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).