ICESHEET 1.0

Comparison of the (a) true and (b) reconstructed topography of the modern Greenland Ice Sheet.Comparison of the (a) true and (b) reconstructed topography of the modern Greenland Ice Sheet, using ICESHEET

This post refers to some hints and tricks to run my ice sheet sheet software, which I called ICESHEET. This was published a few weeks ago in Geoscience Model Development, but due to the chaos of moving and starting a new post-doc in Germany, I have not really had the chance to make some further documentation on it. ICESHEET produces perfectly plastic ice sheets under equilibrium conditions. In reality, ice sheets are probably never in equilibrium, but this is probably the simplest approximation of the form of an ice sheet and not break the laws of physics. For a more rigorous scientific description, I suggest reading the Geoscience Model Development paper, which is open access. You can download the software there, or from the downloads page. In fact, even if you got the download from the Geoscience Model Development, I recommend getting the one from the downloads page, because I forgot to include the shapefiles for the Greenland shear stress (whoops).

Some notes on running this. First off, you need to at a minimum have Generic Mapping Tools, as I make use of it to create the grids and do coordinate transformation so that everything is in Cartesian coordinates. The Greenland sample that is included in the download package also requires some manipulation with Netcdf Tools. I fully recommend using the scripts that I included with the Greenland example, though it is possible to use the program without them as long as you have everything in the correct format.

Here are some steps to getting everything to work. Note that I am assuming you are running Linux or some other Unix based system, have Fortran compilers installed already, and are familiar with the command line.

Compile the programs

The base directory contains all the source code for ICESHEET, plus two additional programs that are used in the scripts. If you are running gfortran, you just need to do this:

make icesheet
make nearest_int
make reduce_dem

If you are running ifort, you have to go into the makefile and uncomment one line that will add a flag that allows the program to read in the binary files. If you decide to put the binaries in another directory (like somewhere in $PATH), you will have to edit the scripts in the later steps to make sure that they can find them.

Basal Shear Stress

The next thing that needs to be done is to set up the basal shear stress files. In the Greenland example, there is a folder called “shear_stress”, everything you need is in there. There are a couple of programs that need to be compiled first, create_ss_grid and convert_grid. Just type

make create_ss_grid
make convert_grid

For the shear stress domains file, you must create them yourself and export them as a polygons csv file. This is pretty easy to do if you use QGIS (open the project file). In the shapefile (which should be formatted as a polygon), you should have a field where you enter the shear stress value in Pascals. Further instructions, from the create_shear_stress_file.sh:

# from QGIS:
# > Open shapefile
# > Layer dropdown menu > save as
# > in the options, change "Symbology Export" to "feature symbology", and "Geometry" as "AS_WKT".
# > Change the CRS to WGS 84, or else it will not export the points as latitude/longitude, if that is desired

Save the file (call it polygons.csv) in the base shear_stress directory, not in the QGIS directory. If you are making your own domains, make sure there are no gaps between your polygons, or it will revert to the default values (set to 50000 Pa). I’d recommend make sure your shear stress model covers the entire domain you are working on.

When you finished with this, run the create_shear_stress_file.sh script, and it will produce a file that will later be used in ICESHEET.

The key to this is that it produces two files, one containing a grid of the shear stress domains, numbered by the polygon ID in QGIS, and another with the relation between those polygon ID numbers and their corresponding shear stress values. The later file (which is called shear_stress_domain_values.txt) can be edited directly, so you don’t have to edit the polygons in QGIS for each configuration you want. Simply run convert_grid again with the edited shear_stress_domain_values.txt file for each run that you want. For my North American ice sheet complex problem, I basically had a file for each time interval I was interested in.

Creating input grids

After creating the shear stress files as above, the next step is to go into the Greenland directory and run convert_grid.sh. Before doing this, you have to download the IceBridge BedMachine Greenland, Version 2 dataset. Extract it in the base directory with the script. Provided you have the programs in the base directory compiled, the script should create an outline text file (outline.xyz), base topography binary (modern_topo.bin) and basal shear stress binary (ss.bin) that are used when running ICESHEET. It also creates text files that are required by ICESHEET to describe the binary files (elev_parameters.txt and ss_parameters.txt). These have the basic format:

binary_filename
min_x
max_x
min_y
max_y
grid_spacing

Note that this script must be run in bash shell (if you are running Debian or its offshoots like Ubuntu, the default shell is dash).

Run ICESHEET

The next step is to run “run.sh”. You can change the settings for the program in this file. In particular, you can change the contour interval and spacing between points along the contour. I have it set to 20 m and 20 km, which should take less than a minute to run on any modern computer. The plot2.sh will automatically create the plot files and put them in the plots directory.

Final remarks

For all of the applications I have used ICESHEET on, I simply have made modifications to the scripts given in the source package. The main thing is that if you are starting from something that is in lat/long (the Greenland example is already in Cartesian coordinates). If you want to run something and are having problems, please feel free to email me (evangowan@gmail.com)! I am more than happy to help out.

Kumamoto Earthquakes (熊本地震)

Wall cracked after the magnitude 7.3 earthquake.

Wall cracked after the magnitude 7.3 earthquake.

Kumamoto, a place that I consider to be my second home, has been hit by a barrage of earthquakes. It is one thing to go through one major earthquake, but Kumamoto was hit by four earthquakes measuring higher than magnitude 5.5 over two days. Just over a week on, and the frequency of earthquakes has diminished. There has been over 1000 earthquakes that were measurable in the  Japanese shindo (shaking) scale (1-7) since the first one on the evening of April 14th. Both the the first earthquake and the major magnitude 7 earthquake had a peak shindo rating of 7. Only a handful of earthquakes in Japan have reached this quantification since they started using it in 1923.

I have to admit, as someone who has spent a lot of time studying geophysics, including earthquake seismology, I did want to experience what a big earthquake is like. After the first one, I found out. It was like being in the box of a mosh pit. It feels like people are pushing you around in all different directions. We were on the second floor of an apartment, which may have amplified this kind of feeling. I’ll admit, it was kind of exciting. After the second big earthquake (about half an hour later), I was kind of thinking that I could do without feeling more earthquakes. By the time that one came, we were outdoors in an open parking lot. Continue reading

Model of the western Laurentide Ice Sheet

I started my PHD in July 2010. On March 12, 2016, the paper that summarizes over five years of work was finally published. Before going on what it is about, you can download your own copy of the paper from this link until May 1st. After that, it is behind a paywall, but feel free to email me if you want a copy. I am always happy to help out, don’t be shy!

A childhood dream

When I was a kid, I was totally obsessed with Earth sciences. I had notebooks full of dinosaur names and facts. I had a big rock collection! I completely wanted to be a geologist or paleontologist when I grew up. When my parents went on a trip to Las Vegas, the gift they got me was a collection of “The rocks and minerals of Nevada” (I actually still have that). Sometime after the age of about 8 or 9, I sort of grew out of those ideas.

I didn’t really get back into the Earth sciences until I randomly took an introductory geology course as an undergrad student as an elective. I was completely enthralled, and remembered the love I had of the Earth that I had as a kid. The class was taught by Jim Teller, an expert on glacial Lake Agassiz.

DSC04573

Upper Campbell strandline, the “Arden Ridge”, Arden, Mantoba

When I was growing up, I went to school on top of one of the largest features in the post-glacial landscape in North America – the Upper Campbell strandline. It formed when there was a large lake known as Lake Agassiz at the south end of the Laurentide Ice sheet. This lake existed because the natural northward flow of water was blocked by the ice sheet. When I was a kid, I played in the gravel pits of this wave sculpted piece of the ancestral Assiniboine River delta, finding interesting rocks and fossils. I always wondered, how did this come to be? Of course, everyone here knew that this was the shoreline of Lake Agassiz, locally known as the Arden Ridge. I knew the Arden Ridge stretched way to the south, and that you could drive a long way to the south on top of it. I remembered the dip in topography just behind our elementary school. I always thought this was really odd. I also wondered why there was another ridge about 1 km to the east, and other smaller ridges further on the road to my parents’ house.

So I went to Australia, and found out about these things. Continue reading

2016 – It’s getting better

IMG_1416-croppedIn Japan, there is this concept called honne and tatemae (本音 and 建前), where you keep your true thoughts to yourself (honne), and project yourself in a more pleasant manner (tatemae). This concept is pretty hard to grasp for a Canadian, where we tend to wallow in our in our (real or imagined) misery. Living in Japan, this is one of the hardest things to get used to. Even simple the simple everyday complaining that I do can be interpreted as a huge grievance.

If I am to live in Japan, even part time, I think it is a must to adjust to honne and tatemae. This is my new year’s resolution that I vaguely made mention of last time. Anyways, here are some notes. Continue reading

Electoral Reform in Canada

2015 has come to an end, and it has been an up and down year for me. I plan on elaborating on this in another post, but I’ll just say for now that posting more on my blog will be a part of what I hope will be a better 2016.

2016 is here, and for the Canadian federal Liberal government, electoral reform is on the docket. Indeed, if the Liberals are serious about this issue, they could make a lasting impact on our democracy, and change how politics are done in our country. However, electoral reform is not really something that is advocated by entrenched parties that have benefited from the current electoral system. So why is electoral reform being pursued? Let’s have a look. Continue reading

State of the World, December 2015

Those who know me are well aware that I usually am pretty tuned into the affairs of the world, and am not afraid of making my views know. Since I finished my PHD, I’ve struggled to deal with the flux of my life, and therefore have stayed further and further from discussing these manners.

But make no mistake, I am paying attention. And it depresses me. Continue reading

Canadian Election 2015

Anyone who knows me knows that I always make a list of observations prior to the Canadian election. Since I no longer live in Canada (but can still vote, because I had to maintain residency during my PHD so the new 5 year rule does not apply), I have been a bit disconnected to the happenings in the run-up to the election. Much of this has been deliberate – the actions of the federal government during the past five years has not been exactly friendly to science (especially climate scientists). I need to mail in the ballot soon, so time to start thinking. Continue reading