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Global Distributions of Climate
The climate in a place is the average of
its weather conditions.
The climate varies across the world
depending on the following four
factors;
Latitude
Altitude
Distance from the sea
Prevailing winds
Latitude
The closer an area is to the equator, the hotter the area will be.
This is because the direct rays from the sun are concentrated along
the equator.
Altitude
Temperature decreases the higher we travel into the atmosphere.
The higher a place is above the sea level, the colder it is likely to be.
Distance from the sea
In the summer, the sea heats up less quickly than the land so places
further inland will have hotter summers.
In the winter, the sea heats up more quickly than the land so people
on the coast will have warmer winters.
Prevailing winds
If the wind blows from the direction of the equator, then it is likely
to be warm.
If the wind blows from either of the poles then it is likely to be cold.
Climate Zones
There are six major climate zones located throughout the world.
Equatorial
Lying between the Tropic of Cancer in the Northern Hemisphere and the Tropic of Capricorn
in the south, equatorial climates are home to most of the world’s rainforests where rainfall
and humidity are high. Temperatures are not that extreme — generally 25 to 35 °C — with
not much variation through the year.
Arid
Deserts are found mainly across the subtropical continents. Here, descending air forms
large, almost permanent, areas of high pressure leading to cloud-free skies virtually all year
round. Annual rainfall is low and, in some deserts, almost non-existent. Because they’re so
dry, the temperature range in deserts is huge, regularly exceeding 45 °C by day in summer
and often falling to below freezing overnight in winter.
Mediterranean
The hot, dry summers of the Mediterranean, South Africa and southern Australia are caused
by a seasonal shift of the descending air that also creates our deserts. Low summer rainfall is
matched by many months of warm, sunny weather. But, at times, dangerously hot spells of
weather engulf these regions with fiercely high temperatures of up to 45 °C. In winter, there
is more rain and cooler temperatures, but little frost.
This classification covers a range of climates from Mediterranean-type climates and humid,
subtropical zones to maritime climates influenced by the oceans —
Snow
In the higher northern latitudes, the vast forests of fir and spruce (often called the
taiga) and the featureless tundra endure long, hard winters with short, bountiful
summers, separated by rapid seasonal changes during spring and autumn. In the
northernmost regions, the land is permanently frozen and will not thaw even during
the brief summer.
Polar
The Arctic is mostly frozen ocean, and while its climate is moderated by the relatively
warm waters of the Atlantic Ocean, winter temperatures can still fall to below -30 °C.
Antarctica is a vast continent of mountains and high plateaux buried under more than 3
km of ice. Temperatures below -80 °C have been recorded and the Antarctic i nterior is
very dry — drier than many deserts. This is because as the temperature falls so does
the atmosphere’s capacity to hold water vapour needed to make snow.
Temperate
This classification covers a range of climates from Mediterranean-type climates and
humid, subtropical zones to maritime climates influenced by the oceans — like ours in
the UK. The UK has a typical maritime climate, where temperatures are quite moderate
although hot summer days and cold winter nights still occur. Summers in maritime
climates can be hot, warm or cool. In the UK we have what’s considered to be a warm
summer, whereas in Iceland the season is classified as cool.
How to measure weather?
• Meteorological Stations
collect many different
types of data.
• Specific instruments are
used to collect this
information
Types of Data
• Temperature (°C)
• Daily Maximum and Minimum Temperature
(°C)
• Pressure (mb – millibar)
• Wind direction
• Wind Speed (km/h)
• Rainfall (mm)
• Relative humidity (%)
• Stevenson Screen
– A device that contains
instruments that record certain
weather data
• Technical details:
– Double louvered sides for air
circulation
– 1,25m above ground
– Double roof, air insulates
against sun
– Painted white, to reflect sun /
heat
– Located in open space, to
reduce interfrerence form
buildings / trees
– Door opens north in northern
hemisphere / south in southern
hemisphere to avoid sun shining
on instruments
Data
Collection
Inside a Stevenson Screen
• Minimum / Maximum Thermometer
• Wet / Dry bulb thermometer
• Barometer
Maxi / Min Thermometer
• Filled with Mercury or Alcohol
• U-shaped capillary tube, min side
bulb filled with liquid, other with
vacuum
• 2 separate temperature readings
• Steel markers show temperature
(can be reset by magnet)
• Heating  expansion
• Cooling  contraction
• Use: recoding of daily temperature
maxima
Wet / Dry Bulb Thermometer
• Aka: Hygrometers
• 1 normal
thermometer
• 1 wet thermometer
• Wet one shows
temperature at 100%
humidity
• Use: The difference
between dry and wet
temperature can be
used to calculate
relative humidity
Barometer
• Measures atmospheric pressure
• Average: 1013,25 mb
• Mercury Barometer:
– Changes in air pressure push mercury up the tube
• Aneroid Barometer:
– Changing pressure causes expansion and
contraction of vacuum container
Rain Gauge
• Collects water to
determine how much
rain falls
• Collection either daily or
hourly
• Location:
– Located away from
buildings to reduce
shelter effect
– Top must be 30cm from
ground to avoid splatter
from ground
– Base sunk into ground to
avoid tripping
– Needs collecting funnel
– Narrow opening to avoid
loss through evaporation
Wind vanes
• Wind vanes
– Show wind direction
– Results can shown on a
circular graph (wind
rose)
Anemometers
• Record the speed
of wind
• Speed is recoded
in km/h or knots
– 1knot =
1,852km/h
– 10knots = 1 barb
• Location
– In the open
– On a high pole
Cloud Cover
• Measures how much of
the sky is covered by
clouds
• Measurement in Oktas
• 1 Okta
= 1/8th of
the sky
= 12,5% of
the sky
Cloud types
•
•
•
•
•
Alto = high
Cirrus = lock of hair
Cumulus = heap
Nimbus = precipitation bearing
Stratus = layer
Cloud types
• High level:
– Cirrus: above 6000m, composed of ice crystals
• Mid level:
– Altostratus: formation due to rising air, condensation, can
bring rain/snow
• Low level:
– Nimbostratus: dark grey, brings persistant rain & low
visibility, formless cloud layer
– Stratocumulus: large, lumpy layered clouds, produce rain
/ drizzle
– Stratus: continuous horizontal layer and level base, can
produce drizzle
– Cumulus: puffy small clouds, fai weather clouds
– Cumulonimbus: large, dense and very tall, invovled in
thunderstorms and intense weather
Clouds …
Cirrus
Cumulus
Altostratus
Stratocumulus
Nimbostratus
Stratus
mammatus
Cumulonimbus
Summary: Meteorological Data
• Stevenson Screen
– Contains: Min / Max thtermometer, Wet / Dry bulb
thermometer, Barometer
– Measures: Daily Min and Maximum temperature, Data for
Relative humidity collection, atmospheric pressure
• Open space observation
–
–
–
–
Rain gauge: measures daily or hourly rainfall
Wind vane: measures wind direction
Anemometer: measures wind speed
Cloud cover: measures the amount of clouds, records type
of cloud
Weather is...
the day to day condition of the
air around us over a short period
of time.
Temperature
• Temperature means
how hot or cold it is
• It is usually
measured with a
thermometer in
degrees
centigrade(ºC)
Pressure
• Pressure is a
measure of how
heavy the air is.
• Pressure is
measured with a
barometer in
millibars (mb)
Cloud Cover
• Cloud Cover tells us
how much of the
sky is covered by
clouds.
• It is measured by
estimating the
amount of cloud
cover in eighths.
Wind Speed
• Wind speed is how fast the
wind is blowing.
• An anemometer measures
wind speed in mph.
• The most common type
looks like a toy windmill.
Three cups are fixed to a
central shaft and the
stronger the wind blows the
faster they spin around.
The wind speed is shown on
a dial, just like a car's
speedometer
Wind Direction
• Wind direction is
where the wind is
blowing from.
• Wind Vane/Wind
Sock: measures
wind direction by
pointing towards
North, East, South
or West
Rainfall/Precipitation
• Precipitation is water
falling from the sky.
• Rain gauge: measures
the amount of rainfall
in mm. Not only does a
rain gauge measure
rainfall, but also all
other forms of
precipitation.
Sunshine
• Sunshine is light and warmth
from the sun.
• A Campbell Stokes Recorder
measures sunshine.
• This type of recorder is made
up of a glass ball which
concentrates sunshine on to a
thick piece of card. The
sunshine then burns a mark on
the card which shows the
number of hours of sunshine in
the day.
Visibility
• Visibility is how far
ahead we can see.
• It is measured
using a tape
measure or trundle
wheel, in metres or
kilometres.