Goh Cheng Leong Chapter 14: Climate YouTube Lecture Handouts

Download PDF of This Page (Size: 1.8M)

Get video tutorial on: https://www.youtube.com/c/Examrace

Watch video lecture on YouTube: Goh Cheng Leong Chapter 14: Climate Goh Cheng Leong Chapter 14: Climate
Loading Video

Atmosphere: Made of gases and vapor and receive incoming solar radiation/energy (insolation)

  • We live in bottom of atmosphere where air is densest

  • Lowest layer where weather is confined is troposphere (for 6 miles and temperature falls with altitude)

  • Lower part of atmosphere – 78% N, 21% O, 0.03% CO2, traces of argon, helium and other gases with variable water content (if atmosphere was dry without water there would be no weather)

  • Above troposphere we have stratosphere – cloudless, thin air, without dust and vapor but has seasonal temperature changes

  • Ionosphere – electrically conducting layers, which make short wave radio transmission possible over long distances – information from modern artificial satellite and balloons

Image of layers of atmosphere

Image of Layers of Atmosphere

Image of layers of atmosphere

Insolation

  • Sun has a surface temperature of more than - radiation is divided in 3 parts – visible white light (more intense and affect climate), less visible UV (cause sunburn) and IR rays (penetrate dust and fog and is used in photography)

  • Sun’s radiation reaching earth is called insolation

  • Of the total radiation – 35% reaches atmosphere and is reflected back to space by dust, clouds (no role in heating)

  • 14% absorbed by CO2, water vapor and gases – interception by air makes it scattered and diffused – visible rays b/w UV and IR gives rise to blue sky

  • 51% reaches earth and warms surface – by conduction (nearest layers), convection (heat as upward movement) and radiation (at night)

Image of Shortwave solar radiation

Image of Shortwave Solar Radiation

Image of Shortwave solar radiation

  • Land gets heated quickly than water. Water is transparent and heat is absorbed slowly as it is always in motion – it is absorbed over more depth and area – so rise in temperature takes more time

  • Most heat in land is absorbed by the surface only

Elements of Climate and Factors Affecting Them

Temperature

  • Affects amount of water vapor in air and governs moisture carrying capacity

  • Decided rate of evaporation and condensation

  • RH is related to temperature and affects cloud formation and precipitation

Latitude: Rays are overhead at tropics (short distance and smaller area); high latitude have low temperature due to oblique angle and spread in surface area (move longer distance and is absorbed by clouds, vapor and dust).

Altitude: Places near earth surface are warmer than higher up – temperature decreases with height and is known as lapse rate (fall of with every 300 feet ascent – usually more in summers around 400 feet while for winters around 280 feet) – more in day than night and more on elevated highlands than plains

Continentality – Land is heated more quickly due to higher specific heat of water – it requires 1/3rd of energy to raise temperature of given volume of land by as for water – accounts for warmer summer, cold winter, more range of temperature of continental interiors

Ocean Currents and Winds – affect temperature by transporting heat and cold – currents. Warm current keep ports in northern areas ice free. Cold currents lower summer temperature when carried landwards by onshore trade winds

Westerlies that come to Britain and Norway tend to be cool winds in summer and warm winds in winter & are most valuable in moderating climate

Slope, Shelter and Aspect – Steep slope experience a rapid change in temperature. East west ranges have higher temperature on south facing sunny slope (good for vine cultivation) than the north facing sheltered slope

Hot day followed by calm night – air cools more rapidly over higher grounds and may induce cold heavy air to flow down the slope and accumulate in valley bottom pushing warm air upwards (temperature would be lower in valley than above) – reversal of lapse rate and is called as Temperature Inversion

Image of warming mountainsides and cooling mountainsides

Image of Warming Mountainsides and Cooling Mountainsides

Image of warming mountainsides and cooling mountainsides

Natural Vegetation and Soil – Thick foliage of Amazon cuts incoming insolation and sunlight does not reach ground. In day trees loose water by evapotranspiration so the air above is cooled – RH increases and mist and fog may form

  • Light soil reflect more heat than darker soil which are better absorbers

  • Dry soil like sand are more sensitive to temperature changes while wet soil retain moisture and warm up and cool down more slowly

Precipitation

  • If air is cool below dew point – water vapor will condense around dust particles

  • If condensation takes place below freezing point it is called as snow (flakes or ice crystals)

  • If moist air ascends to cooler layers, water droplets freezes into ice pellets and fall as hail – as more and more water droplets accumulate it increases in size

  • Ice pellets exist as frozen raindrops, melt and refreeze to form sleet

  • If droplets coalesce into larger particles of 0.2mm to 6 mm – rain falls

Types of Rainfall

Convectional Rainfall – most common due to intense heating during day in summers in tropics – when surface heated by conduction moisture vapor rises as heated air expands and becomes lighter – they form cumulonimbus clouds (maximum in afternoon) – hot rising air holds moisture, which is abundant in areas of high RH.

As air rises, it cools and at saturation torrential downpour occurs – as rainfall is intense it is not used for agriculture

Image of Convectional Rainfall

Image of Convectional Rainfall

Image of Convectional Rainfall

Orographic rainfall or relief rain – moist air ascends the mountain barrier – best developed on windward slope where moisture laden winds come from sea –

  • Air is compelled to rise and is there by cooled by expansion in higher altitudes & subsequent decrease in pressure.

  • Condensation takes place forming clouds (since caused by relief it is known as relief rain).

  • Mainly in W. Malaysia, W. New Zealand, W. Scotland, Wales and Assam.

Image of Orographic rainfall or relief rain

Image of Orographic Rainfall or Relief Rain

Image of Orographic rainfall or relief rain

  • On descending leeward slope, decrease in altitude increases pressure and temperature – air is compressed and warmed with drop in RH – leeward side is called rain shadow area – as Canterbury plains of South Island, New Zealand, western slope of north and south Andes

  • Cyclonic or Frontal Rain: cyclonic activity in temperate region (depression) or tropical region (cyclone) – by convergence of two different air mass – cold air remains close to ground while warm air moves up – in ascent pressure decreases, air expands, condensation takes place and frontal rain occurs

Pressure & Planetary Winds

Pressure Belts

  • Equatorial low pressure belt or doldrums – sailors found themselves becalm here – zone of wind convergence

  • - Subtropical high pressure belt – air is dry, wind is calm and light – descending air current or divergence and anticyclones – Horse latitudes

  • – 2 temperate low pressure belts – zone of convergence with cyclonic activity -Subpolar low pressure belts best developed over oceans where temperature difference between summer and winter are negligible

  • – Polar high-pressure belts – in north hemisphere it is complicated due to land present there

Planetary Winds

  • Winds blow from HP to LP as planetary winds – this is affected by rotation of earth (Coriolis force) which deflect direction of winds

  • NH – deflection to right and SH – deflection to left (called Ferrel’s Law of Deflection). Coriolis is absent towards equator but increases towards poles

  • In NH – from subtropical HP to equatorial LP they are called as NE trade winds while in SH called as SE trade winds – blow with force and in constant direction – helpful for sailors and called trade winds – can hold moisture and bring rain to east coast of continents within tropics. These are offshore on west coast and cause aridity – Sahara, Kalahari, Atacama and Great Australian Desert

Image of Generalized Sketch of Global Atmospheric Circulation

Image of Generalized Sketch of Global Atmospheric Circulation

Image of Generalized Sketch of Global Atmospheric Circulation

  • From subtropical HP to temperate LP – called Westerlies – called as south westerlies in NH and north westerlies in SH. More variable in NH but carry warm waters to west of temperate lands – warming effect. In SH westerlies blow with more force and bring rain to west coast of continents – weather is damp and seas are violent called Roaring forties, furious fifties and screaming sixties

  • Some like Iberia, California, C. Chile, S. Africa and SW Australia receive westerlies only in winter – caused by shifting of wind belts b/w .

  • In June – overhead sun is over Tropic of Cancer & all belts move . Mediterranean part of southern continents come under westerlies and receives rain in June (same happens in SH in December over Tropic of Capricorn)

  • Polar easterlies blow from polar HP belt to temperate LP belt – extremely cold (more regular in south)

Land and Sea Breeze & Monsoons

  • Due to differential heating of land surface

  • Sea Breeze: Day – land gets heated - warm air rises up – LP develops – so sea breeze flows – speed is stronger in tropical than temperate regions – felt when stand facing sea

  • Land Breeze: Night – land cools faster than sea – winds blow towards sea – fishermen in tropics take advantage of it and sail out with winds & return next day with incoming sea breeze

  • Monsoons – rapid heating in hot summer induces heated air to rise up. SW monsoon from ocean is attracted by LP over land and brings rainfall. In winters land is cool and surrounding seas are warm – HP is created and NE monsoon blows out

Fohn Wind or Chinook Wind

  • Dry winds on leeward side of the mountains when descending air becomes compressed with increasing pressure

  • Fohn winds (hot and dry) – N. Alps, Switzerland in spring – air ascends southern slope of Alps expands and cools. Condensation occurs when air is saturated – melts snow and causes avalanches

  • Chinook winds (snow eater) – in eastern slopes of Rockies in USA and Canada in winter – hastens growth of crops and fruits and thaws pastures – can raise temperature by in 15 minutes – means winter is mild

Cyclonic Activities

  • Typhoons – China Sea

  • Tropical cyclones – Indian Ocean

  • Hurricane – West Indian Island in Caribbean - Calm, rainless center where pressure is lowest and called as eye of cyclone & wind speed exceeds 12 on Beaufort scale. 1780 – Hurricane struck Barbados in West Indies and destroyed the whole island

  • Whirl-wind -Tornado – Guinea Island of West Africa & South USA

  • Willy-willies – NW Australia

  • Typhoons - – Mainly July to Oct. Smaller than temperate cyclone with diameter 50 to 200 miles but have steeper pressure gradient – violent winds, overcast sky, torrential downpour, thunder and lightning

  • Tornado – small violent tropical and sub-tropical cyclone – air spirals at 500 mph and appear as dark funnel cloud – most frequent in spring – seen in USA and Mississippi basin

Cyclones or depressions – in temperate latitude – with LP in center and isobars are close together. Depression vary from 150 to 2000 miles and remain stationary.

  • Approach of cyclone – fall in barometric reading, dull sky, oppressive air and strong winds – wind blow anticlockwise in NH and clockwise in SH

  • Precipitation due to convergence of warm tropical and cold polar air. Fronts develop and condensation as rain, snow and sleet

Anticyclone – HP in center and isobars are far apart. Pressure gradient is gentle, winds are light, fine weather, clear skies, calm air, and high temperature in summer and cold in winter. In winters – cooling leads to thick fog. It blows clockwise in NH and anticlockwise in SH