*APR Section

22JAN25

Type

Optional Section

Description

Change default A Priori settings^[1]

Structure

Multiple, optional PARAM=VALUE fields, any order, generally applicable. Optionally followed by a series of subsections defining parameters for particular retrieved species.

Structure
PARAM=[value]	Applicable to all retrievals
PARAM=[value]
...
RTV1[2]	Applicable to retrieved species RTV1
PARAM=[value]
...
RTV2	Applicable to retrieved species RTV2
PARAM=[value]
...
...	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	100 %
RELAX	R	Relaxation factor		≥0	0.0

Notes

1. The hierarchy for retrieved species RTVi is
   • Use value specified in subsection for RTVi
   • Use value specified in general subsection
   • Use default values (set in module asdcon_dat.f90)

2. RTVn has to be one of RTV items listed in the *RTV section, except that CFCs are referenced only by 'F' number instead of chemical formula.

Example

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

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

   SA_i = SX_i-1*R + SC*(1-R)

   where SA_i is the A Priori covariance used for pixel i, SX_i-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