Overview
This lecture reviews key atmospheric processes, including temperature controls, humidity, cloud formation, and precipitation types, crucial for understanding weather and climate patterns.
Temperature and Heat Concepts
- Heat is the total kinetic energy of atoms or molecules in a substance.
- Temperature measures the average kinetic energy of atoms or molecules.
- Convection transfers heat through the movement of mass within a fluid.
Temperature Controls
- Factors affecting temperature: latitude, altitude, albedo, cloud cover, time of day/year, proximity to water, and continentality.
- Higher altitudes are colder due to reduced absorption and emissions in the atmosphere.
- Surfaces with high albedo reflect more solar energy (e.g., snow); dark surfaces absorb more heat (e.g., asphalt).
- Clouds lower daytime temperatures by reflecting sunlight and increase nighttime temps by emitting radiation.
Water Cycle & Humidity
- The hydrologic cycle circulates water through the atmosphere, biosphere, lithosphere, and hydrosphere, powered by the sun.
- 85% of atmospheric water vapor comes from ocean evaporation; 15% from plant transpiration.
- Evapotranspiration refers to combined evaporation and plant transpiration.
Changes of State and Latent Heat
- Water changes state by gaining or losing energy, involving hydrogen bonds between molecules.
- Latent heat is energy absorbed or released during state changes (e.g., evaporation cools, condensation warms).
- Latent heat released in clouds causes updrafts, enhancing cloud growth.
Humidity and Measurement
- Humidity is the water vapor content of air and is crucial for weather processes.
- Relative humidity (RH) is the ratio of vapor content to capacity; inversely related to temperature.
- Dew point is the temperature at which air becomes saturated.
Lifting Mechanisms and Stability
- Air can rise by convective, orographic, frontal, or convergent uplift.
- Unstable air is warmer and rises on its own; stable air is cooler and resists vertical movement.
- Lifting condensation level (LCL) is the altitude where air becomes saturated.
Cloud and Fog Formation
- Clouds are groups of microscopic water droplets or ice crystals; fog is a cloud at Earth's surface.
- Fogs form via radiation, advection, uplift, evaporation, or precipitation mechanisms.
- Condensation nuclei like dust or pollen are needed for droplet formation.
Precipitation Processes
- Raindrop formation occurs via collision and coalescence (warm clouds) or ice crystal processes (cold clouds).
- The temperature profile of the atmosphere determines if precipitation falls as rain, snow, freezing rain, or ice pellets.
- Hail forms in cumulonimbus clouds and has layered structure.
Wind and Air Pressure
- Wind is caused by differences in air pressure, which result from variations in temperature and gas content.
- Air pressure is measured with a barometer; average sea level pressure is 1,013.25 mb.
- Thermal pressure comes from temperature changes; dynamic pressure from air movement.
Key Terms & Definitions
- Albedo — measure of a surface's ability to reflect solar radiation.
- Latent heat — energy absorbed or released during a change of state.
- Relative humidity (RH) — ratio of current water vapor to maximum possible, as a percent.
- Dew point — temperature where air reaches saturation.
- Air parcel — body of air with uniform properties.
- Adiabatic rate — temperature change of air parcel due to expansion or compression.
- Hydrologic cycle — circulation of water among Earth's systems.
- Condensation nuclei — small particles on which water vapor condenses.
Action Items / Next Steps
- Review diagrams of water cycle, cloud types, and precipitation processes.
- Practice identifying temperature controls and their effects on climate.
- Memorize key terms and their definitions.