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Meteorology
• Meteorology is the study of the atmosphere and the processes that cause atmospheric motions and the weather (and climate)
Weather
• State of the atmosphere at a particular place and TIME
• What’s the temperature, precipitation, cloudiness, wind speed etc.
• Affects daily activity
Weather & ClimateWeather & Climate
Weather is comprised of Weather is comprised of measured:measured: a) air temperature a) air temperature b) air pressure b) air pressure c) humidity c) humidity d) clouds d) clouds e) precipitation e) precipitation f) visibilityf) visibilityg) windg) wind
Climate represents long-term Climate represents long-term (e.g. 30 yr) averages of weather.(e.g. 30 yr) averages of weather.
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.
Climate
• Human activities (normal behavior, culture, architecture, agriculture) determined by climate
• The conditions we expect
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
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
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
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.
Pressure and density:
The higher the density the more molecules. More molecules striking a surface means higher pressure
Pressure Units• SI unit Pa (Pascal)
– Or N m-2
– Sea level atmospheric pressure is ~101000 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
Pressure Scale & UnitsPressure Scale & Units
Figure 9.4Figure 9.4
Many scales are used Many scales are used to record atmospheric to record atmospheric pressure, including pressure, including inches of mercury (Hg) inches of mercury (Hg) and millibars (mb).and millibars (mb).
The National Weather The National Weather Service uses mb, but Service uses mb, but will convert to metric will convert to metric units of hectopascals units of hectopascals (hPa).(hPa).
The conversion is The conversion is simply 1 hPa = 1 mb.simply 1 hPa = 1 mb.
Measuring Pressure
• To measure atmospheric pressure we use a barometer
Pressure MeasurementPressure Measurement
Changes in atmospheric pressure Changes in atmospheric pressure are detected by a change in are detected by a change in elevation of a barometric fluid or elevation of a barometric fluid or change in diameter of an aneroid change in diameter of an aneroid cell, which indicates changing cell, which indicates changing weather.weather.Average sea level pressure is 29.92 Average sea level pressure is 29.92 in Hg, or 1013.25 mb.in Hg, or 1013.25 mb.Figure 9.5Figure 9.5
Figure 9.6Figure 9.6
Pressure TrendsPressure Trends
Figure 9.7Figure 9.7
Barographs provide a plot of pressure with time, and are useful in Barographs provide a plot of pressure with time, and are useful in weather analysis and forecasting.weather analysis and forecasting.
Altimeters convert pressure into elevation, and are useful in steep Altimeters convert pressure into elevation, and are useful in steep terrain navigation or flying.terrain navigation or flying.
Both use aneroid cells.Both use aneroid cells.
Earth's AtmosphereEarth's Atmosphere
99% of atmospheric gases, including water vapor, extend only 30 99% of atmospheric gases, including water vapor, extend only 30 kilometer (km) above earth's surface.kilometer (km) above earth's surface.
Most of our weather, however, occurs within the first 10 to 15 km.Most of our weather, however, occurs within the first 10 to 15 km.
Figure 1.2Figure 1.2
There is a lot of Nitrogen!
© 1998 Prentice-Hall -- From The Atmosphere, 7th Ed., byF.K. Lutgens and E.J. Tarbuck, p. 6.
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)
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
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
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
Carbon dioxide
• Used by plants during photosynthesis– 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
Variable & Increasing GasesVariable & Increasing Gases
Figure 1.4Figure 1.4Figure 1.5Figure 1.5
Nitrogen and oxygen concentrations experience little change, Nitrogen and oxygen concentrations experience little change, but carbon dioxide, methane, nitrous oxides, and but carbon dioxide, methane, nitrous oxides, and chlorofluorocarbons are greenhouse gases experiencing chlorofluorocarbons are greenhouse gases experiencing discernable increases in concentration.discernable increases in concentration.
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)
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
Structure of the Atmosphere
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!)
The Relationship Between Air Pressure and Altitude
Pressure decreases as yougo up in height.
The change is pressure isnot constant. The pressuredecreases exponentiallywith increasing height.
Air Density and height
Pressure & DensityPressure & Density
Figure 1.7Figure 1.7
Gravity pulls gases Gravity pulls gases toward earth's toward earth's surface, and the surface, and the whole column of whole column of gases exerts a gases exerts a pressure of 1000 pressure of 1000 hPa at sea level, hPa at sea level, 1013.25 mb or 29.92 1013.25 mb or 29.92 in.Hg.in.Hg.
Pressure and Density Decrease with Height
© 1998 Wadsworth Publishing Co. -- From Ahrens, Essentials of Meteorology
Vertical Pressure ProfileVertical Pressure Profile
Pressure increases at a Pressure increases at a curved rate curved rate proportional to altitude proportional to altitude squared, but near the squared, but near the surface a linear surface a linear estimate of 10 mb per estimate of 10 mb per 100 meters works well.100 meters works well.
Figure 1.8Figure 1.8
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.
Layers of the atmosphere
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
Atmospheric LayersAtmospheric Layers
Figure 1.9Figure 1.9
8 layers are defined by constant 8 layers are defined by constant trends in average air trends in average air temperature (which changes temperature (which changes with pressure and radiation), with pressure and radiation), where the outer exosphere is not where the outer exosphere is not shown.shown.
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
Temperature Structure of the Atmosphere
Warming in thestratosphere
© 1998 Wadsworth Publishing -- From Essentials of Meteorology, 2nd Ed., by C.D. Ahrens, p. 9.
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
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
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
Energy in the Atmosphere
Energy
• It’s what makes things happen
What’s it about?
• Temperature,
• Energy and
• Heat
Definitions
• Before we start we need to get some things straight
• We need definitions of some basic atmospheric parameters
Content
• Basics– The basic properties of the air
• Temperature• Pressure• Density
– We’ve already met the latter two
• 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.
Temperature
Temperature ScalesTemperature Scales
• There are three (3) temperature scales you need to know about. With their units:
• Fahrenheit (F) -- German
• Celsius (C) -- Swedish
• Absolute (K) -- Scientific
Fahrenheit ScaleFahrenheit 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.
Celsius ScaleCelsius 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.
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
Temperature ScalesTemperature Scales
Thermometers detect the Thermometers detect the movement of molecules to movement of molecules to register temperature.register temperature.
Fahrenheit and Celsius scales Fahrenheit and Celsius scales are calibrated to freezing and are calibrated to freezing and boiling water, but the Celsius boiling water, but the Celsius range is 1.8 times more range is 1.8 times more compact.compact.
Figure 2.2Figure 2.2
Temperature ScalesTemperature ScalesConversions between temperature scales can beeasily accomplished by the following three simpleequations.
C = (F - 32)59
F = C + 3295
K = C + 273
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.
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.
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.
Heat
• Energy in the process of being transferred from one object to another (due to temperature differences)
Heat Transfer
• How is heat transferred?– Latent Heat– Conduction– Convection– Radiation
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………...
Conduction - Heat TransferConduction - Heat Transfer
Figure 2.5Figure 2.5
Conduction of Conduction of heat energy heat energy occurs as occurs as warmer warmer molecules molecules transmit transmit vibration, and vibration, and hence heat, to hence heat, to adjacent adjacent cooler cooler molecules.molecules.
Warm ground Warm ground surfaces heat surfaces heat overlying air overlying air by conduction.by conduction.
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.
Energy Transfer
Today you might learn about
• Different forms of energy
• How energy is transported
Heat
• Latent Heat -- “Invisible Heat”– Heat released or absorbed during a phase
change.• Evaporational Cooling• Condensation
• Sensible Heat– Heat transfer we can feel and measure.
Phase Changes of Water
Ice VaporLiquid
Melting
Freezing Condensation
Evaporation
Heat Energy Released
Heat Energy Absorbed
Sublimation
Deposition
• Heat energy, which is a measure of Heat energy, which is a measure of molecular motion, moves between molecular motion, moves between water's vapor, liquid, and ice phases.water's vapor, liquid, and ice phases.
• As water moves toward vapor it As water moves toward vapor it absorbs latent (e.g. not sensed) heat to absorbs latent (e.g. not sensed) heat to keep the molecules in rapid motion.keep the molecules in rapid motion.
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
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
Convection
• Convection– The transfer of heat by the mass movement
of a fluid.– Works well in the atmosphere and oceans.
H
H
H
MIXING
Thermal
Air Parcel
Convection - Heat TransferConvection - Heat Transfer
Figure 2.6Figure 2.6
Convection is heat energy moving as a fluid from hotter to cooler Convection is heat energy moving as a fluid from hotter to cooler areas.areas.
Warm air at the ground surface rises as a thermal bubble, expends Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence cools.energy to expand, and hence cools.
Warming Earth's AtmosphereWarming Earth's Atmosphere
Solar radiation passes first through the upper atmosphere, but only Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface does it generate sensible heat to after absorption by earth's surface does it generate sensible heat to warm the ground and generate longwave energy.warm the ground and generate longwave energy.This heat and energy at the surface then warms the atmosphere This heat and energy at the surface then warms the atmosphere from below.from below.
Figure 2.13Figure 2.13
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
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).
Radiation
The distance between wave crests is the wavelength.
Shorter waves: x-rays, UV, visible light
Longer waves: infrared, microwave, radar, TV, radio
One Wavelength
Solar Spectrum
max = 0.55 m
© 1998 Wadsorth Publishing -- From Ahrens Essentials of Meteorology
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
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.
• 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.)
Radiation
Incident Solar Radiation and Albedo
Radiation
NASA -- Apollo 8
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
Radiation
• Only one half of the earth intercepts sunlight. From the sun, it looks like a disc.
SolarRadiation
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
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!!!
Radiation
E = T4
• 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)
Stefan-Boltzmann Law: Anything that has
a temperature radiates energy. Hotter
objects radiate a lot more energy.
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
Wien’s Law
• The sun has a surface temperature of about 6000K:– λmax = 2900 / 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
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.
Solar and Terrestrial Radiation
© 1999 Prentice-Hall -- From Aguado and Burt, Understanding Weather and Climate Wavelength
Wavelength
SolarRadiation
TerrestrialRadiation
Notice that the earth’s radiationis much, much less than that ofthe sun!
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.
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
Solar energy
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
Today
• We’ll deal with solar radiation
• What’s the “greenhouse effect”?
• Return homework
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
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.
• 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.)
Radiation
Incident Solar Radiation and Albedo
Radiation
NASA -- Apollo 8
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
Radiation
• Only one half of the earth intercepts sunlight. From the sun, it looks like a disc.
SolarRadiation
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
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!!!
Radiation
E = T4
• 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)
Stefan-Boltzmann Law: Anything that has
a temperature radiates energy. Hotter
objects radiate a lot more energy.
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
Wien’s Law
• The sun has a surface temperature of about 6000K:– λmax = 2900 / 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
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.
Solar and Terrestrial Radiation
© 1999 Prentice-Hall -- From Aguado and Burt, Understanding Weather and Climate Wavelength
Wavelength
SolarRadiation
TerrestrialRadiation
Notice that the earth’s radiationis much, much less than that ofthe sun!
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.
Radiation
GOES-8Full-diskVisible
Radiation
GOES-8Full-disk
IR
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
RadiationEarth-Atmosphere Energy Balance
© 1998 Wadsorth Publishing -- From Ahrens Essentials of Meteorology
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
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)
Atmospheric AbsorptionAtmospheric Absorption
Solar radiation passes rather freely through Solar radiation passes rather freely through earth's atmosphere, but earth's re-emitted earth's atmosphere, but earth's re-emitted longwave energy either fits through a narrow longwave energy either fits through a narrow window or is absorbed by greenhouse gases window or is absorbed by greenhouse gases and re-radiated toward earth.and re-radiated toward earth.
Figure 2.11Figure 2.11
The Atmosphere is transparent to solar radiation.
Radiation
• As a first approximation --
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
Radiation
• The atmosphere radiates IR both upwards and downwards.......
• The downward portion re-warms the earth’s surface and is known as the
Greenhouse Effect.
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
What’s this “Greenhouse Effect” Thing anyway?
Climate variation
• Changes in climate– Short period changes – Long term changes
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
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.
Short-term Climate VariabilityChanges 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.
Changes in the solar output.
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).
Sunspots
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.
Maunder Minimum
Changes in the solar output.
Short-term Climate Variability
VolcanoesLarge 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.
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.
Mt. Pinatubo
Short-term Climate Variability
“Greenhouse” GasesCarbon Dioxide, Methane, Water Vapor,
Nitrous Oxide, CFC’sIncrease CO2 (and others) and increase
the temperature of the earth’s surfaceDo feedback mechanisms cancel this
effect?
Regional climates
• Continental areas have extremes
• Coastal areas tend to be more moderate (temperate)
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)
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
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.
Cloud descriptions
Low Clouds
3. Low Clouds- Stratus (St)- Stratocumulus (Sc)- Nimbostatus (Ns)
Low clouds are usually below 2000m and consist primarilyof water droplets. The sun cannot be seen through stratus clouds.
Nimbostratus CloudNimbostratus Cloud
Figure 6.14Figure 6.14
Low clouds Low clouds (below 2000m) (below 2000m) with with precipitation precipitation that reaches the that reaches the ground.ground.
Shredded parts Shredded parts of these clouds of these clouds are called are called stratus fractus stratus fractus or scud.or scud.
Stratocumulus CloudsStratocumulus Clouds
Low clouds with rounded patches that range in color from light to Low clouds with rounded patches that range in color from light to dark gray.dark gray.With your hand extended overhead, they are about the size of your With your hand extended overhead, they are about the size of your palm and cover most of the sky.palm and cover most of the sky.
Figure 6.15Figure 6.15
Stratus CloudsStratus Clouds
Figure 6.16Figure 6.16
Low clouds that resemble a fog, but do not reach the ground, and Low clouds that resemble a fog, but do not reach the ground, and can generate a light mist or drizzle.can generate a light mist or drizzle.
Clouds With Vertical Development
4. Clouds With Vertical Development- Cumulus (Cu)- Cumulonimbus (Cb)
Cumulus Humilis CloudsCumulus Humilis Clouds
Clouds with vertical development that take a variety of shapes, Clouds with vertical development that take a variety of shapes, separated by sinking air and blue sky.separated by sinking air and blue sky.
Shredded sections are called cumulus fractus.Shredded sections are called cumulus fractus.
Figure 6.17Figure 6.17
Cumulus Congestus CloudsCumulus Congestus Clouds
Figure 6.18Figure 6.18
Clouds with vertical development that become larger in height, with Clouds with vertical development that become larger in height, with tops taking a ragged shape similar to cauliflower.tops taking a ragged shape similar to cauliflower.
Cumulonimbus CloudCumulonimbus Cloud
Clouds with vertical development that have grown into a towering Clouds with vertical development that have grown into a towering thunderstorm cloud with a variety of key features, including the thunderstorm cloud with a variety of key features, including the anvil top.anvil top.
Figure 6.18Figure 6.18
Cumulonimbus (Cb) - Thundercloud
Summary of Cloud TypesSummary of Cloud Types
Figure 6.20Figure 6.20
Some Adjectives
Castellanus -- Tower-like vertical development.
Congestus -- Crowded in heaps
Lenticularis -- Lens shaped
Mammatus -- Hanging protuberances
Pileus -- Cap Cloud
Lenticular CloudsLenticular Clouds
Figure 6.21Figure 6.21
An unusual An unusual cloud that cloud that has a lens has a lens shape and shape and forms in the forms in the crest of a crest of a wave.wave.
Banner CloudBanner Cloud
A lenticular cloud that forms downwind of a mountain peak and is A lenticular cloud that forms downwind of a mountain peak and is regularly replenished by condensing water vapor.regularly replenished by condensing water vapor.
Figure 6.22Figure 6.22
Pileus CloudPileus Cloud
Figure 6.23Figure 6.23
An unusual An unusual cloud that cloud that forms above forms above a building a building cumulus by cumulus by deflected deflected moist winds.moist winds.
Mammatus CloudsMammatus Clouds
An unusual cloud that hang like sacks, formed by sinking air with a An unusual cloud that hang like sacks, formed by sinking air with a high water content.high water content.
Figure 6.24Figure 6.24
Jet ContrailsJet Contrails
Figure 6.25Figure 6.25
Jet engine Jet engine exhaust provides exhaust provides vapor and nuclei vapor and nuclei for condensation for condensation trails (contrails), trails (contrails), which evaporate which evaporate quickly in dry quickly in dry air, but linger air, but linger with higher with higher relative relative humidities.humidities.
Nacreous CloudsNacreous Clouds
An unusual cloud best viewed at winter in the poles and forms in the An unusual cloud best viewed at winter in the poles and forms in the stratospherestratosphere..
Figure 6.26Figure 6.26
Noctilucent CloudsNoctilucent Clouds
Figure 6.27Figure 6.27
An unusual wavy cloud that is best viewed at the poles and forms in An unusual wavy cloud that is best viewed at the poles and forms in the upper mesosphere.the upper mesosphere.
Altocumulus (Ac)
Cirrus (Ci)
Stratocumulus (Sc)
Stratus (St)
Cirrus (Ci)
Cirrostratus (Cs)
Cumulus (Cu)
Altostratus (As)
Stratocumulus (Sc)
Cumulonimbus (Cb)
