*APR Section

21OCT24
Type
Optional Section

Description
Change default A Priori settings

Structure
Multiple, optional PARAMETER=VALUE fields, any order. Optionally followed by a series of subsections defining parameters for particular retrieved species.
Structure
PARAM1=VALUE Applicable to all retrievals
PARAM2=VALUE ... etc
RTV1 A retrieved species
    PARAM1=VALUE Applicable to RTV1
    PARAM2=VALUE ... etc
RTV2 Another retrieved species
    PARAM=VALUE Applicable to RTV2
    PARAM2=VALUE ... etc
... etc

Parameter Type Description Units Range Default
CORREL R Correlation length km ≥0 50 km
ABS_SD R Absolute SD [various] ≥0 10 K
PCT_SD R Percentage SD % ≥0 10 K
RELAX R Relaxation factor ≥0 0.0

Notes
  1. Default values are set in module asdcon_dat.f90
  2. [gas] has to be given as 'F' number for CFCs, formula for other species

Example 
*ASD
    CORREL=0 ! Uncorrelated A Priori
    CH4=10   ! Change CH4 to 10% uncertainty

*ACV Section (Optional)

Description
Specify A Priori Covariance
Still need to think about this for new MORSE

Format
Optional PARAMETER=VALUE records, arbitrary order
Field Type Description Range
ACVFIL= ACVFIL C200 [optional] A Priori Covariance Matrix 0-1
RELAX= RELAX R [optional] Relaxation parameter 0

Notes
  1. This section can be used either to specify a more complicated climatological a priori covariance than can be set by the *ASD section, and/or incorporate the previously retrieved covariance as part of a Kalman filter along the orbit.
  2. The A Priori Covariance file only applies to the main target parameters, ie excluding continuum and offset, and is in the same format as morse.cov (or morse.acv) output by the COV Flag. The only check on the file is to make sure that the matrix dimensions agree with the current retrieval.
  3. The relaxation parameter RELAX[R] is defined as
    SAi = SXi-1*R + SC*(1-R)
    where SAi is the A Priori covariance used for pixel i, SXi-1 is the Retrieved covariance from the previous pixel, and SC is the climatological covariance constructed in the same way as the default a priori (including modifications in the *ASD section). A value RELAX=0.0 (which is the default) means that the specified A Priori covariance is used exactly as supplied, a value RELAX=0.1 implies relaxing to climatological covariance with a 1/e time constant equivalent to 10 scans, 0.01 is a hundred scans, etc.

Example 
*ACV
    ACVFIL=morse.cov   ! Use previous output covariance
    relax=0.05  ! Climiatological relaxation length: 20 profiles, or ~1/4 orbit
-->