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Physics of the Atmosphere Physik der Atmosphäre. SS 2010 Ulrich Platt Institut f. Umweltphysik R. 424 [email protected] Last Week. The planetary boundary layer is the layer where surface friction has an impact ( τ ≠ 0 ). It can be subdivided into different regimes:

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Physics of the Atmosphere Physik der Atmosphäre

SS 2010

Ulrich Platt

Institut f. Umweltphysik

R. 424

[email protected]


Last week
Last Week

  • The planetary boundary layer is the layer where surface friction has an impact (τ ≠ 0). It can be subdivided into different regimes:

    • Molecular-viscous layer governed by molecular diffusion

    • Prandl- layer, where shear stress is constant with altitude

    • Ekman- layer, where shear stress decreases with altitude (until it is zero in the free atmosphere)

  • Basic assumption: Turbulent diffusion coefficient is proportional to altitude  Logarithmic wind profile

  • Water vapour has an impact on vertical stability not only due to the release of latent heat, but also due to its lower density

  • The transport of scalar tracers in the boundary layer can be parameterised with the transfer resistance R or the piston velocity v12:

  • In the turbulent regime, the transfer resistance is proportional to the logarithmic ratio of the altitude difference

  • Air/sea gas exchange is a very important issue in the chemistry and climate of the atmosphere (how much anthropogenic CO2 is taken up by the oceans?)

  • It can be investigated using wind-wave facilities, such as the Aelotron at the IUP



Topics
Topics

  • Temperature and Radiation in the Stratosphere

  • Stratospheric Dynamics

    • Circulation

    • Stratosphere – Troposphere Exchange

  • Water Budget of the Stratosphere

  • S in the Stratosphere: Junge Layer


The structure of the atmosphere

Ionosphäre

Heterosphäre

Thermosphäre

Mesosphäre

Homosphäre

Tropopause

Troposphäre

The Structure of the Atmosphere



Mean latitude distribution of temperature and wind velocity
Mean Latitude Distribution of Temperature and Wind Velocity

White lines: Isolinies of zonal (east-west) wind velocity (m/s)

(Source: NASA)


Mean latitude distribution of actual and potential temperature
Mean Latitude Distribution of Actual and Potential Temperature

Drawn lines: Potential Temperature

Dashed lines: Actual Temperature

Holton et al., 1995



Radiation heating and cooling of the atmosphere
Radiation Heating and Cooling of the Atmosphere Temperature

local heating rates:

  • stratosphere ~ radiative equilibrium

  • troposphere ≠ radiative equilibrium - “convective adjustment”

Brasseur and Solomon, 2005

(IUP-Book 1968)

Higher atmosphere is (mainly) cooled by LW and heated by SW radiation


Vertical radiation intensity profile in the atmosphere
Vertical Radiation Intensity Profile in the Atmosphere Temperature

1) For simplicity we first consider a (hypothetical isobaric atmosphere, i.e. c(z) = c0):

We obtain for I(z):

With:

= Optical Density

c = Trace gas concentration (e.g. particles m-3)

 = Absorption cross section

I0 = Intensity outside the atmosphere

2) In reality, of course we have an exponential decrease:

Thus the Optical Density as function of height z:

and the intensity:

The above equation is also known as Chapman Function.


The chapman function

Altitude/Km Temperature

40

35

30

25

20

15

10

5

0

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,90

1,00

The Chapman Function

From a certain altitude (e.g. for  = 1, red line) we can consider the atmosphere as ‘black’.

Intensity I/I0



Turbulent diffusion konstant k m cm 2 s 1
Turbulent Diffusion Konstant K TemperatureM, cm2s-1

Source: Brasseur and Solomon 1986


The brewer dobson circulation i
The Brewer-Dobson Circulation I Temperature

  • In 1948: Alan Brewer discovers that stratospheric air above England is a lot drier than expected from local dew point temperature.

  • latitudinal gradient of Θ: no direct advection of tropical air (radiative cooling rates would have to be unreasonably high)

  • Stratosphere is NOT in radiative equilibrium due to BDC:

    • ascending branch: radiative heating

    • sinking branch: radiative cooling

  • Dehydration of air entering the stratosphere: freeze-drying


The brewer dobson circulation ii
The Brewer-Dobson circulation II Temperature

Slow circulation from the (cold) equatorial tropopause to higher latitudes provides a supply of dry air to the entire stratosphere

Brewer (1949)


Mean air mass ages at different latitudes and altitudes

Alter in Jahren Temperature

Mean Air Mass Ages at different Latitudes and Altitudes

Waugh and Hall 2002


The age of stratospheric air
The „Age“ of stratospheric Air Temperature

Air mass age (from CO2) as function of latitude at 20km

And as Fu. of latitude (5oS, 40oN, 65oN) and altitude






Very short lived source gases

WMO (2003) Temperature

Very Short Lived Source Gases


Freeze drying the stratosphere
Freeze Drying the Stratosphere Temperature

  • most efficient upward transport mechanism: deep convection

  • tropical TP is VERY cold  freeze drying

  • tropical TP temp is lowest in NH winter minimum in specific humidity in tropical lower stratosphere in NH winter



Potential vorticity ertel s vorticity
Potential Vorticity Temperature(Ertel’s Vorticity)

  • In absence of friction and diabatic processes (radiation, latent heat, ..) PV is conserved:

  • measure of vertical stability and circulation

  • measure of ratio of absolute vorticity to effective depth of vortex

  • dynamical tracer of horizontal motion

  • large gradient of PV across the tropopause

  • 1 PVU = 10-6 m2 s-1 K kg-1


Adiabatic flow over mountain range
Adiabatic flow over mountain range Temperature

stretching of Θ0+dΘ layer

initial lifting of Θ0+dΘ layer

Holton (1992)

horizontal spread of vertical displacement at top of column

development of lee-wave due to changes in f

uniform zonal flow


Tropopause definitions
Tropopause Definitions Temperature

  • Focus on increase in stability

  • Θ/PV:

    • tropical TP: Θ=380K

    • extratropics: 2 PVU

  • WMO:

    • lowest level at which dT/dz ≤ 2 K km-1

    • and: dT/dz ≤ 2 K km-1 in “surrounding” 2km

  • Ozone:

    • altitude with first occurrence of [O3] > 0.1 ppm


Stratosphere troposphere exchange
Stratosphere-Troposphere Exchange Temperature

  • Tropics:

    • deep, overshooting convection

  • Extratropics:

    • tropopause folds in jet stream regions

    • cut-off lows

    • isentropic exchange in lower-most stratosphere

  • STE in models: hard problem, vertical resolution near TP has to be fairly high

Shapiro (1980) in Holton et al (1995)


Feb 29, 1800 UTC Temperature

Feb 27, 1800 UTC

Owen R. Cooper


Pv contours
PV Contours Temperature

Owen R. Cooper


Source for stratospheric nox
Source for Stratospheric NOx Temperature

N2O + O(1D)  2 NO (58%)

 N2 + O2 (42%)

N2O + hν  N2 + O(1D)

Brasseur et al., 1999


Sulfur in the stratosphere
Sulfur in the Stratosphere Temperature

  • Sources:

    • volcanic SO2 and sulfate aerosols

    • OCS

  • OCS chemistry:

    (1) OCS + hv  S + CO

    S + O2 SO + O

    (2) OCS + O  SO + CO

    SO + O2 SO2 + O

    SO + NO2 SO2 + NO

  • Formation of sulfate aerosols: Junge layer, condensation nuclei for PSC (discovered by Junge, 1961)

  • Important for radiation balance and ozone chemistry


Pinatubo i
Pinatubo I Temperature

before

after

Photo: NASA


Pinatubo ii
Pinatubo II Temperature

WMO (2003)

NASA


Pinatubo iii
Pinatubo III Temperature

 Temperature increase in the stratosphere

WMO (2003)


The global sulfur cycle
The Global sulfur cycle Temperature

Brasseur et al., 1999


Global atmospheric chlorine cycle
Global Atmospheric Chlorine Cycle Temperature

Graedel and Crutzen [1993]


Summary
Summary Temperature

  • The stratospheric temperature is determined by radiation balance

  • Exchange between Strat. And Trop. Is determined by the Brewer-Dobson circulation and transport along isentropes

  • The Brewer-Dobson circulation also determines the stratospheric water budget in first approximation (polar stratospheric cold trap)

  • S in the Stratosphere: Junge Layer


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