Atmospheric water
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Atmospheric Water. Global energy balance Atmospheric circulation Atmospheric water vapor Reading: Sections 3.3 and 3.4 for next Tues. Atmospheric Water. Global energy balance Atmospheric circulation Atmospheric water vapor. Radiation. Basic laws Stefan-Boltzman Law

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Atmospheric Water

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Atmospheric water

Atmospheric Water

  • Global energy balance

  • Atmospheric circulation

  • Atmospheric water vapor

  • Reading: Sections 3.3 and 3.4 for next Tues


Atmospheric water1

Atmospheric Water

  • Global energy balance

  • Atmospheric circulation

  • Atmospheric water vapor


Radiation

Radiation

  • Basic laws

    • Stefan-Boltzman Law

      • R = emitted radiation (W/m2)

      • T = absolute temperature (K),

      • and s = 5.67x10-8W/m2-K4

      • with e = emissivity (0-1)

        • Water, Ice, Snow (0.95-0.99)

        • Sand (0.76)

Valid for a Black body or “pure radiator”

“Gray bodies emit a proportion of the radiation of a black body


Net radiation r n

Net Radiation, Rn

Ri Incoming Radiation

  • Ro =aRi Reflected radiation

  • = albedo (0 – 1)

Re

Rn Net Radiation

Average value of Rn over the earth and

over the year is 105 W/m2


Net radiation r n1

Net Radiation, Rn

H – Sensible Heat

LE – Evaporation

G – Ground Heat Flux

Rn Net Radiation

Average value of Rn over the earth and

over the year is 105 W/m2


Energy balance of earth

Energy Balance of Earth

70

20

100

6

6

26

4

38

15

19

21

Sensible heat flux 7

Latent heat flux 23

51

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/energy/radiation_balance.html


Diurnal variation

Diurnal Variation

Diurnal variation

of fluxes,

July 2003

San Marcos

Basin

Downward shortwave

Upward Longwave

Downward longwave

Upward shortwave

Ground

Fluxes in W/m2

Latent

Sensible


Energy balance in the san marcos basin from the narr july 2003

Energy Balance in the San Marcos Basin from the NARR (July 2003)

Note the very large amount of longwave radiation exchanged between land and atmosphere

Average fluxes over the day

495

61

72

112

3

310

415

Net Shortwave = 310 – 72 = 238; Net Longwave = 415 – 495 = - 80


Atmospheric water

Increasing carbon dioxide in the atmosphere (from about 300 ppm in preindustrial times)

We are burning fossil carbon (oil, coal) at 100,000 times the rate it

was laid down in geologic time


Absorption of energy by co 2

Absorption of energy by CO2


Atmospheric water2

Atmospheric Water

  • Global energy balance

  • Atmospheric circulation

  • Atmospheric water vapor


Heating of earth surface

Heating of earth surface is uneven

Solar radiation strikes perpendicularly near the equator (270 W/m2)

Solar radiation strikes at an oblique angle near the poles (90 W/m2)

Emitted radiation is more uniform than incoming radiation

Heating of earth surface

Amount of energy transferred from equator to the poles is approximately 4 x 109 MW


Hadley circulation

Hadley circulation

Atmosphere (and oceans) serve to transmit heat energy from the equator to the poles

Warm air rises, cool air descends creating two huge convective cells.


Conservation of angular momentum coriolis force

Conservation of Angular Momentum (Coriolis Force)

No external forces on air, so mV1r1 = mV2r2

mV1r1

r1 < r2 so V1 > V2

mV2r2

Intertropical Convergence Zone

V1

r1

Earth

rotation

r2

V2

Earth rotation

Looking down from North Pole, earth is rotating

counterclockwise

Near equator, air starts to “fall behind” the earth


Atmospheric circulation

Atmospheric circulation

Circulation cells

Polar Cell

  • Hadley cell

  • Ferrel Cell

  • Polar cell

Ferrel Cell

Winds

  • Tropical Easterlies/Trades

  • Westerlies

  • Polar easterlies

Latitudes

  • Intertropical convergence zone (ITCZ)/Doldrums

  • Horse latitudes

  • Subpolar low

  • Polar high


Effect of land mass distribution

Effect of land mass distribution

Uneven distribution of land and ocean, coupled with different thermal properties creates spatial variation in atmospheric circulation

A) Idealized winds generated by pressure gradient and Coriolis Force. B) Actual wind patterns owing to land mass distribution


Shifting in intertropical convergence zone itcz

Shifting in Intertropical Convergence Zone (ITCZ)

Owing to the tilt of the Earth's axis in orbit, the ITCZ shifts north and south. 

Southward shift in January

Creates wet Summers (Monsoons) and dry winters, especially in India and SE Asia

Northward shift in July


Itcz movement

ITCZ movement

http://iri.ldeo.columbia.edu/%7Ebgordon/ITCZ.html


Atmospheric water3

Atmospheric Water

  • Global energy balance

  • Atmospheric circulation

  • Atmospheric water vapor


Structure of atmosphere

Structure of atmosphere


Atmospheric water4

Atmospheric water

  • Atmospheric water exists

    • Mostly as gas or water vapor

    • Liquid in rainfall and water droplets in clouds

    • Solid in snowfall and in hail storms

  • Accounts for less than 1/100,000 part of total water, but plays a major role in the hydrologic cycle


Water vapor

Water vapor

Suppose we have an elementary volume of atmosphere dV and

we want quantify how much water vapor it contains

Water vapor density

dV

ma = mass of moist air

mv = mass of water vapor

Air density

Atmospheric gases:

Nitrogen – 78.1%

Oxygen – 20.9%

Other gases ~ 1%

http://www.bambooweb.com/articles/e/a/Earth's_atmosphere.html


Specific humidity q v

Specific Humidity, qv

  • Specific humidity measures the mass of water vapor per unit mass of moist air

  • It is dimensionless


Vapor pressure e

Vapor pressure, e

  • Vapor pressure, e, is the pressure that water vapor exerts on a surface

  • Air pressure, p, is the total pressure that air makes on a surface

  • Ideal gas law relates pressure to absolute temperature T, Rv is the gas constant for water vapor

  • 0.622 is ratio of mol. wt. of water vapor to avg mol. wt. of dry air (=18/28.9)


Dalton s law of partial pressures

Dalton’s Law of Partial Pressures

John Dalton studied the effect of gases in a mixture. He observed that the Total Pressure of a gas mixture was the sum of the Partial Pressure of each gas.

P total = P1 + P2 + P3 + .......Pn

The Partial Pressure is defined as the pressure of a single gas in the mixture as if that gas alone occupied the container. In other words, Dalton maintained that since there was an enormous amount of space between the gas molecules within the mixture that the gas molecules did not have any influence on the motion of other gas molecules, therefore the pressure of a gas sample would be the same whether it was the only gas in the container or if it were among other gases.

http://members.aol.com/profchm/dalton.html


Avogadro s law

Avogadro’s law

Equal volumes of gases at the same temperature and pressure contain the same number of molecules regardless of their chemical nature and physical properties. This number (Avogadro's number) is 6.023 X 1023 in 22.41 L for all gases.

Dry air ( z = x+y molecules)

Moist air (x dry and y water vapor)

Dry air (21% O2, 78% N2, 1% other)

Md ~ 0.22*32+0.78*28

~ 28.9

Water vapor (H2O)

Mv = 2*1 + 16 = 18

rd = (x+y) * Md/Volume

rm = (x* Md + y*Mv)/Volume

Moist air is lighter than dry air

rm < rd, thus moist air is less dense than dry air


Saturation vapor pressure e s

Saturation vapor pressure, es

Saturation vapor pressure occurs when air is holding all the water vapor

that it can at a given air temperature

Vapor pressure is measured in Pascals (Pa), where 1 Pa = 1 N/m2

1 kPa = 1000 Pa


Relative humidity r h

Relative humidity, Rh

es

e

Relative humidity measures the percent

of the saturation water content of the air

that it currently holds (0 – 100%)


Dewpoint temperature t d

Dewpoint Temperature, Td

e

Td

T

Dewpoint temperature is the air temperature

at which the air would be saturated with its current

vapor content


Water vapor in an air column

Water vapor in an air column

  • We have three equations describing column:

    • Hydrostatic air pressure, dp/dz = -rag

    • Lapse rate of temperature, dT/dz = - a

    • Ideal gas law, p = raRaT

  • Combine them and integrate over column to get pressure variation elevation

2

Column

Element, dz

1


Precipitable water

Precipitable Water

  • In an element dz, the mass of water vapor is dmp

  • Integrate over the whole atmospheric column to get precipitable water,mp

  • mp/A gives precipitable water per unit area in kg/m2

2

Column

Element, dz

Area = A

1


Precipitable water jan 2003

Precipitable Water, Jan 2003


Precipitable water july 2003

Precipitable Water, July 2003


Atmospheric water

January

July


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