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Earth's Energy Balance

• Climate is significantly influenced by the unequal heating of the Earth's surface.
• Unequal heating is primarily due to the angle at which the Sun's rays strike the planet.
• The heating disparity creates climate zones and drives atmospheric and oceanic circulation.
• Circulation patterns transport heat from the equator towards the poles.

Insolation and Latitude

• Insolation (incoming solar radiation) varies with latitude.
• Near the equator, direct sun rays lead to higher energy absorption & warmer temperatures.
• Higher latitudes have oblique sun rays, spreading energy over a larger area, resulting in cooler temperatures.
• Ice and snow reflect solar radiation, further reducing energy absorption in polar regions.

Atmospheric Heating

• The Earth's surface absorbs high energy, shortwave radiation from the Sun.
• It reradiates this energy as lower energy, longwave infrared energy.
• Reradiated energy heats the atmosphere from below, contributing to planetary warmth.
• Efficiency varies globally due to differences in surface reflection and absorption rates.
• The tropics absorb more energy than they lose.
• Polar regions lose more energy than they gain.

Seasonal Variation

• The Earth's axial tilt introduces seasonal insolation variations.
• During summer, a hemisphere tilts towards the Sun receiving direct sunlight and experiencing warmer temperatures.
• During winter, a hemisphere tilts away from the sun receiving less direct sunlight and experiencing cooler temperatures.
• Equinoxes occur when the Sun is over the equator resulting in equal day and night lengths globally.
• Solstices mark maximal tilt towards or away from the Sun.

Atmospheric Circulation

• The atmosphere acts as a conveyor belt moving heat from surplus areas (tropics) to deficit areas (poles).
• This movement is driven by air pressure and temperature differences, resulting from unequal heating.
• Warm air rises at the equator and moves toward the poles at high altitudes before cooling and descending.
• This air movement cycle redistributes heat.

Oceanic Circulation

• Oceans are crucial in Earth's heat balance via surface and deep ocean currents.
• Warmer surface currents transfer heat from the tropics towards the poles.
• Cold currents carry cooler water back towards the equator.
• The Coriolis effect (Earth's rotation), causes currents to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
• Deep ocean currents further aid in transferring heat globally, driven by differences in water density related to temperature and salinity.

Global Air Circulation

• Global air circulation moves thermal energy, air, and water from regions near the Equator (energy surpluses) to polar regions (energy deficits).
• It is driven by the unequal heating of Earth's atmosphere.

World Pressure Belts

• These patterns, which shift seasonally due to the Sun’s varying intensity, are crucial in determining weather and climate.
• Isobars represent lines of equal atmospheric pressure on maps.

Location of Pressure Belts

• The Intertropical Convergence Zone (ITCZ) shifts between the northern and southern hemispheres seasonally.
• The ITCZ shift influences the position of low and high-pressure zones.

Causes and Characteristics of Global Pressure Belts

• Equatorial Low-Pressure Zone: Located between 10° N and 10° S.
• Warm, wet air is due to intense solar heating and consistent daylight.
• Subtropical High-Pressure Zone: Found between 20°-35° N and S.
• Hot, dry air results from descending air that heats upon compression.
• Especially present over deserts.
• Subpolar Low-Pressure Zone: Located at approximately 60°-70° N and S.
• Air spun away by centrifugal forces due to Earth's rotation results in cool, wet conditions.
• Polar High-Pressure Zone: Around the poles (90° N and S).
• Low temperatures and dense, sinking air create cold, dry conditions with limited precipitation.

Air Temperature, Air Pressure, and Wind

• High and low-pressure cell formation is significantly influenced by the differential heating of land and water.
• Differential heating impacts local weather patterns.

Pressure Cells in the Southern Hemisphere

• High-pressure cells exhibit anticlockwise sinking air.
• Low-pressure cells feature clockwise rising air, influencing weather conditions.

Tricellular Model of Global Air Circulation

• Hadley Cell: Operates between the equator and 30° latitudes.
• Responsible for tropical rains and the trade winds.
• Ferrel Cell: Exists between 30° and 60° latitudes.
• Acts as a transitional zone that affects temperate weather patterns.
• Polar Cell: Found from 60° latitudes to the poles, driving polar climates.

Jet Streams

• Strong, high-altitude winds significantly influence weather patterns.
• Jet streams affect storm tracks and temperature distributions.

Forces Influencing Wind

• Pressure Gradient: Drives wind from high to low-pressure areas.
• Coriolis Force: Causes wind to deflect right in the Northern Hemisphere and left in the Southern Hemisphere.
• Affects wind direction and speed.
• Geostrophic Wind: Results from the balance between pressure gradient and Coriolis forces.
• Leads to winds that flow parallel to isobars at high altitudes.

Air Masses and Global Circulation

• Air masses are large bodies of air with uniform temperature and humidity.
• They are classified by their source region's latitude and underlying surface characteristics.
• They significantly impact weather patterns, especially where different air masses converge, forming fronts.

Regional and Local Winds

• Monsoon Winds: Characterized by seasonal reversals in wind direction.
• Cause dry and wet seasons.
• Especially prominent in South and Southeast Asia.
• Föhn Winds: Dry, warm downslope winds, such as the Chinook or the Berg winds.
• Can lead to rapid warming and drying conditions on the leeward sides of mountain ranges.
• The Brickfielder, a northeast summer wind that blows dust and sand across Australia.
• The Sirocco that blows as a south wind across North Africa from the Sahara.

Climate Regions of Africa

• Africa's climate is highly variable across different regions.
• The variation in rainfall patterns is the primary driver.
• Africa experiences high temperatures almost universally, with exceptions only in high altitudes and during winter in the extreme north and south.
• Variability in rainfall is crucial in determining the environmental differences across the continent.

Subsidence and Convergence on Rainfall

• Subsidence: Air descends, warming adiabatically, and becoming drier.
• It plays a significant role in determining the dry seasons in Africa, especially in areas north of the Intertropical Convergence Zone (ITCZ).
• Kano (Nigeria) and Atar (Mauritania) experience prolonged dry seasons due to subsidence and the Harmattan winds.
• Convergence: The convergence of moist air masses, particularly during the shift of the ITCZ northwards, brings about the wet season in the summer months.
• Regions like Calabar and Kano experience high rainfall.

Role of Oceans on Climate

• Oceans drive the global climate, acting as a 'heat engine.'
• Proximity to the sea results in a maritime climate with minimal temperature fluctuations.
• Areas far from the sea experience a continental climate with significant temperature variations.
• Warm and cold ocean currents influence Africa's climate by modifying temperatures over land.
• The Benguela and Canary currents, both cold, contribute to the dry and arid conditions in regions like the Namib Desert.

El Niño and La Niña Events

• Significant climatic phenomena resulting from changes in the Pacific Ocean's surface temperatures.
• They impact global weather patterns.
• El Niño: Characterized by the reversal of normal air and sea water circulation patterns.
• It leads to widespread changes in weather, including heavy rainfall and droughts in different parts of the world.
• La Niña: Essentially the opposite of El Niño.
• Results in stronger trade winds and upwelling of cold water in the Pacific.
• Influences global climatic conditions in distinct ways.

Reading and Interpreting Synoptic Weather Maps

• Synoptic weather maps are vital for understanding current weather conditions.
• They feature symbols that represent various atmospheric phenomena.
• Isobars: Lines connect points of equal atmospheric pressure.
• The spacing between them indicates the strength of winds.
• High and Low-Pressure Cells: Identified by closed circular isobars influence weather patterns.
• Both influence including wind speed and direction.

Dryland Ecosystems and Classification

• Drylands cover approximately 41% of Earth's land area.
• They support over two billion people, predominantly in developing countries.
• These ecosystems are categorized based on their aridity levels into hyperarid, arid, semiarid, and dry subhumid areas.
• Each category faces unique challenges but collectively confronts risks associated with drought and desertification.
• This can lead to degraded land, reduced agricultural productivity, and increased poverty and environmental migration.

Drought: Definition, Types, and Global Extent

• Drought is a prolonged period of deficient rainfall resulting in water scarcity.
• Meteorological Drought: Long periods of below-average rainfall.
• Agricultural Drought: Insufficient soil moisture affecting crops.
• Hydrological Drought: Depletion of water reserves.
• Socioeconomic Drought: Inability to meet water demands affecting society and economy.
• Globally, drought affects all continents.
• Long-term occurrences in regions like Australia and the southwestern USA.
• The Sahel region in Africa experiences the highest frequency of droughts, while equatorial areas have the lowest.

Desertification: Definition, Extent, Causes, and Consequences

• Desertification refers to the process of fertile land transforming into desert primarily due to human activities and climatic changes.
• An estimated 12 million hectares of land degrade into desert annually.
• This jeopardizes the livelihoods of nearly 900 million people worldwide.
• Direct Causes: Climate change, unsustainable agricultural practices, overgrazing, deforestation, and soil erosion.
• Indirect Causes: Inadequate knowledge, policies promoting resource degradation.
• Local and National Consequences: Desertification reduces agricultural yields, threatens food security, prompts migration, and weakens economies.
• Global Consequences: Desertification contributes to biodiversity loss, increases greenhouse gas emissions, and diminishes fresh water reserves.

Management Strategies

• Effective desertification prevention requires sustainable resource use strategies, awareness, funding, and coordinated efforts among stakeholders.
• While prevention is preferable, rehabilitation of already degraded lands remains challenging and expensive.