New Recent cloudy sky photon path pdf measurements from … · 2011. 12. 30. · Recent cloudy sky...

K. Pfeilsticker Institut für Umweltphysik, University of Heidelberg,Germany

K. Pfeilsticker, and T. Scholl, IUP, University of Heidelberg, GermanyA. B. Davis, LANL, Los Alamos, USAH. K. Baltink, KNMI, Utrecht, NLS. Crewell, U. Löhnert, and C. Simmer, Met. Institute Bonn, GermanyJ. Meywerk, and M. Qante, GKSS, Geesthacht, Germany

Overview• introduction• oxygen A-band spectroscopy

and retrieval technique• some examples• Test of

• photon diffusion in plane-parallelcloud geometry

• real clouds (anomalous diffusion)• summary and conclusion

Recent cloudy sky photon path pdf measurements fromHeidelberg


Instrumental Set-Up

• spectral resolution (FWHM) is presently limited to 0.013 nm (not line resolving)• Integration time: < 15s (previously 900 s, but limited

• by the spectral brightness of the sky) Quartz Fiber to the zenithTelescope®MonochromatorMultichannel DetectorBandpassFilter


Data Processing

High Spectral Resolution

Searched quantityp(l) ?

Spectrum

Measurement withgiven spectral

resolution

Measured SpectrumNonlinear Least

Square Fit (10min, 1GHz)

ModeledSpectrum

Spectroscopic Model Temp., PressureProfile

x T(p(aj), Σi ()

Solar Fraunhofer p(l) Model OxygenAbsorption SpectrumLines (VOD)

Low Spectral ResolutionBest estimate p(l)

Convolutionwith instrumentfunction

768.0 768.5 769.0 769.5 770.0 770.5 771.0 771.5

0.0

0.2

0.4

0.6

0.8

1.0

Ni I

(?)

Ni I

Co

IF

e I

IF

e I

K I

Si I

Si I

Mg

I

Si IS

i I

Si I

C I

Si I

I0

Wavelength / nm

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

0

10

20

30

40

50

60

70

767.20 767.25 767.30 767.35 767.40 767.45 767.50

0.00E+000

2.00E-024

4.00E-024

6.00E-024

Wavelength (nm)


Measurements during BBC 2001

Cabauw/NL 51.971o N, 4.927o E in Sept. 2001 together with:• GKSS 95 GHz Cloud Radar • Lidar• Microwave Radiometer • Radio probes, aircraft in-situinstruments

Cloud structure (backscattering ratio measured by the 95 GHz GKSS Radar)on Sept. 17, 2001, UT 9:45 - 10:45


Measured vs Modeled Oxygen A-band spectra

0 2 4 6 8 100.0

0.5

1.0

MODEL Gamma<L> = 2.84 ? VOD

<L2>

0.5 = 8.28

0.5 ? VOD

PD

F

Path Length (VOD)

768.0 768.5 769.0 769.5 770.0 770.5

Wavelength (nm)

768.0 768.5 769.0 769.5 770.0 770.5

0.2

0.4

0.6

0.8

1.0

8

4

-8

-4

0

Re

sid

ua

l [·

10

-3

]

PQ

17,1

8

PP

29,2

9

PQ

28,2

7P

Q 2

8,2

8

PP

27,2

7

RQ

15,1

6

RR

5,5

RQ

5,6

RR

9,9

RQ

9,1

0

PR

11,1

1

PQ

3,4

PP

33,3

3

PQ

33,3

2

K I

PP

31,3

1

PQ

31,3

0

Mg I

PP

29,2

9

PQ

29,2

8

PP

27,2

7

PQ

27,2

6

Si I

PP

25,2

5

PQ

25,2

4

MEASUREMENT SIMULATION

Tra

ns

mis

sio

n

Wavelength (nm)

0 2 4 6 8 100.0

0.5

1.0

MODEL Gamma<L> = 2.84 ? VOD

<L2>

0.5 = 8.28

0.5 ? VOD

PD

F

Path Length (VOD)

768.0 768.5 769.0 769.5 770.0 770.5

Wavelength (nm)

768.0 768.5 769.0 769.5 770.0 770.5

0.2

0.4

0.6

0.8

1.0

8

4

-8

-4

0

Re

sid

ua

l [·

10

-3

]

PQ

17,1

8

PP

29,2

9

PQ

28,2

7P

Q 2

8,2

8

PP

27,2

7

RQ

15,1

6

RR

5,5

RQ

5,6

RR

9,9

RQ

9,1

0

PR

11,1

1

PQ

3,4

PP

33,3

3

PQ

33,3

2

K I

PP

31,3

1

PQ

31,3

0

Mg I

PP

29,2

9

PQ

29,2

8

PP

27,2

7

PQ

27,2

6

Si I

PP

25,2

5

PQ

25,2

4

MEASUREMENT SIMULATION

Tra

ns

mis

sio

n

Wavelength (nm)


Cloud Structure and Inferred PDF

2 4 6 8 10 120.0

0.1

0.2

0.3

0.4

0.5

Ldir

ect

MODEL: Gamma<L> = 2.74 ? VOD

<L2> = 8.38 ? VOD

2

September 17, 2001: 10.30 - 10.31

PD

F

total atmospheric path length Ltot

[VOD]

Inferred PDF assuming a Γ-type PDF distribution.

direct sunPDF

inferred cloudy sky PDF

Note: The inferred first 2 PDF moments are given in units of a vertical optical density(VOD) for oxygen of the atmosphere

<Ltot> = 2.74 VOD√<L2

tot> = 2.89 VOD


Idealized Scheme for Cloudy Sky RT

Direct sun

FOV ~1°

Cloudy sky:<L>=<L>+<L>ges0Clouds

Cloud

Hcloud

Ground

Clear sky <L>0

<L>Cloud

Attention: Oxygen A-band absorption measurement integrates over total atmosphericoxygen column hence in cloud pdf studies need corrections for the clear skyabsorption !

regime (1)

regime (3)

regime (2)


From the total atmospheric paths (<Ltot> and (<L2tot>)

to in-cloud paths (<Lc> and (<L2c>)

regimes:

• above the cloud: <L1> = (L∞ – H cloud top )/cos(SZA) (typical values < 1VOD)

• < Lc> (typical values > 2.5 VOD)• below the cloud: < L3 > = (Lcloud bottom – 0 )·(1+5AgRc/(1-AgRc) (typical value

< 0.5 VOD)

Corrections:

1st moment: <Lc> = <Ltot > – <L1> – <L3>

2nd moment: <L2c> = <L2

tot> - <Ltot >2 + <Lc>2


Testing the pdf solution for photon diffusion through plan-parallel clouds and the anomalous diffusion (Lévy walk) model

- the first two moments -

}*)](1[5.0{ 1 !" cCH

Lc #+#=$

><

}*)](1[20

7{

2

22

2

!"cC

H

Lc#+#=

$

><

1st moment:

2nd moment:

2

32

2

1

*

*

*

)1(

4515016656

14)(

1

34

2)(

2)(

)1(

!

!!!!!

!

!!!

""!

""

+

+++#=

+

+#=

#==

#$=

C

C

const

R

T

g

c

c

ccParameters:

Davis&Marshak (2002)

(α-1)

⋅(α-1)

Lévy index 1 ≤ α ≤ 2; Davis&Marshak (1997)


Measurements over Cabauw on May 22, 2003

radar reflectivites (KMNI, 35Ghz)

<Ltot>, √<L2tot>, and LWP (KMNI,

Uni Bonn)


Radar reflectivity measurements (KMNI, 35 Ghz)over Cabauw on May 22, 2003


Inferred Lévy Indices

0 2 4 6 8 10 12 140

1

2

3

4

5

6

7

8

9

! =2

! =1.5

! =1.1

May 22, 2003

<LC

> /

"H

#c* = (1-g) $ #

c


Testing the pdf solution for photon diffusion through plan-parallel clouds and the Levy walk model (Davis&Marshak,

1997)

- ratio of 1st two moments -

]41.1,18.1[)](1[

)](1[

5

7

1

22

!+

+"=

><

><

#

#

C

C

L

L

c

c

For α = 2:

Davis&Marshak (2002)


Ratio of the 1st two moments of inferred and predicted photon pathlengths

0 2 4 6 8 10 12 140.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

Theory

May 22, 2003

<LC2

>0.5

/ <

LC>

!c* = (1-g) " !

c


Summary&Conclusion

• photon path PDFs (<Ltot>, <L2tot>, <Lc> and <L2c

o>, can reliably bederived from oxygen A-band measurements (every 15 s).

• a wide range of PDF types occur, depending on the type of cloudcover.

• Gamma (log-normal) PDF is reasonably good approximations forphoton path PDF’s under slab like cloud covers (α = 2) .

• for more complicated cloud covers (c.f. multi-layer, broken cloudcovers) anomalous diffusion approximation, c.f. Lévy type photonpath PDFs are better suited (<L>~τ α-1 with α < 2).

• Our measurements confirm the numerical values (prefactors) of theDavis&Marshak (2002) diffusion solution for plane-parallel clouds (α =2).

New Recent cloudy sky photon path pdf measurements from … · 2011. 12. 30. · Recent cloudy sky...

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