# merge.py

Script that contains 3 functions. These are to be used if we want to proceed to merging of thin layers of the firn column. I suggest we specify in json input if merge is true/false and the thickness threshold (‘merge_min’): “merging”: true, “merge_min”: 5e-3 mergesurf(): for layer[0] and layer[1], to be used in time_evolve() of firn_density_nospin mergenotsurf(): for layers[2:], to be used in time_evolve() of firn_density_nospin mergeall(): for all layers, to be used at the end of firn_density_spin CAUTION: - not used for all variables (e.g. du_dx) - nothing is done considering gas neither for isotopes @author: verjans

`merge.``mergeall`(self, thickmin)

  We spot the layers that are under a certain thickness threshold and we merge these with the underlying layer This has to be launched at the end of the spinup, we use other functions in firn_density_nospin. Here we change self.compboxes as we modify the number of layers above 80m depth.

`merge.``mergenotsurf`(self, thickmin)

  This function is to call during time_evolve function of firn_density_nospin. We merge all the layers below a thickness threshold except the layers of indices 0 and 1. This allows layers that became too thin due to compaction to be merged with the layer below. Minimum thickness threshold must be specified as thickmin We don’t do this for surface layer because that would lead to any newly accumulated layer to be merged if RCM forcing is on a short time scale. The surface layer has its own function mergesurf().

`merge.``mergesurf`(self, thickmin)

  This function is to call during time_evolve function of firn_density_nospin. We merge the surface layer[0] with the layer[1] below as long as layer[1] remains under a certain thickness threshold. By applying condition on layer[1] instead of layer[0], we avoid merging all newly accumulated layers in the case we use a RCM forcing on a short time scale. Thickness threshold must be specified and consistent with the one of mergenotsurf().