Weather

Question 1

The atmosphere

Answer 1

• The atmosphere is a thin layer of gases that surrounds the Earth.
• The atmosphere insulates
Oxygen (21%)
the Earth from extreme
Nitrogen
(78%)
temperatures. It traps heat and it also protects the Earth from dangerous rays
© Figure 13.1 Gases in the Earth’s
atmosphere
from the sun.

Question 2

Layers of the atmosphere

Answer 2

• The troposphere is the lowest layer in the Earth’s atmosphere.

• The stratosphere is the next layer.

Question 3

Energy from the sun

Answer 3

Energy from the sun is called solar energy. It is the earths of source of heat

Question 4

The energy that travels through space from the sun

Answer 4

Solar radiation

Question 5

Uneven heating of the earths surface

Answer 5

Solar energy is distributed unevenly both over the surface of the Earth and within the atmosphere. Its strength depends on latitude and the tilt of the Earth on its axis.

• The Earth is divided into the northern hemisphere and the southern hemisphere. The imaginary line dividing these two areas is called the equator. The lines around the Earth that measure distance from the equator are called lines of latitude.

• Because of the Earth’s spherical (round) shape, the equator is closest to the sun. This means that areas closer to the equator are warmer than areas closer to the poles.

• The sun’s rays have a shorter distance to travel to the equator so the heat is more intense here than at higher latitudes.

• The sun’s rays shine directly on the equator and so are concentrated on a smaller area.
The rays at higher latitudes are slanted and therefore cover a larger area and are less intense.

• The Earth spins on its axis so that different parts of the Earth’s surface are tilted towards the sun. This influences the seasons and the length of the day and night.

• A: During our summer, the northern hemisphere is tilted towards the sun. Days are long and we receive more solar radiation.

• B: During our autumn, the northern hemisphere begins to tilt away from the sun.
Days get shorter and temperatures drop as

• C: During our winter, the northern hemisphere is tilted away from the sun.
Days are short and temperatures are low because there is little solar radiation.

• D: During our spring, the northern hemisphere begins to tilt towards the sun again and days grow longer. Temperatures increase with more solar radiation.

Question 6

How are winds formed

Answer 6

• The unequal heating of the atmosphere and the Earth’s surface leads to movements of air, known as wind. Winds blow from areas of high pressure to areas of low pressure.

• The equator receives the sun’s direct rays.
When air is heated, it expands. This makes it lighter and so it rises. This creates areas of low pressure at the equator.

Question 7

Trade winds

Answer 7

• Trade winds are air movements towards the equator.

They are warm, steady breezes that blow almost continuously.

• The rotation of the Earth on its axis causes what is known as the Coriolis effect, which makes the trade winds appear to curve towards the west, regardless of whether they are travelling to the equator from the south or north.

Question 8

Doldrums

Answer 8

• The doldrums is an area of calm weather.

• The trade winds coming from the south and the north meet near the equator. As they are heated, these converging trade winds blow upwards so there is little movement of air near the surface, and so little wind.

Question 9

The prevailing westerlies

Answer 9

• Between 30° and 60° latitude, the winds that move towards the poles appear to curve to the east.
• Because winds are named after the direction from which they come, these winds are called westerlies.

• Prevailing westerlies in the northern hemisphere are responsible for many of the weather movements across Europe, and especially in Ireland.

Question 10

Horse latitudes

Answer 10

• The horse latitudes are found at 30° north and south of the equator. They form a belt that blows between the trade winds and the prevailing westerlies.

• Horse latitude winds tend to be weak and encourage clear, bright weather.

Question 11

Polar easterlies

Answer 11

• At about 60° latitude in both hemispheres, the prevailing westerlies meet the polar easterlies.

• The polar easterlies form when the atmosphere over the poles cools. This cool air then sinks and spreads over the surface.

• As the air flows away from the poles, it is turned to the west by the Coriolis effect.

• Again, because these winds begin in the east, they are called easterlies.

Question 12

Ocean currents

Answer 12

• Ocean waters are always moving. The movement of water is referred to as a current. A current is like a river flowing though the ocean. Ocean currents occur due to:
- Differences in temperature
- The Earth rotating on its axis
- Wind

Question 13

Warm currents

Answer 13

Currents flowing from the equator are warm. The Gulf Stream originates in the Gulf of Mexico and turns north-eastwards into the Atlantic Ocean, where it splits to form the warm North Atlantic Drift (NAD) and the cold Canary Current.

• The NAD flows past the west coast of Ireland where it helps to keep ports ice-free.

Question 14

Cold currents

Answer 14

• Cold currents flow from areas in high latitudes towards the equator.

• The Labrador Current, which flows south along the coast of north-east America, reduces the temperature of the ocean and many ports freeze over as a result.

Question 15

Air masses

Answer 15

• Air masses are large moving pockets of air that are distinct from the surrounding atmosphere.
Warm air masses carry more moisture or water vapour than cold air masses. All air masses have the following characteristics:
- They are large, often stretching more than 1,500 km across the landscape and extending several kilometres into the atmosphere.
- The temperature, pressure and moisture are similar at any point within the air mass.
- They travel across the atmosphere as a single unit.

Question 16

Polar maritime

Answer 16

• Polar maritime These air masses from the northwest Atlantic bring cold, wet air and showery conditions.

Question 17

Artic air masses

Answer 17

• Arctic Air masses from the North Pole bring cold weather conditions.

Question 18

Polar continental

Answer 18

• Polar continental Air masses from north-east
Europe bring dry, cold and frosty nights and heavy snowfall in winter.

Question 19

Tropical continental

Answer 19

• Tropical continental Air masses from the Sahara bring dry sunny weather.

Question 20

Tropical maritime

Answer 20

• Tropical maritime Air masses from the southwest bring rain all year round.

Question 21

Isobars

Answer 21

• Isobars are lines on a weather map which join together places of equal atmospheric pressure.

• Atmospheric pressure is measured in millibars.

• Isobars are usually drawn at intervals of four or eight millibars.

• The closer together the isobars are, the stronger the wind will be.

Question 22

Fronts

Answer 22

• Fronts occur where two different air masses meet.

• The three different types of front are a warm front, a cold front and an occluded front.

Question 23

Three different type of fronts

Answer 23

• The three different types of front are a warm front, a cold front and an occluded front.

Question 24

Warm fronts

Answer 24

• Warm fronts are formed when warm air rises over a mass of cold air.

• As the warm air lifts into areas of lower pressure, it expands, cools and condenses the water vapour as wide, flat sheets of cloud. These clouds bring gentle rain.

• A warm front is shown on a weather map as a solid red line with red semicircles.

Question 25

Cold front

Answer 25

• A cold front occurs where a cold air mass replaces a warmer air mass.

• The cold air follows the warm air and gradually moves underneath it, pushing the warmer air upwards.

• When the warm air is pushed upwards, it will rain heavily. This is because as it rises quickly, moisture in the air condenses, forming rain clouds.
As the cold front passes, the clouds roll by and the air temperature is cooler.

• A cold fronts is shown on a weather map as a solid blue line with blue triangles.

Question 26

Occluded fronts

Answer 26

• Occluded fronts occur at the point where a cold front takes over a warm front or the other way around.

• Occluded fronts bring changeable weather conditions.

• Occluded fronts on a weather map are represented by semicircles and triangles positioned next to each other. The triangles are in blue and the semicircles are in red, or both are purple (mixing red and blue colours together).

Question 27

Anticyclones-high pressure systems

Answer 27

• Descending air and temperatures rise

• High atmospheric pressure

• Winds blow in a clockwise direction

• Isobars are well spaced indicating light winds

• Clear skies and cold nights in winter

• Dry weather

Question 28

Depressions-low-pressure systems

Answer 28

• Ascending air and temperatures fall

• Low atmospheric pressure

• Winds blow in an anti-clockwise direction

• Isobars are close together indicating strong winds

• Cloudy skies

• Wet weather

Question 29

How clouds are formed

Answer 29

• A cloud is a large collection of very tiny droplets of water or ice crystals held in the atmosphere. The droplets are so small and light that they can float in the air.

• All air contains water. Near to the ground it is usually in the form of an invisible gas called water vapour. When warm air rises, it expands and cools. Cool air cannot hold as much water vapour as warm air, so some of the vapour condenses into tiny droplets. When billions of these droplets come together they become a visible cloud.

Question 30

Status clouds

Answer 30

• Stratus clouds occur below 2,000 m.

• They look like flat sheets of cloud, and indicate an overcast or rainy day. These clouds are usually a uniform grey colour, and cover most of the sky.

Question 31

Cumulus clouds

Answer 31

• Cumulus clouds occur below 5,000 m.

• They look like big fluffy balls of cotton wool. They usually mean that the weather will be nice.

• Sometimes they can look very woolly and bring heavy showers, especially in warm weather.

• These clouds are usually flat on the bottom, but have very lumpy tops.

• Cumulus clouds usually form alone and there is a lot of blue sky between individual clouds.

Question 32

Cirrus clouds

Answer 32

• Cirrus clouds usually form above 8,000 m.

• They are wispy clouds. Because there is very little water vapour at this height, big thick clouds cannot form.

• Cirrus clouds are created when water vapour forms ice crystals, which are very thin because of the height at which they form.

Question 33

How rain is formed

Answer 33

• Precipitation is any form of water - liquid or solid - that falls from the sky. It includes rain, sleet, snow, hail and drizzle.

• Rain is the most common type of precipitation. Rain occurs because air has been forced to rise. As air rises it cools and loses its ability to hold water until it is 100 per cent saturated. This is called the dew point and it is above this point that condensation occurs.

• Condensation is the process by which the water vapour held in the air is turned back into water droplets that fall as rain.

Question 34

Convectional rain

Answer 34

• Convectional rain is common in areas where the ground is heated by the sun. Convectional rain can sometimes occur in Ireland during the summer. It occurs all year round in hot regions near the equator such as the tropics.

• The warm air rises because it is less dense.
• As the warm air rises it becomes cooler and condenses to form clouds.
• These clouds produce rain. They also occasionally produce thunder and lightning.

Question 35

Cyclonic/frontal rain

Answer 35

• Cyclonic rain is also called frontal rain because it occurs when two air masses meet, causing a front.
- The lighter, less dense, warm air is forced to rise over the denser cold air.
- This causes the warm air to cool and begin to condense.

• As it rises, further condensation occurs and rain is formed.
• Frontal rain brings a variety of clouds, which cause moderate to heavy rainfall.

Question 36

Relief rain

Answer 36

• Relief rain is very common in Ireland.

• Prevailing winds pick up moisture from the sea as they travel across it, making the air moist.
• When this moist air reaches the coast it is forced to rise up over the coastal mountains and hills where it cool and condense, forming clouds.
• As air continues to be forced over the mountain it drops its moisture as relief rain. Once over the mountain, the air will usually drop down the other side, warming as it does so.

• This means it can hold more moisture and so there is little rain on the far side of the mountain. This area is called the rain shadow.

Question 37

Weather elements

Answer 37

• Weather refers to the state of the atmosphere at a given time and place. Climate describes the common, average weather conditions at a particular place over a long period of time.

• Certain weather elements are measured constantly.

Question 38

Weather forecasts

Answer 38

• A person who studies these elements is called a meteorologist. They use patterns in weather conditions to put together weather forecasts.

• A weather forecast is a prediction of what the weather will be like at a particular time and place. This information is gathered from sources such as satellites, ships and weather stations.

• The forecast is then put onto weather maps and charts and made available to the public.

Question 39

Why is the weather forecast important

Answer 39

• The weather has a big influence in our lives. The weather forecast is especially important to:

• anyone working at sea to make sure they are safe
• farmers so they can plan when to harvest crops and sow seeds
• airlines so they can cancel flights if the weather is forecast to be bad.
• When particularly bad weather is forecast,
  Met Eireann issues weather warnings.

Question 40

Weather stations

Answer 40

• A weather station is a place with equipment and instruments for observing and recording the weather.

• Information from the weather stations in
Ireland is sent to Met Eireann, the Irish National Meteorological Service.

Question 41

Weather maps

Answer 41

• The information gathered from weather stations is put onto weather maps called synoptic charts.

• Synoptic charts use lines and symbols to show what is happening with the weather at a given
time.

• The lines on the charts show areas that have equal atmospheric pressure, temperature, sunshine or rainfall, depending on what is being measured.