Download Coriolis Effect

Influences on Weather and Climate
Weather and Climate
Coriolis Effect
1 Climate is defined as the prevailing weather
conditions, such as temperature, humidity,
rainfall, and wind, in one area over a long period
of time. Climate around the world can be divided
into five general types: tropical, dry, moderate,
continental, and polar. Have you ever wondered
what determines the climate where you live?
Latitude, terrain, altitude, and nearby bodies of
water all play a role in the climate of a given
location. Let’s find out more about how latitude
and air circulation affect climate.
2 Lines of latitude are imaginary horizontal lines drawn across the globe parallel to the equator,
and represent the distance of a location from the equator. Zero latitude is located at the
equator, and each pole is 90 degrees latitude. Latitudes north and south of the equator are
indicated by the angle, followed by the direction. The North American continent is located
entirely north of the equator. For example, Miami, Florida lies at 25 degrees north, while
Anchorage, Alaska lies at 61 degrees north. Latitude determines the amount of sunlight a given
area receives. Within 30 degrees of the equator, the sun shines nearly perpendicular to the
earth’s surface, so that these areas receive the maximum amount of energy from the sun and
therefore the most heat. On the other hand, the angle of the sun’s rays is much shallower at
higher latitudes, and the energy received at these latitudes is much less.
3 The rotational speed of the earth also changes based on latitude. The earth rotates about its
axis once each day, completing one rotation in 24 hours. At the equator, the earth’s
circumference is 40,079 km, so the rotational speed is 1,670 km/hr. Near the poles, the earth’s
circumference is much less but the day is still 24 hours long, so the speed decreases to about
290 km/hr. Differences in rotational speed affect air circulation. Air moves from an area of high
pressure to an area of low pressure. High pressure comes from cooler air sinking towards the
ground, while low pressure comes from warm air rising from the ground. The movement of air
from high to low pressure is known as wind. The rotation of the earth deflects the wind blowing
in a straight line. In the northern hemisphere, wind is deflected to the right; in contrast, wind in
the southern hemisphere is deflected to the left. Strong winds are deflected more than weak
winds. The force responsible for the deflection is called the Coriolis effect. It is a result of the
earth’s rotation. All of this may sound pretty confusing, so let’s look at several examples where
latitude and air circulation come together to create climate.
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Influences on Weather and Climate
Weather and Climate
4 There are three bands of air masses circulating in each hemisphere. Each is generally confined
to 30 degrees latitude. This means that one band exists between 0 and 30 degrees, another
between 30 and 60 degrees, and a third between 60 and 90 degrees. Close to the equator,
climate is characterized by its stability. Temperature varies little between day and night, and
between the seasons. Warm humid air rises, producing low pressure. High in the atmosphere,
the air starts to flow towards the poles. In the northern hemisphere, the airflow deflects to the
right due to the Coriolis effect. As the air mass moves northward, it cools and a portion of it
sinks, flowing back towards the equator along the earth’s surface. This happens in both
hemispheres between 20 and 30 degrees latitude. So, in summary, air rises at the equator,
flows north, sinks at higher latitude and flows back towards the equator. The winds flow from
the east to the west close to the equator and are known as trade winds. Trade winds blow at a
steady speed and were named trade winds because sailors took advantage of them to propel
trading ships across the ocean from Europe toward the West Indies. Right at the equator winds
are generally calm, and sailors named this region the doldrums.
5 Rising air at the equator produces clouds and rain. In some land areas near the equator,
tropical rain forests thrive. The descending air near 30 degrees latitude is very stable and
produces persistent high pressure systems. This band of high pressure circling the earth is
known as the sub-tropical ridge. Few clouds and little rain result in major deserts, such as the
Sahara in Africa and the Mojave and Sonoran in North America, which lie along this latitude. In
the mid latitudes, another mass of air circulates, producing winds generally from west to east,
known as westerlies in both hemispheres. They blow between 30 and 60 degrees latitude. The
westerlies are strongest in winter and weakest in summer. The climate in the mid latitudes
tends to be temperate, meaning that temperature and precipitation vary with the seasons. In
addition to latitude, climate here also strongly depends on proximity to the ocean. Above 60
degrees latitude are the polar regions, where the weather is dominated by cold air sinking at the
poles, producing high pressure. Strong winds are common near the poles, blowing south at the
North Pole and north at the South Pole. Sinking air and the resulting high pressure generate
very little precipitation at the poles.
6 At each latitude, landforms also influence climate. In general, temperature decreases with
altitude. At higher altitude, air pressure is lower, and this lower pressure leads to lower
temperatures. Precipitation depends on both the altitude and the direction of wind. As air rises,
it gets colder and moisture trapped in the air falls as rain. Wind blows from west to east near
Seattle, Washington, picking up moisture from the Pacific Ocean and dropping it over Seattle,
giving the city its rainy reputation. Higher elevations on the western side of the mountains in
Washington still receive lots of rain, but as the air rises over the top of the mountains, most
moisture is left behind. Areas on the east of the mountains receive little rain. Land further inland
tends to receive less precipitation because the wind cannot pick up moisture as it travels.
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Influences on Weather and Climate
Weather and Climate
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2
Which of the following variables influences climate LEAST?
A
Latitude
B
Longitude
C
Altitude
D
Terrain
City A is 30 degrees north latitude, while City B is 30 degrees south latitude? Which city
is closest to the equator?
A
City A
B
City B
C
Both cities are equally close.
D
City A in winter, City B in summer.
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Influences on Weather and Climate
Weather and Climate
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Which statement correctly describes the relationship between air temperature and air
pressure?
A
Warm air rises, creating an area of low pressure.
B
Cool air sinks, creating an area of low pressure.
C
Warm air sinks, creating an area of low pressure.
D
Cool air rises, creating an area of low pressure.
Trade winds blow towards the equator and from east to west. What variable is most
responsible for the east to west direction?
A
The strong solar radiation at the equator.
B
The high pressure at around 30 degrees latitude.
C
The low air pressure at the equator.
D
The rotation of the earth.
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Influences on Weather and Climate
Weather and Climate
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At which latitude would tropical rain forests be most likely?
A
10 degrees north
B
30 degrees south
C
60 degrees north
D
90 degrees south
An animal lives at 20 degrees north latitude. If the animal population expands, in which
direction is it most likely to find suitable habitat?
A
North from its current habitat.
B
South from its current habitat.
C
At lower altitude from its current habitat.
D
East from its current habitat.
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