Atmosphere: Composition, Structure, and Climate Dynamics
Atmospheric Composition
The atmosphere consists of major and minor constituents, including reagents and non-variable elements.
Structure and Function of the Atmosphere
The sun emits ultraviolet, visible, and infrared electromagnetic radiation (shortwave, visible, and longwave). Radiation from the center of the spectrum penetrates atmospheric layers most easily, primarily as visible light. Short wavelengths have high energy and penetrating power. Longer wavelengths are emitted by the Earth and used for communication.
Troposphere
The troposphere is the lowest layer of the atmosphere, ending at the tropopause. Its height varies with latitude and season. It contains 80% of atmospheric gases, making life possible. Atmospheric pressure, measured by a barometer, decreases with altitude and temperature (vertical temperature gradient). The greenhouse effect and weather changes occur here, making it the climate layer. Most clouds and precipitation form, and vertical movement disperses pollutants and dust.
Stratosphere
The stratosphere extends from the tropopause to the stratopause, characterized by horizontal air movements. Noctilucent clouds form in the lower stratosphere. The ozone layer is located between 15 and 30 km, and temperature increases with altitude.
Mesosphere
The mesosphere extends to the mesopause. Air density is sufficient to form meteors. Temperature decreases with altitude.
Thermosphere/Ionosphere
In the thermosphere, also known as the ionosphere, temperature increases. Electrical charges flow from the ionosphere to the Earth’s surface, and negative charges flow from the surface to the ionosphere. Storms play a major role in recharging the Earth’s electrical capacitor. Radio waves emitted from Earth bounce off this layer, enabling communication, but solar radiation can sometimes block them. Auroras, such as the Northern Lights (aurora borealis) and Southern Lights (aurora australis), occur here. Yellow-green light is produced when electrons strike oxygen molecules at low pressure, while red light occurs when collisions happen at very low pressure against nitrogen molecules.
Exosphere
The exosphere is the outermost layer with very low atmospheric density. The sky appears dark because the air cannot scatter sunlight.
Fluid Layers: Atmosphere and Hydrosphere
Both the atmosphere and hydrosphere are fluid, consisting of air and water, respectively.
Water moves from the hydrosphere to the atmosphere through evaporation. Upon cooling, it condenses and forms clouds. Precipitation returns water to the Earth, where it follows several pathways: surface runoff, retention (depending on soil, climate, and biological activity), and infiltration. Infiltration allows water to permeate permeable soil layers and enter groundwater, leading to groundwater runoff into the sea. Water entering the biosphere returns through transpiration and evaporation, collectively known as evapotranspiration.
Operation of the Climate System
The climate system operates based on movements generated by gradients between two points.
Gradients
A gradient is a difference in temperature, humidity, or pressure between two points. Air transport occurs via wind, and water transport occurs via ocean currents. A higher gradient results in more vigorous wind or ocean currents. Flow ceases when parameters equalize, and the gradient reduces to zero.
Atmospheric Behavior
Atmospheric behavior varies due to differences in density, mobility, heat storage capacity, and heat transfer.
Vertical Movements
Air is a poor heat conductor. The Earth’s surface radiates heat, causing surface air to rise and higher altitude air to descend. Water is a better heat conductor, so the surface of the hydrosphere heats up, leaving the water below colder. Vertical movement can only occur in places where the surface water is colder than the water below.
Horizontal Movements
Horizontal movements, such as winds and ocean currents, are due to thermal contrasts generated by uneven solar heating of the Earth’s surface. This heat transport softens thermal differences between the poles and the equator. Landmasses hinder heat transport by slowing and deflecting winds and ocean currents.