RFM Driver Table Sections

*DIM Section: Axis Dimensions for Tabulated Absorption Coefficients

06SEP17

Type
Primary Section#6

Description
Variation of *TAN section if TAB Flag enabled.
(*TAN can also be used as the section label)
This page describes the new implementation of the *DIM section from RFM v4.32 onwards.

Format
Generally: Multiple fields, specific order
FieldTypeDescriptionRange
Pressure axis data (mandatory)
Either
'PLV' C*3 Use internal profile levels for pressure axis Case insensitive [available from RFM v4.33 onwards]
Or
'PCG' C*3 Use internal profile CG values for pressure axis Case insensitive [available from RFM v4.33 onwards]
Or
PFILE C*200 Name of a file containing list of pressure axis values File values must be >0 and monotonic
Or
NP I No. points on regular pressure axis >0 (linear intervals), <0 (log intervals)
P1 R*4 Max/Min pressure [mb] for tabulation >0
P2 R*4 Min/Max pressure [mb] for tabulation >0 (only present if |NP| >1)
Temperature axis data (optional, mandatory if VMR axis data required)
Either
TFILE C*200 Name of a file containing list of temperature axis values File values must be monotonic, at least one value ≥0
Or
NT I No. points on regular temperature axis >0
T1 R*4 Max/Min temperature [K] for tabulation ≥0 if Max T
T2 R*4 Min/Max temperature [K] for tabulation ≥0 if Max T (only present if |NT| >1)
VMR axis data (optional)
Either
QFILE C*200 Name of a file containing list of VMR axis values File values must be >0 and monotonic
Or
NQ I No. points on regular VMR axis >0 (linear intervals), <0 (log intervals)
Q1 R*4 Max/Min VMR scaling [%] for tabulation >0
Q2 R*4 Min/Max VMR scaling [%] for tabulation >0 (only present if |NQ| >1)

Notes
  1. The 3-character string 'PLV' as the first field instructs the RFM to set the pressure axis for the tabulation using the pressure levels of the internal profile loaded in the *ATM section.
  2. The 3-character string 'PCG' as the first field instructs the RFM to set the pressure axis for the tabulation using vertical-path Curtis-Godson pressure values of the internal profile loaded in the *ATM section. This set of values is augmented with the maximum and minimum pressure profile values to slightly extend the p-axis range. This option is intended to create a set of p-axis points as close as possible to the actual values that will be required by the RFM when modelling a plane-parallel atmosphere, minimising the interpolation error in the p-domain. Note that the CG values are those evaluated for only the first absorber listed in the *GAS section, so if creating TAB files for multiple absorbers, it is recommended that each is calculated using a separate driver file to ensure the most appropriate CG pressure axis for each.
  3. Other fields are identified by first attempting to open them as if they were a filename
  4. The files are in .tan file format, i.e., optional header followed by a list of numbers, with the additional requirement that the numbers must be monotonically increasing or decreasing
  5. Pressure axis values are in [mb] (=[hPa]). For a regular axis the user can specify uniform increments in pressure (NP>0) or log(p) (NP<0), with |NP| giving the number of points. Linear is recommended for nadir-viewing, logarithmic for limb-viewing.
  6. Temperature axis values are in [K] but may be absolute (identified by all values being +ve), or relative (at least one -ve or zero value). In the second case the axis specifies increments relative to the temperature profile specified in the *ATM section, interpolated to the pressure axis values.
  7. VMR axis values are expressed as percentages of the VMR profile specified in the *ATM section interpolated to the pressure axis values. The absorption coefficient depends on VMR (or partial pressure) due to the difference betweene the Lorentz self-broadening and air-broadening coefficients. However, with the notable exception of tropospheric water vapour, the VMRs are either so small or almost constant (N2,O2) that this dependence is negligible, so in most cases this dimension can be omitted.

Example
*DIM
     pvalues.txt         ! file containing pressure axis values
   11 -50 50             ! relative temperatures -50,-40 ...+50 K
   -3 50 200             ! VMR profile scaled by 0.5, 1.0 and 2.0

Bugs
Bug#104 (Fixed v4.34)
Bug#101 (Fixed v4.34)