🧭Physical Geography Unit 10 – Weather Systems & Climate Types

Key Concepts & Terminology

• Atmosphere consists of layers (troposphere, stratosphere, mesosphere, thermosphere, exosphere) with varying temperatures and pressures
• Weather refers to short-term atmospheric conditions in a specific area
  • Includes temperature, humidity, precipitation, wind speed, and direction
• Climate describes long-term average weather patterns over a large area
  • Influenced by factors such as latitude, elevation, and proximity to water bodies
• Greenhouse gases (carbon dioxide, methane, water vapor) trap heat in the atmosphere contributing to the greenhouse effect
• Albedo measures the reflectivity of a surface
  • High albedo surfaces (snow, ice) reflect more solar radiation while low albedo surfaces (forests, oceans) absorb more
• Coriolis effect deflects moving objects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere due to Earth's rotation
• Jet streams are fast-moving air currents in the upper atmosphere that influence weather patterns and air mass movement

Atmospheric Processes

• Solar radiation drives atmospheric circulation by heating the Earth's surface unevenly
  • Equatorial regions receive more direct sunlight compared to polar regions
• Convection currents form as warm air rises and cool air sinks creating wind patterns and heat transfer
• Hadley cells are large-scale atmospheric circulation patterns that redistribute heat from the equator to the mid-latitudes
  • Consist of rising air at the equator, poleward movement aloft, descending air in the subtropics, and surface flow back towards the equator
• Ferrel cells are mid-latitude circulation cells driven by the Coriolis effect and temperature gradients
  • Characterized by rising air at 60° latitude, equatorward movement aloft, descending air at 30° latitude, and surface flow towards the poles
• Polar cells are small-scale circulation patterns in the polar regions
  • Feature rising air at 60° latitude, poleward movement aloft, descending air at the poles, and surface flow back towards 60° latitude
• Rossby waves are large-scale atmospheric waves that meander in the upper atmosphere influencing weather patterns and jet stream paths
• El Niño and La Niña are opposite phases of the El Niño-Southern Oscillation (ENSO) that affect global weather patterns
  • El Niño characterized by warmer-than-average sea surface temperatures in the eastern Pacific Ocean
  • La Niña characterized by cooler-than-average sea surface temperatures in the eastern Pacific Ocean

Types of Weather Systems

• Low-pressure systems (cyclones) are areas of rising air, cloudy skies, and precipitation
  • Associated with fronts and unstable atmospheric conditions
• High-pressure systems (anticyclones) are areas of sinking air, clear skies, and stable atmospheric conditions
• Fronts mark the boundary between two air masses with different temperatures and densities
  • Cold fronts occur when cold air advances and displaces warmer air
  • Warm fronts occur when warm air advances and overrides cooler air
  • Stationary fronts occur when two air masses meet but neither advances
  • Occluded fronts form when a cold front overtakes a warm front lifting both air masses off the ground
• Tropical cyclones are low-pressure systems that form over warm tropical oceans
  • Characterized by strong winds, heavy rainfall, and storm surges
  • Also known as hurricanes (North Atlantic, Northeast Pacific), typhoons (Northwest Pacific), or cyclones (South Pacific, Indian Ocean)
• Thunderstorms are localized weather systems featuring lightning, thunder, strong winds, and heavy precipitation
  • Can occur in isolation or as part of larger weather systems (squall lines, supercell thunderstorms)
• Tornadoes are violently rotating columns of air that extend from a thunderstorm to the ground
  • Most common in the United States (Tornado Alley) but can occur worldwide

Global Climate Patterns

• Köppen climate classification system categorizes Earth's climates based on temperature and precipitation patterns
  • Five main climate groups: tropical, dry, temperate, continental, and polar
• Tropical climates are found near the equator and feature high temperatures and abundant rainfall year-round
  • Includes tropical rainforests (Amazon, Congo Basin) and tropical monsoon regions (Southeast Asia, India)
• Dry climates occur in areas with low precipitation and high evaporation rates
  • Includes hot deserts (Sahara, Arabian) and cold deserts (Gobi, Atacama)
• Temperate climates are found in the mid-latitudes and experience distinct seasonal changes
  • Includes Mediterranean climates (California, Southern Europe), humid subtropical climates (Southeastern United States, Eastern Australia), and oceanic climates (Western Europe, New Zealand)
• Continental climates are found in the interiors of large landmasses and feature extreme temperature variations between summer and winter
  • Includes humid continental climates (Northeastern United States, Eastern Europe) and subarctic climates (Alaska, Siberia)
• Polar climates are found in the high latitudes and experience long, cold winters and short, cool summers
  • Includes tundra climates (Northern Canada, Russia) and ice cap climates (Antarctica, Greenland)
• Monsoons are seasonal wind patterns that bring heavy rainfall to certain regions during the summer months
  • Caused by differential heating between land and ocean surfaces
  • Major monsoon regions include South Asia, East Asia, and West Africa

Climate Classification Systems

• Köppen climate classification system is the most widely used and is based on temperature and precipitation patterns
  • Assigns a letter code to each climate type (A-tropical, B-dry, C-temperate, D-continental, E-polar)
  • Further subdivides climates using second and third letters (f-rainforest, m-monsoon, w-desert, s-steppe, h-hot, k-cold)
• Thornthwaite climate classification system emphasizes the role of evapotranspiration in determining climate types
  • Uses a moisture index to classify climates as humid, subhumid, semiarid, or arid
• Trewartha climate classification system is a modified version of the Köppen system
  • Adjusts the temperature criteria for certain climate types and adds a sixth main climate group (F-highland)
• Holdridge life zones classification system relates climate to vegetation patterns
  • Uses mean annual biotemperature and precipitation to define life zones (tropical dry forest, boreal moist forest)
• Spatial Synoptic Classification (SSC) system categorizes daily weather conditions into six main types
  • Dry polar, dry moderate, dry tropical, moist polar, moist moderate, and moist tropical
  • Useful for studying air pollution, human health, and energy consumption patterns

Factors Influencing Climate

• Latitude affects the amount of solar radiation received at the Earth's surface
  • Low latitudes receive more direct sunlight resulting in higher temperatures
  • High latitudes receive less direct sunlight resulting in lower temperatures
• Elevation influences temperature and precipitation patterns
  • Temperature decreases with increasing elevation due to the adiabatic lapse rate
  • Precipitation generally increases with elevation on the windward side of mountain ranges (orographic lift)
• Proximity to water bodies moderates temperature and increases humidity
  • Oceans and large lakes act as heat sinks absorbing and releasing heat slowly
  • Coastal areas experience milder temperatures compared to inland areas at the same latitude
• Atmospheric circulation patterns (Hadley cells, Ferrel cells, polar cells) redistribute heat and moisture globally
  • Rising air in the equatorial regions leads to abundant rainfall (Intertropical Convergence Zone)
  • Descending air in the subtropics creates dry, stable conditions (subtropical high-pressure belts)
• Ocean currents transfer heat and moisture from one region to another
  • Warm currents (Gulf Stream, Kuroshio) bring warmer temperatures and increased precipitation to adjacent coastal areas
  • Cold currents (California Current, Canary Current) bring cooler temperatures and decreased precipitation to adjacent coastal areas
• Topography influences local and regional climate patterns
  • Mountain ranges can block or channel air flow creating rain shadows and föhn winds
  • Valleys and basins can trap cold air leading to temperature inversions and air pollution

Weather Forecasting & Instruments

• Weather forecasting predicts future atmospheric conditions based on current observations and computer models
  • Short-range forecasts (1-3 days) are most accurate and rely heavily on current observations
  • Medium-range forecasts (3-10 days) and long-range forecasts (10+ days) are less accurate due to the chaotic nature of the atmosphere
• Weather satellites provide continuous global coverage of atmospheric conditions
  • Geostationary satellites orbit at a fixed position relative to the Earth's surface
  • Polar-orbiting satellites circle the Earth from pole to pole providing detailed images and data
• Weather radar uses radio waves to detect precipitation and track storm movement
  • Doppler radar measures wind speed and direction by analyzing the frequency shift of returned radio waves
• Weather balloons carry radiosondes that measure temperature, humidity, and pressure at various altitudes
  • Provide valuable data for understanding atmospheric structure and initializing weather models
• Surface weather stations measure temperature, humidity, pressure, wind speed, and direction at ground level
  • Automated stations can provide continuous data while manual stations rely on human observers
• Computer models simulate atmospheric processes using mathematical equations and physical principles
  • Global models (GFS, ECMWF) provide long-range forecasts and cover the entire Earth
  • Regional models (WRF, NAM) provide short-range forecasts and cover smaller areas with higher resolution
• Ensemble forecasting involves running multiple models with slightly different initial conditions
  • Helps quantify uncertainty and improve forecast accuracy by averaging results from multiple model runs

Climate Change & Its Impacts

• Climate change refers to long-term shifts in global or regional climate patterns
  • Primarily caused by human activities that increase greenhouse gas concentrations in the atmosphere
• Greenhouse gases (carbon dioxide, methane, nitrous oxide) trap heat in the atmosphere leading to global warming
  • Burning fossil fuels, deforestation, and industrial processes are major sources of greenhouse gas emissions
• Global average temperature has increased by approximately 1.1°C since pre-industrial times
  • Warming is expected to continue with projected increases of 1.5-4.5°C by 2100 depending on future emissions
• Sea level rise occurs due to thermal expansion of ocean water and melting of land-based ice (glaciers, ice sheets)
  • Projected sea level rise of 0.3-1.0 meters by 2100 depending on future emissions and ice sheet dynamics
• Changes in precipitation patterns are expected with some regions becoming wetter and others becoming drier
  • Wet regions (tropics, high latitudes) are likely to experience increased precipitation
  • Dry regions (subtropics, mid-latitudes) are likely to experience decreased precipitation and more frequent droughts
• Extreme weather events (heatwaves, hurricanes, floods) are becoming more frequent and intense due to climate change
  • Warmer temperatures increase the likelihood of heatwaves and the intensity of tropical cyclones
  • Changes in atmospheric circulation patterns can lead to more persistent weather systems and prolonged extreme events
• Ecosystem impacts include shifts in species ranges, altered phenology, and changes in community composition
  • Many species are moving to higher latitudes and elevations in response to warming temperatures
  • Earlier spring arrival and later fall senescence are altering plant and animal life cycles
  • Some species may face extinction if they are unable to adapt or migrate to suitable habitats
• Human impacts include threats to food security, water resources, and public health
  • Crop yields may decline in some regions due to increased heat stress and changes in precipitation patterns
  • Water scarcity may increase in areas affected by drought and reduced snowpack
  • Heatwaves, air pollution, and vector-borne diseases pose risks to human health, particularly for vulnerable populations