MT_CKD Continuum Model


Date: August 2017


Date: July 2017 (not publicly released)


Date: December 2016

Recent changes have been evaluated with RHUBC-I and RHUBC-II data .


Date: July 2016


Date: February 2016


Date: January 2011


Date: January 2010


Date: June 2009


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

MT_CKD_1.2 (cntnm_progr_v1.3)

September, 2004

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. (2003).

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.

MT_CKD_1.00 (cntnm_progr_v1.1)

May, 2004

1) Made a correction for to the input units for the path length
   (S.A. Clough)

2) Allows for the input of water VMR (with respect to total air, not dry air)
   (S.A. Clough)

3) Made the code cosistent with the continuum in LBLRTM_v_8.4
   (S.A. Clough)

MT_CKD_1.00 (cntnm_progr_v1.0)

February, 2003

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  Transfer models.

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  approximation.

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 physics.

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_2.4.2     2002_08

ckd_2.4.1     2000_05

ckd_2.2.2     1996_12; rev 1999_06

ckd_0         1989

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 models.

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 coefficients.

CNTNM.OPTDPT - continuum optical depths for the defined path.

******   It should be noted that the MT_CKD water vapor continuum model
******   spans the spectral domain from 0 - 20,000 cm-1 (inf - 500 nm).

Atmospheric and Environmental Research