Weather and Climate

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Weather and Climate

• Unit 1B

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Key Question 1

• Elements and measurements of the weather

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What is the difference between weather and
climate ?

• WEATHER
• is about day to day
• changes in the
• atmosphere. It includes changes in temperature,
  rainfall, sunshine wind)

• CLIMATE
• is the average or typical weather of a place
  worked out over a long period of time.

We know that in Britain it gets cold in the
winter and warm in the summer. This is climate.
But we don't know if it is going to be warm
tomorrow or not. This is the weather.
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Weather Elements

• 1. Temperature
• 2. Precipitation
• 3. Wind Speed
• 4. Wind Direction
• 5. Cloud Cover
• 6. Cloud Type
• 7. Visibility
• 8. Air Pressure

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KQ 1- Measuring the weather
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Cloud Cover Chart
RIGHT Types of Cloud
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What type of cloud is this ?
Found at high altitudes - CIRRUS
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What type of cloud is this ?
They rise to very great heights and are
associated with thunderstorms - CUMULONIMBUS
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Name all of the following instruments
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The Stevenson Screen

• Characteristics
• It is white
• It has slatted sides
• It has a double roof
• It is on stilts
• Its door opens northwards

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Other Weather Stations
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Key Question 2

• The Influence of AIR MASSES over the British Isles

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Air Masses
Blackwood Comprehensive School.
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What is an air mass?

• An air mass is a large body of air with similar
  temperature and/or humidity.
• Air masses form in stable source regions such
  as in the sub tropics or near to the poles.

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Air Mass types
Five main air masses affect Europe
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Air mass classification

• Tropical Maritime (Tm) - mild and moist
• Tropical Continental (Tc) - warm and dry
• Polar Maritime (Pm) - cool and moist
• Polar Continental (Pc) - cold and dry
• Arctic Maritime (Am) - cold and moist

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Tropical Maritime
Tm air masses come from the south west and
originate over the Azores or the Caribbean. They
bring mild, damp, cloudy weather.
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Tropical Continental
Tc air masses come from the south and originate
over dry northern Africa . They bring hot, dry
weather and summer heatwaves.
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Polar Maritime
Pm air masses come from the north-west and
originate over the north Atlantic. They bring
cool, moist conditions.
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Polar Continental
Pc air masses come from the east and originate
over Scandinavia and Russia . They bring clear
dry conditions - cold in winter, warm in summer.
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Key Question 3

• Depressions and Anticyclones

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Pressure, Wind and Weather Systems
Air stops rising when it meets air of equal
density, then diverges at high level to produce
more wind which eventually sinks elsewhere to
complete the circulation cell

• WINDS are horizontal flows of air winds blow
  from areas of high pressure to areas of low
  pressure (nature tries to equalise pressure)
• PRESSURE describes the tendency of the air to
  rise or to sink at any given place or time.
• Air tends to rise or sink as a result of its
  density.
• Air density varies with altitude but, at the
  ground level, air density is governed by its
  temperature.
• Thus, variations in radiation and temperature
  control pressure and wind.

Insolation
Air heated by contact with ground expands
becomes less dense and rises
Denser air drawn in at low level to replace
rising, less dense air
LOW PRESSURE
Denser air drawn in at low level to replace
rising, less dense air
Sun heats up ground
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WIND DIRECTION STRENGTH

• Wind strength depends on the difference in
  pressure between the high and low pressure
  systems, and the distance between them.
• This is called the PRESSURE GRADIENT it is a
  similar concept to the physical slope between two
  places, shown on a contour map. Pressure is shown
  by ISOBARS on a weather map.
• Pressure difference essentially depends on the
  temperature difference between the two places.

Locally, wind is channelled down streets (wind
canyons).
Strong winds also occur in low latitudes due to
stronger heating and steeper presure gradients.
Hurricanes and tornadoes are both tropical
phenomena.
A steep pressure gradient results from a large
pressure difference or short distance between
places and causes strong wind.
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HIGH PRESSURE
High Pressure means that air tends to sink.
Sinking air is compressed, warms up as a result
and its relative humidity falls below saturation.
Any clouds evaporate. Rainfall is unlikely, apart
from occasional short, intense convectional
storms due to insolation with lack of clouds in
daytime.

• In Britain, high pressure systems have clear
  skies, little or no wind, little rainfall and
  tend to be stable and slow moving.
• Visibility is intially good, but rapidly
  deteriorates as dust is trapped by sinking air
  and is not washed out by rainfall.
• Cloud cover is slight, resulting in a high
  diurnal ranges of temperature (hot days, cold
  nights). Due to the trapped dust particles and
  cold nights, dew, frost, fog or smog are common.
• Air quality is low as all forms of pollution are
  retained in the lower atmosphere.

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MID-LATITUDE LOW PRESSURE SYSTEMS
Mid-latitude low pressure systems are called
depressions in Britain. They also involve rising
air, clouds, strong winds and rainfall and are
fast moving.
ARCTIC MARITIME from Arctic Ocean Cold, humid.
POLAR CONTINENTAL from E.Europe Cold, dry in
winter Warm, dry in summer.
POLAR MARITIME from Greenland Cool, humid.

• Depressions result from the convergence of warm
  air from the tropical high pressure belt with
  cold air from the poles along the Polar Front.
• The energy of the depresion is a result of the
  difference in temperature and humidity between
  the two air masses.
• This contrast varies with the exact origin of
  the air mass, the season and the nature of the
  surface over which they have passed.

POLAR FRONT this shifts polewards in summer and
equatorwards in winter, hence British seasonal
contrasts.
POLAR MARITIME RETURN Coolish, very humid.
TROPICAL CONTINENTAL From N.Africa Hot, dry
TROPICAL MARITIME from Atlantic near tropic Warm,
humid
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MID-LATITUDE LOW PRESSURE SYSTEMS
Mid-latitude low pressure systems are called
depressions in Britain. They also involve rising
air, clouds, strong winds and rainfall and are
fast moving.
OCCLUDED FRONT Cold warm fronts meet
Depressions (L) over Europe showing FRONTS
COLD FRONT
POLAR MARITIME AIR
WARM FRONT
WARM FRONT
COLD FRONT
TROPICAL MARTIME AIR
COLD FRONT

• Depressions result from the convergence of warm
  air from the tropical high pressure belt with
  cold air from the poles along the Polar Front.
  The systems move rapidly across the Atlantic
  before filling and drifting north-eastwards to
  Scandinavia from Britain.
• The energy of the depresion is a result of the
  difference in temperature and humidity between
  the two air masses.
• This contrast varies with the exact origin of
  the air mass, the season and the nature of the
  surface over which they have passed.

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COLD FRONTS
As the depression moves eastwards, the warm
tropical air continues to be forced upwards by
the colder, denser polar air mass.
POLAR MARITIME
TROPICAL MARITIME

• The cold front is steeper, also due to ground
  level friction slowing the lower air, so uplift
  is more rapid than along the warm front.
• This causes cumulo-nimbus clouds and possible
  thunderstorms rather than thick stratus cloud.
• Eventually, the two fronts meet, forcing the
  warm air off the ground. This is an OCCLUDED
  FRONT (occlusion), and happens to all depressions
  as they fill.
• The whole system takes about 24 hours to pass.

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WARM FRONTS
A FRONT is the boundary betwen two air masses. A
depression has two, a warm (the front of the warm
air) and a cold.
The warm front is angled gently due to ground
level friction which slows the air at low level
as the whole system moves eastwards.
TROPICAL MARITIME AIR
POLAR MARITIME AIR
As the warm tropical maritime air moves eastwards
towards Britain, it is forced upwards by colder,
denser polar maritime air. The speed of uplift
depends on the relative temperature of the two
air masses. Uplift causes expansion, cooling,
falling relative humidity until dew point
temperature is reached when condensation starts
to occur on particles. The amount of
precipitation depends on the hunidity and
temperature of the warm air mass, and the
particles available.
MAINLY STRATUS CLOUDS
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The Passage of a Depression
An example of a LOW PRESSUE System
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Key Question 4

• Factors that affect Climate

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Climate
Factors Affecting Climate
What do you need to know today?

1. There are many factors affecting climate.
2. Weather patterns recorded over long periods of
   time can lead to the construction of climatic
   belts.

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Factors Affecting Climate
1 - Latitude
This is the most important factor. All climate
stems from the equator. This is the hottest place
on earth. As you go north or south from this line
it becomes colder as you travel towards the North
and South Poles as the suns rays are more spread
out.
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Factors Affecting Climate
2 - Altitude
This is the effect of height on temperature - the
higher you go, the colder it gets. The sun heats
up the earths surface and then heat is radiated
back up into the atmosphere. The higher up the
radiated heat goes, the colder it gets.
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Factors Affecting Climate
3 - Prevailing Winds
The movement of the earths winds starts at the
equator, where it is hottest. There are certain
set patterns of winds called prevailing winds,
which means the direction winds travels in most
in a particular place. Two things affect the
direction - the earths tilt (on its axis) and
the revolution (revolving) of the earth. Wind
affects the climate when it has travelled over
a particular feature (land or sea) and from a
particular direction
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Factors Affecting Climate
4 Relief
Relief or orographic rain is formed when air is
forced to cool when it rises over relief features
in the landscape such as hills or mountains. As
it rises it cools, condenses and forms rain. The
highest rainfall totals of over 1,600 mm per year
occur in the mountain areas along the west coast.
There is often a rain shadow effect whereby the
leeward (downwind) slope receives a relatively
small amount of rain.
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Factors Affecting Climate
5 Aspect
North Facing Cold South Facing sunny and
warmer (UK example)
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Factors Affecting Climate
6 Continentality
Air temperature is greatly affected by the
location of a place relative to a large body of
water. The impact of continental location on
weather and climate characteristics of a place is
called "continentality".  Air temperature near or
over bodies of water is much different from that
over land due to differences in the way water and
land heat and cool.
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Key Question 5

• Weather hazards and management