Winds' Climate' Hydrosphere'

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Lecture 26

• Winds. Climate. Hydrosphere.

Chapter 13.8 ? 13.14

• Wind Formation and Directions
• Weather Patterns
• Earths Water Envelope

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Winds
Winds are horizontal movements of air caused by
pressure differences in the atmosphere.
The pressure differences are due to temperature
differences. The higher the differences, the
stronger the winds. This type of air movements is
called convection currents.
Another type of air movements are due to the
Coriolis effect. It is due to Earth rotation and
makes wind paths curved.
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Circulation in the Atmosphere

• The air is heated near the equator, rises and
  flows toward the poles, where it cools down and
  returns back as winds.

Due to rotation, the north and south wind are
deflected by the Coriolis effect. This leads to
westward drift in the middle of each hemisphere
and a eastward drift in the tropics.
The westward winds contain zones of high-speed
winds called jet streams (up to 500 km/h).
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Weather Systems
Weather is changes of the atmospheric parameters
temperature, humidity, air pressure, cloudiness,
rainfall.
The most variable weather occurs in the middle
latitudes. This is due to movements of warm and
cold air masses through the belts of western
winds (westerlies). Air masses are large,
isolated, moving bodies of air. Weather systems
associated with air masses are hundreds to a
thousand kilometers across.
There are 2 distinct types of weather systems
depending on air pressure in their centers
cyclones and anticyclones.
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Cyclones
A cyclone is an air mass in which the pressure is
low at the center. Air moves toward the center
and is deflected by the Coriolis effect to the
right in the Northern hemisphere). Cyclonic winds
blow in a counterclockwise spiral (Northern
hemisphere). The situation reverses in the
Southern hemisphere. Warm air rises, cools down,
and moisture condenses in it. Cyclones bring
unstable weather with rain (snow) and abrupt
temperature changes. Tropical cyclones are named
to ease communication between forecasters and
general public.
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Anticyclones
An anticyclone is centered on a high-pressure
region from which air moves outward. Due to
Coriolis effect, winds in an anticyclone blow
clockwise in the Northern hemisphere. The air
descents, warms, becomes less saturated with
moisture, and brings good weather with clear
skies.
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Fronts
Fronts are boundaries between different air
masses.
When warm air enters a cold air mass, a
low-pressure region is produced and it moves as a
cyclone. In middle northern latitudes, such a
cyclone usually moves eastward. The eastern side
of the warm air region is a warm front, while the
eastern side is a cold front (because cold air
replaces warm air). Warm air rises, cools, and
produces clouds. A warm front typically moves at
150 km/day. A cold front moves faster, overtakes
the warm front, forces warm air upward, and
ceases the cyclone (occluded front).
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Climate
Climate is a summary of the weather in a region.
The most significant weather elements are
temperature and precipitation.
Tropical climates. Near the equator, the
insolation is the highest, a lot of evaporation
and rains. At horse latitudes (30O S N), winds
are calm, air moves downward, less moisture,
drier weather.
Mid-latitude climates. Moderate average
temperatures with great variations between
seasons. Northern hemisphere Air from the
Pacific rises up above the mountains, rain on the
western side, drier on the eastern.
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Climatic Changes
Daily, seasonal, and yearly weather changes are
due to variations, sometimes not well understood,
in the atmospheric physical parameters.
Climatic changes are rare (for example, ice
ages). Little ice age 1645?1715 due to lower
solar activity. Ice age 1800 years ago due to 4
km ice sheets covering both Europe and North
America. Warming since the end of the 19th
century.
Origin periodic changes in the tilt of the
Earths rotation axis. The basic reason is
thought to be insolation of polar regions
(Milankovitch hypothesis).
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Hydrosphere
70 of the Earths surface is covered by oceans
and connected seas, which are full of
life. Surface water evaporates and influences
weather. Water absorbs solar energy and
distributes it around the world.
Oceans are large basins bounded by continents. An
ocean bottom gradually slopes down to 130m with
an average width of 65 km (varying from 1 to 1000
km). This continental shelf turns into
continental slope (down to 2 km), which joins
the abyssal plain via continental rise.
Oceans average depth is 3.7 km. Marianas
Trenches 11 km below the surface.
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Ocean Currents

• Two ways oceans affect climate
• Store heat (the first few meters contain more
  heat than the entire atmosphere).
• Surface currents, produced by friction of air and
  water.

Heat transfer between air and water can exceed
the rate of arriving solar energy at the
Earth. This is why continents are cooler in
winters than coastal regions and islands.
Surface currents are wind-driven and mostly
parallel to major wind streams and form
equatorial current. This current runs into South
America in the Atlantics and into the East Indies
in the Pacific.
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Ocean Currents
At each of the contacts the current divides into
2 parts. One flows to the south, the other one to
the north. Then westerlies drive them eastward
across the oceans. This mechanism produces 4
large whirlpools.
The Gulf Stream
Gulf Stream is a warm current moving partly into
the Gulf of Mexico, partly straight north along
the US eastern coast. It splits on the European
side one part moves south and completes the
whirl, the other one moves into the Arctic
Ocean. Gulf Stream makes climate of NW Europe
milder.
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Summary
Earths atmosphere was developed over a large
period of time and is hospitable for life due to
the right distance from the Sun. Weather is
mostly due to the large amount of vaporized
water and winds, which exist due to the planet
rotation and uneven distribution of continents
and oceans. Water in oceans generally follows
the wind directions and is affected by the
current distribution of continents.