Download Weather and the Atmosphere

Weather and the
Atmosphere
Earth Science
What is Weather?
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Weather is the state of the atmosphere at a
given time and place.
A description of the weather includes:
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The amount and type of clouds
Temperature
Air pressure
Wind speed and direction
Humidity: amount of moisture in the air
Meteorology
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Meteorology is the study of the atmosphere
including the weather.
It includes the study of :
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How the atmosphere heats and cools?
How clouds form and produce rain?
What makes the wind blow?
What makes up the atmosphere?
What causes changes in the climate?
Observing Weather
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Direct observation includes: the
presence of rain, wind speed
and direction, and the presence
of different types of clouds.
Wind direction can be shown
by clouds or dust.
Wind speed is measured using
an anemometer and rated for
it’s effects by the Beaufort
scale.
Other Measurable
Observations
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Temperature can be an important indicator of the
weather and during the winter is adjusted by the
wind speed according to the wind-chill factor.
Increased humidity (water vapor in the air) makes
hot temperatures feel hotter and cold temperatures
feel colder.
Changes in air pressure are most easily detected
when changing elevations and ear popping occurs
(measured by a barometer).
Composition of the Atmosphere
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Earth’ s lower atmosphere is composed of a mixture of
gas (mostly nitrogen and oxygen) called air.
Air thins out as altitude increases, however its
composition remains the same.
The most prominent gas is Nitrogen (N2) at 78%
Secondly, oxygen (O2) makes up 21% (20.8%) of air
Carbon dioxide, is found in very small amounts of
almost 0.04% (400 ppm; was at 350 ppm) & there is
0.93% argon
There are also trace amounts of helium, hydrogen, and
other gases
Water Vapor
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Air always contains some water vapor.
Water vapor enters the air through the
process of evaporation.
Water vapor varies with location,
season, and time of day.
Most water vapor is near the surface of
the earth and decreases with altitude.
Ozone
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Ozone is a form of oxygen
that consists of 3 oxygen
atoms bonded together.
Ozone forms when UV rays from the
sun strike oxygen in the Earth’s
atmosphere.
Ozone exists mainly in a layer of the
atmosphere between 10-50 km up
called the ozone layer, primarily over
the pole regions.
Ozone absorbs approximately 99%
of the harmful rays from the sun.
The ozone layer thinned over the
last several decades due to
chlorofluorocarbons found in
aerosols but is regaining strength
since those chemicals were banned.
Dust
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Dust in the air helps form fog
and rain.
Water vapor condense
around the small particles of
dust and forming tiny water
droplets.
When the droplets become
heavy enough, they fall to
the Earth as rain or snow.
Structure of the Atmosphere
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Scientists divided the atmosphere into four
layers that are based on temperature
changes.
The layers are:
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Troposphere
Stratosphere
Mesosphere
Thermosphere
Troposphere
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The troposphere is the lowest layer.
It starts at Earth’s surface and continues up to
approximately 18 km at the equator and 8 km at the
poles.
All of Earth’s weather occurs in the troposphere.
Temperatures decrease gradually with altitude to
approximately -55°C at the top of the troposphere,
an area called the tropopause.
Stratosphere
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The stratosphere is the second
layer from the bottom.
It extends from the tropopause to
about 50 km above Earth.
The stratosphere is clear and dry
with strong, steady winds and few
weather changes.
The bottom of the stratosphere is
cold, but it warms up steadily with
altitude due to the absorption of
sunlight by ozone.
Mesosphere and
Thermosphere
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The mesosphere is the third layer in which
temperatures drop again.
The fourth layer is the thermosphere where
temperatures rise again.
The top of the thermosphere is about 500 km from
Earth’s surface.
Nitrogen and oxygen in the thermosphere absorb
sunlight causing the temperature rise.
Ionosphere
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The ionosphere is an area
between the heights of 65-500
km above Earth where the air is
highly ionized.
The ionosphere is responsible
for reflecting radio waves back
to Earth which makes
communication by radio
possible.
The ionosphere is affected by
solar events and produces the
auroras or northern and
southern lights.
Heating of the
Atmosphere
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Energy that causes changes in the weather comes
from the sun.
Heat energy enters and moves through the
atmosphere in three ways:
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Radiation: The sun radiates energy through short waves
that are seen as visible light or felt as infrared
Conduction: An object receives heat when it comes into
contact with a hotter object, example air that contacts
warm ground or ocean
Convection: heat transfer through liquids and gases where
the heated substances rises and cooler substance sink
Heat Balance of Earth and
Atmosphere
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The Earth’s heat budget is balanced when equal
amounts of heat are entering and leaving the
atmosphere.
Incoming solar radiation is called insolation.
Conduction from the heated ground warms the
lowest layer of air.
Convection causes air to rise into higher parts of the
atmosphere.
Absorption and Greenhouse Effect
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Earth’s surface radiates infrared waves that warm the
atmosphere as they are absorbed by water vapor &CO2 as
well as other greehouse gases.
The water vapor and CO2 work to trap heat in a process called
the greenhouse effect.
The greenhouse effect in Earth’s atmosphere is increasing as
the level of gases such as CO2 and methane are increasing.
If the atmosphere warms too much the Earth will heat causing
temperatures to rise and glaciers to melt.
Temperature
Drops with
Altitude
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As altitude increases temperature
drops approximately 1°C per 160 m.
The drop in temperature is called the
normal lapse rate.
Air is warmer at the surface of the
earth due to the actions of
conduction, convection and radiation.
Rising air cools and expands as it
travel higher in the atmosphere.
Adiabatic cooling describes
temperature changes that occurs
with the compression or expansion of
air particles.
Temperature Inversions
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A temperature inversion occurs
when air at the surface is colder
than the air above it.
Temperature inversions typically
form during clear, dry nights.
Air on the ground cools quickly
and is trapped on the ground
because it is heavier than warm
air.
Seasons and the Sun’s Rays
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Temperature varies with the seasons because the
sun does not heat Earth’s surface evenly.
The sun’s rays strike the earth at angles from 0° to
90°.
The more vertical the rays the more heat.
As the angle decreases, energy is spread out over a
larger area and less heat is generated.
Also the smaller the angle the larger distance the
energy waves must travel before reaching Earth.
Warmest and Coldest Hours
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Varying insolation also changes the temperature
during the day.
The warmest hour of the day is typically in the
afternoon because the air and the ground are
receiving more heat than they are losing.
The coldest hour of the day is typically just before
sunrise after the ground and air have been losing
heat all night.
The difference between highest and lowest
temperatures is called the temperature range.
Warmest and Coldest Months
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In the northern hemisphere, June 21 typically has the
strongest sunlight, but July is the hottest month.
December 21 has the weakest sunlight and January is the
coldest month.
Typically, oceans have small temperature ranges and
continents tend to have large temperature ranges.
Heating of Land and Water
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Water and land warm up and cool off at different rates.
Why?
 Water absorbs heat for a depth of many meters, land
only absorbs in the top few centimeters.
 Water spreads heat easily because it is a fluid.
 Water needs more energy than land to raise the
temperature the same amount.
 Solar energy is used up in the process of evaporation.
Water also cools more slowly than land.
Surfaces that warm up faster also tend to cool off faster.
Land surfaces that warm up faster include: dark soils, wet
soil and rough soil.
Atmospheric Circulation
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Pressure differences in the atmosphere
cause air to move.
Air generally moves from the poles to the
equator.
The poles are areas of high pressure where
cold air sinks.
The equator is an area of low pressure where
warm air rises.
The Coriolis Effect
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The circulation of the atmosphere and the
oceans is affected by Earth’s rotation.
The Earth has the greatest rotation at its
equator and the least at its poles.
Therefore, when air moves toward the poles
it curves.
The curving of the air flow is called the
Coriolis effect.
The Coriolis Effect cont.
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The Coriolis effect is altered by speed,
latitude and direction.
Objects in the Northern Hemisphere are
deflected right and in the Southern
Hemisphere they turn to the left.
The faster an object is moving the greater the
Coriolis effect.
Global Winds
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The air flow in the Northern and Southern Hemispheres is
divided into three distinct looping patterns called convection
cells.
Each is located in a wind belt, that is characterized by wind
that flows in one main direction.
The major global winds are:
 Trade Winds: flow toward the equator between latitudes of
0° and 30°.
 Westerlies: between 30° and 60° latitude moving toward
the poles
 Polar Easterlies: located over the poles and flowing in a
generally easterly direction
 Doldrums and Horse Latitudes: areas of high pressure
with weak winds that occur at the equator and 30° latitude.
Atmospheric Convection Cells
Winds and Pressure Shifts
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As the seasons change due to shifts in the angle the
sun’s rays hit the Earth, the pressure and wind belts
also shift.
Most winds occur in the lower troposphere.
The jet streams are narrow bands of high-speed
winds that occur in a margin between the
troposphere and the stratosphere.
Two types of jet streams include the polar jet
streams and the subtropical jet streams.
The jet streams are typically 100 km wide, 2 to 3 km
thick and can reach speeds of 500 km/hr.
Global Wind Patterns
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Local Winds
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Local winds are movements of air that are caused
by local conditions and temperature variations.
Land/sea breezes:
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Sea breezes – cool sea air moves over warm land during
the day
Land breeze – cool land air moves over warm sea at night
Mountain/valley breezes:
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Mountain breeze – cold air from the mountains flows
downslope at night
Valley breeze – warm air from the valley flows upslope
during the day