Geography ch1-2

• Weather is the condition of the air over a short period of time.
• Climate is the average weather conditions over many years.
• Elements that we use to describe weather and climate:

  • Air temperature: amount of heat in the air
  • Wind direction and wind speed(m/s): movement of air
  • Air pressure(hPa): weight of air
  • Precipitation(mm): amount of water falling from the sky
  • Relative humidity(%): amount of moisture in the air
  • Sunshine duration(hour): total amount of time that a place can receive sunshine
• On a map, temperature is shown by isotherms, which are lines joining places with the same temperature.
• The surface temperature of the world decreases with increasing latitude.
• Tropical regions are located between 23.5 N and 23.5 S. These regions are very hot and they are low-latitude regions.

  Temperate regions are located between 23.5 and 66.5 (both N and S).

  Polar regions are located within 66.5 and 90 (both N and S). These regions are very cold and they are high-latitude regions.
• Low-latitude regions receive more intense sunlight and high-latitude regions receive less intense sunlight due to the angle of the sun.
• Precipitation is unevenly distributed over the world. Polar regions are dry, coastal areas are usually wetter than inland areas, and areas around the Equator have large amounts of precipitation.
• Monsoons are winds that change directions seasonally, blowing from one direction in summer and from the opposite direction in winter. The whole region of South China, including Hong Kong, has a monsoon climate. Monsoons bring us wet summers, as well as cool and dry winters.
• A climatic graph shows the average monthly temperature and rainfall characteristics of a place over many years. The monthly mean temperature is shown by a line graph. The monthly rainfall is shown by a bar graph.
• Formation of summer monsoon:

  1. The land absorbs heat from the sun quickly. The air above becomes hot and rises. Air pressure over the land is low.
  2. Water absorbs heat more slowly than the land, so the air over the sea is cooler. Cool air sinks. Air pressure over the sea is higher.
  3. Air moves from high-pressure areas to low-pressure areas. Therefore, winds blow from the sea towards the land.
  4. Winds blowing from the sea to the land are onshore winds. They are the south-east and south-west summer monsoons. They carry much moisture and bring us wet summers.
• Formation of winter monsoon:

  1. The land loses heat quickly, so that the land surface is cold. Cold air sinks. Air pressure over the land is high.
  2. Water loses heat more slowly than the land, so the air over the sea is warmer.
  3. Air moves from high-pressure areas to low-pressure areas. Therefore, winds blow from the land towards the sea.
  4. Winds blowing from the land to the sea are offshore winds. They are the north, north-west and north-east winter monsoons. They are dry and bring us cool and dry winters.
• A rainstorm is a weather condition that brings heavy rain. In summer, high temperatures and moist onshore monsoons often bring heavy rain to South China. A large amount of rainfall may disrupt traffic and lead to floods and landslides.
• A typhoon (or tropical cyclone) is a strong tropical storm. It is a low-pressure system that develops over tropical waters. It is usually associated with very strong winds, dense clouds, heavy rain, storm surge and lightning. However, the centre of a typhoon, known as the eye, is calm and has no clouds. Strong winds and heavy rain are only found outside the eye.
• Typhoons can be formed over warm tropical oceans and move towards the west after they are formed.
• Tropical oceans offer warm water with surface temperatures over 26.5 degrees celsius and an abundant supply of moist air.
• Typhoons get stronger when travelling over warm water. However, as they travel over cold water, or reach the land, the supply of warm, moist air is cut off. Therefore, they weaken and dissipate.
• Typhoons can disrupt our lives and lead to the loss of life and property. It may trigger other natural hazards such as landslides and floods.

  It causes disruption to economic activity (eg: loss of crops), transport and people's daily lives, loss of property, and injuries / deaths.
• Precipitation is unevenly distributed across the world.
• In terms of global precipitation,

  polar regions are dry,

  coastal areas are usually wetter than inland areas, and

  areas around the Equator have large amounts of precipitation.
• Wet areas become wetter and dry areas become even drier.

  Intense rainfall over a short duration has become more common across the world.

  This shows that precipitation has become more extreme.

  However, there is no big change in the total amount of global precipitation as a whole, just significant changes in the regions.
• Rainstorms become more intense.

  The number of days with precipitation decreases.

  There is a shorter duration of rainfall.

  Precipitation often falls as rain rather than snow.
• Greenhouse gases include water vapor, carbon dioxide, methane, chlorofluorocarbons and nitrous oxide are the four major types of greenhouse gases that are responsible for causing global warming. Carbon dioxide is the most significant greenhouse gas leading to global warming.
• The greenhouse effect is a natural process. The current problem is that the amount of greenhouse gases in the atmosphere is increasing. An excessive amount of such gases in the atmosphere infensifies the greenhouse effect, which leads to global warming.
• Under the excess amount of greenhouse gases, global warming occurs when:

  1. The sun's energy reaches the earth's surface
  2. The earth's surface absorbs some of this energy and is heated
  3. Energy is emitted into the atmosphere
  4. More greenhouse gases absorb more energy
  5. More energy is re-radated back to the earth's surface
  6. The earth becomes warmer.
• The concentration of greenhouse gases has increased over the past decades due to rapid population growth and increase in human activity.
• Chlorofluorocarbons do not exist naturally in the atmosphere. They are released during the production of foams and refrigerants used in air conditioners and refrigerators.
• The greenhouse gases (in descending order of warming effect) are:

  carbon dioxide (66%), methane (16%), chlorofluorocarbons (8%), nitrous oxide (7%).
• Carbon dioxide is released when:

  1. Fossil fuels are burned for power generation.
  2. Fossil fuels are burned to power industrial processes that require a lot of energy.
  3. The burning of trees. (Deforestation)
  4. The lack of trees after forests are cleared to obtain land for development. (Less trees are left to absorb co2)
  5. Waste is burned in incinerators.
• Methane is released during:

  1. farming activities such as paddy farming and cattle rearing
  2. the decomposition of organic waste materials in landfills.
• Nitrous oxide is released when:

  1. fossil fuels are burned in power plants, factories, and transport
  2. Nylon is produced in factories (Industrial activity)
  3. Nitrogen fertilizers are used in farming activities
  4. Waste is burned in incinerators