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Weather and climate
Answers
5- the wind
Question 28
G32 Wind
► 2 key facts
● - the air around us is made up of billions of molecules
- molecules are so small you can’t see them, only feel them when they come
to you in a mass
Wind = A mass of moving air molecules along the earths
surface
● wind speed is measured with a wind meter
Question 29
GG 43 Buijs Ballot’s Law
►High pressure a mass of air is pressed together and is pushing down on the
earth
Also called: high pressure area or maximum
The weight of the atmosphere is higher than 1013 mb (millibar/ hectopascal)
►Low pressure a mass of air is stretched out and is rising
Also called: low pressure area or minimum
The weight of the atmosphere is lower than 1013 mb (millibar/ hectopascal)
Air travels from a high pressure
area (maximum) to a low
pressure area (minimum)
Buijs Ballot’s Law
The wind in the northern hemisphere
turns to the right and in the southern
hemisphere to the left
Question 29
G44 The wind systems
►The fixed air pressure areas:
● tropical minimum at 0˚L
● sub-tropical maximum at 30˚L
● sub-polar minimum at 60˚L
● polar maximum at 90˚L
►These fixed maximums and minimums cause the wind systems in the world.
Three wind systems on Earth:
● trade winds (from 30˚L towards 0˚L) (passaten)
● westerly winds (from 30˚L towards 60˚L)
● polar winds (from 90˚L towards 60˚L)
G45 High pressure and low pressure
►High and low pressure areas are usually more or less circular
● When air flows towards a low pressure area, the rotation of the earth makes it
turn to the right
 Air goes up and cools down causing condensation
So in low pressure areas it is often cloudy and rainy
● In high pressure areas the air flows along the surface of the earth

Air comes down and warms up. It can contain more water vapour
So in high pressure areas the sky is blue and cloudless
►Isobar = a line through places with the same air pressure
Question 30
Extra
explanation
Question 31
a- to sail towards 30˚N they often had strong head winds, so they needed to
wait for the wind to lay down. (storm = no sailing)
- to sail towards the equator they had to wait for the wind to start blowing
again (no wind = no sailing)
b- when they were in the shadow of the land, there was not enough wind to sail
and there was more chance to get robbed by pirates.
Question 32
a- The predominant wind direction in the Netherlands is a south western wind
b- This wind has in summer a moderating influence on the temperature,
causing a lower temperature. It also causes more precipitation, because this
wind brings moist air along.
In winter this wind brings relatively warm wind from the sea. This wind is moist
and causes precipitation
Question 33 a/b
July
Question 33
a/b
January
Question 33
c. Boxes X:The wind direction is the same in January and July
Boxes Y: In Map A the wind direction is southwest (it's a monsoon) during
summer (northern hemisphere)
In map B the wind direction is northeast (it's a monsoon) during summer
(southern hemisphere)
d. Boxes X: Those winds are “normal” trade winds because the wind flows
from a high pressure area (30º NL) towards the low pressure (0º L)
Boxes Y: Those winds are monsoons because the low pressure areas
aren't at the equator (0º L) but at a higher latitude. The wind moves from one
hemisphere to the other hemisphere, over the equator. This is why the winddirection isn't the same.