cloud sensitivity studies for stratospheric and lower mesospheric

Envisat Symposium, April 23 – 27, 2007, Montreux

[email protected]@iup.physik.uni-bremen.de -bremen.de

SADDU Meeting, 16-17 June SADDU Meeting, 16-17 June 2008, IUP-Bremen2008, IUP-Bremen

Cloud sensitivity studies for stratospheric and lower mesospheric Cloud sensitivity studies for stratospheric and lower mesospheric ozone profile retrievals from limb scattered solar radianceozone profile retrievals from limb scattered solar radiance

T. Sonkaew, C. von Savigny, A. Rozanov, V. Rozanov, H. Bovensmann and J.P. Burrows

Institute of Environmental Physics and Remote Sensing, University of Bremen, Bremen, Germany




OutlineOutline

IntroductionMethodologyRetrieval algorithm and Forward simulationLinear approximationSensitivity studies

Weighting functions Cloud parameters Ground albedo Viewing angles

ConclusionsFuture work

2




IntroductionIntroduction

Clouds cover 60% of atmosphere, 7% of tropospheric volume. [Lelieveld et al., 1989 and Pruppacher and Jaenicke, 1995]

Photo by R. Macatangay The reflectance at 443 nm from SCIAMACHY data using SACURA, 1 Jan 2006 – 31 Dec 2006

3




Introduction Introduction

Clouds interact with the incoming solar radiation and long wavelength radiation emitted from the Earth.

Clouds have an impact on the trace gas retrieval.

4

line of sight




truei3

truei3i3i )](z[

)](z[)](z[)(zerror Retrieval

O

OO cloud

How to estimate the impact of clouds on the ozone retrieval?How to estimate the impact of clouds on the ozone retrieval?

Cloudiness scenario

Cloud free scenarioSimulated limb radiance spectra

Retrieval in cloud free scenario

Ozone vertical profile

Ozone profile in cloudy atmosphere

True ozone profile

Radiative transfer code

“SCIATRAN”

Vertical P, T and albedo

5




Retrieval Algorithm Retrieval Algorithm

Combined the O3 profile in the Hartley, Huggins and Chappuis bands

Burrows et al., [1999]

1= 525 nm 3=675 nm

2=602 nm

The Chappuis bands in visible allow to retrieve O3 between 15-40 km [Flittner,2000; McPeters,2000; von Savigny,2002]

The absorption cross section of O3 in different temperatures and wavelengths in the Chappuis band (red arrows) used for O3 retrievals.

6




Retrieval AlgorithmRetrieval Algorithm

The Hartley bands in UV allow to retrieve O3 between 35-65 km. Wavelengths 264, 267.5, 273.5, 283, 286, 288, 290 and 305 nm are chosen. [Rohen,2006]

Burrows et al., [1999]

8

7




Retrieval AlgorithmRetrieval Algorithm Normalization step: reduce impact of ground albedo and cloud on O3 retrieval.

Reference tangent heights:

Combination of the Chappuis bands wavelengths:

Combination of the Hartley and Chappuis bands wavelengths: employ the retrieval vectors

)(

)()(

,

,,/

refi

THiTHk

nCH I

II

ii

i

i

THnmTHnm

THnm

THnC

II

Iy

,625,523

,602

,

,)( ,,Tn

THkTHk iiyy }9,,1{ k

Wavelengths (nm) 264 267.5 273.5 283 286 288 290 305 525 602 675

THstart(km)

THref (km)

52 52 52 45 45 45 45 35 9 9 9

71 71 71 68 65 65 61 55 41 41 41

8





Numerical retrieval step: nonlinear Newtonian iteration optimal estimation [Rodger, 1976] SCIATRAN V 2.2 radiative transfer model [Rozanov et al., 2007] using Discrete Ordinate Method (DOM) [Chandrasekhar, 1950]

SCIATRAN set up • Aerosol : none• Ground albedo : 0.3 (for general cases)• Weighting function : single scattering• Cloud model : Mie phase function

9




Use linear approximation to estimate the error.Use linear approximation to estimate the error.

H

fcfcfc dzzωzωSSnSnS0

)]()([)0()0()()(

,)(

)()()()0(

0

dzzn

znδzωnSS

H

c 1)(

)(0

)(

)(

zn

zn

zn

znδ

dzzωnSSH

c0

)()()0(

10




Error EstimationError Estimation

+ : S = I0 at 600 nm

◆ : S = Normalized triple

+ : S = I0 at 600 nm

◆ : S = Normalized triple

11




Error EstimationError Estimation

dzzωzωdzzεzω

dzzεzωdzn

nδzω

dzzωzωny

H

fc

H

f

H

f

H

f

H

fc

00

00

0

)]()([)()(

)()()(

)]()([)(

0)( zε

< 0, always

< 0+- > 0Can we use linear approximation to predict the error?

12

H


)]()([)0()0()()(




Sensitivity studiesSensitivity studies

Weighting functions of cloud-free

13





Weighting functions of cloud-free and cloudy atmosphere

14





Different weighting functions of cloud-free and cloudy atmosphere 264 nm 273 nm 286 nm

290 nm 305 nm CHAPPUIS

15




The retrieval ozone profiles from synthetic dataThe retrieval ozone profiles from synthetic data

The combined Hartley, Huggins and Chappuis bands O3 profiles in

from modeled calculation in cloud-free and cloudy atmosphere.

Cloud parameters: cloud height 4-7 km, τ=20, re=10 m, SZA = 30o, SAA = 30o

16





• Cloud types : (cloud level and cloud optical thickness)

Cirrus

Cirrostratus

Deep convection

Altocumulus

Altostratus

Nimbostratus

Cumulus

Stratocumulus

Stratus

0 - 3.6

3.6 – 23

23 – 379

High cloud (6-15 km)Middle cloud (2-7 km)Low cloud (1-3 km)

The cloud reflectance at 630 nm as function of . [Roebeling et al., 2005]

The relative O3 error

for low cloud, re = 10 m, and SZA = SAA = 30o

(SZA ~ 22o and SAA ~ 70o at TH = 25 km )


for middle cloud, re=10 m and SZA = SAA = 30o



for high cloud, re=10 m and SZA = SAA = 30o


17




a) different cloud altitudes

The relative error of O3 retrieval profiles for cloud parameters: τ = 10, re = 10 m and SZA = SAA = 30o.


Geometrical cloud thickness

18





Geometrical cloud thickness

The relative error of O3 retrieval profiles for cloud parameters: τ = 10, re = 10 m and SZA = SAA = 30o.

b) cloud center 4.9 km c) cloud center 10.5 km

19





Cloud effective radius

The reflection function of water clouds for different values of re at τ = 30 and SZA = 45o. [Kokhanovsky, 2001]

1

0.8

0.6

0.4

0.2

00

.5

1 1.5

2.0

2.5

The relative error of O3 retrieval profiles for different re. Cloud parameters: τ = 10, 2-7 km and SZA = SAA = 30o

20





Surface ground albedo

The relative error of O3 retrieval profiles for different ground albedo .

Cloud parameter: τ = 10, re = 10 m, SZA = SAA= 30o and cloud altitude 2-7 km.

21





Solar zenith angle Solar azimuth angle

The relative error of O3 retrieval profiles for different SZAs . Cloud parameter: τ = 10, re = 10 m, SAA = 30o and cloud altitude 2-7 km.

22

The relative error of O3 retrieval profiles for different SAAs . Cloud parameter: τ = 10, re = 10 m, SZA = 30o and cloud altitude 2-7 km.





Viewing angles represent for SCIAMACHY

(SZA ≈ 62, SAA ≈ 33 at TH 25 km)

(SZA ≈ 30, SAA ≈ 55 at TH 25 km)

(SZA ≈ 40, SAA ≈ 130 at TH 25 km)

(SZA ≈ 70, SAA ≈ 160 at TH 25 km)

(SZA ≈ 78, SAA ≈ 175 at TH 25 km)

Cloud parameter: τ = 10, re = 10 m and cloud altitude 2-7 km.

23





Overview of cloud sensitivity to O3

The optical cloud thickness (left) and cloud effective radius (right) from SCIAMACHY data, using SACURA, 19 September 2007. [http://www.iup.physik.uni-bremen.de/~sciaproc/SACURA]

Frequent cloud : < 10, re = 20 m

24





Overview of cloud sensitivity to O3 for frequent cloud Altitude (km)Altitude (km) 15 km 20 km 30 km 40 km 50 km 60 km 15 km 20 km 30 km 40 km 50 km 60 km

SZA = 50SZA = 50oo , SAA = 32 , SAA = 32o o (SZA ~(SZA ~ 30 30oo , SAA , SAA = 55= 55oo) ) **

SZA = 85SZA = 85oo , SAA = 22 , SAA = 22oo (SZA = 62(SZA = 62oo , SAA = 33 , SAA = 33oo) *) *

SZA = 68SZA = 68oo , SAA = 157 , SAA = 157oo(SZA = 78(SZA = 78oo , SAA = 175 , SAA = 175oo) *) *

< 3 % < 2.5 % < 2 % < 0.5 % < 0.1 % < 0.1 % < 3 % < 2.5 % < 2 % < 0.5 % < 0.1 % < 0.1 %

< 5 % < 5 % < 2.5 % < 0.5 % < 0.1 % < 0.1 %< 5 % < 5 % < 2.5 % < 0.5 % < 0.1 % < 0.1 %

< 10 % < 7 % < 3 % < 1 % < 0.5 % < 0.1 %< 10 % < 7 % < 3 % < 1 % < 0.5 % < 0.1 %

* = at TH 25 km

25




Low bias error ( ε = - ) High bias error ( ε = + )

dzzωzωdzzεzωH

fc

H

f 00

)]()([)()(

26

Comparison results with the error estimationComparison results with the error estimation




H


)]()([)0()0()()(

* exact

x approximation

* exact

x approximation

~ 70% ~ 40%

Triplet 600 nm

27




H


)]()([)0()0()()(

* exact

x approximation

* exact

x approximation

Triplet 600 nm

28

)(

)()(

,

,,/

refi

THiTHk

nCH λI

λIλI

ii

i

i

THnmTHnm

THnm

THnC

II

Iy

,625,523

,602

,




ConclusionsConclusions

The combined Chappuis and Hartley band retrieval allows us to obtain the O3 profiles from the lower stratosphere to lower mesosphere.

The O3 retrievals are sensitive to clouds in the Chappuis bands, between 15 -25 km sensitive to cloud parameters τ, high cloud and viewing angles not much sensitive to cloud parameters: re.

The effect of neglecting clouds in the retrievals is less than 10 % at all altitudes for frequent clouds.

Linear approximation can not apply to estimate the O3 retrieval error from clouds.

29




Future activitiesFuture activities

Test, how clouds sensitivity to ozone retrieval depends on SZA and SAA on TH references.

30




THE END….THE END…. …… ……..Thank you..Thank you





8

),()(),,(),(0

,,, iklik

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fcikfcfc hλεdzznδzhλωhλyy

)],(),([)()()( ikfikcfcf hλyhλyznznzn

)],(),([)(

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znzn

znzε

)],(),([)()( ikcikccc hλyhλyznzn )],(),([)()( ikfikcff hλyhλyznzn

In linear approximation, limb radiance corresponding to the perturbed ozone profile can be written:

)()()( znznznδ





Low bias error

Low bias error Low bias error Low bias error

High bias error High bias errorTH

dzzωzωdzzεzωH

fc

H

f 00

)]()([)()(

26





19

Low bias error


High bias error High bias errorTH




19

Low bias error


High bias error High bias error

dzzωzωdzzεzωH

fc

H

f 00

)]()([)()(




19





Solar azimuth angle

17

Cloud parameter: τ = 10, re = 10 m and cloud altitude 2-7 km.

a) viewing angles represent for SCIAMACHY

b) viewing angles represent for OSIRIS




Low bias error High bias error


High bias error

dzzωzωdzzεzωH

fc

H

f 00

)]()([)()(

26


cloud sensitivity studies for stratospheric and lower mesospheric

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