Atmospheric 301 Notes
By Benya Vahdat
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Thermodynamics
This document covers the fundamental concepts of thermodynamics and atmospheric moisture, including the hydrological cycle, representation of water vapor content, and thermodynamic principles. It explains various measures of water vapor content such as vapor pressure, absolute humidity, mixing ratio, specific humidity, and relative humidity. The document also discusses the ideal gas law, hydrostatic equilibrium, and thermodynamic processes including adiabatic and diabatic processes. Key concepts include the role of temperature and pressure in determining atmospheric moisture and the principles governing the behavior of moist air.
Key Takeaways
- The document highlights the importance of understanding the hydrological cycle and the various ways to represent water vapor content in the atmosphere, which is crucial for analyzing weather phenomena.
- The ideal gas law and hydrostatic equilibrium are fundamental principles that govern the behavior of atmospheric gases and the balance of forces in the atmosphere.
- The distinction between adiabatic and diabatic processes is critical in understanding how air temperature changes and how these changes impact atmospheric conditions.
Precipitation Processes
This document discusses the various processes involved in precipitation formation, including the effects of curvature and solution on cloud droplets, the role of ice nuclei, and the different mechanisms of cloud droplet growth. It explains how precipitation forms in warm, cool, and cold clouds, and describes the different forms of precipitation such as rain, snow, graupel, hail, sleet, and freezing rain. The document highlights the importance of factors such as curvature, solution, and ice nuclei in determining the type and intensity of precipitation. It also explains the Bergeron Process, which is critical for the formation of precipitation in cool clouds, and the collision-coalescence process, which is important for warm clouds. The document provides detailed information on the different forms of precipitation, including their characteristics and formation mechanisms.
Key Takeaways
- The formation of precipitation is influenced by factors such as curvature and solution, which affect the saturation vapor pressure and the growth of cloud droplets.
- The Bergeron Process is a critical mechanism for the formation of precipitation in cool clouds, where the coexistence of ice and supercooled water leads to rapid growth of ice crystals.
- The collision-coalescence process is an important mechanism for the formation of precipitation in warm clouds, where large collector drops collide and merge with smaller drops to form larger droplets.
2. Vertical Structure of the Atmosphere
The document discusses the vertical structure of the Earth's atmosphere, focusing on the distribution of atmospheric variables such as density, pressure, and temperature with height. The atmosphere is divided into four distinct thermal layers: the troposphere, stratosphere, mesosphere, and thermosphere. The troposphere is the lowest layer, where most weather processes occur, and is characterized by a steady temperature decrease with height. The stratosphere is a layer of inverted temperature due to ozone absorption of ultraviolet radiation. The mesosphere is the coldest layer, with temperatures decreasing with height, while the thermosphere is characterized by increasing temperatures with height. The document also explains the concept of atmospheric pressure and density, and how they change with height.
Key Takeaways
- The troposphere contains 80% of the atmosphere's mass and is where most weather processes occur, with temperature decreasing at a lapse rate of 6.5°C/km.
- The stratosphere's temperature inversion is caused by ozone absorption of ultraviolet radiation, with the ozone layer existing between 20-30 km altitude.
- The mesosphere and thermosphere combined account for only 0.1% of the total atmospheric mass, with the mesosphere being the coldest layer and the thermosphere having increasing temperatures with height.
- Atmospheric pressure decreases exponentially with height, following the formula p = p0 e^(-z/H), where H is the scale height, approximately 8-8.5 km in the lower atmosphere.
Composition and Vertical Structure of the Atmosphere
The document discusses the composition and vertical structure of the atmosphere, including its evolution, key components such as nitrogen, oxygen, water vapor, carbon dioxide, and aerosols, and their roles in atmospheric processes. It covers the formation of the atmosphere, the hydrologic cycle, and the impact of human activities on atmospheric composition, particularly the increase in CO2 and the depletion of the ozone layer due to chlorofluorocarbons. The document also touches on the importance of these components in Earth's energy balance and climate.
Key Takeaways
- The atmosphere's composition has evolved significantly since its formation, with the early atmosphere being lost to space and a secondary atmosphere forming through volcanic outgassing and cometary impacts.
- Water vapor is the most abundant variable gas in the atmosphere, playing a crucial role in Earth's energy balance and atmospheric processes.
- Human activities, such as combustion and industrial processes, have significantly impacted atmospheric composition, leading to an increase in CO2 and depletion of the ozone layer.
- The ozone layer's depletion is primarily attributed to chlorofluorocarbons, which react with ozone in the stratosphere, and is exacerbated by the Antarctic circumpolar vortex.
- Understanding the composition and structure of the atmosphere is essential for grasping its role in climate and weather patterns, as well as the impacts of human activities on these processes.
Atmospheric Observations and Weather Information
The document provides an overview of various methods and instruments used for atmospheric observations and weather information. It covers temperature scales (Celsius, Fahrenheit, Kelvin) and their conversion formulas. Different types of barometers (mercury and aneroid) are discussed for pressure measurements. The document also explains various techniques for measuring wind and rainfall, including basic rain gauges and tipping bucket rain gauges. It highlights the importance of surface station observations, weather radar, and satellite observations in understanding weather patterns. Examples of radar observations, including those of hurricanes Katrina and Hugh, are provided. Additionally, the document touches upon airborne and shipborne observations as other means of gathering atmospheric data.
Key Takeaways
- The document emphasizes the diversity of methods used in atmospheric observations, from ground-based surface stations to advanced radar and satellite technologies, highlighting the comprehensive approach needed for weather monitoring.
- The inclusion of specific examples, such as radar observations of hurricanes, underscores the practical application of these measurement techniques in understanding severe weather events.
- The variety of measurement techniques discussed (temperature, pressure, wind, rainfall) indicates the complexity and multidimensionality of weather observation, requiring multiple data sources for accurate forecasting.