© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 7.2What is the normal global distribution global distribution pattern of pattern of temperature? temperature? Part A

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What is the relationship between location and annual mean temperature of the following three places? What is the major factor affecting air temperature? Monthly mean temperatures What makes the air temperature vary among latitudes and at different times of a year? Insolation.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What is insolation? In order to have a better understanding of the issue of global warming, we have to know more about insolation. Space The atmosphere Earth’s surface Insolation Solar radiation The sun is constantly releasing energy in all directions. This energy is known as solar radiation. Solar radiation that is received in the atmosphere or on the earth’s surface is known as insolation.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What is insolation? Is insolation evenly distributed on the earth? The distribution of insolation on the earth’s surface is ( even / uneven ). Average annual insolation over the earth’s surface In general, insolation received ( declines / increases ) with increasing latitude More insolation Less insolation

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What is insolation? Is insolation evenly distributed on the earth? Which areas receive the highest value of insolation? The areas around _______ N and S receive the highest value of insolation. Average annual insolation over the earth’s surface Why does insolation vary with latitudes?

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What is insolation? What factors affect insolation received on the earth’s surface? Factors affecting insolation received on the earth’s surface Angle of the sun Duration of daylight The atmosphere Latitude Time of a day Season

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit In Part B, we will discuss the relationship between insolation and air temperature.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 1Angle of the sun The angle of the sun refers to the angle at which sunlight strikes the earth’s surface. When the sun is directly overhead, or when the angle of the sun is 90°, it is known as the overhead sun. Overhead sun How does the angle of the sun affect the intensity of insolation? Area AArea B Angle of the sun Area to warm up Intensity of insolation 90° / Right angle< 90° / Acute angle Smaller High / More intense Larger Low / Less intense

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 1Angle of the sun ALatitude In low-latitude regions: The angle of sun is ( smaller / larger ). The insolation concentrates on a ( smaller / larger ) area. Therefore, the insolation is ( weaker / stronger ). (Credit: NASA)

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 1Angle of the sun ALatitude In high-latitude regions: The angle of sun is ( smaller / larger ). The insolation concentrates on a ( smaller / larger ) area. Therefore, the insolation is ( weaker / stronger ). (Credit: NASA)

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 1Angle of the sun BTime of a day The amount of insolation received in a mid-latitude site in the Northern Hemisphere around the spring equinox The angle of sun ( decreases / increases / reaches maximum ) The sun at noon is called the midday sun The angle of sun ( decreases / increases / reaches maximum ) How is the amount of insolation received in this site different in winter? The amount of insolation received will be lower in winter.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit What is the relationship between the seasons in Hong Kong and insolation? 1Angle of the sun CSeason Please click above for animation N In summer solstice, the overhead sun is located at _______ which is close to Hong Kong. It is the time that Hong Kong receives the ( least / largest ) amount of insolation. In autumnal equinox, the overhead sun is located at the _________. Hong Kong receives less insolation in autumn than in summer. Equator S In winter solstice, the overhead sun is located at _________. It is the time that Hong Kong receives the ( least / largest ) amount of insolation. In spring equinox, the overhead sun is located at the Equator. Hong Kong receives ( more / less ) insolation in spring than in winter.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 2Duration of daylight The longer the duration of daylight, the ( less / more ) insolation received. The duration of daylight in equatorial regions is almost 12 hours daily throughout a year. Equator Is the case in polar areas different?

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit In polar regions, daylight can last for 24 hours in summer. While in winter, there is no sunlight at all. 2Duration of daylight When does the North Pole receive the largest amount of insolation?

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit How does the atmosphere affect the amount of solar radiation reaching the earth’s surface? The dust particles, gas molecules and clouds in the atmosphere are able to reflect, absorb or scatter solar radiation. 3The atmosphere Only about 58 units of solar radiation reaches the earth’s surface.

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit 3The atmosphere Maximum insolation received Why does the maximum insolation received occur at around N and S but not at the Equator?

© Oxford University Press 2009 Part 7 Global warming─Are humans responsible? Quit Space The atmosphere Dense cloud cover Insolation is reflected by clouds Less cloud cover 3The atmosphere The amount of cloud cover in the equatorial regions is high. Much of the solar radiation is reflected by clouds. This may reduce the amount of insolation reaching the earth’s surface. The climate is drier and there is less cloud cover at around N and S. The earth’s surface receives more insolation, so the amount of insolation is greatest here. 0°0° N S