temperature and Low Heat Energy
Although the thermosphere exhibits extremely high temperatures, it contains very low heat energy due to its rarefied nature.
D. Mesosphere
The mesosphere serves as a transition zone between the stratosphere and the thermosphere. It cools with increasing altitude and is characterized by the presence of noctilucent clouds, which do not cause rain.
E. Isothermal Transition Zones
Between temperature layers, there are regions known as isothermal transition zones where the rise and fall of temperature come to a halt.
F. Tropopause
The tropopause acts as a lid, trapping all atmospheric processes and circulations within the troposphere. It is often referred to as the upper tropospheric inversion layer. Notably, the tropopause’s height varies between the equator and the poles due to differences in convection and lapse rate.
Other Layers Based on Composition
Apart from the distinct layers based on temperature and characteristics, there are additional layers defined by atmospheric composition.
A. Ozonosphere
The ozonosphere extends from approximately 15-20 kilometers to around 55 kilometers above the Earth’s surface. The ozone layer reaches its maximum concentration between 20-30 kilometers within the stratosphere. However, ozone is not present in significant quantities in the troposphere and is considered a pollutant when found in this region.
B. Ionosphere
The ionosphere is located between 80 and 800 kilometers above the Earth’s surface and is a part of the thermosphere. It plays a vital role in radio communication, particularly in long-distance transmissions. The ionosphere consists of lower layers known as the Kennelly-Heaviside layer, capable of reflecting medium waves, and the Appleton layer, which reflects shortwave radio waves.
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