1.3 Fundamental atmospheric processes and phenomena

The atmosphere is a complex system of gases, particles, and processes that shape our weather and climate. From its layered structure to the interplay of temperature, pressure, and moisture, understanding these elements is crucial for grasping atmospheric behavior.

Atmospheric phenomena like clouds, precipitation, and winds arise from intricate physical and chemical interactions. These processes, along with global circulation patterns and factors like solar radiation and topography, drive the ever-changing weather we experience daily.

Physical and Chemical Processes in the Atmosphere

Atmospheric processes and behavior

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• Composition of the atmosphere comprises nitrogen (78%), oxygen (21%), argon (0.93%), carbon dioxide (0.04%), and water vapor (variable)
• Atmospheric layers include the troposphere, the lowest layer containing most of the atmosphere's mass where temperature decreases with height; the stratosphere, containing the ozone layer that absorbs UV radiation and where temperature increases with height; the mesosphere, where temperature decreases with height; and the thermosphere, where temperature increases with height due to absorption of solar radiation
• Atmospheric pressure decreases with height and is measured in millibars (mb) or hectopascals (hPa)
• Ideal Gas Law: $PV = nRT$, where $P$ represents pressure, $V$ represents volume, $n$ represents the number of moles, $R$ represents the gas constant, and $T$ represents temperature
• Atmospheric stability refers to the atmosphere's ability to suppress (stable) or enhance (unstable) vertical motion, determined by the lapse rate (change in temperature with height)
• Greenhouse effect occurs when atmospheric gases (CO2, water vapor) absorb and re-emit infrared radiation, warming the Earth's surface and lower atmosphere

Formation of atmospheric phenomena

• Cloud formation occurs through condensation of water vapor on aerosol particles (cloud condensation nuclei) when air cools to its dew point temperature, resulting in various types of clouds (cumulus, stratus, cirrus)
• Precipitation forms when cloud droplets or ice crystals grow large enough to fall, leading to rain, snow, sleet, or hail
• Wind is the horizontal motion of air caused by pressure gradients and the Coriolis force, with geostrophic wind representing the balance between pressure gradient force and Coriolis force
• Thunderstorms develop in unstable atmospheres with strong vertical motion, characterized by lightning, thunder, heavy rain, and sometimes hail
• Tornadoes are rotating columns of air extending from a thunderstorm to the ground, formed in highly unstable atmospheres with strong wind shear

Atmospheric circulation and weather patterns

• General circulation includes the Hadley cell (rising motion near the equator, sinking motion in the subtropics), Ferrel cell (rising motion in the mid-latitudes, sinking motion in the polar regions), and Polar cell (rising motion in the polar regions, sinking motion in the subpolar regions)
• Jet streams are fast-moving, narrow bands of strong winds in the upper atmosphere, with the polar jet stream located between the Ferrel and Polar cells and the subtropical jet stream located between the Hadley and Ferrel cells
• Rossby waves are large-scale atmospheric waves that influence weather patterns, caused by the variation of the Coriolis force with latitude
• El Niño-Southern Oscillation (ENSO) involves fluctuations in ocean temperatures and atmospheric pressure in the Pacific Ocean, affecting global weather patterns
• North Atlantic Oscillation (NAO) involves fluctuations in atmospheric pressure differences between the Icelandic Low and the Azores High, influencing weather patterns in Europe and North America

Factors in atmospheric development

• Solar radiation is the primary energy source for atmospheric processes, varying with latitude, season, and time of day
• Topography influences local and regional weather patterns by blocking or deflecting air flow, creating rain shadows, and generating orographic precipitation (mountains)
• Land-sea interactions, driven by differences in heat capacity and surface properties between land and water, influence the development of sea and land breezes, monsoons, and lake-effect precipitation
• Anthropogenic factors, such as urbanization (urban heat island effect), land use changes, and greenhouse gas emissions, affect atmospheric processes
• Teleconnections are linkages between atmospheric and oceanic phenomena in distant parts of the world (ENSO, NAO, Arctic Oscillation)
• Feedback mechanisms are processes that amplify or dampen initial changes in the atmosphere (ice-albedo feedback, water vapor feedback)