routThis README.txt file was generated on 20180704 by Ruza F Ivanovic **DUE TO SIZE THE ZIP FILES ARE SPLIT INTO SMALLER ARCHIVE PARTS** It is important to note that with a “split” archive the individual split files are not valid on their own (i.e. as smaller stand-alone archives). They are only valid when combined together to form a single large archive. Linux - there are generic commands and utilities which facilitate the production of split archives and more general ones to split any type of file into smaller parts. There are similar commands and utilities to join split files to form the original, single file. Windows - the 7-zip utility is particularly useful since, in addition to supporting all popular file archive formats, it also supports splitting an archive into smaller parts, and extracting all files from a “split” archive. ------------------- GENERAL INFORMATION ------------------- 1. TITLE OF DATASET Climate model data presented in “Acceleration of northern ice sheet melt induces AMOC slowdown and northern cooling in simulations of the early last deglaciation" 2. AUTHOR INFORMATION Principal Investigator Contact Information Name: Ruza F. Ivanovic Institution: University of Leeds Email: r.ivanovic@leeds.ac.uk ORCID: orcid.org/0000-0002-7805-6018 Co-investigator Contact Information Name: Lauren J Gregoire Institution: University of Leeds Email: l.j.gregoire@leeds.ac.uk Co-investigator Contact Information Name: Andrew D Wickert Institution: University of Minnesota Email: awickert@umn.edu Co-investigator Contact Information Name: Jerry Mitrovica Institution: Harvard University Email: jxm@eps.harvard.edu 3. HOW TO CITE THIS DATASET / ASSOCIATED PUBLICATION Please cite the publication in which these data are presented: Ivanovic, R. F., Gregoire, L. J., Burke, A., Wickert, A. D., Valdes, P. J., Ng, H. C., et al. (2018). Acceleration of northern ice sheet melt induces AMOC slowdown and northern cooling in simulations of the early last deglaciation. Paleoceanography and Paleoclimatology. https://doi.org/10.1029/2017PA003308 --------------------- DATA & FILE OVERVIEW --------------------- The climate model results were produced using HadCM3 (Unified Model version 4.5) MOSES2.1 with dynamic TRIFFID. Each simulation has a unique 5-letter identifier, which can also be used to access the simulation on the puma.nerc.ac.uk facility. 1. LIST OF SIMULATIONS This dataset contains two HadCM3 climate simulations for which the input boundary conditions (e.g. greenhouse gases, orbit, geography) have been set to 21.0 thousand years BP (ka). One of the simulations is forced with a transient freshwater flux from global ice sheet melting 19-15.5 ka. See the associated publication for a detailed description of the meltwater forcing and associated ice sheet evolution. In this data set, the simulations are labelled as follows: - lgm_control: tecac - hs1: tecad Note that hs1/tecad (the simulation with the transient freshwater forcing) is the main focus of the manuscript. lgm_control/tecac is provided as a useful reference state. The equilibrium-type snapshot simulations briefly described in the manuscript (and shown in Figure S6) are available upon request. 2. FILE STRUCTURE There is one zip file per simulation ('lgm_control', 'hs1'), which contains the following structure of subdirectories: {simulation}.zip |-simulation |-freshwater_forcing |-output_time-series where: {simulation} is: 'lgm_control', 'hs1'. Within each of the sub-directories are files beginning with '{expt}.', where {expt} is: 'teca[cd]', as per the labelling above. There is a further zip file that contains the routed meltwater discharge calculated for ICE-6G_C (VM5a; Peltier et al., 2015, J. Geophys. Res. Solid Earth; see Ivanovic et al., 2017 for details): routed_meltwater.zip |-routed_meltwater Within this directory are two files that contain the ICE-6G_C meltwater discharged to the ocean routed to single point sources (HS1_ICE6GC_fwf-point.nc), and redistributed from these single point sources into the plumes used in the associated manuscript (HS1_ICE6GC_fwf-plume.nc ; e.g. see Figure S3 for this mask). 3. FRESHWATER FORCING FILES The freshwater forcing fields used by the simulations are contained in directories {simulation}/freshwater_forcing/ The files are: {expt}.qrparm.wfix.nc Where {expt} is 'teca[cd]', as above. This contains the freshwater forcing to the ocean surface (kg/m2/s). (Note that the forcing for both simulations includes the standard freshwater forcing from iceberg calving and melting, as present in the pre-industrial.) For lgm_control, the forcing is fixed in time (it is the standard iceberg etc. forcing mentioned above). For hs1, the forcing is transient (it is consistent with the ICE-6G_C ice sheet history 21-15.5 ka and is based on HS1_ICE6GC_fwf-plume.nc, described below). 4. OUTPUT TIME-SERIES FILES In directories {simulation}/output_time-series The files have the following naming convention: {expt}a.variable.timestep.nc Where: {expt} is 'teca[cd]', as above. {variable} is an identified for each specific variable (see section, 5 below). {timestep} is the temporal resolution of the output, either 'annual' or 'monthly'. 5. VARIABLES IN THE OUTPUT_TIME-SERIES FILES For each simulation, each {variable} is as follows: - evap2: total evapotranspiration (kg m-2) - iceconc: sea ice concentration (0-1; where 0 is none and 1 is total cover) - icedepth: sea ice depth (m) - merid: meridional overturning files for Atlantic, Pacific, Indian and Global Ocean basins (Sv) - mslp: air pressure at sea level (Pa) - oceanmixedpf: ocean mixed layer depth (m) - oceansalipf01: ocean salinity in ocean level 1 ((psu-35)/1000) - oceansalipg: ocean salinity at all depths ((psu-35)/1000) - oceantemppf01: ocean potential temperature in ocean level 1 (deg C) - oceantemppg: ocean potential temperature at all depths (deg C) - oceanUMdens: ocean water density and potential density (minus 1000 kg m-3) - oceanuvelpf01: surface ocean zonal (u) component velocity (cm s-1 towards E) - oceanuvelpg: ocean zonal (u) component velocity at all depths (cm s-1 towards E) - oceanvvelpf01: surface ocean meridional (v) component velocity (cm s-1 towards N) - oceanvvelpg: ocean meridional (v) component velocity at all depths (cm s-1 towards N) - precip: monthly total precipitation (kg m-2) - streamFnpf01: horizontal streamfunction (cm3 s-1) - temp2m: air temperature at 1.5 m above the surface (deg K) - u10m: westerly (u) component winds at 10 metres (m s-1, towards E) - u200: westerly (u) component winds at 200 mbar (m s-1, towards E) - u850: westerly (u) component winds at 850 mbar (m s-1, towards E) - v10m: southerly (v) component winds at 10 metres (m s-1, towards N) - v200: southerly (v) component winds at 200 mbar (m s-1, towards N) - v850: southerly (v) component winds at 850 mbar (m s-1, towards N) - vegfrac: fractional covering of functional types (0-1; where 0 is none and 1 is total cover). [z] levels are: 1 = Broadleaf, 2 = Needleleaf, 3 = C3 Grasses, 4 = C4 Grasses, 5 = Shrub, 6 = Urban, 7 = Lakes, 8 = Bare Soil, 9 = Ice - z500: geopotential height at 500 mbar (m) 6. ROUTED MELTWATER FILES As described above, these contain the meltwater discharge used in HS1 given as point sources to the ocean (HS1_ICE6GC_fwf-point.nc) and redistributed into plumes (HS1_ICE6GC_fwf-plume.nc. The plume-discharge is what is used in the associated manuscript and forms the basis for the freshwater forcing file for hs1/tecad (section 3, above). The meltwater discharges are consistent with the ICE-6G_C ice history 21-15.5 ka, run through a high-resolution drainage network model to see where ice melt would flow to the ocean. See the description in section 2.2 of the associated manuscript). The two freshwater forcing files provided here have exactly the same routing and exactly the same meltwater discharge from the ice sheets. The difference between them is where the freshwater is put into the ocean: - HS1_ICE6GC_fwf-point.nc gives the point source data as it was computed by the drainage network model, but gridded onto the HadCM3 ocean grid (1.25 x 1.25 degrees, horizontal resolution). This means that the water enters the ocean in the single ocean grid box that the runoff outlet is located in. The units are m3/s. - HS1_ICE6GC_fwf-plume.nc gives the plume data, where the point-source output has been redistributed over adjacent grid boxes, along the coastline and off the continental shelf (>500 m). Thus the forcing starts with HS1_ICE6GC_fwf-point.nc data, but is then spread-out, which avoids violating the ocean's equation of state in the event of extreme freshening in a rigid-lid ocean model. It also avoids reaching zero salinity and potentially losing some of the forcing. The units are kg/m2/s. NOTE, that the 'discharge' fields in the two files have different units, as above. The data are provided on the HadCM3 21 ka land sea mask (according to ICE6GC). If using a different land-sea mask, ensure that all meltwater forcing is routed to the ocean and not caught in-land. -------------------------- METHODOLOGICAL INFORMATION -------------------------- 1. DESCRIPTION OF THE MODEL USED TO GENERATE THE DATA The data was generated using the Met Office Hadley Centre Coupled Model version 3 (HadCM3) ocean-atmosphere-vegetation general circulation model. The atmosphere has a regular latitude-longitude grid of 2.5° × 3.75° resolution and 19 hybrid sigma-pressure coordinate layers, from the surface up to ~10 hPa. The ocean has a horizontal resolution of 1.25° × 1.25° with 20 vertical layers. The land-surface shceme is MOSES 2.1, and the model has dynamic vegetation (TRIFFID). See the asssociated publication (cited above) for more details. 2. METHODS FOR PROCESSING THE DATA Raw model output (saved at monthly and annual intervals, as described above) was concatenated sequentially to create the timeseries provided in this dataset. Running means can be calcualted from these data, or excerpts can be extracted in order to examine climatological means. 3. SOFTWARE-SPECIFIC INFORMATION NEEDED TO INTERPRET THE DATA The data is provided in Netcdf-3 classic format. This format can be read and plotted to produce maps and other types of plots using software such as Panoply, Ferret, NCL, python, Matlab, IDL...