aoss 321 winter 2009 earth system dynamics lecture 2 1 13 2009 n.
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AOSS 321, Winter 2009 Earth System Dynamics Lecture 2 1/13/2009. Christiane Jablonowski Eric Hetland 734-763-6238 734-615-3177. Characteristics of the Atmosphere. Composition of the air, greenhouse gases Temperature, atmospheric layers

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aoss 321 winter 2009 earth system dynamics lecture 2 1 13 2009

AOSS 321, Winter 2009Earth System DynamicsLecture 21/13/2009

Christiane Jablonowski Eric Hetland

734-763-6238 734-615-3177

characteristics of the atmosphere
Characteristics of the Atmosphere
  • Composition of the air, greenhouse gases
  • Temperature, atmospheric layers
  • Pressure, pressure systems
  • Wind
  • General circulation of the atmosphere, seasons, ocean circulation, albedo, heat & heat transport
  • Humidity, clouds, precipitation
  • Sun, electromagnetic waves, Earth’s energy balanceLet’s form groups and discuss the elements, e.g.
  • physical characteristics and units, how measured or observed, graphical representation, characteristics of the global circulation & distribution, typical values
composition of the air
Composition of the air


  • Nitrogen (N2) 78.08%
  • Oxygen (O2) 20.95%
  • Argon (Ar) 0.93%
  • CO2 383 ppm
  • Neon (Ne) 18.2 ppm
  • Helium (He) 5.2 ppm
  • Methane (CH4) 1.7 ppm
  • Water vapor (H2O) (1%-4%)highly variable
greenhouse gases co 2
Greenhouse gases: CO2
  • CO2 measurements in Mauna Loa, Hawaii
  • Well-mixed trace gas (greenhouse gas) in the lower atmosphere
  • Barren lava field of an active volcano19º32' N, 155º 35' W, 3397 m above mean sea level (MSL)
greenhouse gases co 21
Greenhouse gases: CO2
  • Carbon dioxide (CO2) concentrations in ppm (parts per million) in Mauna Loa, Hawaii

380 ppm



May 2005

greenhouse gases ghg
Greenhouse gases (GHG)
  • Earth's most abundant greenhouse gases
    • water vapor (H2O)
    • carbon dioxide (CO2)
    • methane (CH4)
    • nitrous oxide (NO2), commonly known as "laughing gas"
    • ozone (O3)
    • chlorofluorocarbons (CFCs)
  • Ranked by their contribution to the greenhouse effect, the most important ones are:
    • water vapor, which contributes 36–70%
    • carbon dioxide, which contributes 9–26%
    • methane, which contributes 4–9%
    • ozone, which contributes 3–7%
  • What are the atmospheric lifetimes of the GHGs?
global co 2 and t trends

CO2 2100

460 ppm

Global CO2 and T Trends

CO2 2005

380 ppm

  • Carbon dioxide (CO2) is, because of our emissions, much higher than ever experienced by human kind
  • Temperature is expected to follow
  • Do we need to be worried?

350,000 years of Surface Temperature and Carbon Dioxide (CO2)

at Vostok, Antarctica ice cores

  • Weather maps:
  • Station data, Boulder, CO
  • Lines of equal temperature are called isotherms
  • Typical plots:
    • Time series at a fixed location (station)
    • 1D vertical temperature profiles at a station (radiosonde sounding, skew-T diagrams)
    • 2D horizontal cross section near the surface or at a specific pressure level, e.g. 500 hPa
    • 2D meridional-vertical cross section (zonal-mean)
  • Pay attention to the horizontal and vertical axis labels
temperature typical vertical profiles
Temperature: Typical Vertical Profiles
  • Weather: takes place in the troposphere, the lower 10-15 km of the atmosphere
temperature latitude pressure cross section
Temperature:Latitude-pressure cross section
  • Annual mean, zonal-mean temperature T in oC,linear pressure scale (vertical direction)



10 km











temperature latitude pressure cross section1
Temperature:Latitude-pressure cross section
  • Temperature T (annual mean, zonal-mean) in K, logarithmic pressure scale, includes the stratosphere


Pressure (hPa)











surface pressure
Surface Pressure


  • Surface pressure map (at mean sea level)
  • Isobars: Contour lines that connect equal pressure values

Weather maps:

NCAR weather station:

mean sea level pressure mslp
Mean sea level pressure (MSLP)
  • Extrapolate the surface pressure to mean sea level
  • Effects of surface pressure differences due to mountains (orography) are eliminated
  • Plot of annual-mean MSLP in hPa






mean sea level pressure
Mean Sea Level Pressure
  • Annual-mean zonal-mean MSLP in hPa




pressure units
Pressure: Units
  • Conversion of pressure units
  • 29.92”Hg = 1.0 atm = 101.325 kPa = 1013.25 mb101.325 kPa = 1013.25 hPa
  • We use the unit: hPa (= 100 Pa)
zonal w e wind
Zonal (W-E) wind


  • Zonal-mean, annual-mean zonal wind u in m/s
  • Typical scale: 10 m/s, jet streams over 30 m/s

Pressure (hPa)




jet stream
Jet stream
  • Narrow band with high wind speeds
  • Wind direction is mostly from west to east (west wind)
  • Approximate height: 10-12 km (just under the tropopause around 200 hPa)
  • Aircraft pay attention to the position of the jet stream, why?
meridional s n wind
Meridional (S-N) wind
  • Monthly-mean, zonal-mean meridional wind v in m/s are relatively weak (a few m/s)
  • Compare to instantaneous v (typical scale: 10 m/s)

Height (km)

Pressure (hPa)

vertical velocity
Vertical velocity
  • Vertical velocity (Cartesian system) in m/s w = dz/dt
  • Vertical pressure velocity in Pa/s  = dp/dt
  • Typical scale of w in midlatitudinal weather systems is on the order of 1 cm/s
  • Typical vertical velocity in thunderstorms: on the order of 10 m/s (and more)
  • Upward motion in low pressure systems
  • Downward motion in high pressure systems
vertical pressure velocity
Vertical pressure velocity
  • Monthly-mean, zonal-mean vertical pressure velocity  = dp/dt in Pa/s

Height (km)

Pressure (hPa)

wind direction speed wind shear
Wind direction, speed & wind shear
  • Wind direction is the direction from which the wind is blowing
    • West wind: blows from west to east
    • South wind: blows from south to north
    • Eastward: means a west wind
    • Easterly: means an east wind
  • Wind speed: Magnitude of the wind vector
  • Isotach: lines with equal wind speed
  • Wind shear: difference between the wind directions and speeds at two different heights (subtract the two wind vectors)
wind direction
Wind direction
  • Cardinal directions (NESW) and azimuth degrees









how to draw wind vectors
How to draw wind vectors

Length of a wind vector indicates the speed


  • Wind vector with speed 10 m/s and wind vector with speed 20 m/s (identical direction)
  • Westerly wind
  • West wind
  • Westward wind
  • SSE wind
  • Wind from 30°
  • Wind shear between a NW wind at 10 km and NE wind at 5 km. Both wind speeds are identical.
wind symbols on weather maps
Wind symbols on weather maps

Zoom into some surfacemeasurements (stationreports)

Wind barbs

  • International convention
  • Indicate wind direction and speed in knots
  • 1 knot = 0.51 m/s
general circulation of the atmosphere


General Circulation of the Atmosphere
  • Global wind and circulation systems
  • Due to tilt of the Earth's axis to its orbital plane
  • Tilt is about 23.5 degrees
  • Solstices and equinoxes
heat transport ocean atmosphere equally important
Heat transport: Ocean & Atmosphere equally important


Northward heat transport (1015 W)




90° N


  • Defined as:Ratio of diffusely reflected to incident electromagnetic radiation
  • Most often expressed as a percentage
  • Also depends on the direction of incoming radiation
  • Highly variable
heat and heat transport
Heat and Heat transport
  • Heat is a form of energy that can change the temperature of an object
  • Measured in energy units, e.g. Joule (J) which is equivalent to Nm
  • Mechanisms of heat transfer:
    • Conduction: molecular transfer of energy
    • Convection: transfer by fluid motion
    • Radiation: transfer by electromagnetic waves even through vacuum
  • Check the difference between conduction and convection:
humidity clouds precipitation


Humidity, Clouds & Precipitation
  • Annual mean zonal-mean specific humidity (g/kg): ratio of water vapor (in g) to moist air (in kg)

Almost all moisture is in the troposphere

  • Convective clouds in Intertropical Convergence Zone (ITCZ)
  • Cloud bands associated with frontal zones in midlatitudes
  • What Are Clouds?Clouds are made up of billions of tiny droplets of ice or water. Each cloud droplet is so small and light that it is held up by air currents.
  • How Are Clouds Made?Clouds are condensation, formed when warm air rises and is cooled to below a certain temperature, called the 'dew point'.
  • Why Study Clouds?Clouds provide one of the keys to understanding the weather. Modeling clouds and their feedbacks is a key challenge when assessing climate change.
clouds precipitation
Clouds & Precipitation
  • Cloud classifications according to their vertical position:
    • Low
    • Mid-level
    • High clouds (ice clouds: cirrus)
  • Cloud photos:
  • UCAR’s digital image library:
  • Fun facts: Earth’s annual mean globally-averaged precipitation: Rainiest spot on Earth:
  • Clouds influence the planetary albedo
  • Cloud classification depends primarily on the cloud altitude
vertical distribution of clouds
Vertical distribution of clouds

ice clouds

water clouds

role of low clouds
Role of low clouds
  • Stratus clouds, which are mostly composed of liquid water droplets, reflect most of the incoming shortwave radiation (thin lines), but re-emit large amounts of outgoing longwave radiation (thick lines).
  • Their overall effect is to cool the Earth.
role of ice clouds
Role of ice clouds
  • Cirrus clouds, which are mostly composed of ice crystals, transmit most of the incoming shortwave radiation (thin lines), but trap some of the outgoing longwave radiation (thick lines).
  • Their overall effect is to warm the Earth.
  • Annual-mean precipitation in mm/day






the sun
The Sun


  • Wikipedia:
  • Solar constant: amount of incoming solar radiation per unit area, measured on the outer surface of Earth’s atmosphere, in a plane perpendicular to the rays.
  • The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite to be roughly S0 = 1366 W/m2
  • Annually averaged radiant flux received on Earth per unit area: S0/4 = 342 W/m2
radiation spectrum
Radiation Spectrum


UV (ultraviolet)

radiated energy black body
Radiated Energy: Black-Body
  • Planck curves (radiative flux)
earth s energy balance
Earth’s energy balance

Balance requires: Incoming energy = Outgoing energy

incoming solar radiation
Incoming solar radiation


  • Incoming solarradiation at the top of the atmosphere, displayed for each month and latitude
  • Global mean annual-mean value342 W/m2
  • Based on ERBEsatellite measurements





energy balance
Energy balance
  • Earth’s temperature: Balance between the amount of energy received from the sun and the amount of energy radiated outward.
  • Top: Solar radiation reflected from the Earth by clouds, ice, and bright surfaces like desert.
  • Bottom: Heat radiated from the Earth. More energy is emitted by warmer surfaces, except where there are high, cold clouds.

Clouds and the Earth’s Radiant Energy System (CERES) instrumentJanuary 2002.

energy surplus and deficit regions
Energy: Surplus and deficit regions
  • Earth’s radiation balance (annual mean)




But the Earth’s surface temperature is observed to be, on average, about 15 C (~59 F).

The Greenhouse Effect

Based on conservation of energy: If the Earth did NOT have an atmosphere, then, the temperature at the surface of the Earth would be about -18 C ( ~ 0 F).



This greenhouseeffect in not controversial.

  • Cyclone: low pressure system
  • Anticyclone: high pressure system
  • Isotherms
  • Isobars
  • Isotach
  • Lapse rate
physical constants and parameters
Physical Constants and Parameters
  • g: gravitational acceleration of the Earth, approximately constant, g = 9.81 m/s2
  • Rd: gas constant for dry air, Rd = 287 J/(kg K)
  • Radius of the Earth: a = 6371 km
  • E-W Circumference of the Earth at latitude  : 2a*cos(), at the equator (=0): 2a
  • Total surface area of the Earth: 4a2
  • Volume of the Earth: 4/3 a3
  • SI units: kg, s, K, m, J
  • Energy in Joule: J = N m
  • Force in Newton: N = kg m / s2
  • Pressure in Pascal: Pa = N / m2
  • Some prefixes and factors:
    • h (hecto) 102
    • k (kilo) 103
    • c (centi) 10-2
    • m (milli) 10-3