ACCESS-ESM-PMIP4

ACCESS-ESM Last Interglacial

The configuration parameters for the Last Interglacial (LIG) should follow the experiment setup in LIG Design.

The configuration for the Last Interglacial Model of ACCESS-ESM is based on the payu version of ACCESS-ESM piControl.

See pre-industrial on how to configure payu.

Differences between piControl and LIG

The differences between piControl and LIG fall in two categories:

Atmospheric

Some concentrations are different between piControl and LIG:

Molecule	pIControl (MMR)	LIG
CO2	4.314801e-04	275 ppm
CH4	4.470459e-07	695 ppb
N2O	4.143596e-07	225 pbb

These values are set in the payu control directory, under Template:Atmosphere/namelists, with the variable names CO2_MMR, CH4MMR, and N2OMMR, respectively. Since ACCESS-ESM expects these values to be in Mass-Mixing Ratio, the desired values have to be converted from ppm/ppb to MMR.

Astronomical

The path of earth around the sun has changed since the last interglacial, so changes have to be accommodated.

Parameter	pIControl	LIG
eccentricity	1.6710222E-02	0.039378
obliquity	0.409092804	24.04°
perihelion-180°	102.94719*PI/180.0	275.41°
Date of vernal equinox	March 21 at noon	March 21 at noon
Time of parahelion passage in days	2.667	170.9046

These specifications are hardcoded in the UM (at least in version 7.3 which we are using for ACCESS-ESM) in the header file include/constant/astron.h.

 

!     ! Eccentricity of the orbit
      Real, Parameter    :: E_DFLT         = 1.6710222E-02
!
!     ! Longitude of the perihelion in radians
      Real, Parameter    :: LPH_DFLT       = 102.94719*PI/180.0
!
!     ! Obliquity of the orbit - corresponds to 23.43929111 degrees
      Real, Parameter    :: OBLQ_DFLT      = 0.409092804
!
!     ! Reference year for setting the date of the vernal equinox
      Integer, Parameter :: YEAR_REF_VE    = 2000
!
!     ! Date of the vernal equinox in days after the start of the year
!     !  This date is for the year 2000.
      Real, Parameter    :: DATE_VE_DFLT   = 79.3159
!
!     The final parameter required is the time of the perihelion
!     passage, TAU0. For a pure Keplerian orbit, with a specified
!     eccentricity and longitude of the perihelion, this can be
!     deduced from the date of the vernal equinox (as is specified
!     in AMIP-2, for example). In practice it is somewhat more
!     complicated to calculate the time of the perihelion.
!     For simplicity, a mean value for the years 1995-2005 is used
!     here: note that the range of TAU0 in this period is from
!     1.0 to 3.75 and that there is no simple relationship with leap
!     years.
!
!     ! Time of the perihelion passage in days
      Real, Parameter    :: TAU0_DFLT      = 2.667

The values were changed to the new values, checked into the repository at https://access-svn.nci.org.au/svn/cmip5/branches/dev/hxw599/pmip, and compiled into the executable /short/public/access-esm/payu/bin/coe/um_hg3.exe-20190412-pmip-r327 (where the r327 stands for the revision number in the subversion repository).