Chapter 13: Weather Flashcards
Atmosphere
Is a thin layer of gases that surrounds the Earth.
Layers within the atmosphere
Troposhere
Stratosphere
Troposhere
The lowest layer in the Earths atmosphere.
It reaches from sea level to about 17km
Weather and clouds occur in the troposhere
The temperature decreases the higher the altitude.
The stratosphere
It extends from 17km to 50km from the Earths surface
The ozone layer is located in the stratosphere.
Some of the highest clouds can be found in the lower stratosphere.
Solar heat
The amount of heat kept in the atmosphere depends on the amount of greenhouse gases in the atmosphere.
The uneven heating of the Earth
Latitude
The Earths adis
Latitude
The earth is divide into the Northern hemisphere and the southern hemisphere.
Because of the spherical shape, the equator is closest to the sun.
The sun rays have a shorter distance to travel to the equator.
The sun 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 Earths axis
During our summer, the northern hemisphere is tilted towards the sun.
During our winter, the northern hemisphere begins to tilt away from the sun.
How winds are formed
The unequal heating of the atmosphere and the Earth’s surface leads to movements of air.
When air is heated, it expands. This makes it lighter and so it rises. This creates areas of low pressure at the equator.
At about 30 degrees north and south of the equator, the warm air begins to cool. When air is cooled it becomes heavy and sinks towards the surface of the Earth. This creates areas of high pressure.
Between 30 degrees latitude and the equator, most of the cooling, sinking air moves back to the equator. The rest of the air flows towards the poles.
Global winds
Trade winds The doldrums The prevailing westerlies The horse latitudes The polar easterlies
Trade winds
Trade winds are air movements towards the equators. 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.
The Coriolis effect
It makes the trade winds appear to curve towards the west, regardless of whether they are travelling to the equator from the south or north
The doldrums
The doldrums is an area of calm weaher. 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
The prevailing westerlies
Between 30 degrees and 60 degrees latitude, the wind that move towards the poles appear to curve to the east. 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
The horse latitude
The horse latitude are found at 30 degrees 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.
The polar easterlies
At about 60 degrees 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.
Ocean currents
Ocean waters are always moving. The movement of water is referred to as a current. Ocean currents occur due to:
Differences in temperature
The Earth rotating on its axis
Wind
Warm currents
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.
Cold currents
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.
Air masses
Air masses are large moving pockets of air that are distinct from the surrounding atmosphere. Warm air masses carry more moisture or water vapour then cold air masses.
All air masses have the following characteristics
They are large, often stretching more than 1500 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
Polar maritime
These air masses from the north-west Atlantic bring cold, wet air and showery conditions.
Artic
Air masses from the North Pole bring cold weather conditions
Polar continental
Air masses from north-east Europe bring dry, cold and frosty nights and heavy snowfall in winter
Tropical continental
Air masses from the Sahara bring dry sunny weather
Tropical maritime
Air masses from the south-west bring rain all year round
Isobars
Isobars are lines on a weather map which join together places of equal atmosheric pressure.
The closer together the isobars are, the stronger the wind will be
Fronts
Fronts occur where two different air masses meet.
Warm front- red semicircles
Cold Front- blue triangles
Occluded front - semi circles and triangles
Warm fronts
Warm fronts are formed when warm air rises over a mass of cold air.
Cold fronts
A cold front occurs when a cold air mass replaces a warmer air mass. The cold air moves underneath the warm air and pushes it upwards.
Occluded fronts
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.
Depressions - low pressure systems
H is used to show areas of high atmospheric pressure
L is used to show areas of low atmospheric pressure
L can bring cool, windy, wet conditions
H can bring hot, calm, warm weather
What measures atmospheric pressure
Milibars (mb)
Barometer
Anticyclones
Descending air and temperature 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
Depression
Ascending air and temperature fall Low atmospheric pressure Winds blow in anti-clockwise direction Isobars are close together indicating strong winds Cloudy skies Wet weather
How clouds are formed
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.
Types of clouds
Stratus clouds
Cumultus clouds
Cirrus clouds
Stratus clouds
Stratus clouds occur below 2000m.
They look like flat sheets of cloud. These clouds are usually a uniform grey colour, and cover most of the sky
Cumulus clouds
Cumulus clouds occur below 5000m.
They look like big fluffy balls of cotton wool. (Similiar to cloud you draw). There is a lot of blue sky between them
Cirrus clouds
Cirrus clouds usually form above 8000m.
They are wispy clouds. Because there us very little water vapour at this height
How rain is formed
As air rises it cools and loses its ability to hold water. Eventually it reaches a point where it is 100% saturated which means it cannot hold any more water. This is called the dew point and it is above this point that condensation occur.
Types of rain
Convectional rain
Cyclonic (or frontal) rain
Relief rain
Convectional rain
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 lighting
Cyclonic (or frontal) rain
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
Relief rain
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 monuntains and hills
This forces the air to cool and condense, forming clouds.
As air continues to be forced over the mountians it drops 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.
Why is weather forcast important?
People working at the sea are safe
Farmers so they can plan to harvest crops
Airline, so they cancel flights if weather is bad
Temperature
Measure hot or cold
Thermometer is the instrument
Celisius or Fahrenheit
Isotherms
Isotherms
Are lines on a weather map that join places of equal temperature
How to find Temperature range
Highest temperature - Lowest temperature
Atmospheric pressure
The weight of atmospheric pressure down on the Earth
Barograph is the instrument
Milibars (mb)
The lines on a weather map that show areas of equal atmospheric pressure are called isobars.
Humidity
The amount of water vapour or moisture in the air.
The instrument is a hygrometer
The relative humidity is measured as a percentage of the maximum moisture that could be in the air at a certain temperature.
Humidity is shown as a percentage
Wind direction
The direction from which wind is coming can be measured
The insturment is a wind vane
Wind direction is given by the point of the compass from which it is blowing
It is shown using arrows on a map.
Wind speed
The strength or speed of the wind
The instrument is an anemometer
Kilometers per hour (kph)
When the isobars are closer together on a weather map, the wind will be stronger. When they are further apart, the wind will be lighter
Precipitation
And form of liquid particles that fall from the atmosphere.
The instrument is a rain gauge.
Milimetres (mm)
Isohyets
Isohyets
The lines on a weather mapmshowing areas of equal rainfall are called isohyets
Sunshine
Sunshine is when the suns rays reach the surface of the Earth.
The instrument is the Campbell-Strokes sunshine recorder.
Sunshine is measured in hours per day
Isohels
Isohels
The lines on a weather map showing areas of equal sunshine are called isohels
