Module clim_glacialindex

Module clim_glacialindex loads two climate snapshots (associated with certain periods) and interpolates them using a climate signal and a glacial index approach [1]. It is suitable for paleo-glacier modeling.

For this purpose, we define a function GI (Glacier Index) that maps time \(t\) to a scalar with two extreme states: one state \({\rm CL}_0\) with nearly no ice corresponding to GI=\(0\), and one maximum state \({\rm CL}_1\) in terms of glacier extent corresponding to GI=\(1\). The climate \({\rm CL}\) consists of a set of variables: mean temperature, temperature variability, mean precipitation, and lapse rate:

\[{\rm CL}(t) =(T^{\rm mean}(t),T^{\rm std}(t),P^{\rm mean}(t), {\rm LR}(t)),\]

and is assumed to be a linear combination:

\[{\rm CL}(t) = {\rm GI}(t) \times {\rm CL}_{\rm 1} (t) + (1-{\rm GI}(t)) \times {\rm CL}_{\rm 0} (t),\]

where the two climate states are:

\[\begin{align} {\rm CL}_0(t) & = ( T_0^{\rm mean}(t),T_0^{\rm std}(t),P_0^{\rm mean}(t), {\rm LR}_0(t)), \\ {\rm CL}_1(t) & = ( T_1^{\rm mean}(t),T_1^{\rm std}(t),P_1^{\rm mean}(t), {\rm LR}_1(t)), \end{align}\]

corresponding to GI=\(0\) and GI=\(1\), respectively. Lastly, the GI function is built by linearly rescaling a climate proxy signal so that GI is close to 1 at the ice maximum and close to 0 at the ice minimum. For example, we may use the Antarctica EPICA temperature anomaly signal, which is available for the last 800,000 years.

Note that the two climates \({\rm CL}_0\) and \({\rm CL}_1\) are defined on two different reference topographies. Therefore, it is necessary to correct the temperature for a shift in elevation using a vertical lapse rate between the modeled ice surface elevation and the reference surface.

Contributors: G. Jouvet

Reference: [1] Jouvet, Guillaume, et al. "Coupled climate-glacier modelling of the last glaciation in the Alps." Journal of Glaciology 69.278 (2023): 1956-1970.

Config Structure

clim_glacialindex:
  update_freq: 100
  climate_0_file: data/climate.nc
  climate_1_file: data/climate1.nc
  signal_file: data/GI.dat
  vertical_lapse_rate_0: 6.0
  vertical_lapse_rate_1: 5.74
  temporal_resampling: 12

Parameters

Name	Type	Units	Description	Default Value
update_freq	float	y	Frequency at which to update the climate module	100
climate_0_file	str	dimless	Climate file for glacial index 0	data/climate.nc
climate_1_file	str	dimless	Climate file for glacial index 1	data/climate1.nc
signal_file	str	dimless	Climate signal file for GI	data/GI.dat
vertical_lapse_rate_0	float	^\circC km^{-1}	Vertical lapse rate for glacier index 0	6.0
vertical_lapse_rate_1	float	^\circC km^{-1}	Vertical lapse rate for glacier index 1	5.74
temporal_resampling	int	y^{-1}	Temporal resampling, number of time steps per year	12

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