DOI: 10.5281/zenodo.1134979
title: Model Output For: Rate Of Mass Loss Across The Instability Threshold For Thwaites Glacier Determines Rate Of Mass Loss For Entire Basin

description: <strong>Results from “Rate of mass loss across the instability threshold for Thwaites Glacier determines rate of mass loss for entire basin.”</strong>

The tar files herein contain multi-resolution grounding line position data and 4 km resolution output of modeled fields for all model runs. The region of interest represented is the Thwaites catchment in West Antarctica. The files for modeled fields have been coarsened or “flattened” to 4 km from their original adaptive mesh refinement (AMR) structure.

Metadata contents

<em>1. Grounding line position data – text files</em>

<em>2. Modeled Fields – HDF5 files</em>

<em>3. BISICLES grid and coordinate system</em>

 

<em>1. Grounding line position data</em>

Tar Files with "GLposition" in the title contain the annual grounding line positions, at cell faces, over the discretized Thwaites catchment for the specified model run. Each tar file contains a series of text files for a particular model run that used a specific background melt rate. The background marine melt rate is specified in the third field of the tar file name as delimited by the underscore character (“_”). Additionally, the last year of anomalous forcing before it was turned off leaving only the background marine melting is listed in the third field.

nonuniformMM indicates the non-uniform background marine melting.

uniformMM indicates the uniform background marine melting.

260 and 270 are the last model years where anomalous marine melting were applied.

After untarring a file, the naming convention for the individual text files is seen to be similar to the name of the respective tar file. The first field as delimeted by the underscore character contains either “glnonMM” or “gluniMM” followed by the last year of anomalous forcing used; e.g “gluniMM260”. The second field indicates the model year. Note that the last year forced is included for all runs.

The text files contain three columns of data: an indicator of model resolution followed by <em>x- </em>and<em> y-</em>coordinates, respectively. Location coordinate units are meters and are BISICLES physical coordinates (see 3. BISICLES grid and coordinate system).

For the first column:

1 is 2 km resolution

2 is 1 km resolution

3 is 500 m resolution

4 is 250 m resolution

Zero (0) would be the base resolution of 4 km, however, all grounded ice was tagged to refine to level 1 so it does not appear in these files. Additionally, if a region was refined at a high resolution, then the grounding line positions for this region are not reported at any lower resolutions below this.

 

<em>2. Modeled fields</em>

Modeled fields are 4 km resolution in Chombo HDF5 file format. Each tar file contains the annual data as individual HDF5 files for the specified model run. The second field of the tar file as delimited by the underscore character specifies the background melt rate used and the last year of anomalous marine forcing (ramp).

NonUniformMM260 indicates the non-uniform background marine melt rate with ramp shutoff after year 260.

NonUniformMM270 same as above but ramp shutoff at year 270

UniformMM260 indicates the spatially uniform background marine melt rate with ramp shutoff after year 270

UniformMM270 same as above but ramp shutoff at year 270

HDF5 files: The third field as delimited by the period (“.”) character shows the background melt rate used in individual HDF5 files and the fifth field indicates the model year.

Contents of HDF5 files (field name: variable)

xVel: velocity in the direction of the x-axis (m/a)

yVel: velocity in the direction of the y-axis (m/a)

Z_surface: upper ice surface elevation (masl)

Z_bottom: underside surface ice elevation (masl)

Z_base: bed elevation (masl)

basal_friction: Basal friction coefficients

div_uh: mass divergence

mask: differentiates physical setting of cells (Note that coarsening introduces averages of numbers below at interfaces)

                          grounded ice = 1

                          floating ice = 2

                          ocean = 4

                          rock = 8

basalThicknessSource: melt rate (m/a)

surfaceThicknessSource: accumulation rate (m/a)

surfaceThicknessBalance: sum of melt rate and accumulation rate (m/a)

 

<em>3. BISICLES grid and coordinate system</em>

The BISICLES model uses cell-centered grids with each cell represented by (i, j) pairs that begin numbering at (0,0) typically in the lower left hand corner of a domain. This project maintained the number ordering for the continental dataset such that (i = 366, j = 561) is the lower left cell for the included 4 km resolution HDF5 files and (i = 504, j=732) is the upper right cell. As the resolution is 4 km, this is noted as dx = 4000 in the HDF5 files.

Since the data is located at cell centers, the physical coordinates relative to the BISICLES grid for a variable at (i, j) in meters is:

(dx*(i + 0.5), dx*(j + 0.5)) = (BISICLES_X, BISICLES_Y)

where dx is the cell resolution

The translation from BISICLES physical coordinates (m) to polar stereographic projection in meters (standard parallel at -71 degrees) is as follows:

(BISICLES_X – 3071500, BISICLES_Y – 3072500)

<br>
 

<br>
 

<br>
 

<br>