MITgcm, 36km resolution, Arctic Ocean regional simulation ‘How to’ guide Dr Jonny Williams, School of Geographical Sciences, Bristol University, UK jonny.williams@bristol.ac.uk 1. cd to your MITgcm central directory and check out the code and (some of the) required input files a. cvs co -d cs_36km_tutorial MITgcm_contrib/arctic/cs_36km/ 2. cd to this new directory and make a ‘build’ directory 3. Personally I recommend outputting NetCDF files. You will need to do the following if you want to do this a. add a line with “mnc” on it to cs_36km_tutorial/code/packages.conf b. add a line with “useMNC=.TRUE.,” to cs_36km_tutorial/input/data.pkg c. add a “data.mnc” file which you can copy from the input directory of any of the verification experiments that use NetCDF output 4. Compile in the usual way (system dependent) 5. The following files are all required in the run directory a. the executable you get when compiling “mitgcmuv” b. http://ecco2.jpl.nasa.gov/data2/data/runoff/runoff-360x180x12.bin c. http://ecco2.jpl.nasa.gov/data2/data/atmos/jra25/*1979* i. note that the following files may need their “.txt” suffixes removed 1. jra25_v10m_1979 2. jra25_u10m_1979 3. jra25_spfh2m_1979 4. jra25_temp2m_1979 d. Also, the run requires the following files which are not included in the http://ecco2.jpl.nasa.gov/data2/data/atmos/jra25/ directory (I have simply created cymbolic links to the 1979 equivalents). i. jra25_dlw_1978 ii. jra25_dsw_1978 iii. jra25_rain_1978 e. http://ecco2.jpl.nasa.gov/data1/arctic/run_template2/* 6. There are some duplicate file names in http://ecco2.jpl.nasa.gov/data1/arctic/run_template2/ and cs_36km_tutorial/input and it is crucial that those in the latter are used. I have done this by copying them to my run directory (platform dependent) second to automatically overwrite the other ones. 7. The model also requires several files which need to be renamed and so I have created symbolic links to them. a. ln -s OBWv_arctic_210x192.bin OBWv_arctic_210x192_19792014m.bin b. ln -s OBWu_arctic_210x192.bin OBWu_arctic_210x192_19792014m.bin c. ln -s OBWt_arctic_210x192.stable OBWt_arctic_210x192_19792014m.stable d. ln -s OBWt_arctic_210x192.bin OBWt_arctic_210x192_19792014m.bin e. ln -s OBWs_arctic_210x192.stable OBWs_arctic_210x192_19792014m.stable f. ln -s OBWs_arctic_210x192.bin OBWs_arctic_210x192_19792014m.bin g. ln -s OBNv_arctic_210x192.bin OBNv_arctic_210x192_19792014m.bin h. ln -s OBNu_arctic_210x192.bin OBNu_arctic_210x192_19792014m.bin i. ln -s OBNt_arctic_210x192.stable OBNt_arctic_210x192_19792014m.stable j. ln -s OBNt_arctic_210x192.bin OBNt_arctic_210x192_19792014m.bin k. ln -s OBNs_arctic_210x192.stable OBNs_arctic_210x192_19792014m.stable l. ln -s OBNs_arctic_210x192.bin OBNs_arctic_210x192_19792014m.bin m. ln -s OBEv_arctic_210x192.bin OBEv_arctic_210x192_19792014m.bin n. ln -s OBEu_arctic_210x192.bin OBEu_arctic_210x192_19792014m.bin o. ln -s OBEt_arctic_210x192.stable OBEt_arctic_210x192_19792014m.stable p. ln -s OBEt_arctic_210x192.bin OBEt_arctic_210x192_19792014m.bin q. ln -s OBEs_arctic_210x192.stable OBEs_arctic_210x192_19792014m.stable r. ln -s OBEs_arctic_210x192.bin OBEs_arctic_210x192_19792014m.bin 8. I suggest changing the following in the “data” file just to get you going a. endtime=86400., i. i.e. 1 day in seconds b. dumpFreq = 2400., i. i.e. outputting data on every timestep, i.e. every 40 minutes in seconds 9. Submit the job (platform dependent) 10. Note that the NetCDF output from this simulation will consist of one file for each processor (80 by default here, nPx × nPy in the cs_36km_tutorial/code/SIZE.h file). Acknowledgments Getting this simulation to run would not have been possible without Fanny Monteiro in the author’s home institution, members of the MITgcm-support online community and in particular, Dimitris Menemenlis, Renske Gelderloos and Patrick Heimbach.