Heating Earths surface and Atmosphere

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Heating Earths surface and Atmosphere

• Chapter 2

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• This chapter discusses
• Temp and heat transfer
• Conduction, convection, radiation
• Solar radiation, earth energy balance
• The seasons
• Local variations

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Temperature and Heat Transfer

• Temperature is the quantity that tells us how hot
  or cold something is relative to some set
  standard value.
• Air is made up of billions of atoms and
  molecules, moving in all directions, spinning and
  bumping around. They dont all move at same
  speed.
• Energy associated with this motion is called
  kinetic energy, the energy of motion.
• Temperature of air is the measure of its average
  kinetic energy
• Temperature is a measure of the average speed of
  the atoms and molecules, where higher
  temperatures correspond to faster average speeds.
• Absolute zero at this temp the atoms and
  molecules would posses a minimum amount of energy
  and theoretically no thermal motion

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Temperature Scales

• Kelvin Scale - a temp scale begins at absolute
  zero (no motion)
• Fahrenheit Scale assigned 32 as the number
  where water freezes and 212 where water boils.
  180 equal divisions called degrees
• Celsius Scale Zero on this scale assigned to
  the temperature at which pure water freezes and
  100 to temp where pure water boils. Divided into
  100 equal degrees
• C5/9(F-32)
• KC273

Comparison of the Kelvin, Celsius, and Fahrenheit
scales
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Latent Heat

• Change of State (Phase Change)- changes
• from gasliquidsolid (ice)
• The heat energy required to change a substance
  (water), from one state to another is called
  latent heat. (Why?)
• Examine a drop of water evaporating faster
  moving molecules escape most easily and the
  average motion of all the molecules left behind
  decreases as each additional molecule evaporates.
  Slower motion suggest a lower water temperature.
  Evaporation is, therefore, a cooling process.
• The energy lost by the liquid water during the
  evaporation can be thought of as carried away by,
  and locked up within the water vapor molecules.
  The energy is in a stored or hidden
  condition and is called latent heat.
• The heat is latent (hidden) in that the
  temperature of the substance changing from liquid
  to vapor is still the same.

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Heat energy absorbed and released
This latent heat energy will reappear as sensible
heat (that we can feel and measure with a
thermometer) when the vapor condenses back into
liquid water. Condensation (opposite of
evaporation) is a warming process.
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Latent heat is an important source of atmospheric
energy! Water vapor rising into the air cools
and becomes liquid water and ice particlesthis
process releases heat into the environment
Every time a cloud forms, it warms the
atmosphere. Inside this developing thunderstorm a
vast amount of stored heat energy (latent heat)
is given up to the air, as invisible water vapor
becomes countless billions of water droplets and
ice crystals. In fact, for the duration of this
storm alone, more heat energy is released inside
this cloud than is unleashed by a small nuclear
bomb.
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Conduction and Convection

• The transfer of heat from the hot
• end of the metal pin to the cool
• end by molecular contact is called
• conduction. Molecules in the end
• of the pin absorb energy from the
• flame and vibrate faster than
• those farther away from flame,
• energy is eventually transferred
• from molecule to molecule to
• hand.
• The transfer of heat by the mass movement of a
  fluid (such as water and air) is called
• convection. Convection
• happens naturally in the
• atmosphere. (I.e. Thermals rising bubbles of
  air.)

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Note In our atmosphere, air that rises
expands and cools air that sinks is compressed
and warmed!
The development of a thermal. A thermal is a
rising bubble of air that carries heat energy
upward by convection
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Radiation

• The energy transferred from the sun to your
• face on a warm day is called radiant
• energy or radiation. The sunlight travels
• through the air with little effect on the air
• itself. The energy travels in the form of
• waves that release energy when they are
• absorbed by an object. These are called
• electromagnetic waves because they have
• magnetic and electrical properties.

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micrometer
Radiation characterized according to wavelength.
As the wavelength decreases, the energy carried
per wave increases.
Note different wave lengths, micrometer is 10-6
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Photons

• Think of radiation as streams of particles,or
• photons, that are discrete packets of
• energy. UV photons carry more energy
• than a photon of visible light. UV photons
• produce sunburns, penetrate skin, can
• cause cancer.

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The sun's electromagnetic spectrum and some of
the descriptive names of each region. The numbers
underneath the curve approximate the percent of
energy the sun radiates in various regions.
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Solar radiation and Earth radiation

• The hotter sun not
• only radiates more energy
• than that of the cooler earth
• (the area under the curve),
• but it also radiates the
• majority of its energy at
• much shorter wavelengths.
• (The area under the curves
• is equal to the total energy
• emitted, and the scales for
• the two curves differ by a
• factor of 100,000.)

Solar radiation is shortwave radiation. Earth
radiation is longwave radiation
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Balancing Act Absorption, Emission, and
Equilibrium

• If the earth and all things on it are continually
  radiating
• energy, why doesn't everything get progressively
  colder?
• The rate at which something radiates and absorbs
  energy depends strongly on its surface
  characteristics, such as color, texture, moisture
  and temperature.
• Blackbody an object that is a perfect absorber
  (it absorbs all the radiation that strikes it)
  and a perfect emitter (emits the maximum
  radiation possible at its given temperature).
  Does not have to be black in color. Earths
  surface is nearly 100 efficient and thus behaves
  like a blackbody
• Radiative equilibrium temperature Average temp
  at which the rate of absorption of solar
  radiation equals the rate of emission of infrared
  earth radiation.

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Selective Absorbers and the Atmospheric
Greenhouse Effect

• Many selective absorbers in the environment.
• Snow, good absorber of IR radiation, but poor
  absorber of sunlight. Good emitter of IR energy.
  At night snow emits more IR energy than it
  absorbs (loss of IR radiation helps cause the air
  above the ground to become very cold).
• Others are water vapor and CO2

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Absorption of radiation by gases in the
atmosphere. The shaded area represents the
percent of radiation absorbed. The strongest
absorbers of infrared radiation are water vapor
and carbon dioxide.
Water vapor and carbon dioxide (CO2) are strong
absorbers of IR Radiation and poor absorbers of
visible solar radiation. They radiate a portion
of the IR energy toward the ground and act as act
as an insulating layer around the earth, keeping
part of the radiation emitted by the earth from
escaping into space.
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Insolation
Sunlight warms the earth's surface only during
the day, whereas the surface constantly emits
infrared radiation upward.Without water vapor,
CO2, and other greenhouse gases, the earth's
surface would constantly emit infrared radiation
(IR) incoming energy from the sun would be equal
to outgoing IR energy from the earth's surface.
Without the greenhouse effect, the earth's
average surface temperature would be -18C.
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With greenhouse gases, the earth's surface
receives energy from the sun and infrared energy
from its atmosphere. Incoming energy still equals
outgoing energy, but the added IR energy from the
greenhouse gases raises the earth's average
surface temperature about 33C, to a comfortable
15C.
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If convection were to suddenly stop - the
average Earth temp would rise about 18F
Air in the lower atmosphere is heated from below.
Sunlight warms the ground, and the air above is
warmed by conduction, convection, and radiation.
Further warming occurs during condensation as
latent heat is given up to the air inside the
cloud. Most absorption takes place near the
surface lower atmosphere is mainly heated from
below.
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At sunrise and sunset, when the white beam of
sunlight must pass through the a thick portion of
the atmosphere, scattering by air molecules
removes the blue light, leaving the longer
wavelengths of red, orange and yellow to pass on
through
A brilliant red sunset produced by the process of
scattering
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On the average, of all the solar energy that
reaches the earth's atmosphere annually, about 30
percent (30/100) is reflected and scattered back
to space, giving the earth and its atmosphere an
albedo of 30 percent. Of the remaining solar
energy, about 19 percent is absorbed by the
atmosphere and clouds, and 51 percent is absorbed
at the surface.
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The earth-atmosphere energy balance. Numbers
represent approximations based on surface
observations and satellite data. While the actual
value of each process may vary by several
percent, it is the relative size of the numbers
that is important.
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Aurora caused by charged particles from the sun
interacting with the atmosphere. Solar wind
collides with atmospheric gases. Gases get
excited and emit light aurora borealis in NH
and aurora australis in SH
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When an excited atom, ion, or molecule
de-excites, it can emit visible light. The
electron in its normal orbit becomes excited by a
charged particle...
...and jumps into a higher energy level.
When the electron returns to its normal orbit, it
emits a photon of light.
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Aurora Belt

• The aurora belt (solid red line) represents the
  region where you would most likely observe the
  aurora on a clear night. (The numbers represent
  the average number of nights per year on which
  you might see an aurora if the sky were clear.)
  The flag MN denotes the magnetic north pole,
  whereas the flag NP denotes the geographic north
  pole.

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Why do we have seasons?

• Earth has an elliptical path around the sun that
  takes a little over 365 days
• One spin on its own axis in 24 hours
• Average distance from earth to sun is 93 million
  miles
• Elliptical path takes us closer to sun in January
  than it does in July Say what?
• Seasons are regulated by sun angle and the number
  of daylight hours

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The elliptical path (highly exaggerated) of the
earth about the sun brings the earth slightly
closer to the sun in January than in July.
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Sunlight that strikes a surface at an angle is
spread over a larger area than sunlight that
strikes the surface directly. Oblique sun rays
deliver less energy (are less intense) to a
surface than direct sun rays.
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As the earth revolves about the sun, it is tilted
on its axis by an angle of 23.5. The earth's
axis always points to the same area in space (as
viewed from a distant star). Thus, in June, when
the Northern Hemisphere is tipped toward the sun,
more direct sunlight and long hours of daylight
cause warmer weather than in December, when the
Northern Hemisphere is tipped away from the sun.
(Diagram, or course, is not to scale.)
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Land of the Midnight Sun. A series of exposures
of the sun taken before, during, and after
midnight in northern Alaska during July. Note
The sun never sets from Mar 20 Sept 22.
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Equinox

• Autumnal (fall) Equinox Sept 22 Sun is
  directly above the
• equator. Except for poles, days and nights
  throughout the world are
• Equal length. After this in the NH there are
  fewer hours of daylight and
• The noon sun is slightly lower in the sky.
• Winter Solstice Dec 21 - The shortest day of
  the year, and the astronomical beginning of
  winter in NH.
• Summer Solstice June 21 Sun is highest in sky
  in N.H. and directly over 23 ½ N (Tropic of
  Cancer)
• Vernal (spring) Equinox March 20, once again
  the noonday sun is
• Shining directly on the equator, days and nights
  are of equal length,
• And at the North pole the sun rises above the
  horizon after 6 long dark
• Months.

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During the Northern Hemisphere summer, sunlight
that reaches the earth's surface in far northern
latitudes has passed through a thicker layer of
absorbing, scattering, and reflecting atmosphere
than sunlight that reaches the earth's surface
farther south. Sunlight is lost through both the
thickness of the pure atmosphere and by
impurities in the atmosphere. As the sun's rays
become more oblique, these effects become more
pronounced.
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The average annual incoming solar radiation (red
line) absorbed by the earth and the atmosphere
along with the average annual infrared radiation
(blue line) emitted by the earth and the
atmosphere.
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The changing position of the sun, as observed in
middle latitudes in the Northern Hemisphere.
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In areas where small temperature changes can
cause major changes in soil moisture, sparse
vegetation on the south-facing slopes will often
contrast with lush vegetation on the north-facing
slopes.
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Temperature

• Chapter 3

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Overview

• Daily Temperature Variations
• Daytime Warming, Nighttime cooling
• Cold Air near the surface
• The Controls of Temperature
• Air Temperature data
• Daily, Monthly, and Yearly Temps
• The use of temp data
• Measuring air temp

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Daily Temperature Variations

• Air temperature is a very important weather
  element. Impacts us every day. If it is warm we
  dont always mind the rain, but if its cold..Or
  if it is 40C outside
• A sunny day has its own cycle of warming
• and cooling.
• Temperature lag Sun directly overhead at noon,
  but noon is not warmest point of a sunny day.
  Why?

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The daily variation in air temperature is
controlled by incoming energy (primarily from the
sun) and outgoing energy from the earth's
surface. Where incoming energy exceeds outgoing
energy (orange shade), the air temperature rises.
Where outgoing energy exceeds incoming energy
(blue shade), the air temperature falls.
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On a sunny, calm day, the air near the surface
can be substantially warmer than the air a meter
or so above the surface. Sunlight warms ground
and ground warms air very near the surface of the
earth. EX Higher Field temperatures than air
temperatures. Higher track temperatures than air
temperatures.
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Nighttime Cooling

• As sun lowers, its energy is spread over a larger
  area, which reduces the heat available to warm
  the ground.
• Sometime in the late afternoon or early evening,
  the earths surface and air above begin to lose
  more energy than they receive, they start to
  cool.
• Radiational Cooling ground and air above cool
  by radiating infrared energy. The ground, being
  a much better radiator than air, is able to cool
  more quickly. Shortly after sunset the earths
  surface is slightly cooler than the air directly
  above it.
• By late night or early morning the coldest air is
  next to the ground with slightly warmer air
  above.

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On a clear, calm night, the air near the surface
can be much colder than the air above. The
increase in air temperature with increasing
height above the surface is called a radiation
temperature inversion
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Radiation Inversion

• Strong radiation inversion occurs when the
• air near the ground is much colder than the
• air higher up.
• Ideal conditions
• Calm conditions no mixing
• Long nights more time for radiative cooling
• Dry air, cloud-free clear skies allow maximum
  cooling at the surface

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On cold, clear nights, the settling of cold air
into valleys makes them colder than surrounding
hillsides. The region along the side of the hill
where the air temperature is above freezing is
known as a thermal belt
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Orchard heaters circulate the air by setting up
convection currents.
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Wind machines mix cooler surface air with warmer
air above.
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Controls of Temperature

• Latitude (colder near the poles, warmer near
  equator)
• Geographic position plus Land and water
  distribution
• Ocean currents (warm/cold currents, upwelling)
• Elevation (air cools with increased elevation)
• Cloud cover and albedo
• Specific Heat the amount of heat needed to
  raise the temperature of one gram of a substance
  by one degree Celsius.
• Water has a higher specific heat than land
• Heats/cools more slowly than land

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Isotherms

• Lines of equal temperature.
• Displayed on weather charts

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Average air temperature near sea level in January
(F). Isotherms lines connecting places that
have the same temperature
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Average air temperature near sea level in July
(F).
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The daily range of temperature decreases as we
climb away from the earth's surface. Hence, there
is less day-to-night variation in air temperature
near the top of a high-rise apartment complex
than at the ground level.
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Daily, Monthly and Yearly Temperatures

• Daily Diurnal range of temperature difference
  between the daily maximum and daily minimum
• Mean daily temperature average of the highest
  and lowest temperature for a 24 hour period.
• Annual range of temperature difference between
  the average temperature of the warmest and
  coldest months
• Mean annual temperature average temperature of
  a station for the entire year.

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Temperature data for San Francisco, California
(37N), and Richmond, Virginia (37N) - two
cities with the same mean annual temperature.
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Use of Temperature Data

• Heating degree day means of estimating energy
  needs. People begin to use furnaces when
  temperature drops below 18C. Subtract the mean
  temperature for the day from 18C. (If mean
  temperature for day is 17C, there would be 1
  heating degree day)
• Cooling degree day subtract 18C from mean for
  day (23- 18C 5 cooling degree days)
• Growing degree day --

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Air Temperature and Human Comfort

• Air temperatures can feel different on different
  occasions. 15C in March can feel warm after a
  long winter, but can feel cool on a summer
  afternoon.
• Sensible heat Temperature we perceive
• Evaporation A cooling process
• Wind Chill factor how cold the wind makes us
  feel

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A section of a maximum thermometer.
As air temp increases the mercury expand and
freely moves past The constriction up the tube
until max temp is reached. As air temp drops, the
constriction prevents the mercury from
flowing Back into bulb. Must be reset by
whirling.
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A section of a minimum thermometer showing both
the current air temperature and the minimum
temperature.
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Instrument Shelter

• 32F in the shade?

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The max-min instrument shelter (middle box) and
other weather instruments that comprise the ASOS
system