MT_CKD Continuum Model
Date: August 2017
- New self continnum coeffients in window regions for wavenumbers greater than 2000 cm-1 were added and
self continuum temperature dependence from 1800-3500 cm-1 were updated
(E.J. Mlawer, M.J. Alvarado, K.E. Cady-Pereira).
Date: July 2017 (not publicly released)
- Collision-induced absorption in the oxygen A-band was added
(E.J. Mlawer, D. Gombos, V.H. Payne, B. Drouin, K.E. Cady-Pereira).
Date: December 2016
- Includes modifications to H2O foreign continuum coefficients in the
far-infrared based on the analysis of REFIR-PAD (Bianchini and Palchetti, 2008)
measurements taken at Cerro Toco, Chile, as part of the ARM RHUBC-II campaign and a
re-analysis of the AERI-ER measurements from the ARM NSA site (first analyzed
in Delamere et al., (2010)).
- The foreign continuum was also changed in the sub-millimeter and microwave regions as
a result of the analysis of SAO FTS (Paine and Turner,
2013) measurements taken during the RHUBC-II campaign, which led to modification
of the H2O self continuum in this region to maintain good agreement with the
microwave measurements analyzed in Payne et al. (2008 and 2011). (E.J. Mlawer, D.D.
Turner, S.N. Paine, V.H. Payne)
Recent changes have been evaluated with
RHUBC-I and RHUBC-II data .
Date: July 2016
- A number of changes were made to water vapor continuum absorption in the window past the fundamental H2O band (E.J. Mlawer, M.J. Alvarado):
- Self continuum coefficients were modified from 1880-2390 cm-1 to fix issues in the CO fundamental region that were pointed out by Alvarado et al. (2013).
- Foreign continuum coefficients from 1800-3000 cm-1 were modified to improve agreement with Baranov and Lafferty (2012); in the 1900-2150 cm-1 region, attention was
also paid to IASI measurements (Alvarado et al., 2013).
- Coefficients for N2-H2O relative efficiency from 2000-2900 cm-1 were determined from Baranov and Lafferty simultaneously with
the H2O foreign and self continuum coefficients in this region (as described above).
- Foreign continuum coefficients at wavenumbers greater than 4000 cm-1 were modified based on Baranov and Lafferty (2012) and Mondelain et al. (2014) measurements
(E.J. Mlawer and M.J. Alvarado).
Date: February 2016
- Added N2 collision-induced first overtone (E.J. Mlawer, D. Gombos).
- Fixed bug in calculation of temperature analytic Jacobians (E.J. Mlawer, K.E. Cady-Pereira).
Date: January 2011
- Added ‘if’ tests needed for speed improvements in monortm (K. E. Cady-Pereira, E.J. Mlawer)
- Other software updates include:
- In N2 pure rotation band, fixed incorrect indexing related to contribution from N2-O2 (E.J. Mlawer, A.E. Lipton, V.H. Payne)
- Increased number of output points in all continuum modules to
prevent possible truncation at high wavenumber end (E.J. Mlawer, S.A.
Clough, C.H. Kohler)
- Near-IR O2 continuum to allow for calculations over domains greater
than 2000 cm-1; needed by standalone continuum code (E.J. Mlawer, P.
- O2 fundamental to correct 5 cm-1 shift (E.J. Mlawer, S.A. Clough, C.H. Kohler)
- Rayleigh is now computed for IAERSL=5 (E.J. Mlawer, K.E. Cady-Pereira)
- Corrected coding issue related to pure water vapor atmospheres in stand-alone continuum model (E.J. Mlawer).
- Updated historical information (E.J. Mlawer, V.H. Payne)
- Modified directory structure for source codes, makefiles, and documentation.
- Added makefile system to compile the stand-alone continuum model. Includes new platforms such as Windows and capability
to easily add new platforms.
Date: January 2010
- MT_CKD_2.5 continuum modifications included in this release are
based on analyses of IASI, AIRS, and AERI measurements in the region
past the bandhead of the CO2 v3 band (~2385 cm-1):
- Introduction of temperature dependence of CO2 continuum absorption from 2386-2434 cm-1 based on line shape calculations; validated with IASI measurements (E.J. Mlawer and V.H. Payne)
- Modification of CO2 continuum coefficients from 2000-3000 cm-1 from IASI and AERI (from ARM) measurements (E.J. Mlawer, V.H. Payne, and M.W. Shephard)
- Modification of water vapor self continuum coefficients from 2000-3200 cm-1 from
IASI and AIRS measurements; fit based on near-IR studies of Bicknell et
al. (2006) and Fulghum and Tilleman (1991) (E.J. Mlawer and V.H.
Date: June 2009
Modifications to the water vapor continuum
arise from new analyses of ARM measurements in the microwave and far-IR
regions (S.A. Clough, J. Delamere, V.H. Payne, E.J. Mlawer)
Analyses of measurements in the microwave are based
primarily on the two-channel MWR (23.8 and 31.4 GHz) at SGP, with supporting
evidence from 150 GHz MWRHF measurements during the COPS campaign and from
170 GHz GVRP measurements at SGP (Payne et al., 2009).
Measurements in the far-IR were from the AERI_ext
at the NSA site, in the time surrounding and including the RHUBC-I campaign
(Delamere et al., 2009).
Solved the issue of N2 Jacobians being included in
the Jacobians generated for other molecules (MT_CKD_2.2)(S.A. Clough and
Fixed an issue with the water vapor Jacobians in
which the analytic Jacobians were dependent on the starting wavenumber
(MT_CKD_2.3)(K.E. Cady-Pereira and S. Tjemkes)
Date: November, 2007
1) CO2: Fundamental change in the
lblrtm fourth function with consequent changes in continuum.
2) Bug fix impacting the nitrogen continuum in
the 0-350 cm-1 region.
Date: September 2007
1) CO2: Based on Hartmann P-Q-R line mixing.
Modification to v3 band based on AIRS data. (July 2007)
2) H2O foreign modified in 250-550 cm-1 region
based on analyses of nsa aeri_xr data. (September 2007)
Date: May 2006
1) Nu2 CO2: with P-R line mixing included; factor
of 7 increase has been reduceed to 4.5
1) MT_CKD_1.2 includes a modification to the collision
induced absorption by N2 in the 0-350 cm-1 regime, Boissoles et al.
2) The structure of cntnm_progr.f has been altered
somewhat to ensure closer correlation betweem this continuum program and
the continuum used in lblrtm. The actual continuum module, contnm.f,
is introduced into the present program with an include statement.
The contnm.f module is that archived with lblrtm.
1) Made a correction for to the input units for the path
2) Allows for the input of water VMR (with respect to total air, not
3) Made the code cosistent with the continuum in LBLRTM_v_8.4
This is the initial release of the MT_CKD water vapor continuum and
represents the first recomputation of the entire self and foreign
broadened continuum since the original model was developed in the
1980s. This version of the continuum is implemented in the line-by-line
model LBLRTM v7.0 and will be utilized in all related AER Radiative
The MT_CKD continuum is based on a new formulation: The self and foreign
continuum models are each based on the contributions from two components:
a collision induced component and a line shape component. This change
in perspective has resulted from the difficulty in developing a line shape
model based on sound physics that explains the magnitude of the increased
absorption in the intermediate wing over that provided by the impact
These two components are applied consistently to all water vapor lines
from the microwave to the visible, and the results summed to obtain self
and foreign continuum coefficients from 0-20,000 cm-1. Eight and
seven parameters are needed to specify the two components for the
self and foreign continua, respectively, which are sufficient to
generate the entire continuum spectrum over this spectral domain.
The ratio of the self continuum at 296 K to that at 260 K has been
kept the same as in the CKD model. The only temperature dependence
for the foreign continuum arises from the radiation term as with
CKD. The MT_CKD model as with CKD, should be regarded as a
semi empirical model with strong constraints provided by the known
The data that have been used to develop the new continuum model has
come predominantly from spectral atmospheric measurements.
Only cases for which the characterization of the atmospheric state
has been highly scrutinized have been used. This new model
has been developed by E.J. Mlawer, D.C. Tobin and S.A. Clough building
on the original CKD formulation; hence the name MT_CKD.
In this release only the stand alone program,
is being provided. The driver for this program has been changed slightly
so that pressure, temperature and path length may be entered as input.
A negative value for the pressure provides a default result from
0 - 5000 cm-1 with P = 1013 mb, T = 296 k and X (path) = 1 cm.
In addition to the original version of ckd_0, there are three updated
versions of ckd available with the release dates indicated:
ckd_2.2.2 1996_12; rev 1999_06
ckd_2.2.2 1996_12; rev 1999_06
These models with associated readme files are contained in the directories
associated with the continuum. Information on the nature of the modifications
is contained in the respective readme files. The continuum module
and associated continuum program (_program_) are very similar except
that the latter includes a driver and a small modification has been
made in 'SUBROUTINE CONTNM' to provide the appropriate interface.
The main substance of the code are data statements which are not
only identical between continuum module and program, but up to this
point are similar between the three evolutionary versions of the CKD continnum
Remarks on implementing the stand alone program are contained in comments
in the main progam: 'drcntnm' (driver for continuum). The program
provides the following output files:
WATER.COEF - the mt_ckd_# self and foreign broadened water continuum
CNTNM.OPTDPT - continuum optical depths for the defined path.
****** It should be noted that the MT_CKD water vapor continuum
****** spans the spectral domain from 0 - 20,000 cm-1 (inf
- 500 nm).
Atmospheric and Environmental Research