Presentation on theme: "Atmospheric Science Dr"— Presentation transcript:
1Atmospheric Science Dr Atmospheric Science Dr.Gamal El Afandi Tuskegee University
2MeteorologyMeteorology is the study of the atmosphere and the processes that cause atmospheric motions and the weather (and climate)
3Weather State of the atmosphere at a particular place and TIME What’s the temperature, precipitation, cloudiness, wind speed etc.Affects daily activity
4Weather & ClimateWeather is comprised of measured:a) air temperatureb) air pressurec) humidityd) cloudse) precipitationf) visibilityg) windClimate represents long-term(e.g. 30 yr) averages of weather.
5Weather and Climate Climate is Long-term average of atmospheric variablesSuch asTemperaturePressureWind speed and directionPrecipitationOthersAnd maxima, minima, extreme values, etc.
6ClimateHuman activities (normal behavior, culture, architecture, agriculture) determined by climateThe conditions we expect
7Weather Journal You are required to keep a weather journal Each day you should recordMaximum temperatureMinimum temperatureWhat the weather was likeYou can use any source of information BUTYOU MUST REVEAL YOUR SOURCES
8DensityThe 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 roomNumber of water drops in a cubic centimeter of cloud
9Density Is measured in kg m-3 (or sometimes g cm-3)Number density is in (number) m-3The air in this room (at the surface of the Earth) has a density of ~1.2 kg m-3A fluid with a lower density will float on a fluid with a higher densityDecrease the density and it could rise
10PressureThe 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.
11Pressure and density:The higher the density the more molecules. More molecules striking a surface means higher pressure
12Pressure Units SI unit Pa (Pascal) Or N m-2Sea level atmospheric pressure is ~ PaMeteorologists also use millibars – mbSea level atmospheric pressure is ~1000mbThey even sometimes use millimeters (inches) of mercury – mm Hg, inches HgSea level atmospheric pressure is ~760 mmHg or 30” Hg
13Pressure Scale & UnitsMany 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
14Measuring PressureTo measure atmospheric pressure we use a barometer
15Pressure MeasurementFigure 9.6Changes 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
16Pressure TrendsFigure 9.7Barographs 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.
17Earth's AtmosphereFigure 1.299% 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.
19Permanent GasesPermanent gases have fixed proportions in the atmosphere, both in time and spaceFor Dry Air78% Nitrogen (N2)21% Oxygen (O2)0.93% Argon (Ar)The rest is other stuffTrace gases and variable gases (eg. CO2)
20Variable gasesVariable gases can have different concentrations in the atmosphere, both in time and spaceThe most important variable gas is water vaporOther variable gases include carbon dioxide (CO2), methane and ozone
21Water vapor Is variable We measure this variability as the humidity (see later)From evaporationProximity to bodies of waterAir temperatureWhen it condenses get clouds and precipitation
22Water 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 EarthIt can ‘hold’ a lot of energy and transport that energy around the planetWe need waterIt absorbs a lot of radiation
23Carbon dioxide Used by plants during photosynthesis Exhaled by animals Plants take in and store carbon as they growExhaled by animalsReleased by the burning of oil, gas, wood, coalConcentrations have been rising around the world for 200 years
24Variable & Increasing Gases Figure 1.5Figure 1.4Nitrogen and oxygen concentrations experience little change, but carbon dioxide, methane, nitrous oxides, and chlorofluorocarbons are greenhouse gases experiencing discernable increases in concentration.
25Why is the change in CO2 important? Carbon dioxide absorbs longwave (infra-red) radiationThis creates an imbalance between energy received by the Earth and energy leaving the EarthIf you want to know why we should care wait for next chapter or look at the atmosphere of Venus (in the book)
26OzoneAt the surfaceIs caused by chemical reactions between a variety of pollutant gases (such as nitrogen oxides)Mostly caused by vehicle emissionsIs an irritant
28ThicknessThe atmosphere is a very thin (relatively) layer of gas over the surface of the EarthEarth’s radius ~ 6400kmAtmospheric 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!)
29The Relationship Between Air Pressure and Altitude Pressure decreases as yougo up in height.The change is pressure isnot constant. The pressuredecreases exponentiallywith increasing height.
33Vertical 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
34Layers by temperatureThe 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.
35Layers of the atmosphere TroposphereStratosphereMesosphereThermosphere
36Atmospheric Layers8 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
37The Troposphere Where we live (all the time) Contains 80% of the mass of the atmosphereIs between 8-16km (5-10 mi) deepDeeper at the equator than the polesWHERE WEATHER HAPPENS
39The Stratosphere Contains the ozone layer Where ultra-violet radiation is absorbedThis means that we are protected from harmful high-energy radiation from the sunThis also means that the stratosphere is warmer than the top of the troposphere because it has absorbed that energy
40Ozone 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 emissionsIs an irritant
41Ozone In the stratosphere Is a beneficial gas that absorbs ultra-violet radiationProtects us from this harmful radiationIs broken down by chemical reactions with chlorine containing gases (chlorofluorocarbons – CFCs): Man-made compounds used in aerosol sprays, refrigerators and air-conditioners
45Definitions Before we start we need to get some things straight We need definitions of some basic atmospheric parameters
46Content Basics The basic properties of the air Temperature Pressure DensityWe’ve already met the latter two
47TemperatureTemperature: The temperature of a substance is a measure of the average kinetic energy of the molecules in that substance.Thus atmospheric temperature isproportional to the speed of the airmolecules.
48Temperature ScalesThere are three (3) temperature scales you need to know about. With their units:Fahrenheit (F) -- GermanCelsius (C) -- SwedishAbsolute (K) -- Scientific
49Fahrenheit 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.
50Celsius 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.
51Thermodynamic (Kelvin) Scale Kelvin or Absolute Scale (1800’s):No molecular motion at 0 K.Uses Celsius’ degree incrementIce melts at 273 KWater boils at 373 K
52Temperature ScalesThermometers 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
53Temperature Scales 5 C = (F - 32) 9 9 F = C + 32 5 K = C + 273 Conversions between temperature scales can beeasily accomplished by the following three simpleequations.59C = (F - 32)95F = C + 32K = C + 273
54EnergyEnergy - The ability to do work or exchange heat with the surroundings.Examples of types of energyPotential Energy -- Energy of positionKinetic Energy -- Energy of motionInternal Energy -- Energy of motion of the molecules.Radiant Energy -- Electromagnetic radiation.
55First 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.
56Second 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.
57HeatEnergy in the process of being transferred from one object to another (due to temperature differences)
58Heat Transfer How is heat transferred? Latent Heat Conduction ConvectionRadiation
59Temperature GradientA 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………...
60Conduction - 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
61Temperature GradientHeat 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.
63Today you might learn about Different forms of energyHow energy is transported
64Heat Latent Heat -- “Invisible Heat” Sensible Heat Heat released or absorbed during a phase change.Evaporational CoolingCondensationSensible HeatHeat transfer we can feel and measure.
65Phase Changes of Water Vapor Liquid Ice Heat Energy Absorbed SublimationEvaporationMeltingVaporIceLiquidFreezingCondensationDepositionHeat Energy Released
66Heat 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.
67ConductionThe movement of energy through a body without the movement of the particles of that body (molecule to molecule)Eg. Heating your food in a panIn the atmosphere this is only important for a very thin layer of air in contact with the ground
68Convection 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
69Convection Convection Air Parcel The transfer of heat by the mass movement of a fluid.Works well in the atmosphere and oceans.Air ParcelMIXINGHHHThermal
70Convection - Heat Transfer Figure 2.6Convection 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.
71Warming Earth's Atmosphere Figure 2.13Solar 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.
72Radiation All objects emit electro-magnetic radiation in some form This radiation moves through space until it hits somethingThe thing it hits may then absorb the radiation and obtain its energyAlternatively it may deflect, scatter or reflect the radiation
73Radiation We can describe the radiation by: Wavelength The actual length (meters) between wave peaks.Wavelengths for radiation vary greatlyradio waves (100 cm to 160 meters)Light (10-9 meters).FrequencyThe number of wave crests that pass by a point per second (Hertz).
74Radiation One Wavelength The distance between wave crests is the wavelength.Shorter waves: x-rays, UV, visible lightLonger waves: infrared, microwave, radar, TV, radio
76Radiation What heats the Earth??? The Sun!!! How does it do it??? Radiation -- Energy transfer from one place to another by electromagnetic waves.LightRadio WavesMicrowaveInfraredUltravioletNote EM radiation does not require a ‘medium’ to pass through, it can get from the sun to the earth through the vacuum
77Radiation 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.
78RadiationSolar 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.)
79RadiationIncident Solar Radiation and AlbedoNASA -- Apollo 8
80Albedo But we must consider reflections: Albedo = Amount reflected (x 100%)Amount incomingEarth’s albedo = 30%This 30% is due to:cloudsdust, haze, smokescattering by air moleculesreflections from land, oceans, ice
81RadiationOnly one half of the earth intercepts sunlight. From the sun, it looks like a disc.SolarRadiation
82Which half of the Earth is light? The Earth rotates on its own axisOnly the daytime side receives energy directly from the sunThe nighttime side often receives a smaller amount of energy reflected off the moon
83RadiationAll things, whose temperature is above absolute zero, emit radiation They radiate!!!Radiation is emitted at all wavelengths -- some more so than othersExamplesDogs The atmosphereSnow Your BooksTrees and …..The oceans You!!!
84Radiation Stefan-Boltzmann Law: Anything that has a temperature radiates energy. Hotterobjects 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-4T = Temperature (K)
85Wien’s Law This tells us the peak wavelength that an object will emit λmax = 2900 / TWhere λmax is the wavelength in micrometersT is the temperature in Kelvin
86Wien’s Law The sun has a surface temperature of about 6000K: λmax = / 6000 ≈ 0.48μmThis is green lightThe Earth has a surface temperature of about 290K:λmax = 2900 / 290 ≈ 10μmThis is infra red radiation
87RadiationOUTPUTThe 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.
89RadiationWhat 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.
90Summary Energy comes in many forms Energy can be moved from hot things to cold things in 4 waysAll these ways have some importance in the atmosphereThe spectrum of radiation
92We’ll contemplate little things like… Why there’s life on EarthWhy you don’t want to live at the South PoleWhy you don’t want to live in San AntonioWhy the weather changes every day these days
93Today We’ll deal with solar radiation What’s the “greenhouse effect”? Return homework
94Radiation What heats the Earth??? The Sun!!! How does it do it??? Radiation -- Energy transfer from one place to another by electromagnetic waves.LightRadio WavesMicrowaveInfraredUltravioletNote EM radiation does not require a ‘medium’ to pass through, it can get from the sun to the earth through the vacuum
95Radiation 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.
96RadiationSolar 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.)
97RadiationIncident Solar Radiation and AlbedoNASA -- Apollo 8
98Albedo But we must consider reflections: Albedo = Amount reflected (x 100%)Amount incomingEarth’s albedo = 30%This 30% is due to:cloudsdust, haze, smokescattering by air moleculesreflections from land, oceans, ice
99RadiationOnly one half of the earth intercepts sunlight. From the sun, it looks like a disc.SolarRadiation
100Which half of the Earth is light? The Earth rotates on its own axisOnly the daytime side receives energy directly from the sunThe nighttime side often receives a smaller amount of energy reflected off the moon
101RadiationAll things, whose temperature is above absolute zero, emit radiation They radiate!!!Radiation is emitted at all wavelengths -- some more so than othersExamplesDogs The atmosphereSnow Your BooksTrees and …..The oceans You!!!
102Radiation Stefan-Boltzmann Law: Anything that has a temperature radiates energy. Hotterobjects 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-4T = Temperature (K)
103Wien’s Law This tells us the peak wavelength that an object will emit λmax = 2900 / TWhere λmax is the wavelength in micrometersT is the temperature in Kelvin
104Wien’s Law The sun has a surface temperature of about 6000K: λmax = / 6000 ≈ 0.48μmThis is green lightThe Earth has a surface temperature of about 290K:λmax = 2900 / 290 ≈ 10μmThis is infra red radiation
105RadiationOUTPUTThe 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.
107RadiationWhat 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.
110Solar absorbed = Long Wave emitted RadiationFor 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 emittedInput = Output
112Scattering of Radiation Radiation can be scattered or absorbed by the gases and particles (dust) in the atmosphereDifferent wavelengths of light are scattered in different waysA certain proportion will be scattered straight back into space
113Absorption of Radiation Radiation can be absorbed by molecules of gas in the atmosphereDifferent gases absorb different wavelengths of lightThe major atmospheric gases absorb infra-red, but not visible, radiationWhen the gas absorbs radiation it gains energy (is warmed)
114Atmospheric 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
115The Atmosphere is transparent RadiationAs a first approximation --The Atmosphere is transparentto solar radiation.
116RadiationThus the earth’s atmosphere is essentially opaque (not transparent) to IR radiation from the earth’s surface.Absorption by:a. H2Ov c. CO2b. Clouds d. O3
117Radiation Greenhouse Effect. The atmosphere radiates IR both upwards and downwardsThe downward portion re-warms the earth’s surface and is known as theGreenhouse Effect.
118SummaryWe’ve seen what the Greenhouse Effect is and what it isn’t and why we should avoid the term altogetherNext time we’ll talk about ‘climate variation’ and why it happens
120Climate variation Changes in climate Short period changes Long term changes
121ClimateThe 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
122Climate 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.
123Short-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.
125Short-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).
127Short-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.
130Short-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.
131Short-term Climate Variability A year after the eruption of Tambura, New England experienced the “year without a summer.”Heavy snow in JuneFrost in July and AugustJune mean temperatures were 3.5oC below normalAugust temperatures were 1-2oC below normalCold weather was experienced in England and EuropeA year after the eruption of Pinatubo, the mean global air temperature dropped by almost 0.5oC compared to the previous 9-year average.
133Short-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?
134Regional climates Continental areas have extremes Coastal areas tend to be more moderate (temperate)
135Water surfacesWater is dark and absorbs a lot of heat (except when the sun is low in the sky)Water surfaces stay cool becauseWhen hot a lot of evaporation takes placeWater 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)
136Is 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 fluidAnd it takes longer to heat up and cool down than rockIt stays relatively warm through winter and cool through summerCoastal areas have less variation in temperature than inland regions
137Summary How energy reaches the earth How it gets into the atmosphere How it is transported vertically within the atmosphereHow these transport processes affect the climate.
139Low 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.
140Nimbostratus CloudLow clouds (below 2000m) with precipitation that reaches the ground.Shredded parts of these clouds are called stratus fractus or scud.Figure 6.14
141Stratocumulus CloudsFigure 6.15Low 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.
142Stratus CloudsFigure 6.16Low clouds that resemble a fog, but do not reach the ground, and can generate a light mist or drizzle.
143Clouds With Vertical Development - Cumulus (Cu)- Cumulonimbus (Cb)
144Cumulus Humilis Clouds Figure 6.17Clouds with vertical development that take a variety of shapes, separated by sinking air and blue sky.Shredded sections are called cumulus fractus.
145Cumulus Congestus Clouds Figure 6.18Clouds with vertical development that become larger in height, with tops taking a ragged shape similar to cauliflower.
146Cumulonimbus CloudFigure 6.18Clouds with vertical development that have grown into a towering thunderstorm cloud with a variety of key features, including the anvil top.