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Questions and Answers
What provides food for anchovies and other fish?
Plankton
What economic resource is derived from the harvesting of bird excrement?
Fertilizer
What is one economic consequence of El Niño?
Match the effects of El Niño and La Niña in different regions of Africa:
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What does the dipole refer to?
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The eastern Pacific becomes significantly cooler during El Niño.
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What does the Indian Ocean Dipole (IOD) influence?
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What is Earth's energy balance?
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What is insolation?
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Higher latitudes receive more insolation than lower latitudes.
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What causes seasonal differences?
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What happens during a winter solstice?
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What occurs due to the Coriolis force?
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What is the radiation budget?
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The ______ current is a warm ocean current found in the southwest Indian Ocean.
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The polar front is where cold polar air converges with warm surface air.
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Which cell in atmospheric circulation is located between the equator and 30° latitude?
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Match the following ocean currents with their characteristics:
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What type of air mass is characterized by high temperatures and high humidity?
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Stable air is associated with high pressure and typically leads to rain.
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What causes monsoons?
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Föhn winds can cause droughts and increase the risk of ______.
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Which air mass is classified as moderately moist and slightly unstable?
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Match the following air mass types with their characteristics:
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What happens during an El Niño event?
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La Niña is characterized by cooling of the central and eastern tropical Pacific Ocean.
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The process of air rising and cooling is described by ______.
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What leads to flooding during wet monsoons?
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Which climatic event involves weaker tropical easterlies?
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Study Notes
Earth’s Energy Balance
- The balance between incoming solar radiation (insolation) and outgoing radiation from Earth.
- Depends on latitude and seasons.
- Insulation is absorbed by the Earth's crust and surface, heating the atmosphere through sensible and latent heat transfer.
Key Terms
- Insolation: Incoming solar radiation falling on a unit area of the Earth's surface.
- Radiation Budget: The balance of energy gain and energy loss.
- Conduction: Energy transfer by contact, passing from one molecule to the next.
- Convection: Energy transfer by movement of molecules with lots of energy.
- Latent Heat: Heat or energy absorbed or released during a phase change of a substance.
Altitude, Aspect, and Latitude
- Altitude: Natural decrease in temperature at higher altitudes due to less dense air molecules.
- Aspect: The angle at which the sun's rays strike the Earth (insolation angle of incidence) influences temperature.
- Latitude: Distance from the equator; temperature decreases as distance from the equator increases due to less direct insolation.
Ocean Currents
- Benguela Current: Cold, northward flowing current in the southeast Atlantic Ocean.
- Agulhas Current: Warm current found in the southwest Indian Ocean, flowing down the east coast of South Africa.
Latitudinal Influence
- The sun's radiation hits Earth in parallel waves due to the vast distance between the Sun and Earth.
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Latitudinal Factors:
- Distance of atmosphere
- Insolation angle of incidence
- Length of day and night
- Albedo of Earth’s surface
- The curvature of the earth
Albedo
- The fraction of insolation reflected from the Earth’s surface back into space.
- High albedo (1) reflects more insolation, Low albedo (0) absorbs more insolation.
Lower Latitudes (0°—30°)
- Shorter distance for heat to travel, less insolation lost through absorption, reflection, and scattering.
- Greatest angle of incidence, more direct rays.
- Less annual variation in length of day and night.
- Lower albedo, vegetation-covered surfaces absorb more insolation.
Higher Latitudes (60°—90°)
- Greater distance for heat to travel, more insolation lost through absorption, reflection, and scattering.
- Smallest angle of incidence, more oblique rays.
- Greater annual variation in length of day and night, noticeable fluctuations as seasons change.
- Higher albedo, white snow and ice reflect more insolation.
Seasonal Influence
- Caused by the Earth’s axis tilt (23.5°) and revolution around the sun.
- Solstice: When one hemisphere is facing directly towards the sun and the other is facing away.
- Equinox: When the sun's rays are directly at the equator, resulting in equal lengths of day and night.
Southern Hemisphere
- Summer Solstice (December 22nd): Tropic of Capricorn, longer days and shorter nights.
- Autumn Equinox (March 21st): Equator, days and nights are equal across the world.
- Winter Solstice (June 21st): Tropic of Cancer, shorter days and longer nights.
- Spring Equinox (September 22nd): Equator, days and nights are equal across the world.
Northern Hemisphere
- Winter Solstice (December 22nd): Tropic of Capricorn, shorter days and longer nights.
- Spring Equinox (March 21st): Equator, days and nights are equal across the world.
- Summer Solstice (June 21st): Tropic of Cancer, longer days and shorter nights.
- Autumn Equinox (September 22nd): Equator, days and nights are equal across the world.
Annual Radiation Budget
- The balance of energy gain (from insolation) and energy loss (terrestrial radiation).
- To achieve this balance, the same amount of energy that is received must be lost.
- Net radiation surplus: some places receive more insolation than they lose.
- Net radiation deficit: some places receive less insolation than they lose.
- The atmosphere and oceans move surplus energy from the tropics to the poles to maintain the Earth's overall energy balance.
Heat Transfer
- Excess heat is transferred away from the equator.
- Vertical heat transfer: Radiation, conduction, convection, and latent heat release.
- Horizontal heat transfer: Surface winds and ocean currents.
Ocean Currents
- Ocean circulation moves heat stored in water from lower latitudes to higher latitudes.
- Atmospheric circulation influences ocean currents.
- Wind blowing over the ocean surface creates drag, moving surface water.
- Warm ocean currents carry heat from the tropics towards the polar regions.
- Cold ocean currents carry cold water from higher latitudes towards lower latitudes.
Wind
- Uneven heating of Earth creates pressure differences in the atmosphere.
- Pressure Gradient Force (PGF): The force producing air flow from regions of high pressure to regions of low pressure.
- Equatorial low pressure: Forms due to more intense insolation, less dense rising air.
- Polar high pressure: Forms due to less intense insolation and greater heat loss, more dense sinking air.
Global Air Circulation
- Pressure differences cause cold, dry surface winds to flow from polar high regions to the equatorial low pressure.
- Warm, moist air rises at the equator, diverges in the upper atmosphere and flows towards the poles.
- Over the polar regions, air cools, becomes more dense and sinks back down to the equator.
Atmospheric Circulation Cells
- Hadley Cell: Atmospheric circulation cell between the equator and 30° latitude.
- Ferrell Cell: Atmospheric circulation cell between 30° latitude and the polar front.
- Polar Cell: Atmospheric circulation cell between the polar front and the poles.
Global Pressure Belts
- Equatorial Low-pressure Belt (ELPB): Warm, light, ascending and converging air in the equatorial region.
- Subtropical High-Pressure Belt (STHPB): Hot dry air that forms as warm air descending from the tropics heats adiabatically.
- Subpolar Low-pressure Belt (SPLPB): Cool wet weather caused by the meeting of cold air masses from higher latitudes and warm air masses from lower latitudes.
- Polar High-Pressure Belt (PHPB): Area of high pressure located at 90° N/S, extremely cold and dry air.
Intertropical Convergence Zone (ITCZ)
- Equatorial low-pressure belt where trade winds of the two hemispheres converge.
Global Winds
- Polar Easterly: Dry, prevailing winds blowing from the high-pressure areas near the north and south poles towards the low-pressure areas.
- Subtropical Westerly: Warm, prevailing winds in the middle latitudes, blowing from the subtropical high-pressure belt towards the subpolar low-pressure belt (west to east).
- Tropical Easterly (Trade Winds): Warm, moist winds blowing from the east to the west, originating from the subtropical high-pressure belt and flowing towards the equatorial low-pressure belt.
The Coriolis Force
- Earth’s rotation on its axis deflects surface winds off their normal north and south directions.
- Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
- Strengthens when wind is blowing faster.
Geostrophic Flow
- A theoretical wind formed when there is a balance between the pressure gradient force and the Coriolis force.
- Occurs in ocean currents and winds when there is a geostrophic balance.
- The geostrophic wind blows parallel to the isobars.
- Often occurs in the upper atmosphere where surface friction is eliminated, enabling geostrophic balance.
- Jet Streams: Strong geostrophic winds blowing from west to east in the upper atmosphere.
Adiabatic Processes
- Adiabatic cooling: Decreasing heat through a change in air pressure caused by an air mass expanding.
- Adiabatic heating: Increasing heat through a change in air pressure caused by an air mass compressing.
Global Pressure Belts and Cells
- Equatorial Low Pressure Belt: Near the equator, warm air rises in huge convection currents.
- Subtropical High Pressure Belt: Cooling air diverges in the upper atmosphere towards the poles, sinks, and heats adiabatically.
- Subpolar Low Pressure Belt: Cool polar air converges with warm surface air, creating a front and forcing warm air to rise.
- Polar High Pressure Belt: Cold polar air sinks creating high pressure on the surface.
Atmospheric Circulation Cells Explained
- Hadley Cell: Rising air at the equator cools and condenses, forming thunderstorms. Diverging sinking air heats adiabatically, creating warm and dry conditions at the subtropical high-pressure belt. Surface winds are called tropical easterly winds (trade winds).
- Ferrel Cell: Convergence of warm westerly winds and cold polar easterly winds at the polar front creates frontal rain.
- Polar Cell: Sinking air at the Polar high pressure flows towards the subpolar low pressure belt, forming polar easterly winds.
Air Masses
- A large volume of air with similar characteristics (temperature, atmospheric pressure, and humidity).
- Stable Air: Subsidin (sinking), heavy air associated with high pressure and no rain.
- Unstable Air: Rising, condensing air associated with low pressure and rain.
Air Mass Types
- Equatorial Air Masses (mE, cE): High (hot) temperatures, very humid, extremely unstable.
- Tropical Air Masses (mT, cT): Warm temperatures, mT: very humid (unstable), cT: hot and dry (stable).
- Polar Air Masses (mP, cP): mP: very cool, moderately moist (slightly unstable), cP: very dry (stable) or very cold on land in subpolar regions.
- Arctic and Antarctic Air Masses: Extremely cold, extremely dry, stable.
Monsoons
- Seasonal reversal of atmospheric pressure and winds, accompanied by rainfall.
Monsoon Causes
- Differential heating and cooling of land and sea areas causes changes in atmospheric pressure and winds.
- The Intertropical Convergence Zone (ITCZ) shifts north in the Northern Hemisphere and south in the Southern Hemisphere during summer, leading to the convergence of trade winds and convectional rainfall.
- The Himalayan mountain range influences the ITCZ's movement, triggering heavy rainfall on the Indian side in July.
Wet Monsoon Effects
- Irrigation provides water for agriculture, industrial use, and domestic consumption.
- Flooding can damage crops and infrastructure, leading to loss of habitats and fatalities.
- Drought conditions during the wet monsoon can cause water shortages for agriculture, industry, and domestic use, leading to reduced crop yields and increased wildfire risk.
Dry Monsoon (Winter)
- Dry monsoons occur during winter.
- Land experiences cold temperatures and high atmospheric pressure, while the ocean is warmer and experiences low pressure.
- Air flows from the land's high pressure to the ocean's low pressure.
- This results in intense rainfall over the ocean and drought conditions over land.
Wet Monsoon (Summer)
- Wet monsoons occur during the summer.
- Land experiences warm temperatures and low atmospheric pressure, while the ocean is cooler and has high pressure.
- Air moves from the ocean's high pressure to the land's low pressure.
- This results in intense temperatures and rainfall over the land, often leading to flooding.
Föhn Winds
- Föhn winds are dry, hot winds that descend on the leeward side of mountains, originating in areas with significant altitude changes.
- Air rises on the windward side, cooling, becoming saturated, and forming clouds, rain, or snow.
- Descending air on the leeward side heats up, resulting in hot, dry winds at the foot of the mountain.
Fohn Wind Examples
- Berg Wind: Coastal areas of southern Africa
- Chinook: Rocky Mountains in the USA
- Zonda: Andes Mountains in Argentina
- Santa Ana: Southern California, USA
Lapse Rate
- The lapse rate measures how much air temperature changes per 100 meters of altitude change.
- Dry Adiabatic Lapse Rate (DALR): 1°C change per 100 meters for unsaturated air.
- Wet Adiabatic Lapse Rate (WALR): 0.5°C change per 100 meters for saturated air.
Africa's Weather & Climate
- Africa has seven distinct climate regions influenced by its location over the equator, land and sea proximity, topography, and ocean currents.
- About 70% of Africa lies within the tropics, leading to mostly tropical climates.
- The three broad categories of climate in Africa are:
- Tropical: Equatorial and Savanna
- Semi-Desert & Dryland: Semi-desert and Desert
- Humid Mid-latitude: Mediterranean, Highveld, and Humid Subtropical
Equatorial Climate
- Found between 6° and 7° north and south.
- High temperatures year-round due to consistent high solar angle.
- Receives convectional rainfall from intense daytime heat, often resulting in thunderstorms.
- High annual rainfall.
Savanna Climate
- Found between 5° and 15° north and south.
- Transitional zone between equatorial and desert climates.
- Summer: Hot temperatures and rainfall.
- Winter: Cool temperatures and dry conditions.
- Progressive decline in annual rainfall during the dry season, lasting 3-8 months in Tanzania.
- Warm temperatures year-round due to the warm Mozambique current.
- High annual rainfall due to the wetting effect.
Semi-arid Climate
- Winter: Cold and dry.
- Summer: Rainfall.
- Found on the dry sides of savanna and the Namibian Sahara.
- Very hot summers, exceeding 32°C.
Desert Climate
- Winter: Moderately warm.
- Very high temperatures.
- Minimal to no rainfall.
- Low humidity.
Highveld Climate
- Found in the highveld of South Africa.
- Summer: Rainfall.
- Winter: Dry and sunny.
- Plateau is located at high altitudes.
Mediterranean Climate
- Found in the northern and southern tips of Africa.
- Hot, sunny, and dry summers due to cold ocean currents bringing dry air.
- Rainfall mostly in winter from wet, moist air brought by warm ocean currents.
Humid Subtropical Climate
- Occurs in Southeast Africa.
- Characterized by year-round rainfall, heaviest in summer.
- Long, hot, and humid summers.
- Daily intense, brief convective thundershowers.
- Mild or slightly above-freezing winter temperatures.
Pacific Ocean
- The largest and deepest ocean on Earth.
- Plays a crucial role in forming trade winds, influencing weather patterns, marine life, and ocean currents.
- Wind drag creates ocean currents.
Walker Air Circulation (Walker Cell) – Normal Conditions
- Tropical easterlies blow across the Pacific Ocean, carrying moist air and warm surface water (South Equatorial Current) towards the Western Pacific (Indonesia and Australia).
- This creates low pressure over the Western Pacific.
- Cold, nutrient-rich water (Peruvian Current) upwells along the Eastern Pacific (coast of South America), creating a temperature gradient with warm water in the West and cooler water in the East.
- Results in rising air and low pressure over the warm Western Pacific and sinking air and high pressure over the cooler Eastern Pacific.
- Thermocline: Transition layer between warm surface water and cold deep water.
- Upwelling: Rising of cold, nutrient-rich water from the deep ocean to the surface, often occurring off the coast of South America.
El-Niño
- An event characterized by warming of the central and eastern Pacific Ocean, leading to significant global weather changes.
- Tropical easterlies weaken, causing warm surface waters to flow eastwards towards the eastern Pacific.
- This suppresses upwelling of cold water in the east, leading to lower pressure over the eastern and central Pacific.
- Cooler than normal waters collect toward the western Pacific, resulting in less rainfall and higher pressure.
- This creates wetter conditions over South America and the central Pacific and drier conditions in the western Pacific (Indonesia).
Extreme El-Niño
- Characterized by reversed trade winds, stronger warm water flow toward the eastern Pacific, and increased pressure differences between east and west.
- Leads to extremely warm conditions, flooding in the east, and drier conditions in the west.
La-Niña
- An intensified Walker atmospheric circulation cell, characterized by cooling of the central and eastern tropical Pacific Ocean.
- Stronger tropical easterlies blow across the tropical Pacific, carrying warm, moist air and warmer surface waters towards the western Pacific.
- This creates lower pressure over the western Pacific.
- Increased cold water upwelling along the eastern Pacific (cold Peruvian Current) creates higher pressure over the eastern Pacific.
- This results in drier conditions over South America and wetter conditions in the western Pacific.
Factors Triggering El Niño and La Niña
- Warm ocean waters in the central and eastern Pacific.
- Atmospheric pressure changes.
- Tropical cyclones.
- Seasonal changes in global patterns.
- Local land and sea interactions.
- Human activities (e.g., burning fossil fuels, cloud seeding).
Effects of El Niño and La Niña
El Niño Effects
- Drought conditions in Africa, leading to smaller harvests, livestock shortages, food insecurity, and malnutrition.
- Devastating impact on Peruvian anchovy fisheries, leading to decreased fish and seabird populations.
La Niña Effects
- Flooding in Africa south of the equator.
- Drought in Africa north of the equator.
The Dipole
- Referes to the difference in ocean temperatures between two regions of the Pacific Ocean.
- The ENSO dipole has two contrasting poles:
- Eastern Pacific becomes significantly warmer during El Niño.
- Western Pacific becomes significantly cooler.
- The Indian Ocean Dipole (IOD) is a similar phenomenon, characterized by temperature differences between the western and eastern parts of the Indian Ocean, influencing weather patterns across the region.
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