NMES115 Session 4 Notes: Natural Environment - Global Phenomena

Weather and Climate

  • Weather: Temperature, moisture, and wind conditions at a specific place and time, including short-term changes and variations.

  • Climate: Long-term weather patterns in a locality, region, or globally, typically assessed over 30 years. Climate includes not only average conditions but also the frequency and intensity of extreme weather events.

  • Averages and Extremes: Averages and extreme conditions (maxima and minima), such as droughts and floods, are important. While extremes have less effect on long-term averages, they significantly impact ecosystems and human activities.

Solar Radiation

  • Earth's Energy Source: Earth receives all its energy from the sun as solar electromagnetic radiation. This energy drives weather patterns, ocean currents, and all life processes.

  • Basic Unit of Energy: Photon (packet of energy traveling as a wave). Photons exhibit wave-particle duality, carrying energy and momentum.

  • Wavelength and Frequency: Relation between frequency and wavelength of light. Different wavelengths correspond to different types of radiation, such as visible light, ultraviolet, and infrared.

Wavelength and Frequency Relation

  • Shorter Wavelength: Higher frequency. High-frequency radiation carries more energy.

  • Determination: Wavelength and frequency are determined by the amount of energy in the photon. The relationship is described by the equation E = h \cdot f, where E is energy, h is Planck's constant, and f is frequency.

Energy and Temperature

  • Absolute Zero: Any object above absolute zero (-273^\circ C or 0 Kelvin) possesses energy. Absolute zero is the theoretical point at which all molecular motion ceases.

  • Kinetic Energy: Energy causes atoms and molecules to vibrate. The faster the vibration, the higher the kinetic energy.

  • Temperature Measurement: Temperature measures the amount of kinetic energy. Common scales include Celsius, Fahrenheit, and Kelvin.

  • Atmospheric Layers: Earth's atmosphere has layers defined by temperature and pressure differences. These layers play crucial roles in protecting the Earth and regulating its climate.

The Atmosphere

  • Troposphere:

    • Lowest layer

    • 7-20 km: Varies with latitude and season, thinner at the poles and thicker at the equator.

    • 80% of atmosphere's mass: Contains most of the atmosphere's water vapor and aerosols.

    • Weather occurs here: Site of most weather phenomena, including cloud formation and storms.

    • Contains clouds, precipitation, and air pollutants

  • Stratosphere:

    • Up to 50 km from the top of the Troposphere

    • Ozone layer: Protects from harmful UV radiation. The ozone layer absorbs significant amounts of ultraviolet radiation from the sun.

    • Temperature increases due to UV absorption: Absorption of UV radiation heats the stratosphere.

    • Ozone concentration changes impact climate and weather: Variations in ozone levels affect temperature profiles and atmospheric circulation.

  • Mesosphere:

    • Middle layer (mésos in Greek)

    • Extends 50-80 km from the stratosphere

    • Temperature decreases with height: Reaching the coldest temperatures in the atmosphere.

    • Decrease in solar heating from stratosphere: Less direct solar radiation reaches this layer.

    • Meteors burn up here: Due to friction with the sparse air molecules.

  • Thermosphere:

    • Outermost layer

    • 80-600 km: Extends to the exosphere, gradually thinning into space.

    • Contains the ionosphere (reflects radio waves, aiding communication and navigation): Ionization occurs due to solar radiation, creating a layer of charged particles.

    • Temperature increases with height: Absorption of highly energetic solar radiation.

    • Absorption of highly energetic solar radiation: Including X-rays and extreme UV radiation.

The Earth’s Energy Budget

  • Solar-Powered System: Earth uses sunlight for photosynthesis, climate regulation, and other processes. Solar energy is the primary driver of Earth's climate system.

  • Balancing Uneven Heating: Atmosphere and oceans balance uneven solar heating through evaporation, convection, wind, and ocean circulation (Earth's heat engine). These processes redistribute heat from the equator towards the poles.

  • Energy Balance: Incoming solar radiation and outgoing heat create an energy budget. Maintaining equilibrium is crucial for stable temperatures.

  • Radiative Equilibrium: Incoming and outgoing energy balance, maintaining global temperature stability. Any imbalance leads to warming or cooling trends.

The Earth’s Energy Budget in Detail

  • Energy Emission: Sun emits shortwave light and ultraviolet energy; Earth radiates heat in thermal infrared wavelengths. The difference in wavelengths is due to the temperature difference between the sun and the Earth.

  • Temperature Stability: Requires balance between incoming and outgoing energy, regulated by Earth's energy budget. This balance is affected by factors such as greenhouse gas concentrations and albedo.

  • Analysis Levels: Surface, atmosphere, and top of the atmosphere. Each level has unique energy balance characteristics.

  • Energy Distribution: Approximately 29% of solar energy is reflected back into space (albedo); 71% is absorbed (48% by Earth surface, 23% by Earth's atmosphere); necessitating equal energy radiation for balance. Albedo is influenced by clouds, ice, and land cover.

Energy Absorption and Distribution

  • 71% Absorbed:

    • 48% by Earth's surface: Land and water absorb solar radiation, warming the surface.

    • 23% by Earth's atmosphere: Absorption by gases, clouds, and aerosols.

  • 48% Energy Emission: Required at Earth's surface (land and water)

    • Evaporation: 25%. Water absorbs heat when it evaporates, cooling the surface and adding moisture to the atmosphere.

    • Convection: 5%. Transfer of heat through the movement of air or water.

    • Infrared radiation (heat): 18%. Earth radiates heat in the infrared spectrum. Some of this heat is trapped by greenhouse gases.

The Greenhouse Effect

  • Natural Warming: The greenhouse effect naturally warms Earth's surface, making it habitable. Without the greenhouse effect, Earth would be too cold to support life as we know it.

  • Gases: Certain atmospheric gases trap heat from the Sun. These include carbon dioxide, water vapor, methane, and nitrous oxide.

  • Mechanism: Gases allow sunlight in but prevent some heat from escaping. This process is similar to how a greenhouse traps heat, hence the name.

The Unnatural Greenhouse Effect

  • Carbon Dioxide: CO_2 is a potent greenhouse gas, trapping heat. It is released through burning fossil fuels, deforestation, and industrial processes.

  • Atmospheric Lifetime: CO2 has a long atmospheric lifetime, remaining in the atmosphere for hundreds of years. This long lifetime means that the effects of CO2 emissions are long-lasting.

  • Intensified Effect: Increased CO_2 levels due to human activities intensify the greenhouse effect, trapping more heat. This leads to changes in global temperature and climate patterns.

  • Heat Imbalance: Earth continues to absorb solar energy, but less heat escapes into space. This creates an energy imbalance that drives global warming.

  • Global Warming: Imbalance in Earth's heat budget leads to global warming, primarily driven by greenhouse gas accumulation. This warming has significant impacts on ecosystems, sea levels, and human societies.

Global Patterns of Wind, Ocean Currents, and Precipitation

  • Seasonality: Temperature seasonality results from Earth's axial tilt of 23.5^\circ, which divides the Earth into latitudinal regions. This tilt causes different parts of the Earth to receive more direct sunlight at different times of the year.

  • Latitudinal Regions:

    • Regions north or south of equator at 10-degree intervals.

    • Arctic and Antarctic Circles at 66.5^\circ N and S: Boundaries where the sun does not set (summer solstice) or rise (winter solstice) for 24 hours.

    • Tropic of Cancer at 23.5^\circ N and Tropic of Capricorn at 23.5^\circ S: Boundaries where the sun is directly overhead at noon on the solstices.

    • Equator at 0^\circ

Seasonal Daylight Patterns

  • Summer Solstice (June 21):

    • Arctic Circle (66.5^\circ N): 24 hours of daylight (polar day)

    • Tropic of Cancer (23.5^\circ N): 13.5 hours of daylight

    • Equator (0^\circ): 12 hours of daylight

    • Tropic of Capricorn (23.5^\circ S): 10.5 hours of daylight

    • Antarctic Circle (66.5^\circ S): 0 hours of daylight (polar night)

Wind Patterns

  • Influences: Solar radiation and Earth's rotation. Solar radiation heats the Earth unevenly, and the Earth's rotation creates the Coriolis effect, both of which influence wind patterns.

  • Air Density: Warm air rises (less dense), cool air sinks (denser). This density difference drives atmospheric circulation.

  • Unequal Heating: Creates winds as warm air rises and cool air replaces it. This process is a major driver of global wind patterns.

  • Rain Formation: Rising warm air cools, causing condensation and rain. This is why many tropical regions experience high rainfall.

  • Moisture Source: Moist air from contact with Earth's surface, especially oceans. Oceans are a major source of atmospheric moisture.

  • Subsidence Zones: Upper atmosphere air cools, becomes denser, and sinks. These zones are characterized by high pressure and clear skies.

  • Dry Air: Subsidence zones have dry air lacking moisture. This is because the air has already lost its moisture through condensation and precipitation.

  • Convection Cells: Warm air rising and sinking shapes atmospheric circulation. These cells distribute heat and moisture around the globe.

Wind Patterns and Convection

  • Equatorial Air: Warm air rises at the equator and travels to around 30^\circN and 30^\circS. This rising air is part of the Hadley cell circulation.

  • Subtropical Highs: At these latitudes, the warm air cools and sinks, creating high-pressure zones (N and S subtropical highs). These highs are associated with deserts and clear skies.

  • Equatorial Low: Rising warm air creates a low-pressure area at the equator. This low-pressure zone is associated with high rainfall and thunderstorms.

  • Air Movement: Warm air also rises at about 60^\circN and 60^\circS and moves north and south. This rising air is part of the Ferrel cell circulation.

  • Air Cooling: Air heading towards the equator cools at 30^\circN and 30^\circS, joining the subtropical highs. This cooling and sinking air reinforces the subtropical high-pressure zones.

  • Polar Air: Air heading towards the poles cools and sinks there. This sinking air forms the polar high-pressure zones.

  • Convection Cells: This setup forms three large convection cells in each hemisphere, from the equator towards the poles. These cells (Hadley, Ferrel, and Polar) are fundamental to global climate patterns.

Coriolis Effect

  • Description: The Coriolis effect is a phenomenon that causes moving air and water to be deflected due to the Earth's rotation. In the Northern Hemisphere, deflection is to the right; in the Southern Hemisphere, it is to the left.

Regions of Winds

  • Doldrums:

    • Location: Near the equator

    • Characteristics: Calm waters, little to no wind

    • Challenges: Difficulties for sailing ships

    • Associated with: Intertropical Convergence Zone (ITCZ). The ITCZ is a zone of low pressure where trade winds converge, leading to rising air and thunderstorms.

  • Horse Latitudes:

    • Location: Near 30^\circN and 30^\circS

    • Characteristics: High pressure, calm winds

    • Consequences: Stagnant and unnavigable waters

    • Subsidence Zones: No winds due to sinking air

  • Trade Winds (Northeast and Southeast):

    • Location: Between the doldrums and horse latitudes

    • Direction: Deflected to the left, eastward (northeast in the Northern Hemisphere, southeast in the Southern Hemisphere)

  • Westerlies:

    • Location: Between horse latitudes and 60^\circN and 60^\circS zones

    • Direction: Deflected to the right, westward (northwest in the Southern Hemisphere, southwest in the Northern Hemisphere)

  • The Roaring Forties:

    • Description: Strong westerly winds, especially from 40^\circS to Marion Island. These winds are particularly strong due to the lack of landmasses to obstruct them.

Ocean Currents

  • Description: Massive systems of moving water influenced by wind, density variations, and Earth's rotation. Ocean currents redistribute heat, affecting regional and global climate.

  • Impact: Significant effect on coastal climate and weather patterns. Warm currents bring milder temperatures, while cold currents bring cooler temperatures and often drier conditions.

  • Gulf Stream: Originates in the Gulf of Mexico, flows along the eastern coast of North America, crosses the Atlantic, and warms Western Europe. The Gulf Stream is a major heat transporter, keeping Western Europe significantly warmer than other regions at similar latitudes.

  • Antarctic Circumpolar Current: Largest ocean current, circulating clockwise around Antarctica. This current isolates Antarctica, contributing to its cold climate.

Ocean Currents - Upwellings and Gyres

  • Upwellings: Bring cold, nutrient-rich water to the surface. Upwellings support high levels of marine productivity.

  • Downwellings: Transport surface water downward, carrying oxygen and nutrients to deeper layers.

  • Surface Currents: Driven by wind and form circular movements (gyres). Gyres are large rotating systems of ocean currents.

  • Gyre Influence: Westerly winds at high latitudes move east, and easterly trade winds near the equator move west. This wind pattern drives the formation and movement of gyres.

Ocean Currents - Gyre Characteristics

  • Gyre Direction: Move anticlockwise in the southern hemisphere and clockwise in the northern hemisphere. This is due to the Coriolis effect.

  • Climate Impact: Transport warm or cool water towards land. This transport of heat affects regional climate patterns.

  • Warm Currents: Agulhas, Mozambique, and Gulf Stream warm adjacent land areas. These currents moderate temperatures and increase humidity.

  • Cold Currents: Benguela and California currents cool land climate. These currents often lead to drier conditions and coastal fog.

  • Upwelling Zones: Winds push surface water away from continents, drawing up nutrient-rich water from ocean depths. These zones are highly productive, supporting large fisheries.

  • Productivity: Upwelling zones are cold and highly productive, such as the west coast of southern Africa.

Rain Shadows

  • Cause: Mountain chains. Mountains force air to rise, leading to condensation and precipitation on the windward side.

  • Windward Side: Air pushed up from lower elevations.

    • Rising air cools (adiabatic cooling) and moisture condenses, forming rain.

  • Leeward Side: Descending, heating air (katabatic heating). This air is dry, leading to arid conditions.

  • Examples:

    • The Drakensberg in South Africa causes a rain shadow to the west.

    • The dry Karoo is in the rain shadow of the southern Cape mountains.

    • The area north of the Soutpansberg is drier.

El Niño and La Niña

  • El Niño:

    • Cyclical Phenomenon: Occurs every 3-7 years in the Pacific Ocean. El Niño is part of the El Niño-Southern Oscillation (ENSO) cycle.

    • Trade Winds: Weaken, allowing warm equatorial water to accumulate in the central and eastern Pacific. This reduces upwelling and alters ocean temperatures.

    • Marine Impact: Disrupts the marine food chain, diminishing fish populations. The warm water reduces nutrient availability, affecting marine life.

    • Global Weather: Brings drought to the western Pacific, rains to South America, and storms to the central Pacific. El Niño affects weather patterns worldwide.

  • La Niña:

    • Counterpart: Stronger trade winds cause cold water accumulation in the central and eastern Pacific. La Niña is also part of the ENSO cycle, representing the opposite phase of El Niño.

    • Global Weather: Leads to heavy monsoons in India and Southeast Asia, cool and wet weather in southeastern Africa, and various other weather anomalies worldwide. La Niña also has widespread impacts on global weather patterns.

  • South Africa:

    • El Niño: Drought Conditions

    • La Niña: Flooding and soil erosion