Purpose of your product: Freshwater discharge. Part mass balance. Part fjord ecology.
Geographic region: Greenland
Upstream
Citterio & Ahlstrøm basins
What upstream mask product did you use? Citterio & Ahlstrøm (2013)
Reason for using this mask
used the PROMICE product as the base mask because that was estimated to be the “truest” representation of the glaciated area of Greenland, including small peripheral glaciers.
- Effort required by you if upstream product changed (to a community standard)
The effort to change masks in a future release is trivial - probably a few days of effort for testing and documenting the changes. The downstream effects should be negligible, as this is a dynamic product that updates every few years - not just extended time series, but using the latest BedMachine for example, which changes location and number of outlets. Therefore, downstream users are cautioned to use a programmatic interface and not expect stability between product versions.
- If you used internal basins, which product and why?
N/A
- Type: vector
- Resolution if raster:
Vector digitized to 100 m because that's the resolution of the ArcticDEM product used for sub-aerial off-ice surface routing. That resolution appeared to correctly route all terrestrial streams when comparing with streams visible in Google Earth satellite imagery.
- Projection information:
- EPSG: EPSG:3413
- PROJ: `+proj=stere +lat_0=90 +lat_ts=70 +lon_0`-45 +x0=0 +y0=0 +datum=WGS84 +units=m +nodefs +type=crs=
- WKT:
```
PROJCRS["WGS 84 / NSIDC Sea Ice Polar Stereographic North",
BASEGEOGCRS["WGS 84",
ENSEMBLE["World Geodetic System 1984 ensemble",
MEMBER["World Geodetic System 1984 (Transit)"],
MEMBER["World Geodetic System 1984 (G730)"],
MEMBER["World Geodetic System 1984 (G873)"],
MEMBER["World Geodetic System 1984 (G1150)"],
MEMBER["World Geodetic System 1984 (G1674)"],
MEMBER["World Geodetic System 1984 (G1762)"],
MEMBER["World Geodetic System 1984 (G2139)"],
ELLIPSOID["WGS 84",6378137,298.257223563,
LENGTHUNIT["metre",1]],
ENSEMBLEACCURACY[2.0]],
PRIMEM["Greenwich",0,
ANGLEUNIT["degree",0.0174532925199433]],
ID["EPSG",4326]],
CONVERSION["US NSIDC Sea Ice polar stereographic north",
METHOD["Polar Stereographic (variant B)",
ID["EPSG",9829]],
PARAMETER["Latitude of standard parallel",70,
ANGLEUNIT["degree",0.0174532925199433],
ID["EPSG",8832]],
PARAMETER["Longitude of origin",-45,
ANGLEUNIT["degree",0.0174532925199433],
ID["EPSG",8833]],
PARAMETER["False easting",0,
LENGTHUNIT["metre",1],
ID["EPSG",8806]],
PARAMETER["False northing",0,
LENGTHUNIT["metre",1],
ID["EPSG",8807]]],
CS[Cartesian,2],
AXIS["easting (X)",south,
MERIDIAN[45,
ANGLEUNIT["degree",0.0174532925199433]],
ORDER[1],
LENGTHUNIT["metre",1]],
AXIS["northing (Y)",south,
MERIDIAN[135,
ANGLEUNIT["degree",0.0174532925199433]],
ORDER[2],
LENGTHUNIT["metre",1]],
USAGE[
SCOPE["Polar research."],
AREA["Northern hemisphere - north of 60°N onshore and offshore, including Arctic."],
BBOX[60,-180,90,180]],
ID["EPSG",3413]]
```
## MAR and RACMO
- What upstream mask product did you use? MAR, RACMO, and HIRHAM
- Reason for using this mask
Although the bask mask was Citterio & Ahlstrøm (2013), the bulk of the inputs were from the HIRHAM, MAR, and RACMO RCMs, and significant work was spent aligning these three, and adjusting to match ‘reality’ as defined by : cropping and scaling down RCM pixels that were only partially glaciated, or extrapolating RCM values into neighboring cells that were not glaciated in the RCM but were glaciated in .
- Effort required by you if upstream product changed (to a community standard)
A few days to re-validate workflow.
- Type: Rasters
- Resolution if raster: 1 km
- Projection information: EPSG:3413
## HIRHAM
- What upstream mask product did you use? HIRHAM
- Projection information
Working with HIRHAM took a lot of extra effort because it's native format is 'rotated pole' with Greenland near the equator. If it is reprojected to EPSG:3413, significant aliasing occurs. Therefore, it was easier to reproject the vectorized hydrologic basins to the HIRHAM domain. This work is fully documented in (both the publication and the online digital workbooks that contain everything that went into the work), but that work is ~5 years old, and the specific reasons for the decisions around HIRHAM are not well remembered at this point.
# Downstream
Output is a vector product of stream discharge locations. There is no mask. Metadata provides the nearest internal ice basin for each stream outlet for a variety of products (e.g. Zwally basin, Mouginot basin and sector, Rignot region, etc.)
# Other notes
This work also assumed subglacial routing, which required the use of the BedMachine bed and a surface DEM to estimate ice thickness. Because the ArcticDEM surface DEM was different than both and BedMachine, hydraulic “jumps” occurred at the ice edge when streams transitioned from subglacial to subaerial. We could not use the BedMachine surface because we need a DEM at higher than 250 m resolution when off-ice for sub-aerial stream routing.
Overview
Upstream
Citterio & Ahlstrøm basins
What upstream mask product did you use? Citterio & Ahlstrøm (2013)
Reason for using this mask