Earth's Energy Balance PDF

Earth’s Energy Balance This is the balance between incoming solar radiation and outgoing radiation from the Earth. The energy balance depends on latitude and seasons. Insulation Through Absorption: Insulation is absorbed by the Earth's crust and surface. Heating The Atmosphere: Sensi...

Earth’s Energy Balance This is the balance between incoming solar radiation and outgoing radiation from the Earth. The energy balance depends on latitude and seasons. Insulation Through Absorption: Insulation is absorbed by the Earth's crust and surface. Heating The Atmosphere: Sensible heat transfer: The absorbed heat from the Earth's surface warms the air directly through conduction and convection. Latent heat transfer: Some of the absorbed heat is used to evaporate water, turning it into water vapor, which then rises into the atmosphere, carrying latent heat energy. Outgoing terrestrial radiation: The Earth's surface also emits long-wave radiation due to its temperature, which heats up the overlaying atmosphere when absorbed. KEY WORDS Insolation – incoming solar radiation falling on a unit area of the Earth’s surfaced 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 – the heat or energy that is absorbed or released during a phase change of a substance  ALTITUDE ASPECT Height above sea level LATITUDE The angle at Natural decrease in temp Distance which the Less dense air molecules from the sun’s rays at high altitudes equator strike the Decrease in earth temp as Insolation is (insolation distance received from equator angle of incidence) UNEQUALLY increases across the OCEAN CURRENTS earth's surface Benguela (cold) Agulhas (warm) DISTANCE FROM THE OCEAN Circulate anti- COSTAL—maritime, low temperature clockwise in SH range Circulate HINTERLANDS—continental climate, clockwise in NH high temperature range Latitudinal Influence The Sun's radiation hits the Earth in parallel waves because of the vast distance between the Indirect rays Sun and the Earth combined with the Sun's immense size. LATITUDINAL FACTORS concentrated rays 1. Distance of atmosphere 2. Insolation angle of incidence Indirect rays 3. Length if day and night 4. Albedo of Earth’s surface 5. The curvature of earth KEY WORDS Albedo – the fraction of insolation reflected from the Earth’s surface back into space (1 = high albedo; 0 = low albedo). Insolation angle of incidence – the angle at which the sun’s rays strike the earth. LOWER LATITUDES HIGHER LATITUDES (0°—30°) (60°—90°) Distance of Atmosphere Distance of Atmosphere In the lower latitudes the In the higher latitudes the heat has a shorter heat has a greater distance to travel, distance to travel, therefore less insolation is therefore more insolation lost through absorption, is lost through absorption, reflection and scattering. reflection and scattering. Angle of Incidence Angle of Incidence The lower latitudes The higher latitudes receive the greatest angle receive the smallest angle of incidence and more of incidence and oblique direct rays. rays. Length of Day and Length of Day And Night Night Less annual variation—no Greater annual variation— significant change in the significant change in duration of daylight and duration of daylight and darkness darkness Remains consistent Fluctuates noticeably as throughout the year the seasons change Albedo Albedo Lower albedo Higher albedo Vegetation covered White snow and ice surfaces absorbs more reflects insolation insolation Effect & Result Effect & Result Dispersed solar rays Concentrated solar rays Absorbed by a larger Absorbed by a smaller surface area of earth surface area of earth Cooler atmospheric Hotter atmospheric temp temperature Most intense at Equator Least intense at the Poles  Seasonal Influence Seasonal differences are caused by: THE EARTH’S AXIS Axis is tilted at 23,5° to the north-south pole It rotates on this axis once every 24 hours (creating day and night) Atmospheric temperatures are influenced by how many hours of daylight an area receives. THE REVOLUTION AROUND THE SUN One revolution around the sun takes 365 ¼ days (this path is called an orbital) Throughout this orbit, the amount of light each area receives varies in length The angle of earth’s axis does not change, but the relative position of this axis to the sun does change Therefore, the seasons are caused by amount of daylight and darkness hours and the type of insolation (oblique or direct) KEY WORDS Solstice – when one hemisphere is facing Autumn Equinox directly towards the sun and the other is facing away Insolation angle of incidence – the sun’s rays are Winter Summer Solstice directly at the Solstice equator, resulting in equal lengths of day and night Spring Equinox  Southern Hemisphere Season & Date Position of Direct Length of Day & Night Insolation Summer solstice — Tropic of Capricorn Longer days and shorter nights 22nd December Autumn equinox — Equator Days and nights are equal across the 21st March world Winter solstice — Tropic of Cancer Shorter days and longer nights 21st June Spring equinox — Equator Days and night are equal in length 22nd September across the world Northern Hemisphere Season & Date Position of Direct Length of Day & Night Insolation Winter solstice — Tropic of Capricorn Shorter days and longer nights 22nd December Spring equinox — Equator Days and nights are equal across the 21st March world Summer solstice — Tropic of Cancer Longer days and shorter nights 21st June Autumn equinox — Equator Days and night are equal in length 22nd September across the world Annual Radiation Budget Radiation Budget – the balance of energy gain (from insolation) and energy loss (terrestrial radiation). This describes how the energy is used and returned to space. To achieve this balance the same amount of energy that is received must be lost. Higher latitudes should get colder, and lower latitudes should get hotter. But the atmosphere and oceans move surplus energy from the tropics to the poles to maintain the earth’s overall energy balance Net radiation surplus – some places receive more insolation than they lose Net radiation Deficit – some places receive more insolation than they lose Heat Transfer There is an energy surplus within the tropics There is an energy deficit within the polar regions The excess heat is transferred away from the equator. Heat is transferred vertically through radiation, conduction, convection and laten heat release Heat is transferred horizontally through surface winds and ocean currents. Ocean Currents Ocean circulation moves heat that is stored in the water from lower latitudes to higher latitudes. Atmospheric circulation influences the ocean currents. Wind blowing over the ocean surface creates drag because of friction. This drag moves the surface water. Warm ocean currents carry the stored heat from the tropics towards the polar regions. Cold ocean currents from the higher latitudes carry cold water towards the lower latitudes where it is heated up again. Colder water is more still and has more marine wildlife, sea vegetation and nutrients. West winds drift Agulhas current – a warm current found in the southwest Indian ocean. It flows down the east coast of South Africa. Benguela current – a cold, northward flowing ocean current that can be found in the southeast Atlantic Ocean. Wind The uneven heating of earth creates pressure differences in the atmosphere. These differences create a pressure gradient force, causing wind to blow from regions of high pressure (HP) to regions of low pressure (LP). A belt of low-pressure forms in the equatorial regions This occurs because of more intense insolation. The air above the surface becomes less dense and rises. This causes equatorial low pressure. A belt of high-pressure forms in the polar regions This occurs because of less intense insolation and greater heat loss. The air above the surface becomes more dense and sinks. This causes polar high pressure. Pressure Gradient Force (PGF) – the force producing air flow from regions of high pressure to regions of low pressure.  Global Air Circulation The pressure difference causes cold, dry surface winds to flow from polar high regions to the equatorial low pressure. At the equator warm moist air rises. This warm air diverges in the upper atmosphere and flows towards the poles. Over the polar regions, the air cools, becomes more dense and sinks back down to the equator. Southern Hemisphere Northern Hemisphere High Pressure (anticyclones) Air cool, dry and dense HP Air sinks and diverges HP Clockwise in NH Anticlockwise in SH Low Pressure (cyclones) Air warm, moist and less LP dense LP Air rises and converges Anticlockwise in NH Clockwise in SH  90° Tropics HP Subtropical regions 60° Subpolar Low Pressure Belt LP Polar regions 30° Subtropical High Pressure Belt HP Horse latitudes 0° Equatorial Low Pressure Belt LP ITCZ (doldrums) 30° Subtropical High Pressure Belt HP Horse latitudes 60° Subpolar Low Pressure Belt LP 90° HP HORIZONTAL WIND VERTICAL CELLS Tropical easterlies (trade winds) Hadley cell Subtropical westerlies Ferrell cell Polar easterlies Polar cell BELTS AND CELLS Equatorial Low-pressure Belt – in the equatorial region and composed of warm, light, ascending and converging air. Subtropical High-Pressure Belt – a zone of hot dry air that forms as the warm air descending from the tropics heats adiabatically. Subpolar low-pressure Belt – a zone of 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 – an area of high pressure located at 90° N/S, the air is extremely cold and dry 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 Intertropical Convergence Zone (ITCZ) – equatorial low pressure belt along which the trade winds of the two hemispheres converge. WINDS Polar Easterly – dry, cold prevailing winds that blow 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 that blow from the subtropical high-pressure belt towards the subpolar low-pressure belt. These blow from the west to the east. Tropical Easterly (trade winds) – warm, moist winds that blow from the east to the west. They originate from the subtropical high-pressure belt and flow towards the equatorial low-pressure belt. The Coriolis Force The earth's rotation on its axis causes surface winds to be deflected off their normal North and South directions. Coriolis Force – a force which causes a body that moves freely with respect to the rotating earth to veer to the right in the northern hemisphere and to the left in the southern hemisphere. This force is not found between 0° — 5°N & S This force strengthens when wind is blowing faster Ferrell’s law dictates what direction wind will be deflected in. Ferrell’s law – due to the Coriolis force winds are deflected to the right in the Northern hemisphere and to the left in the Southern hemisphere. (Buy’s Ballot law) Geostrophic Flow This is a theoretical wind that is formed when there is a balance between the pressure gradient force and the Coriolis force. This balance occurs in ocean currents and winds when there is a geostrophic balance. The geostrophic wind blows parallel to the isobars. This wind often occurs in the upper atmosphere where surface friction is eliminated, enabling geostrophic balance to occur. Nearer to the surface, friction weakens the Coriolis force and so geostrophic balance cannot be reached. Because there is no Coriolis force between 0°— 5°, there is no geostrophic flow here. Jet streams – strong geostrophic winds blowing from west to east in the upper atmosphere. Adiabatic cooling – the process of decreasing heat through a change in air pressure caused by an air mass expanding. Adiabatic heating – the process of increasing heat through a change in air pressure caused by an air mass compressing. Norther Hemisphere (coriolis force is deflected to the right) Low pressure PGF Air PGF flow Coriolis force High pressure  Global Pressure Belts EQUATORIAL LOW PRESSURE BELT Near the equator, warm air expands and rises in huge convection currents (A) In the upper atmosphere, the air is the same temperature as the surrounding particles, so it stops rising. SUBTROPICAL HIGH PRESSURE BELT Airs starts to cool and diverges in the upper atmosphere towards the poles. (B) The cool air sinks. (C) While sinking, the air is compresses and heated adiabatically. (D) SUBPOLAR LOW PRESSURE BELT Cool polar air converges with warm surface air. (E) This creates a front and the warm air rises. It diverges in the upper atmosphere towards the poles. POLAR F E HIGH PRESSURE C BELT D The cold B polar air sinks. A This creates a high B pressure on D the surface. C (F) E F  Cells HADLEY CELL Air rises, creating a LP at the surface. Rising air cools in the atmosphere and condenses at DPT. Cumulonimbus clouds form with thunderstorms. In the troposphere, the air diverges and sinks at 30°. As the air sinks, it heats adiabatically creating warm and dry conditions at the subtropical HP belt. On the surface, air converges towards the ELPB at the ITCZ – these surface winds are known as tropical easterly winds (trade winds). FERREL CELL Air arrives from the subtropical HP belt as warm westerly winds and from the subpolar HP belt as cold polar easterly winds Two planetary winds converge at the polar front Cooler air squeezes beneath warm air, forcing it to rise dramatically. Frontal rain forms POLAR CELL Air sinks on the Polar HP belt and runs along the surface towards the subpolar LP belt. Surface air is called polar easterly winds.  Cell Profiles Hadley Cell Ferrel Cell 30°N 0° 30°S 60°N 30°N 0° 30°S 60°S Polar Cell 90°N 60°N 30°N 0° 30°S 60°S 90°S Air Masses An airmass is a large volume of air with similar characteristics (in terms of temperature, atmospheric pressure and humidity) to the area that it covers. Air mass can be stable or unstable. Stable air à subsiding (sinking), heavy air that is associated with high pressure and thus no rain. Unstable air à rising condensing air that is associated with low pressure and can cause rain. AIR MASS TYPE TEMPERATURES MOISTURE Equatorial air masses High (hot) Both = extremely Maritime (mE) humid (very Continental (cE) unstable) because of tropical oceans & forests Tropical Air masses Both are warm as mT à very humid Maritime (mT) they are formed in the (unstable) Continental (cT) lower tropics cT à hot + dry (stable) Polar air masses mP à very cool mP à moderately Maritime (mP) (not cold due to moist (slightly Continental (cP) warm currents unstable) moderating cP à very dry temperatures) (stable) cP à very cold on land in sub polar regions Artic & Antarctic air Extremely cold Extremely dry masses because of extremely Continental artic cold and frozen (CA) waters (stable) Continental Antarctic (CAA)  Monsoons Monsoons refer to the seasonal reversal of atmospheric pressure and winds and their accompanying rainfall. CAUSES Differential heating & cooling of land and adjacent sea areas = changes in atmospheric pressure & winds ITCZ moves northwards in the northern hemisphere and southwards in the southern hemisphere (in summer) causing trade winds to converge = convectional rain Himalayan mountain range influences movement of the ITCZ and triggers high rainfall on the Indian side during July. Wet monsoon +s Wet monsoon -s Dry monsoon -s Irrigation = Flooding Drought conditions crop yields Destruction of Water shortages for Water for crops agriculture industrial use Loss of Reduced crop yields Water for habitats Water scarcity for domestic use Fatalities and industrial & domestic use Drinking injuries Increased risk of wildfires water Destruction of Negative impact on Cleans up infrastructure ecosystems and habitats environment Economic Economic stress on farming Cools down impact communities environment Spread of Increased air pollution due diseases to lack of rain to cleanse the air Dry Monsoons (Winter) Dry monsoons occur Cold plateau, higher pressure during winter Land experiences cold temperatures and has an intense high-pressure. Ocean is warmer and has a low-pressure. Air moves from a high- pressure on land to a low- Warm sea, lower pressure on the ocean. pressure Results in intense rainfall over the ocean And drought and arid/dry conditions over land Wet Monsoons (Summer) Hot plateau, lower pressure Wet monsoons occur during summer. Land experiences warm temperatures and has an intense low-pressure. Ocean is cooler and has a high-pressure. Colder sea, Air moves from a high- higher pressure pressure on the ocean to a low-pressure on land. Results in intense temperatures and rainfall over the land. This rain is mostly relief rain and often results in flooding Föhn Winds A föhn wind is a dry, hot wind that descends on the windward side of a mountain that originates in a mountainous area or in an area where there are significant changes in altitude. PROCESS Air rises up the windward side of a mountain and it cools at the dry adiabatic laps rate. The air becomes saturated and continues to rise up the slope, but now cools at the wet adiabatic lapse rate. This cooling causes condensation to occur and clouds, rain or snow to form on the windward slope. Air descends on the leeward side and heats up at the dray adiabatic lapse rate. The wind at the foot of the slope is hot and dry. Examples Föhn winds can cause droughts, dry out forest areas and increase the risk of wildfires, and cause snow to melt which may result in avalanches and flooding. WINDS LOCATION 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 A measure of how much a pocket or air changes (in °C) with a change in height (per 100m) DRY ADIABATIC WET ADIABATIC LAPSE RATE LAPSE RATE (DALR) (WALR) If air is unsaturated If air is saturated (very little (very moist) then it moisture) and dry will heat/cool fairly then it will slowly heat/cool faster that Measure: 0,5°C if there was water change per 100m on vapour present the windward side Measure: 1°C 0,5°C/100m change per 100m on the leeward side 1°C/100m Africa’s Weather & Climate Africa has 7 different climate regions that is influenced by: Its position over the equator. Almost symmetrical halving between hemispheres Land and sea proximity Topography (shape) Ocean currents About 70% of Africa lies between the tropics, therefore most climates are tropical. However, there are 3 broad categories: Tropical: equatorial & savanna Semi-desert & dryland: semi-desert & desert Humid mid-latitude: mediterranean, highveld & humid subtropical Equatorial Savanna (grasslands) Semi-arid Desert Mediterranean Highveld Humid subtropical  Equatorial Found between 6°—7° north & south High temperatures throughout the year because of high solar angle throughout the year. Receives convectional rainfall (because of intense heat during the day) often thunderstorms High annual rainfall Savanna Found between 5°—15° north & south This is a transition zone between equatorial and desert climatic areas Summer = hot temperatures + rainfall Winter = cool temperatures + dry The dry season is a progressive decline in total annual rainfall (usually 3—8 months long in Tanzania) Temperatures are warm throughout the year because of the warming effect of the warm Mozambique current High annual rainfall throughout most of the year due to the wetting effect Semi-arid Winters = cold and dry Rainfall in summer Saturated on dry sides of savanna and Namibian Sahara Summers are very hot >32° Desert Winters = warm Very high temperatures Little to no rainfall Low humidity Highveld Winters this region is found in the highveld of the republic of South Africa It is the smallest of all the climatic zones Experiences summer rainfall Winter is dry and sunny Plateau is situated at high altitudes.  Mediterranean Found in the northern and southern tips of Africa A hot, sunny (bright) and dry summer season – cold ocean currents that bring dry air Receives rainfall mostly in winter – wet, moist air from warm ocean currents brings rain Humid Subtropical Occurs in Southeast Africa Characterized by year-round rainfall, heaviest in summer. Summers are long, hot, and humid. Deep tropical air current dominates. Daily intense, brief convective thundershowers occur. Winter temperatures may be mild or slightly above freezing.  The Pacific Ocean This is the largest and deepest ocean on earth. There is a strong link between ocean and atmosphere. It is crucial for the formation of trade winds and influences weather patterns, marine life and ocean currents. Wind has a dragging effect which creates ocean currents. Walker Air Circulation (Walker Cell) normal conditions The tropical Easterlies blow across the pacific ocean and push moist air and warm surface water (South Equitorial Current) towards the Western pacific (Indonesia and Australia). This creates a low pressure over the western pacific Cold, nutrient-rich water (Peruvian current) upwells along the eastern pacific (coast of South America). Creates a temperature gradient with warm water in the western Pacific and cooler water in the eastern Pacific. Results in rising air and low pressure over the warm western Pacific, and sinking air and high pressure over the cooler eastern Pacific. Thermocline: the transition layer between the warmer mixed water at the surface and the cooler deep water below Upwelling: The rising of cold, nutrient-rich water from the deep ocean to the surface, typically occurring off the coast of South America. ATMOSPHERE – WALKER CELL LP HP Trade W inds Equatorial cu rrent oc lin e South ng Indonesia Th er m America lli we & PACIFIC OCEAN – Dry, cold condition from up Australia Rising sea level, CONVECTION CURRENT rising cold possible floods water and no & rainfall rainfall  El-Niño El Niño: A climatic event characterized by the warming of the central and eastern Pacific Ocean, leading to significant weather changes globally. PROCESS: The tropical easterlies weaken and the warm surface waters start to flow eastwards towards the eastern pacific. This suppresses the upwelling of cold water in the east. This creates a lower pressure (than normal) over the eastern and central pacific. Cooler than normal waters collect towards the western pacific and there is less rainfall. This creates a higher pressure than normal over the western pacific. Creating wetter conditions over south America and the central pacific And drier conditions in the western pacific (Indonesia). El Niño HP HP LP Trade W inds Equatorial cu rrent The South rm America N o of w Indonesia o c li ne up at & w er Warmer el Australia PACIFIC OCEAN – lin conditions & Cooler than g normal & receives CONVECTION CURRENT flooding from rising sea level, less rainfall = droughts no more fishing  Extreme El-Niño Extreme EXTREME El Niño Extreme LP HP e W inds Reversed Trad Equatorial cu rrent The rm South Up wa Indonesia o c li ne America w te & el r lin Warmer Australia PACIFIC OCEAN – go conditions & Cooler than f normal & receives CONVECTION CURRENT flooding from rising sea level, less rainfall = droughts no more fishing  La-Niña La Niña: is the cooling of the central and eastern tropical Pacific Ocean, which also influences global weather patterns. La Niña is an intensified walker atmospheric circulation cell. Stronger tropical easterlies blow across the tropical pacific ocean. And brings warm, moist air and warmer surface waters towards the western pacific. This creates a lower pressure than normal over the western pacific. An increase of cold water upwells along the eastern pacific (cold Peruvian current). This creates a higher pressure than normal over the eastern pacific. This creates drier conditions over south America and wetter conditions in the western pacific. La Niña LP HP Trade W inds Equatorial cu rrent oc lin e South ng Indonesia er m America Th lli & we Australia PACIFIC OCEAN – Dry, cold condition from up Rising sea level, possible floods CONVECTION CURRENT rising cold & increased water and no rainfall rainfall What factors Trigger El- Nin1o and La-Niña Events? Warm ocean waters in the central and eastern pacific ocean Atmospheric pressure changes Tropical cyclones Seasonal change global patterns Local land and sea interactions Human activities (burning fossil fuels and cloud seeding)  Effects of El Niño and La Niña Events During an El Niño, AFRICA experiences Drought conditions: Smaller harvests - especially maize in Africa. Stock farmers slaughter their animals to avoid high food costs. Meat prices drop at first, then rise sharply when meat becomes scarce. Food insecurity occurs = Starvation and malnutrition. In PERU- Peruvian fishermen: Normal conditions = upwelling of cold water, rich in nutrients, near Peru. (One of the world's richest fisheries is off the coast of Peru) These provide nourishment for plankton. Plankton provides food for anchovies and other fish. The fish in turn supply food for seabirds. Not only is the fish catch economically important, but the harvesting of bird excrement (guano) provides a supply of valuable fertilizer. Economic consequences of El Niño: devastating effect on the Peruvian anchovy fisheries, populations of fish and seabirds vanish, and anchovy catches dwindle (decrease) during El Niño.  Effect in Africa South of Africa North of Africa Below the equator Above the equator La Niña = flooding La Niña = drought El Niño = drought El Niño = flood El Niño La Niña The Dipole The dipole refers to the difference in ocean temperatures between two regions of the pacific ocean The ENSO dipole has 2 contrasting poles The eastern pacific becomes significantly warmer during the El Niño (one pole) And the western pacific becomes significantly cooler (the opposite pole) The Indian Ocean Dipole (IOD) is a climate phenomenon characterized by differences in sea surface temperatures between the western and eastern parts of the Indian Ocean. Similar to the El Niño-Southern Oscillation (ENSO) in the Pacific Ocean, the IOD influences weather patterns across the Indian Ocean region and beyond.