1. Atmospheric Science Dr
Atmospheric Science Dr.Gamal El Afandi Tuskegee University

2. Meteorology
Meteorology is the study of the atmosphere and the processes that cause atmospheric motions and the weather (and climate)

3. Weather State of the atmosphere at a particular place and TIME
What’s the temperature, precipitation, cloudiness, wind speed etc.
Affects daily activity

4. Weather & Climate
Weather is comprised of measured:
a) air temperature
b) air pressure
c) humidity
d) clouds
e) precipitation
f) visibility
g) wind
Climate represents long-term
(e.g. 30 yr) averages of weather.

5. Weather and Climate Climate is
Long-term average of atmospheric variables
Such as
Temperature
Pressure
Wind speed and direction
Precipitation
Others
And maxima, minima, extreme values, etc.

6. Climate
Human activities (normal behavior, culture, architecture, agriculture) determined by climate
The conditions we expect

7. Weather Journal You are required to keep a weather journal
Each day you should record
Maximum temperature
Minimum temperature
What the weather was like
You can use any source of information BUT
YOU MUST REVEAL YOUR SOURCES

8. Density
The density of a substance is defined as the amount of mass of a substance in a given volume.
It can also be defined by a number density that tells us the number of “things” in a given volume.
Number of students in this room
Number of water drops in a cubic centimeter of cloud

9. Density Is measured in kg m-3
(or sometimes g cm-3)
Number density is in (number) m-3
The air in this room (at the surface of the Earth) has a density of ~1.2 kg m-3
A fluid with a lower density will float on a fluid with a higher density
Decrease the density and it could rise

10. Pressure
The air pressure is the force per unit area that the atmosphere exerts on any surface it touches.
The molecules of the air are in constant rapid motion.
When a molecule collides with a surface, such as your skin, the molecule exerts a force on that surface.

11. Pressure and density:
The higher the density the more molecules. More molecules striking a surface means higher pressure

12. Pressure Units SI unit Pa (Pascal)
Or N m-2
Sea level atmospheric pressure is ~ Pa
Meteorologists also use millibars – mb
Sea level atmospheric pressure is ~1000mb
They even sometimes use millimeters (inches) of mercury – mm Hg, inches Hg
Sea level atmospheric pressure is ~760 mmHg or 30” Hg

13. Pressure Scale & Units
Many scales are used to record atmospheric pressure, including inches of mercury (Hg) and millibars (mb).
The National Weather Service uses mb, but will convert to metric units of hectopascals (hPa).
The conversion is simply 1 hPa = 1 mb.
Figure 9.4

14. Measuring Pressure
To measure atmospheric pressure we use a barometer

15. Pressure Measurement
Figure 9.6
Changes in atmospheric pressure are detected by a change in elevation of a barometric fluid or change in diameter of an aneroid cell, which indicates changing weather.
Average sea level pressure is in Hg, or mb.
Figure 9.5

16. Pressure Trends
Figure 9.7
Barographs provide a plot of pressure with time, and are useful in weather analysis and forecasting.
Altimeters convert pressure into elevation, and are useful in steep terrain navigation or flying.
Both use aneroid cells.

17. Earth's Atmosphere
Figure 1.2
99% of atmospheric gases, including water vapor, extend only 30 kilometer (km) above earth's surface.
Most of our weather, however, occurs within the first 10 to 15 km.

18. There is a lot of Nitrogen!
© 1998 Prentice-Hall -- From The Atmosphere, 7th Ed., by
F.K. Lutgens and E.J. Tarbuck, p. 6.

19. Permanent Gases
Permanent gases have fixed proportions in the atmosphere, both in time and space
For Dry Air
78% Nitrogen (N2)
21% Oxygen (O2)
0.93% Argon (Ar)
The rest is other stuff
Trace gases and variable gases (eg. CO2)

20. Variable gases
Variable gases can have different concentrations in the atmosphere, both in time and space
The most important variable gas is water vapor
Other variable gases include carbon dioxide (CO2), methane and ozone

21. Water vapor Is variable
We measure this variability as the humidity (see later)
From evaporation
Proximity to bodies of water
Air temperature
When it condenses get clouds and precipitation

22. Water vapor Is important because
It is the only common substance that can change between gas, liquid and solid at temperatures and pressures that are normal on Earth
It can ‘hold’ a lot of energy and transport that energy around the planet
We need water
It absorbs a lot of radiation

23. Carbon dioxide Used by plants during photosynthesis Exhaled by animals
Plants take in and store carbon as they grow
Exhaled by animals
Released by the burning of oil, gas, wood, coal
Concentrations have been rising around the world for 200 years

24. Variable & Increasing Gases
Figure 1.5
Figure 1.4
Nitrogen and oxygen concentrations experience little change, but carbon dioxide, methane, nitrous oxides, and chlorofluorocarbons are greenhouse gases experiencing discernable increases in concentration.

25. Why is the change in CO2 important?
Carbon dioxide absorbs longwave (infra-red) radiation
This creates an imbalance between energy received by the Earth and energy leaving the Earth
If you want to know why we should care wait for next chapter or look at the atmosphere of Venus (in the book)

26. Ozone
At the surface
Is caused by chemical reactions between a variety of pollutant gases (such as nitrogen oxides)
Mostly caused by vehicle emissions
Is an irritant

27. Structure of the Atmosphere

28. Thickness
The atmosphere is a very thin (relatively) layer of gas over the surface of the Earth
Earth’s radius ~ 6400km
Atmospheric thickness ~ 100km
(If you travel 100km horizontally you don’t even get to St. Louis. If you do it vertically you’d be in space!)

29. The Relationship Between Air Pressure and Altitude
Pressure decreases as you
go up in height.
The change is pressure is
not constant. The pressure
decreases exponentially
with increasing height.

30. Air Density and height

31. Pressure & Density
Gravity pulls gases toward earth's surface, and the whole column of gases exerts a pressure of 1000 hPa at sea level, mb or in.Hg.
Figure 1.7

32. Pressure and Density Decrease with Height
© 1998 Wadsworth Publishing Co. -- From Ahrens, Essentials of Meteorology

33. Vertical Pressure Profile
Pressure increases at a curved rate proportional to altitude squared, but near the surface a linear estimate of 10 mb per 100 meters works well.
Figure 1.8

34. Layers by temperature
The atmosphere can be divided into layers based on temperature characteristics.
This layering of the atmosphere also represents real physical barriers in that within the layers there is lots of vertical motion and mixing of air.
This does not happen between layers.

35. Layers of the atmosphere
Troposphere
Stratosphere
Mesosphere
Thermosphere

36. Atmospheric Layers
8 layers are defined by constant trends in average air temperature (which changes with pressure and radiation), where the outer exosphere is not shown.
Figure 1.9

37. The Troposphere Where we live (all the time)
Contains 80% of the mass of the atmosphere
Is between 8-16km (5-10 mi) deep
Deeper at the equator than the poles
WHERE WEATHER HAPPENS

38. Temperature Structure of the Atmosphere
Warming in the
stratosphere
© 1998 Wadsworth Publishing -- From Essentials of
Meteorology, 2nd Ed., by C.D. Ahrens, p. 9.

39. The Stratosphere Contains the ozone layer
Where ultra-violet radiation is absorbed
This means that we are protected from harmful high-energy radiation from the sun
This also means that the stratosphere is warmer than the top of the troposphere because it has absorbed that energy

40. Ozone Is a variable gas At the surface
Is caused by chemical reactions between a variety of pollutant gases (such as nitrogen oxides)
Mostly caused by vehicle emissions
Is an irritant

41. Ozone In the stratosphere
Is a beneficial gas that absorbs ultra-violet radiation
Protects us from this harmful radiation
Is broken down by chemical reactions with chlorine containing gases (chlorofluorocarbons – CFCs): Man-made compounds used in aerosol sprays, refrigerators and air-conditioners

42. Energy in the Atmosphere

43. Energy
It’s what makes things happen

44. What’s it about?
Temperature,
Energy and
Heat

45. Definitions Before we start we need to get some things straight
We need definitions of some basic atmospheric parameters

46. Content Basics The basic properties of the air Temperature Pressure
Density
We’ve already met the latter two

47. Temperature
Temperature: The temperature of a substance is a measure of the average kinetic energy of the molecules in that substance.
Thus atmospheric temperature is
proportional to the speed of the air
molecules.

48. Temperature Scales
There are three (3) temperature scales you need to know about. With their units:
Fahrenheit (F) -- German
Celsius (C) -- Swedish
Absolute (K) -- Scientific

49. Fahrenheit Scale Fahrenheit Scale (1714): Ice melts at 320 F,
Water boils at 2120 F.
180 Degrees between melting and boiling point of pure water at sea level.

50. Celsius Scale Celsius Scale (1742): Ice melts at 00 C
Water boils at 1000 C
 One of several
“Centigrade Scales.”
100 Degrees between melting and boiling point of pure water at sea level.

51. Thermodynamic (Kelvin) Scale
Kelvin or Absolute Scale (1800’s):
No molecular motion at 0 K.
Uses Celsius’ degree increment
Ice melts at 273 K
Water boils at 373 K

52. Temperature Scales
Thermometers detect the movement of molecules to register temperature.
Fahrenheit and Celsius scales are calibrated to freezing and boiling water, but the Celsius range is 1.8 times more compact.
Figure 2.2

53. Temperature Scales 5 C = (F - 32) 9 9 F = C + 32 5 K = C + 273
Conversions between temperature scales can be
easily accomplished by the following three simple
equations. 5 9
C = (F - 32) 9 5
F = C + 32
K = C + 273

54. Energy
Energy - The ability to do work or exchange heat with the surroundings.
Examples of types of energy
Potential Energy -- Energy of position
Kinetic Energy -- Energy of motion
Internal Energy -- Energy of motion of the molecules.
Radiant Energy -- Electromagnetic radiation.

55. First Law of Thermodynamics
In a system with constant mass, energy can be neither created or destroyed.
Energy is conserved.
Energy may be changed to a different form.
Example: The change in kinetic energy may go to a change in potential or internal energy.

56. Second Law of Thermodynamics
It is impossible to construct a device to transfer heat from a colder system to a warmer system without the occurrence of other simultaneous changes in the two systems or the environment.
Heat transfer is one way: Hot to cold.

57. Heat
Energy in the process of being transferred from one object to another (due to temperature differences)

58. Heat Transfer How is heat transferred? Latent Heat Conduction
Convection
Radiation

59. Temperature Gradient
A gradient is the change in something over a given distance. A temperature gradient is the change in temperature over a given distance.
A gradient has both magnitude and direction.
The gradient points in the direction of maximum (temperature) change toward higher values.
Consider an example………...

60. Conduction - Heat Transfer
Conduction of heat energy occurs as warmer molecules transmit vibration, and hence heat, to adjacent cooler molecules.
Warm ground surfaces heat overlying air by conduction.
Figure 2.5

61. Temperature Gradient
Heat transfer occurs in the direction of hotter regions to colder regions.
If there is a temperature gradient, the heat transfer will act to destroy the gradient.

62. Energy Transfer

63. Today you might learn about
Different forms of energy
How energy is transported

64. Heat Latent Heat -- “Invisible Heat” Sensible Heat
Heat released or absorbed during a phase change.
Evaporational Cooling
Condensation
Sensible Heat
Heat transfer we can feel and measure.

65. Phase Changes of Water Vapor Liquid Ice Heat Energy Absorbed
Sublimation
Evaporation
Melting
Vapor
Ice
Liquid
Freezing
Condensation
Deposition
Heat Energy Released

66. Heat energy, which is a measure of molecular motion, moves between water's vapor, liquid, and ice phases.
As water moves toward vapor it absorbs latent (e.g. not sensed) heat to keep the molecules in rapid motion.

67. Conduction
The movement of energy through a body without the movement of the particles of that body (molecule to molecule)
Eg. Heating your food in a pan
In the atmosphere this is only important for a very thin layer of air in contact with the ground

68. Convection The movement of a fluid due to differences in temperature
When air gets warm it expands, this makes it less dense (lighter) than surrounding air that is not warm. Therefore it starts to float above that air – it rises. Warmer air moves to a region of cooler air taking its energy with it.
We will return to convection later on in the course

69. Convection Convection Air Parcel
The transfer of heat by the mass movement of a fluid.
Works well in the atmosphere and oceans.
Air Parcel
MIXING H H H
Thermal

70. Convection - Heat Transfer
Figure 2.6
Convection is heat energy moving as a fluid from hotter to cooler areas.
Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence cools.

71. Warming Earth's Atmosphere
Figure 2.13
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface does it generate sensible heat to warm the ground and generate longwave energy.
This heat and energy at the surface then warms the atmosphere from below.

72. Radiation All objects emit electro-magnetic radiation in some form
This radiation moves through space until it hits something
The thing it hits may then absorb the radiation and obtain its energy
Alternatively it may deflect, scatter or reflect the radiation

73. Radiation We can describe the radiation by: Wavelength
The actual length (meters) between wave peaks.
Wavelengths for radiation vary greatly
radio waves (100 cm to 160 meters)
Light (10-9 meters).
Frequency
The number of wave crests that pass by a point per second (Hertz).

74. Radiation One Wavelength
The distance between wave crests is the wavelength.
Shorter waves: x-rays, UV, visible light
Longer waves: infrared, microwave, radar, TV, radio

75. Solar Spectrum max = 0.55 m
© 1998 Wadsorth Publishing -- From Ahrens Essentials of Meteorology

76. Radiation What heats the Earth???  The Sun!!! How does it do it???
Radiation -- Energy transfer from one place to another by electromagnetic waves.
Light
Radio Waves
Microwave
Infrared
Ultraviolet
Note EM radiation does not require a ‘medium’ to pass through, it can get from the sun to the earth through the vacuum

77. Radiation Incoming Solar Radiation (Insolation)
The sun radiates a huge amount of energy but in all directions.
The amount reaching a point in space depends on the distance from the sun.

78. Radiation
Solar Constant: The amount of solar energy arriving at the top of the atmosphere perpendicular to the sun’s rays. (Not really “constant” but close enough for government work!)
= 1375 W m-2
(Sometimes written as 1365 W m-2, depending on source.)

79. Radiation
Incident Solar Radiation and Albedo
NASA -- Apollo 8

80. Albedo But we must consider reflections:
Albedo = Amount reflected (x 100%)
Amount incoming
Earth’s albedo = 30%
This 30% is due to:
clouds
dust, haze, smoke
scattering by air molecules
reflections from land, oceans, ice

81. Radiation
Only one half of the earth intercepts sunlight. From the sun, it looks like a disc.
Solar
Radiation

82. Which half of the Earth is light?
The Earth rotates on its own axis
Only the daytime side receives energy directly from the sun
The nighttime side often receives a smaller amount of energy reflected off the moon

83. Radiation
All things, whose temperature is above absolute zero, emit radiation  They radiate!!!
Radiation is emitted at all wavelengths -- some more so than others
Examples
Dogs The atmosphere
Snow Your Books
Trees and …..
The oceans You!!!

84. Radiation Stefan-Boltzmann Law: Anything that has
a temperature radiates energy. Hotter
objects radiate a lot more energy.
E =The amount of energy (W m-2) emitted by an object per unit area
 = Stefan-Boltzmann constant = 5.67 x 10-8 W m-2 K-4
T = Temperature (K)

85. Wien’s Law This tells us the peak wavelength that an object will emit
λmax = 2900 / T
Where λmax is the wavelength in micrometers
T is the temperature in Kelvin

86. Wien’s Law The sun has a surface temperature of about 6000K:
λmax = / 6000 ≈ 0.48μm
This is green light
The Earth has a surface temperature of about 290K:
λmax = 2900 / 290 ≈ 10μm
This is infra red radiation

87. Radiation
OUTPUT
The earth’s surface has a temperature so it radiates according to the Stefan-Boltzmann Law.
Wien’s Law tells us this is primarily infrared (IR) radiation. But, only 6% of this passes directly to space.

88. Solar and Terrestrial Radiation
Notice that the earth’s radiation
is much, much less than that of
the sun!
Wavelength
Terrestrial
Radiation
© 1999 Prentice-Hall -- From Aguado and Burt, Understanding Weather and Climate
Wavelength

89. Radiation
What have we discovered about the radiation of the sun compared to the earth?
The sun has a radiation maximum in the visible part of the spectrum.
The Earth has a radiation maximum in the infrared part of the spectrum.

90. Summary Energy comes in many forms
Energy can be moved from hot things to cold things in 4 ways
All these ways have some importance in the atmosphere
The spectrum of radiation

91. Solar energy

92. We’ll contemplate little things like…
Why there’s life on Earth
Why you don’t want to live at the South Pole
Why you don’t want to live in San Antonio
Why the weather changes every day these days

93. Today We’ll deal with solar radiation What’s the “greenhouse effect”?
Return homework

94. Radiation What heats the Earth???  The Sun!!! How does it do it???
Radiation -- Energy transfer from one place to another by electromagnetic waves.
Light
Radio Waves
Microwave
Infrared
Ultraviolet
Note EM radiation does not require a ‘medium’ to pass through, it can get from the sun to the earth through the vacuum

95. Radiation Incoming Solar Radiation (Insolation)
The sun radiates a huge amount of energy but in all directions.
The amount reaching a point in space depends on the distance from the sun.

96. Radiation
Solar Constant: The amount of solar energy arriving at the top of the atmosphere perpendicular to the sun’s rays. (Not really “constant” but close enough for government work!)
= 1375 W m-2
(Sometimes written as 1365 W m-2, depending on source.)

97. Radiation
Incident Solar Radiation and Albedo
NASA -- Apollo 8

98. Albedo But we must consider reflections:
Albedo = Amount reflected (x 100%)
Amount incoming
Earth’s albedo = 30%
This 30% is due to:
clouds
dust, haze, smoke
scattering by air molecules
reflections from land, oceans, ice

99. Radiation
Only one half of the earth intercepts sunlight. From the sun, it looks like a disc.
Solar
Radiation

100. Which half of the Earth is light?
The Earth rotates on its own axis
Only the daytime side receives energy directly from the sun
The nighttime side often receives a smaller amount of energy reflected off the moon

101. Radiation
All things, whose temperature is above absolute zero, emit radiation  They radiate!!!
Radiation is emitted at all wavelengths -- some more so than others
Examples
Dogs The atmosphere
Snow Your Books
Trees and …..
The oceans You!!!

102. Radiation Stefan-Boltzmann Law: Anything that has
a temperature radiates energy. Hotter
objects radiate a lot more energy.
E =The amount of energy (W m-2) emitted by an object per unit area
 = Stefan-Boltzmann constant = 5.67 x 10-8 W m-2 K-4
T = Temperature (K)

103. Wien’s Law This tells us the peak wavelength that an object will emit
λmax = 2900 / T
Where λmax is the wavelength in micrometers
T is the temperature in Kelvin

104. Wien’s Law The sun has a surface temperature of about 6000K:
λmax = / 6000 ≈ 0.48μm
This is green light
The Earth has a surface temperature of about 290K:
λmax = 2900 / 290 ≈ 10μm
This is infra red radiation

105. Radiation
OUTPUT
The earth’s surface has a temperature so it radiates according to the Stefan-Boltzmann Law.
Wien’s Law tells us this is primarily infrared (IR) radiation. But, only 6% of this passes directly to space.

106. Solar and Terrestrial Radiation
Notice that the earth’s radiation
is much, much less than that of
the sun!
Wavelength
Terrestrial
Radiation
© 1999 Prentice-Hall -- From Aguado and Burt, Understanding Weather and Climate
Wavelength

107. Radiation
What have we discovered about the radiation of the sun compared to the earth?
The sun has a radiation maximum in the visible part of the spectrum.
The Earth has a radiation maximum in the infrared part of the spectrum.

108. Radiation
GOES-8
Full-disk
Visible

109. Radiation
GOES-8
Full-disk IR

110. Solar absorbed = Long Wave emitted
Radiation
For the Earth’s temperature to remain constant over a long period of time (decades), the amount of solar radiation absorbed must equal the amount of long wave radiation emitted to space.
Solar absorbed = Long Wave emitted
Input = Output

111. Radiation Earth-Atmosphere Energy Balance
© 1998 Wadsorth Publishing -- From Ahrens Essentials of Meteorology

112. Scattering of Radiation
Radiation can be scattered or absorbed by the gases and particles (dust) in the atmosphere
Different wavelengths of light are scattered in different ways
A certain proportion will be scattered straight back into space

113. Absorption of Radiation
Radiation can be absorbed by molecules of gas in the atmosphere
Different gases absorb different wavelengths of light
The major atmospheric gases absorb infra-red, but not visible, radiation
When the gas absorbs radiation it gains energy (is warmed)

114. Atmospheric Absorption
Solar radiation passes rather freely through earth's atmosphere, but earth's re-emitted longwave energy either fits through a narrow window or is absorbed by greenhouse gases and re-radiated toward earth.
Figure 2.11

115. The Atmosphere is transparent
Radiation
As a first approximation --
The Atmosphere is transparent
to solar radiation.

116. Radiation
Thus the earth’s atmosphere is essentially opaque (not transparent) to IR radiation from the earth’s surface.
Absorption by:
a. H2Ov c. CO2
b. Clouds d. O3

117. Radiation Greenhouse Effect.
The atmosphere radiates IR both upwards and downwards
The downward portion re-warms the earth’s surface and is known as the
Greenhouse Effect.

118. Summary
We’ve seen what the Greenhouse Effect is and what it isn’t and why we should avoid the term altogether
Next time we’ll talk about ‘climate variation’ and why it happens

119. What’s this “Greenhouse Effect” Thing anyway?

120. Climate variation Changes in climate Short period changes
Long term changes

121. Climate
The average of the day-to-day weather over a long period of time at a specific place.
The “normals” reported on television are really just climatological averages!
Different parts of the world have different climates

122. Climate Variability Climate can change over time.
There were once Glaciers over Britain and before that shallow tropical seas.
But we are really interested in a more short-term climate change.
A change that can be observed over a few years, or at least in our lifetime.

123. Short-term Climate Variability
Changes in the solar output.
The solar constant really isn’t.
Between 1981 to 1986, the solar output was measured to decrease by 0.018% per year.
The total reduction was almost 0.1% in six years.
Had this trend continued for another six years, the effects of the reduction in solar output may have had a noticeable effect on the global climate.

124. Changes in the solar output.

125. Short-term Climate Variability
Changes in the number of sunspots.
Sunspots are relatively large dark spots that appear on the surface of the sun.
The temperature of the core of the sunspot is usually 4000 K compared to the 5800 K normal temperature of the surrounding solar surface.
Sunspot numbers tend to fluctuate in an 11 year cycle (22 years if magnetic fluctuations are included).

126. Sunspots

127. Short-term Climate Variability
There have been noted correspondence between sunspot number minima and colder temperatures on earth.
Between 1645 and 1715 there was a period of few sunspots. This is called the Maunder Minimum.
The Maunder Minimum corresponds to the “little ice age” where the average global temperature was estimated to be about 0.5oC cooler.

128. Maunder Minimum

129. Changes in the solar output.

130. Short-term Climate Variability
Volcanoes
Large volcanic eruptions can have an impact on the climate of a region.
Particles are ejected into the atmosphere that can alter the amount of radiation received at the surface.
Sulfur compounds in ejected material can create sulfuric acid (H2SO4).
This sulfuric acid absorbs solar radiation and increases the albedo.

131. Short-term Climate Variability
A year after the eruption of Tambura, New England experienced the “year without a summer.”
Heavy snow in June
Frost in July and August
June mean temperatures were 3.5oC below normal
August temperatures were 1-2oC below normal
Cold weather was experienced in England and Europe
A year after the eruption of Pinatubo, the mean global air temperature dropped by almost 0.5oC compared to the previous 9-year average.

132. Mt. Pinatubo

133. Short-term Climate Variability
“Greenhouse” Gases
Carbon Dioxide, Methane, Water Vapor, Nitrous Oxide, CFC’s
Increase CO2 (and others) and increase the temperature of the earth’s surface
Do feedback mechanisms cancel this effect?

134. Regional climates Continental areas have extremes
Coastal areas tend to be more moderate (temperate)

135. Water surfaces
Water is dark and absorbs a lot of heat (except when the sun is low in the sky)
Water surfaces stay cool because
When hot a lot of evaporation takes place
Water is a fluid and can mix within itself, therefore energy can be distributed quickly throughout the body of water (compared to soil/rock where heat is conducted slowly)

136. Is that why oceans are important in climate?
As well as this water has a high heat capacity – it can hold a lot of energy and transport it around the planet because it is a fluid
And it takes longer to heat up and cool down than rock
It stays relatively warm through winter and cool through summer
Coastal areas have less variation in temperature than inland regions

137. Summary How energy reaches the earth How it gets into the atmosphere
How it is transported vertically within the atmosphere
How these transport processes affect the climate.

138. Cloud descriptions

139. Low Clouds 3. Low Clouds - Stratus (St) - Stratocumulus (Sc)
- Nimbostatus (Ns)
Low clouds are usually below 2000m and consist primarily
of water droplets. The sun cannot be seen through stratus clouds.

140. Nimbostratus Cloud
Low clouds (below 2000m) with precipitation that reaches the ground.
Shredded parts of these clouds are called stratus fractus or scud.
Figure 6.14

141. Stratocumulus Clouds
Figure 6.15
Low clouds with rounded patches that range in color from light to dark gray.
With your hand extended overhead, they are about the size of your palm and cover most of the sky.

142. Stratus Clouds
Figure 6.16
Low clouds that resemble a fog, but do not reach the ground, and can generate a light mist or drizzle.

143. Clouds With Vertical Development
- Cumulus (Cu)
- Cumulonimbus (Cb)

144. Cumulus Humilis Clouds
Figure 6.17
Clouds with vertical development that take a variety of shapes, separated by sinking air and blue sky.
Shredded sections are called cumulus fractus.

145. Cumulus Congestus Clouds
Figure 6.18
Clouds with vertical development that become larger in height, with tops taking a ragged shape similar to cauliflower.

146. Cumulonimbus Cloud
Figure 6.18
Clouds with vertical development that have grown into a towering thunderstorm cloud with a variety of key features, including the anvil top.

147. Cumulonimbus (Cb) - Thundercloud

148. Summary of Cloud Types
Figure 6.20

149. Some Adjectives Castellanus -- Tower-like vertical development.
Congestus -- Crowded in heaps
Lenticularis -- Lens shaped
Mammatus -- Hanging protuberances
Pileus -- Cap Cloud

150. Lenticular Clouds
An unusual cloud that has a lens shape and forms in the crest of a wave.
Figure 6.21

151. Banner Cloud
Figure 6.22
A lenticular cloud that forms downwind of a mountain peak and is regularly replenished by condensing water vapor.

152. Pileus Cloud
An unusual cloud that forms above a building cumulus by deflected moist winds.
Figure 6.23

153. Mammatus Clouds
Figure 6.24
An unusual cloud that hang like sacks, formed by sinking air with a high water content.

154. Jet Contrails
Jet engine exhaust provides vapor and nuclei for condensation trails (contrails), which evaporate quickly in dry air, but linger with higher relative humidities.
Figure 6.25

155. Nacreous Clouds
Figure 6.26
An unusual cloud best viewed at winter in the poles and forms in the stratosphere.

156. Noctilucent Clouds
Figure 6.27
An unusual wavy cloud that is best viewed at the poles and forms in the upper mesosphere.

157. Altocumulus (Ac)

158. Cirrus (Ci)

159. Stratocumulus (Sc)

160. Stratus (St)

161. Cirrus (Ci)

162. Cirrostratus (Cs)

163. Cumulus (Cu)

164. Altostratus (As)

165. Stratocumulus (Sc)

166. Cumulonimbus (Cb)