.xsc File

RFM File Formats: Molecular Cross-Section Data

12MAR25
Type
Input(s), mandatory if any cross-section molecules used (unless absorption coefficients supplied from look-up tables).

Description
Tabulated cross-section data for one or more heavy molecules (or aerosol extinction [11]).

Filename(s)
Specified in *XSC section of the Driver Table.

Structure
The file is an optional RFM-specific header [1] followed by a set of concatenated [HITRAN format] Data Tabulations.
The HITRAN data tabulation consists of a single header record, followed by data records each containing up to 10 values. All records are 100 characters in length.
File Structure
!CMNT (optional) comment records
*** IDX NTAB [FMT] [WNLSET] [WNUSET] (optional) RFM Header record
Repeat until [eof] Loop over data tabulations
    MOLEC WMIN WMAX NPT TEM PRE [XMAX] [RES] [NAM] [DUM] [BRD] [REF] HITRAN header record [3]
    XSC[1] XSC[2] ... XSC[1]) Formatted data records, 10 values per record, '(10E10.3)'
    XSC[11] XSC[12] ... XSC[20]
    ... XSC[NPT]
[eof] End-of-file

Fields
FieldFormatDescriptionUnits Range
!CMNT A80 Comment record(s) (optional) Record starts with '!'
IDX I7 RFM index for molecule (optional) [6] ≥100
NTAB I10 No.of (p,T) tabulations in dataset >0
FMT A10 File Format (optional) [5] ' ' or 'HITRAN2K'
WNLSET F10.4 Min. Wavenumber of dataset (optional) cm-1 0 ≤ : ≤ WNUSET
WNUSET F10.4 Max. Wavenumber of dataset (optional) cm-1 ≥ WNLSET
MOLEC A20 Chemical Formula (right justified) [7]
WMIN F10.4 Lower Wavenumber of tabulation cm-1 >0
WMAX F10.4 Upper Wavenumber of tabulation cm-1 > WMIN
NPT I7 No. of tabulated points >0
TEM F7.2 Temperature of tabulation K >0
PRE F6.1 Pressure of tabulation Torr ≥ 0 [8]
XMAX E10.3 Max value of XSC [3] cm2/molec 10-17 – 10-20
RES F5.2 Instrument Resolution [3] [9] cm-1 >0
NAM A15 Common name (right justified) [3]
DUM A4 (Reserved for future use) [3] '    '
BRD A3 Broadener (right-justified) [3] 'air', ' N2' or '   ' [4]
REF I3 Index pointing to source of data [3]
XSC[:] E10.3 (NPT) Absorption Cross-Section [10] cm2/molec

Notes
  1. The RFM format is the same as the HITRAN format with the addition of
    (a) initial comment records.
    (b) RFM identifier record (molecule index, wavenumber range)
    While the option to have initial comment records will be maintained as these can be used to provide useful additional information eg on data source, the RFM identifier record is only supported for backward compatibility. You should now use the HITRAN files directly.

  2. The HITRAN data are provided as single files for each (p,T) and spectral band. These have to be concatenated for use in the RFM (see Absorption Cross-sections), which expects a single file for each molecule.

  3. The RFM only reads the HITRAN header variables up to PRE, ie the first 60 characters.

  4. BRD Blank used to indicate measurements made with a pure gas, i.e., self-broadening.

  5. FMT This was originally used to distinguish the current HITRAN format (in use since 2000) from older format files. However, the older files are no longer supported (contact me if you really do need to use these).

  6. IDX The RFM uses an extension of the HITRAN numbering system to provide unique identification for cross-section molecules, with indices starting at 100 (See List of Absorbers). However, in the absence of an RFM header, molecules are now directly identified from the MOLEC field in the HITRAN header and, if not already assigned an index, will be assigned a temporary index on execution.

  7. MOLEC The RFM recognises a variety of names for the same molecule, eg F11, CCl3F, CFCl3, independent of case (See List of Absorbers), although HITRAN now has a single specific name for each molecule. See subroutine molidx_sub.f90 for the RFM's internal list. For the RFM it is also possible to specify an entirely arbitrary name of up to 7 characters — as long as a matching profile is supplied in the *ATM section.

  8. PRE Note that 760 Torr = 1 atmosphere = 101325 Pa. A value of 0 in older data is interpreted as 760.

  9. RES The actual spacing of the data is usually not a number conveniently represented within the 5-character limit of the RES field, so instead, the RFM calculates it from
    Resln = ( WMAX - WMIN ) / ( NPT - 1)
  10. XSC The data values are written with format '(10E10.3)' which, for positive numbers, leaves a space between each field so that the data could be read 'free-format'. However some .xsc files contain small negative numbers, filling the space with the '-' character. So it is safer, and quicker, always to read the data with a format statement.

  11. Aerosol When used for aerosol extinction, the XSC values are is multiplied by the aerosol vertical profile values in the .atm to get the actual extinction [/km], so there is an arbitrary normalisation factor which can be applied to either the cross-section or profile data.

Example
aerosol.xsc (Unit aerosol extinction covering spectral range 1–2500 cm-1)

Bugs
Bug#23 (Fixed RFM v5.10)