MERRA-2 climate reanalysis over the Greenland Ice Sheet subsetted for forcing the Community Firn Model

WHEN USING THESE DATA, PLEASE CITE THE ORIGINAL MERRA-2 DATA! (See citation information below.) This dataset is a subset of MERRA-2 climate reanalysis data over the Greenland Ice Sheet (GrIS) created to provide forcing for the Community Firn Model (CFM; https://doi.org/10.5281/zenodo.3585884). It comprises five (zip) zarr stores, each containing reanalysis data for a decade collated from several MERRA-2 data collections. The spatial grid is the native MERRA-2 grid (0.5° lat x 0.625° lon) but only includes data between 55° and 90° latitude and -80° and -10° longitude. The data is temporally resampled to daily resolution. The files contain variables from four different collections, listed below. The variables are all in the same zarr store, regardless of collection they are taken from (as opposed to the native MERRA-2 formatting, which has different variables in different files.) tavg1_2d_rad_Nx: (doi:10.5067/Q9QMY5PBNV1T) - 'ALBEDO','LWGAB','LWGEM','SWGDN','SWGNT','TS','EMIS' tavg1_2d_int_Nx: (doi:10.5067/Q5GVUVUIVGO7) - 'PRECCU','PRECLS','PRECSN' tavg1_2d_flx_Nx: (doi:10.5067/7MCPBJ41Y0K6) - 'EVAP','HFLUX','EFLUX','GHTSKIN','HLML' tavg1_2d_slv_Nx: (doi:10.5067/VJAFPLI1CSIV) - 'T2M' tavg3_2d_glc_Nx: (doi:10.5067/9ETB4TT5J6US) - 'RUNOFF','ASNOW_GL','SNOMAS_GL' As MERRA-2 does not provide surface melt as an output variable, this dataset contains an estimate of the surface meltwater generated (variable SMELT). This is calucated using the radiation fluxes from MERRA-2 assuming a top layer that is 8 cm thick with a density of 400 kg/m3. With this assumption and using the turbulant fluxes from MERRA-2, the SEB calculation is a 4th-order polynomial that can be solved directly. This caculation provided both the melt flux and a surface temperature estimation (TScalc), which is slightly different than TS from the tavg1_2d_rad_Nx collection. There is also an variable called "EMIS_eff" (effective emissivity), which calculated by: sigma = 5.670374419e-8 lwd_s = sigma * T2M**4 EMIS_eff = LWGAB/lwd_s Although this is a crude estimate, it is helpful in a SEB calculation (as it allows for an estimate of how much longwave radiation is reaching the surface given a 2-m temperature). There are five zarr stores: one for each decade, 1980-01-01 to 2025-06-25. They are subsetted in time this way to keep file sizes reasonable. Note that these are zip zarr stores, which are effectively uncompressed zips of directories. These can be read directly by xarray (i.e., you do not need to unzip them to use them). The CFM repository includes an example script (run_CFM_example.py) and notebook (run_CFM_example_notebook.ipynb) that are configured to use these zarr stores for model runs. Note that you will need to edit file paths in those scripts to ensure that they point to the zarr stores on your system. The script used to create these zarr stores is presently hosted here: https://github.com/maximusjstevens/ATL_masschange/blob/main/MERRA2_subsetter_array.py CITATION INFORMATION: Any use of these data for publication should include reference to the original MERRA-2 data and follow NASA GMAO citation recommendations, which can be found here: https://gs6101-gmao.gsfc.nasa.gov/gmao-products/merra-2/citing-merra-2-data_merra-2/. The DOIs for each collection are listed above for convenience. The MERRA-2 file specifications, which include details about the variables can be found here: https://gmao.gsfc.nasa.gov/pubs/docs/Bosilovich785.pdf.使用本数据集时，请引用原始MERRA-2数据！（引用信息见下文。） 本数据集为专为**社区粒雪模型（Community Firn Model, CFM；https://doi.org/10.5281/zenodo.3585884）**提供强迫场而构建的格陵兰冰盖（Greenland Ice Sheet, GrIS）区域MERRA-2气候再分析数据子集。数据集包含5个压缩式zarr存储包（zip zarr stores），每个存储包整合了多组MERRA-2数据集合的十年期再分析数据。其空间网格采用原生MERRA-2网格（0.5°纬度×0.625°经度），但仅包含纬度55°至90°、经度-80°至-10°范围内的数据。所有数据已被时间重采样至日分辨率。 本数据集包含4个不同数据集合的变量，详情如下。与原生MERRA-2格式（不同文件存储不同变量）不同，无论变量源自哪个数据集合，所有变量均存储于同一个zarr存储包中： tavg1_2d_rad_Nx：（DOI：10.5067/Q9QMY5PBNV1T） - 变量列表：'ALBEDO'、'LWGAB'、'LWGEM'、'SWGDN'、'SWGNT'、'TS'、'EMIS' tavg1_2d_int_Nx：（DOI：10.5067/Q5GVUVUIVGO7） - 变量列表：'PRECCU'、'PRECLS'、'PRECSN' tavg1_2d_flx_Nx：（DOI：10.5067/7MCPBJ41Y0K6） - 变量列表：'EVAP'、'HFLUX'、'EFLUX'、'GHTSKIN'、'HLML' tavg1_2d_slv_Nx：（DOI：10.5067/VJAFPLI1CSIV） - 变量列表：'T2M' tavg3_2d_glc_Nx：（DOI：10.5067/9ETB4TT5J6US） - 变量列表：'RUNOFF'、'ASNOW_GL'、'SNOMAS_GL' 由于MERRA-2未提供表面融水输出变量，本数据集包含地表融水生成量的估算值（变量SMELT）。该估算值基于MERRA-2的辐射通量计算，假设表层粒雪厚度为8 cm、密度为400 kg/m³。结合该假设与MERRA-2的湍流通量，**地表能量平衡（Surface Energy Balance, SEB）**计算采用可直接求解的四阶多项式。该计算可同时输出融水通量与地表温度估算值（TScalc），其与tavg1_2d_rad_Nx集合中的TS略有差异。 此外，本数据集还包含名为`EMIS_eff`（有效发射率，effective emissivity）的变量，其计算公式如下： sigma = 5.670374419e-8 lwd_s = sigma * T2M**4 EMIS_eff = LWGAB / lwd_s 尽管该估算较为粗略，但在SEB计算中颇具实用价值——可基于2米气温估算到达地表的长波辐射量。 本数据集包含5个zarr存储包，分别对应1980年1月1日至2025年6月25日的每一个十年时段。按时间分片存储旨在控制文件体积。需注意，此类zip zarr存储包本质为目录压缩包，可直接通过xarray读取（无需提前解压即可使用）。 CFM代码仓库中包含适配本数据集zarr存储包的示例脚本（run_CFM_example.py）与Jupyter Notebook（run_CFM_example_notebook.ipynb），可用于模型运行。请注意，需修改脚本内的文件路径，使其指向本地系统中的zarr存储包。 用于生成本数据集zarr存储包的脚本目前托管于：https://github.com/maximusjstevens/ATL_masschange/blob/main/MERRA2_subsetter_array.py ### 引用说明 若将本数据集用于学术发表，需同时引用原始MERRA-2数据，并遵循NASA GMAO的引用规范，相关规范可访问：https://gs6101-gmao.gsfc.nasa.gov/gmao-products/merra-2/citing-merra-2-data_merra-2/。为方便查阅，各数据集合的DOI已在上文列出。MERRA-2数据文件规范（含变量详细说明）可访问：https://gmao.gsfc.nasa.gov/pubs/docs/Bosilovich785.pdf。