THE EARTH'S ATMOSPHERE, WATER AND CLIMATES

The Earth's Atmosphere, water and climates

The atmosphere is a layer of gases that surrounds the Earth. It is about 1,000 kilometres thick. Oxygen and nitrogen make up most of the atmosphere, but it has other gases, including carbon dioxide, ozone and argon.

            The layers:

1.      Troposphere: Meteorological phenomena, such as clouds and precipitation, take place in this layer.

2.      Stratosphere: This layer contains the ozone layer that absorbs ultraviolet rays from the Sun. This prevents harmful radiation from reaching the Earth's surface.

3.      Mesosphere: Temperatures are very low. The top part of the mesosphere is the coldest part of the atmosphere.

4.      Thermosphere: The northern lights occur in the thermosphere. Temperatures are very high, up to 1,000ºC.

5.      Exosphere: This is the last layer before the outer space. Artificial satellites orbit in the exosphere. Temperatures are extremely high.

                       

Weather and climate

Meteorological phenomena, such as precipitation and wind, occur in the atmosphere and give rise to weather and climate.

·         Weather refers to the meteorological conditions in a place at a specific time.

·         Climate is the usual state of the atmosphere over a long period of time.

As a result of the Earth's rotational tilt, different climate zones receive different amounts of solar radiation. The Earth has cold, polar zones near each pole, temperate zones in both hemispheres, and hot, tropical zone near the Equator.

The hydrosphere is all the water on the planet. It is made up of oceans, seas, rivers, lakes, glaciers, groundwater and water vapour.

The Earth's climates

·         Equatorial climate: Temperatures are very high all year round. The average annual temperature is over 25ºC. Precipitation is abundant, over 1,500 mm annually.

·         Tropical climate:

§  Humid tropical: Temperatures are high all year round. The average annual temperature is over 20ºC. Precipitation is abundant, over 1,500 mm annually, but there is a dry season.

§  Dry tropical climate. Temperatures are high all year round. The average annual temperature is over 20ºC. Precipitation is scarce, between 300 and 600 mm annually.

·         Hot desert climate: Temperatures are high all year round. The average annual temperature is over 25ºC. It is much colder at night than during the day. Precipitation is very scarce, less than 300 mm annually.

·         Humid sub-tropical: temperatures are hot and humid during the summer with cool, mild winters. Precipitation varies between 760 and 1,500 mm per year and falls mostly in summer.

·     Steppe climate: Temperatures are very high in summer (over 25ºC), but very low in winter (below 5ºC). Temperatures fall at night. Precipitation is very scarce, less than 300 mm annually.

·         Continental climate: Temperatures are high in summer (20ºC), and low in winter (less than 5ºC). Precipitation varies between 300 and 1,000 mm, and mainly falls in summer.

·         Mediterranean climate: Temperatures are very hot in summer and mild in winter. Precipitation varies between 300 and 800 mm, and mainly falls in autumn and spring.

·         Oceanic climate: Temperatures are mild all year round, between 10ºC and 20ºC. Precipitation is regular and abundant, between 1,000 and 1,500 mm annually.

·         Mountain climate: Temperatures drop as altitude increases. Winters are cold and summers are cool. Precipitation is high due to altitude but it varies according to the geographical area.

·         Polar climate: Temperatures are very low (below 0ºC) nearly all the year round. Precipitation is scarce (less than 300 mm), and falls as snow.

The water cycle

There us always the same amount of water on Earth. It sometimes changes state, and it can be in liquid, gas or solid form. It moves continually between the atmosphere, the oceans and the continents. This continual movement of water is called the water cycle. This cycle is made up of three phases:

1.      Evaporation. Water evaporates, rises and cools in the atmosphere.

2.      Condensation. It condenses in the air and forms clouds.

3.      Precipitation. When the clouds cannot absorb any more water, there is precipitation in the form of rain, snow or hail.

Saltwater

About 97% of the Earth's water is saltwater, located in the oceans and seas.

·         Salinity is the amount of salt dissolved in water. Salinity is higher in hot, enclosed seas because the proportion of salt rises when the water evaporates. It is lower in cold, open oceans.

·         The temperature of salt varies. It is warmer near the surface (between 12ºC and 30ºC) and colder in deep water (between 4ºC and -1ºC).

Oceans are huge bodies of water that affect temperatures. In summer, deep cold water cools the ocean's surface and the air above it. In winter, the water retains heat, which is slowly released. Consequently, coastal areas have mild climates.

·         Saltwater is denser than fresh water. For that reason navigation is easier.

Fresh water

About 3% of the Earth's water is fresh water found on continents and island.

·         Most of this water is ice at the Polar Regions and in glaciers.

·         Some of it is groundwater under the Earth's surface.

·         Only a small proportion of it is found in water vapour and in lakes or rivers

How to read and interpret a hydrograph

An annual hydrograph shows how much water a river carries in a year. The river regime is how this flow rises and falls.

·         The vertical axis shows the discharge, or rate of flow. We calculate this figure by dividing the average monthly discharge by the average annual discharge. The result shows us whether the flow in a particular month is above or below average.

·         The horizontal axis indicates the months of the year.

·         A line connects the data to show the river regime of a particular river.

How to interpret the graph

We need to think about the following questions:

·         Is the river regime simple or complex?

o   A river has a simple regime when it receives all its water from a single source, such as rain or melting ice.

o   A river has a complex regime it receives water from both rain and melting ice. It will reach its highest and lowest levels twice a year.

·         How regular is the flow?

§  The river will flow regularly all year round in areas where rainfall is regular.

§  The graph will rise and fall sharply in areas where there are rainy and dry seasons. There may be droughts during the months when rainfall is low.