NON-LTE DIAGNOSTICS OF BROADBAND INFRARED EMISSIONS FROM MESOSPHERE AND LOWER THERMOSPHERE:

APPLICATIONS TO SABER/TIMED

A.G. Feofilov1,2, A.A. Kutepov1,2,W.D. Pesnell2, and R.A. Goldberg2

36th Annual European Meeting on Atmospheric Studies by Optical Methods

August 17-22, 2009. Kyiv, Ukraine

1 – The Catholic University of America, Washington, DC, USA2 - NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

Outline

• Broadband emission limb radiometry: advantages and disadvantages

• LTE and non-LTE in molecular levels.

• ALI-ARMS non-LTE research code.

• SABER instrument onboard TIMED satellite.

• Peculiarities of temperature, CO2, and H2O retrievals from SABER.

• Conclusions.

Broadband infrared emission limb radiometry

“Broadband“ here and below refers to the radiance in optical transitions of the molecular bands that covers both the fundamental and hot bands of the

considered molecule. The typical spectral window is 100200 cm-1.

Advantages:• large signal-to-noise ratio.• both day- and nighttime measurements.• good latitudinal and longitudinal coverage.

Difficulties:• Non-LTE in molecular levels.• Uncertainties in parameters of rates involved in the model.

E , g1 1

E , g2 2

C12

C21

2

1

B12

B21

A21

LTE and non-LTE:two-level atomic gas example

n1 + n = n2

=A21 + B J21 + C21 ( ) n2 B J12 + C12 ( ) n1

R21 R12

R << C

R21n2 ~ R12n1

n2C21 = n1C12

n2

n1

g2

g1

= eE2-E1

kT LTE

Otherwise - non-LTE !!!

1000

2000

3000

4000

0

02 10

02 12

10 10

01 11

00 10

01 01

03 11

03 13

11 11

02 00

02 02

10 00

N (1)2

O (1)2

00 10

01 01

02 0002 0210 00

(626) (636)(628)(627)

}Earth

Mars

V-V

Energy exchange processes important forCO2 vibrational levels populations

V-V

Multi-level non-LTE problem

L

D

L x L x D = DL2 (L x D) x (L x D) = D L2 2

Unsöld, 1920sWintersteiner et al, 1992

Curtis & Goody, 1956Lopez-Puertas et al, 1986

Lambda iterationJ = Λ [S]

Matrix method

nl Σ(Rll’+Cll’) = Σ nl’(Rl’l + Cl’l) + Pl Lll’ l’

Σ nl = nl

Accelerated Lambda Iteration(ALI)

Λ = Λ* + (Λ - Λ*)

Rybicki & Hummer, 1991Kutepov et al., 1998

ALI technique avoids expensive radiative transfer calculations for

the photons trapped in the optically thick cores of spectral lines.

Current status of ALI-ARMS non-LTE model

O 1D

N 2 and O2

Electronic-Vibrational

Energy Reservoir

CO2 model

350 viblevels

200 000 lines

H2 O model

14 viblevels

20 000 linesO3 model

23 viblevels

150 000 lines

O 2/O 3 photolysis

model

43 viblevels

of O 2(X,A,B)

Other molecules:

CO, NO, N2 O, OH

Applications of ALI-ARMS non-LTE code

• Radiative cooling/heating rate calculations in the molecular bands in the atmospheres of: - Earth [Kutepov et al., 2007] - Mars [Hartogh et al., 2005].

• Analysis of satellite measurements: - CRISTA-1,2 [Kaufmann, 2002, 2003; Gusev 2006], - SABER [Kutepov et al., 2006; Feofilov et al, 2009].

The SABER instrument aboard the TIMED satellite TIMED: Thermosphere, Ionosphere, Mesosphere Energetics & DynamicsSABER: Sounding of the Atmosphere Using Broadband Emission Radiometry

Latitudinal coverage

Mission launched on December 7, 2001Data available since January 25, 20024 instruments: GUVI, SEE, TIDI, SABER

SABER instrument:• Designed to study the Mesosphere and Lower Thermosphere (MLT).

• Limb scanning infrared radiometer.

• 10 broadband channels (1.2717 µm)

• Products: kinetic temperature, CO2, O3, H2O, NO, O2, OH, O, H.

Bandpass functions of SABER

Temperature retrieval channels

Peculiarities of non-LTE modeling

Example 1:

energy exchange among CO2 isotopes

Energy exchange processes for 15m levels

Radiative excitation and de-excitation

Collisional excitation and de-excitation

Vibrational-translational (VT)energy exchange (N2, O2, O)

Vibrational-vibrational (VV)energy exchange (CO2)

15 m

Isotope 1 Isotope 2

O

O2

N2

VTVV

15 m

CO2 CO2

Temperature retrieval from 15 m CO2 radiance

Retrieval with modified SABER non-LTE model

02-JUL-2002

Peculiarities of non-LTE modeling

Example 2:

adjusting rate coefficients for H2O retrievals

Non-LTE model of H2O

radiative transitionsV-V, V-T processes

O1D

Uncertainties of V-V and V-T rate coefficients

Updating the H2O non-LTE model

• Selecting the correlative dataset that is not sensitive to non-LTE effects: ACE-FTS.• Identifying the set of rates that are important for 6.6m radiance calculation.• Performing the 7x3x3x40=2520 test runs for 40 overlapping mea- surements and calculating 2.

Minimum 2 corresponds to:kV-V{H2O-O2}=1.2 x 10-12 cm3s-1

kV-T{O2-O}=3.3 x 10-12 cm3s-1

kV-T{H2O-M}=1.4 x current rates

Retrievals with updated non-LTE model 2004

2007

SE

SE SS

AE

AE

SS WS

WS

Conclusions

• Broadband infrared molecular emission radiometry is a powerful technique that provides information about atmospheric temperature and composition up to lower thermosphere both for day and night conditions.

• The analysis of this information requires complicated non-LTE models that describe all the processes governing the vibrational levels populations.

• In some cases the reaction rates involved in non-LTE models need verification that can be done using nearly simultaneous measurements (or climatology) made by the instruments that are free of non-LTE effects (lidars, microwave, occultation technique).