The Sun's Impact on Earth's Climate: Understanding Cycles & Changes

14 The Earth and the Sun Of all celestial bodies, the Sun has the greatest influence on the Earth, affecting its movements, determining the day-night and seasonal cycles, driving climatic systems and longer term climate cycles, and providing the energy for most life on the planet. The Sun also plays a part in tidal movement on Earth. modifying the effect of the Moon to produce monthly variations in the tidal range. The Sun emits various types of radiation, but most is absorbed high in the Earth's atmosphere. Only visible light, some infra-red radiation, and some ultraviolet light reach the surface in significant amounts. Visible light is pivotal to the producer base of Earth's biological systems, but infra-red is also important because it heats the atmosphere, oceans, and land. The intensity of solar radiation is not uniform around the Earth and this uneven heating effect, together with the Earth's rotation, produce the global patterns of wind and ocean circulation that profoundly influence the Earth's climate. Solar Year The Earth has orbited the sun in a regular cycle for the last 4.5 billion years, since the formation of the solar system. The journey around the sun takes 365.25 days. The motions of the Earth, moon, and sun result in complex and interdependent cycles. These create environmental changes that range trom short term (just a few hours) to long term (many hundreds of days). The tidal cycle is not shown on this diagram, but involves the gravitational pull of the moon as well as centrifugal forces on the oceans, Northern hemisphere winter solstice Northern hemisphere Summer solstice December 21 SUN June 21 MOON Southern hemisphere summer solstice Southern hemisphere winter solstice EARTH Lunar Month The time between successive full moons is 29.5 days. This is slightly different from the moon's orbit around the Earth, which is once every 27.3 days. Because the moon spins on its own axis once every 27.3 days, the same side of the moon always faces the Earth.

Earth Day The Earth spins on its axis once every 23 h 56 min 4,09 s (called one sidereal day). Earth's Axls The Earth does not spin upright; it has a 23.5o tist. This tilt always faces the same way, resulting in seasonal changes in sunlight and weather. For questions 1 to 4, circle the letter with the correct answer: 1. The solar year is based on: A. The number of rotations of the Earth B. The time for the Earth to complete one orbit of the Sun The number of orbits of the Moon D. The time taken for four seasons to pass 3. The time for the Earth to complete one rotation on its axis is; A. 24 hours, 0 minutes, and 0 seconds B. 23 hours, 56 minutes, and 4.09 seconds C. The time taken for the Sun to reach its zenith D. One day od The seasons experienced on Earth are caused by: A. A change in distance from the Earth to the Sun B. A reduction in sunshine hours due to cloud formation The angle of the Earth relative to the Sun D. A reduction in solar output B. The movement of the Earth's atmosphere is due to: A. The rotation of the Earth The unequal intensity of solar radiation over the globe Air rising at the equator and descending at the poles D. A, B, and C 5. (a) Explain why tropical regions receive a greater input of solar radiation than the poles: (b) Describe the consequences of this to the Earth's climate: -

The Atmosphere and Climate The Earth's atmosphere is a layer of gases surrounding the globe and retained by gravity. It contains roughly 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, trace amounts of other gases, and a variable amount (average around 1%) of water vapor. This mixture of gases, known as air, protects life on Earth by absorbing ultraviolet radiation and reducing temperature extremes between day and night. The atmosphere consists of layers around the Earth, each one defined by the way temperature changes within its limits. The outermost troposphere thins slowly, fading into space with no boundary. The air of the atmosphere moves in response to heating from the sun and, globally, the atmospheric circulation transports warmth from equatorial areas to high latitudes and returning cooler air to the tropics. It is the interaction of the atmosphere and the oceans that creates the Earth's the longer term pattern of atmospheric conditions we call climate (as opposed to shorter-term weather). The world's climates are not static; they have been both warmer and cooler in the past. At present, the average global temperature is increasing, but this rise is not evenly spread around the globe. The present climate warming is most likely to be due, at least in part, to an enhanced greenhouse effect, caused by higher concentrations of greenhouse gases in the atmosphere. Cloud marks a westerly jet stream across the Red Sea . Aurora caused by collisions between protons and electrons from the Sun and the nitrogen and oxygen atoms in the atmosphere. . 2

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. .. 140 km . .. . . . . APA www c . 130 km re UNI .. " Average temperature 2 .. . The Earth's Systems S.. 120 km . MANUM 60°C _ 22. WARE E Sie - 110 km

-10°C Thermosphere This layer extends as high as 1000 km. Temperature increases rapidly after about 88 km. . . -80°C- Jet streams are narrow, winding ribbons of strong wind in the upper troposphere. They mark the boundary between air masses at different temperatures. Cloud forms in the air that is lifted as it is driven into the core of the jet stream. 90 km -90°C 90 km borbundle 80 km -80°C - Aurora borealis - 70 km -50°C - Mesosphere Temperature is constant in the lower mesosphere, but decreases steadily with height above 56 km. ." - 60 km -30°C – - 50 km -10°C - — 40 km

-20°C - - 30 km Stratosphere Temperature is stable to 20 km, then increases due to absorption of UV by the thin layer of ozone. -40°C - - 20 km •60°C – - 10 km The Northern and Southern Lights (the Aurora Borealis and the Aurora Australis respectively), appear in the thermosphere. Typically, auroras appear either as a diffuse glow or as "curtains" that extend in an approximately east to west direction. -60°C - elementum Sea-level ] Troposphere Air mixes vertically and horizontally. All weather occurs in this layer, 15°c 1000 mb 1. Describe two important roles of the atmosphere: 2. Explain what drives the atmospheric circulation: 3. Describe a characteristic feature and environmental issue for each of the following layers of the atmosphere:

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(a) Troposphere: (b) Stratosphere: 26 The Tricellular Model of Atmospheric Circulation High temperatures over the equator and low temperatures over the poles, combined with the rotation of the Earth, produce a series of cells in the atmosphere. This model of atmospheric circulation, with three cells in each hemisphere, is known as the tricellular model. Polar cell Rising mid-latitude air divides, flowing to the poles and the equator forming the Ferrel cells. These mid-latitudinal cells produce westerly winds. 60°N At the poles, air cools and descends as a cold, dry high pressure area, moving away from the pole to produce the polar easterlies. Autos Westerlies..7 Ferrel cell HIGH 30°N Status Northeasterly trade winds 4341" it! how In the tropics, wind blowing towards the equator as part of the Hadley cells is deflected by the Coriolis effect) and forms the northeasterly and southeasterly trade winds.

EQUATOR Warm air rises at lower latitudes and moves poleward through the upper troposphere at both the north and south poles. . Southeasterly trade winds _ нан HIGH O Air within the Hadley cells rises moist at the equator and subsides dry at the tropics. "ri11 Ferrel.cell Westerlies } The atmospheric circulation in each hemisphere consists of -three cells (at polar, midlatitude, and equatorial regions). These cells, produce belts of prevailing winds around the world. { ੦ d }} Polar air circulation is caused by subsiding air at the poles flowing towards the equator. * ITCZ

North America Three typhoons in various stages of tormation uw * 3 Early turik Late South America NA! NASA Dunes form in sandy deserts and polar The Intertropical Convergence zone (ITCZ) Tropical cyclones (also called typhoons or regions, where prevailing winds create drifts marks the meeting of trade winds at the equator. hurricanes), are low pressure systems that with characteristic shapes. Sand or snow grains It is characterized by varying, often calm winds, develop mainly over warm seas where winds start are blown up the slope and fall down the far as well as violent thunderstorms. The position the air spiralling, producing low surface pressure side to create sinuous crests extending for of the ITCZ can drastically affect the rainfall in into which air accelerates. great distances. equatorial nations. 4. (a) Explain what is meant by a prevailing wind: (b) Describe some of the physical and biological effects of prevailing winds: --. . . -. 5. The ITCZ was also called the doldrums by early sailors.

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Suggest why it was given this name: _ Variation and Oscillation Energy from the Sun is distributed through a global system conditions are never exactly the same from one year to the next. of atmospheric and ocean circulation that creates the Earth's However, it is possible to find periodic patterns or oscillations climate. Heated air moving towards the poles from the equator in climate. The El-Niño-Southern Oscillation, which has a does not flow in a single uniform convection current. Friction, drag, periodicity of three to seven years, is one such climate cycle. and momentum cause air close to the Earth's surface to be pulled El- Niño years cause a reversal of the ordinary climate regime in the direction of the Earth's rotation. This deflection is called the and are connected to such economically disastrous events as Coriolis effect and it is responsible for the direction of movement the collapse of fisheries stocks (e.g the Peruvian anchovy stock), of large-scale weather systems in both hemispheres. The severe flooding in the Mississippi Valley, drought-induced crop interactions of atmospheric systems are so complex that climatic failures and forest fires in Australia and Indonesia. The Coriolis Effect Frontal Weather A weather front marks the boundary between two air- masses at different densities. A front is about 100-200 km wide and slopes where warm and cool air masses collide. A front appears on a weather map as a line with triangles (cold front) or semicircles (warm front) attached. Air flowing towards, or away from, the equator follows a curved path that swings it to the right in the northern hemisphere and to the left in the southern hemisphere (right). This phenomenon, known as the Coriolis effect, is caused by the anticlockwise rotation of the Earth about its axis, so

as air moves across the Earth's surface, the surface itself is moving but at a different speed. The magnitude of the Coriolis effect depends on the latitude and the speed of the moving air. It is greatest at the poles and is responsible for the direction of the rotation of large hurricanes. VA The Earth's Systems - . + . . In a cold front, cold air undercuts warm air, forcing it steeply upwards along the line of the front and triggering the formation of towering cumulus clouds and rain. Cold fronts are often associated with lowpressure systems and unsettled weather conditions. As the front passes the cold air mass behind it can cause a rapid drop in temperature. -... Air flows from high pressure to low pressure (see inset). In the northem hemisphere, the Coriolis effect deflects this moving air to the right, causing cyclonic (low pressure) systems to rotate counter-clockwise as seen here in a low pressure system over Iceland. Cyclonic weather is usually dull, with grey cloud and persistent rain, .. 26.7 . . 17 . 7' . ! TA NASA INT

In the southern hemisphere, cyclonic systems spiral in a clockwise direction, seen in this photograph of cyclone Catarina, a rare South Atlantic tropical cyclone which hit Brazil in March 2004. As air rushes into the low pressure area, it is defected to the left, causing a clockwise spiral. .... w . . .. : . Gradual slope of a warm front * In a warm front, warm air rises over cold air more gradually, producing flattened, stratus-type clouds. Warm fronts produce low intensity rainfall that may last for some time and preceed warm weather. Because it moves more quickly, a cold front will eventually overtake a warm front, creating an occlusion. NASA 1. Explain the role of the Coriolis effect in creating the prevailing winds in different regions of the globe: - - 2. In the spaces provided below, draw schematic diagrams to show: -- -- (a) The movement of a cold front into an area of warm air: (a) - (b) The movement of air in a Southern Hemisphere cyclone and a Northern Hemisphere hurricane: 28

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Variation and Oscillation Normal climatic conditions Rising warm moist air associated with heavy rainfall and low pressure Descending warm air associated with high pressure and dry conditions Interactions between the atmosphere and the oceans are at the core of most global climate patterns. These climate patterns are referred to as oscillations because they fluctuate on time scales ranging from days to decades. The El-Niño- Southern Oscillation cycle (ENSO) is the most prominent of these global oscillations, causing weather patterns involving increased rain in specific places but not in others. It is one of the many causes of drought. Thermocline Southeast trade winds 1 TER ::. South Equatorial Current N14 In non-El-Niño conditions, a low pressure system over Australia draws the southeast trade winds across the eastern Pacific from a high pressure system over South America. These winds drive the warm South Equatorial Current towards Australia's coast. Off the coast of South America, upwelling of cold water brings nutrients to the surface.

iuation on per 12 .06. veling otcoORY RYONE TE 22011 3 El Niño effect Descending air and high pressure brings warm dry weather do Southeast trade winds reversed or weakened Low pressure and rising air associated with rainfall se TE Warm water In an El Niño event, the pressure systems that normally develop over Australia and South America are weakened or reversed, beginning with a rise in air pressure over the Indian Ocean, Indonesia, and Australia. Warm water extends deeper and flows eastwards, blocking the nutrient upwelling along the west coast of the Americas. This has a devastating effect on fish stocks, El Niño brings drought to Indonesia and northeastern South America, while heavy rain over Peru and Chile causes the deserts to bloom. flows eastwards 745 wiwi HT W

e stirea Thermocline Wealoog War warm water which Taccumulates Of REX SATU 1174 3. Describe the events that cause El Niño conditions and its effects on ocean circulation: 4. Describe the effect of an El Niño year on: (a) The climate of the western coast of South America: - -- . - - - (b) The climate of Indonesia and Australia: - ..- Ocean Circulation and Currents Throughout the oceans, there is a constant circulation of water, both across the surface and at depth. Surface circulation, much of which is in the form of circular gyres, is driven by winds. In contrast, the deep- water ocean currents (the thermohaline circulation) is driven by the

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cooling and sinking of water masses in polar and subpolar regions, Cold water circulates through the Atlantic, penetrating the Indian and Pacific oceans, before returning as warm upper ocean currents to the South Atlantic. Deep water currents move slowly and once a body of water sinks it may spend hundreds of years away from the surface. The polar oceans comprise the Arctic Ocean in the northern hemisphere and the Southern Ocean in the south, They differ from other oceans in having vast amounts of ice, in various forms, floating in them. This ice coverage has an important stabilizing effect on global climate, insulating large areas of the oceans from solar radiation in summer and preventing heat loss in winter, Thermohaline Circulation High salinity water cools and sinks in the North Atlantic. sf Stream ar *** Gulf Syu Deep water returns to the surface in the Pacific and Indian * Oceans through upwelling. --- . . NAAtlantic we . 1 Ocear - Pacific Ons

The Earth's Systems Indian Ocean . Atlantic waters are saltier and therefore more dense than those in the Paciifc. . Ocean . . . . JAYA . shallow current CAMP . --- ... VI-- Cold water circulates through the Atlantic, penetrating the Indian and Pacific Oceans. Warm shallow it JE The polar oceans (the Arctic and Southern Oceans) are sources of cold dense bodies of water that drive the Earth's deep water circulation. Cold and deer TIT. and deep high salinity current . .. . .. .

the . - Antarctica A V • 2L Wikimedia Commons NOAA . F . . Southern ocean Arctic Ocean w ianice The Southern Ocean encircles Antarctica and is covered in ice for much of the year. Complex currents in the Southern Ocean produce rich upwelling zones that support abundant plankton and complex food webs. The vast amounts of ice associated with the polar oceans has an important stabilizing effect on the global climate, insulating large areas of foceans from solar radiation in the summer and preventing heat loss in winter. Satellite observations show that the Arctic sea ice is melting earlier and more rapidly than previously reported. The loss of ice cover will dramatically reduce the surface albedo (reflectivity) in the Arctic region. 1. Explain the basis of the Earth's thermohaline circulation: 2. Explain how thermohaline circulation could

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influence global climate: - - - - - --- --- -- 3. Describe a possible consequence if the melting of sea ice significantly reduces the surface albedo of the Arctic region; - . .. 30 Local Currents and Upwelling Local currents and vertical transport of water (upwelling and downwelling) are important phenomena around coastal regions. Upwelling in particular has important biological effects because it returns nutrients to surface waters, which promotes the growth of plankton. COM -. - - W HEMISPHERE . .... ... Surface Circulation in the Oceans The surface circulation of the oceans is driven by winds, but modified by the Coriolis effect. Winds in the northern hemisphere, the Coriolis effect deflects the wind-driven water movements slightly to the right and in the southern hemisphere to the left. North Pacific gyre Drag

accentuates the Coriolis effect so that the average water motion in the top few hundred metres of the m Equator ocean surface is almost at right angle to the wnd direction. The overall effect is a pattern of large scale circular movements of water, South Pacific gyre or gyres, which rotate clockwise in the northern hemisphere and anticlockwise in the southern (below and right). These currents carry warm water away from the equator and colder water towards it. NORTHERN Pilots WHNO SPHERE istock The Great Pacific Garbage Patch is an accumulation of plastic and other debris in an area in the center of the North Pacific gyre that spans approximately 1.2 million km2. Overall Pattern of Surface Currents Local currents are the result of interactions between tidal forces and coastlines. The whirlpools (vortices), seen above at Saltstraumen in Norway, are created by exceptionally strong tidal movements as water forces its way through a long narrow strait. et B - SHE Ireland B England Atlantic' AN Indian

. Ocean . 'ocean NASA/GSFC Plankton blooms, seen here as bright spots around the coast of England and Ireland, often occur in upwelling zones, as nutrients are brought to the surface. Upwelling occurs to replace the seawater that is moved offshore by surface circulation. ...» Cold ocean currents → Warm ocean currents 4. Contrast the mechanisms operating to drive deep water and surface water circulation: 5. Match each description below with its appropriate letter on the above diagram "Overall Pattern of Surface Currents": (a) Antarctic circumpolar current i (d) North Atlantic gyre: - (b) Perų current: (e) South Atlantic gyre:_ (c) South Pacific gyre: 6. Describe a similarity between atmospheric circulation and surface ocean circulation patterns: 7. (a) Describe the biological importance of upwelling in coastal regions:

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(b) Explain how normal patterns of upwelling are affected during an El Niño year:

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