using satellite measurements of stellar scintillation for mapping turbulence in the stratosphere

Using satellite measurements of stellar scintillation for mapping turbulence in the stratosphere

V. F. Sofieva(1), A.S. Gurvich(2), F. Dalaudier(3), and the GOMOS team(4)

(1) Finnish Meteorological Institute, Helsinki, Finland

(2) A.M. Oboukhov Institute of Atmospheric Physics, Moscow, Russia

(3) LATMOS (Service d’Aeronomie du CNRS), France

(4) FMI, Finland; Service d’Aeronomie, France; IASB, Belgium, ACRI-ST, France, ESA/ESRIN, Italy; ESA/ESTEC, Netherlands

Turbulent mixing and beyond, ICTP, Trieste, 3 August 2009

Outlines

• Methodology: using space-borne stellar scintillation measurements for studies of small-scale processes in the atmosphere

• Application: results of analysis of GOMOS/Envisat scintillation measurements


Atmospheric layers

www.singularvortex.com

Stratosphere


Introduction• Gravity waves, their generation, propagation

and breaking

• Global effects of (relatively) small-scale gravity waves influence the stratospheric circulation

affect ice cloud formation and polar ozone loss

they play an important role in driving atmospheric circulations (including quasi-biennial oscillation)

play an important role in controlling temperatures in the Antarctic ozone hole

• Satellite observations of stellar scintillations is the new approach for study of small-scale processes in the atmosphere


Scintillation of stars


Scintillation of stars: a simplified qualitative explanation

direction of the light

Tw

inkle, twinkle


Past and present space-borne stellar scintillation measurements• Past:

EFO-2 photometer, Russian MIR station (1996-1999)

– Sampling frequency up to 16 kHz

– Central wavelength 485 nm

– Man-controlled photometer (~100 occultations, within 60° latitudinal band)

• Present: scintillation measurements by GOMOS fast photometers (since March 2002)

First bi-chromatic scintillation measurements

– Blue 470-520 nm

– Red 650-700 nm

Sampling frequency 1 kHz Global coverage Objectives

– Scintillation correction of spectrometer data

– High resolution temperature profile

– Small scale structures of air density, stratospheric dynamics GOMOS fast photometer

EFO-2 fast photometer


GOMOS measurements

movie


General strategy for retrieval of information about air density irregularities

• 3D distribution from 1D scintillation measurements? The problem is severely ill-posed

• Approach proposed in [Gurvich and Kan, 2003]

1 step. The spectrum of the air density irregularities is parameterized

2 step. 3D-spectrum of air density irregularities 1d-scintillation spectrum at observation point (The theoretical relations are found)

3 step. The parameters of the spectral model are retrieved via fitting experimental scintillation spectra


Structure of air density irregularities

• Anisotropic irregularities Elongated in horizontal direction Generated by internal gravity

waves

• Isotropic irregularities (turbulence) Result from breaking of internal

gravity waves Dynamic instabilities

• Two-component spectral model of relative fluctuations of air density

KW

anisotropicisotropic


Spectrum of anisotropic irregularities

• corresponds to anisotropic irregularities generated by a random ensemble of internal gravity waves

CW is the structure characteristic is the anisotropy coefficient 2/0 is the outer scale 2/W is the inner scale

• The associated 1D vertical spectrum for 0 << z << W corresponds to the model of the saturated gravity waves

3

3

2)( zWz CV

32

4 z

BVTT g

AV

WzWW

kηC

2/52

02222

2222zk

222yx


Spectrum of isotropic irregularities

• Spectrum of locally isotropic turbulence (Kolmogorov model)

CK is the structure characteristic

K is the wavenumber corresponding to inner scale of isotropic irregularities (Kolmogorov scale)

• The corresponding 1D spectrum follows well-known -5/3 power law

• Individual turbulent patches are not resolved, CK represents the effective value in the region of interaction of light wave and the turbulent atmosphere

))/(exp(033.0)( 23/11KKK kkCk

2222zyx kkkk


Model of 1D vertical spectra of air density irregularities

0

K


• Stratospheric distortion of light rays Distortion of optical path (eikonal)

• Frozen field assumption

• Phase screen approximation

• Scintillation spectrum (weak scintillation)

Modelled scintillation spectra

3d spectrum of air density irregularities

kx, ky, kz

2d spectrum of eikonal fluctuations

F (ky, kz)

2d spectrum of scintillation

1d spectrum of scintillation

raydlN r


Scintillation spectra in phase screen approximation (weak scintillation)

F ,y z

eikonal fluctuations on phase screen plane

22

2

22

2

1exp,,

1),(F

H

Haxd

H

Ψ

z

xEzyx

zyz

2D spectrum of on phase screen plane

qz

yzyzyJ ,F,),(F

F ,J y z 2D spectrum of observed light flux on observation plane

2 22 20

0

4( , ) sin

2z

z y yk L

q k q

(Gurvich, 1984)

V ( ; ) F ( , ) sJ s y z J y z s

s

d d

κ κ

VJ is 1D spatial scintillation spectrum in observation plane


Scintillation spectra

10-4

10-3

10-2

10-1

100

0

0.5

1

1.5

2

2.5

wavenumber, 1/m

psd/

varia

nce

Iso

0

30

60

75

0

w

Fr

K

i2/

w2 =4

),,()()( 0mod WanisoWisoK kVCkVCkV


The main approach to scintillation analysis

• To separate the anisotropic and isotropic components

• To retrieve essential parameters of IGW and turbulence spectra


Inversion• Vmeas=CK Viso+CW Vaniso(W, 0)+

• Maximum likelihood method, which is equivalent to minimization of

• Combination of linear and non-liner optimization

Non-linear fit (Levenberg-Marquardt) for W and 0

Linear fit (weighted least-squares method) for CK and CW

measWanisoWisoK

TmeasWanisoWisoK CVCCVC VVSVV ),(),( 0

10

2


Filtering quasi-periodic structures


Examples of retrievals : 1.photometer data


Examples of retrievals: moderate turbulence

10-3

10-2

10-1

0

2

4

6

8

10

wavenumber, 1/m

psd

Ck= 1.6e-9 m-2/3

CW

=3.6e-11 m-2

lW

= 4.7 m

L0=0.42 km

10-3

10-2

10-1

0

0.5

1

1.5

2

wavenumber, 1/m

psd

Ck= 2.3e-9 m-2/3

CW

=4e-11 m-2

lW

= 8.7 m

L0=0.76 km

10-3

10-2

10-1

0

0.2

0.4

0.6

0.8

1

wavenumber, 1/m

psd

Ck= 5.7e-9 m-2/3

CW

=4.9e-11 m-2

lW

= 15 m

L0=3.1 km

10-3

10-2

10-1

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

wavenumber, 1/m

psd

Ck= 1e-8 m-2/3

CW

=1.3e-10 m-2

lW

= 36 m

L0=2.3 km

measured uncertainty used in 2nd step fit anisotropic isotropic

30 km 35 km

40 km 45 km

R02908/S001 (=67, 35S, 106W, 20 September 2002)

Sofieva et al.,

JGR, 2007


Examples of retrievals: strong turbulence

10-3

10-2

10-1

0

1

2

3

4

5

6

7

8

9

wavenumber, 1/m

psd

Ck= 3.2e-9 m-2/3

CW

=1.8e-10 m-2

lW

= 14 m

L0=1 km

10-3

10-2

10-1

0

0.5

1

1.5

2

2.5

3

wavenumber, 1/m

psd

Ck= 2e-8 m-2/3

CW

=1.8e-10 m-2

lW

= 16 m

L0=3.5 km

10-3

10-2

10-1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

wavenumber, 1/m

psd

Ck= 7.5e-8 m-2/3

CW

=2e-10 m-2

lW

= 62 m

L0=0.78 km

10-3

10-2

10-1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

wavenumber, 1/m

psd

Ck= 1.4e-7 m-2/3

CW

=1.6e-10 m-2

lW

= 21 m

L0=1.6 km

measured uncertainty used in 2nd step fit anisotropic isotropic

30 km 35 km

40 km 45 km

R07741/S001 (=40, 62S, 7E, 23 August 2003)

Sofieva et al.,

JGR, 2007


Indication on gravity wave breaking in polar night jet• Qualitative: Sofieva et al. (2007), Global analysis of scintillation variance: Indication of gravity wave

breaking in the polar winter upper stratosphere, Geophys. Res. Lett., 34, L03812, doi:10.1029/2006GL028132

latitude latitude

KT CTC22

Gravity wavestructure characteristic

CW(m-2)

Turbulencestructure characteristic

CT2(K2m-2/3)

Jan-Mar, Dec 2003 June-Sep 2003

Sofieva et al., GRL, 2009


CT2 in tropics (at 42 km)

• Turbulence intensity is smaller in tropics than in polar regions; it has a pronounced zonal structure

• Average values of CT2

follow the sub-solar latitude

• Almost all of the local enhancements are over continents

• Many of enhancements correspond well to the typical regions of deep convection

• No systematic increase of CT

2 over large mountain regions is observed

Gurvich et al., 2007, GRL


Evolution of CT2 at 80 N

during the sudden stratospheric warming in December 2003

altit

ude,

km

Equivalent latitude (deg)

date07/12 14/12 21/12

30

35

40

45

50

altit

ude,

km

Temperature (K)

date07/12 14/12 21/12

25

30

35

40

45

50

55

date

altit

ude,

km

CT

2 ( K2 m-2/3)

07/12 14/12 21/1230

35

40

45

50

0.5

1

1.5

2

x 10-3

200

210

220

230

240

250

260

45

50

55

60

65

70

75

80

Sofieva et al., (2007): Reconstruction of internal gravity wave and turbulence parameters in the stratosphere using GOMOS scintillation measurements, Journal of Geophys. Res., 112, D12113,

doi:10.1029/2006JD007483


Summary, discussion, future work

• The presented results are the start in studying small-scale air density irregularities

• Strength of scintillation method: It covers the wavenumber range of transition of GW spectrum to

turbulence -> possibility of visualizing GW breaking

Scintillation are affected by small-vertical-scale GW -> importance for GW parameterizations in GCM models

Other measurements at such small vertical resolution are scarce in this altitude range

• The processing of the 2002-Jan 2005 dataset has been recently completed, the data analyses are on-going

using satellite measurements of stellar scintillation for mapping turbulence in the stratosphere

Documents

d scintillation measurements

dscintillation spectrum

d vertical spectrum

d distribution

study of smallscale

gomos fast photometers

important role

found3 step