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How can I read data from .nc4 AgMerra files?

You can use Netcdf Extractor for extracting time series from .nc, or .nc4 files. Netcdf Extractor version 2.0 can merge many netcdf4, or netcdf files and extract once.

As you know, AgMERRA dataset has different weather variables, namely mean Temperature, Max and Min Temperature, Precipitation, humidity, wind speed, and sun hour (radiation). All the variables are saved in nc4 files. The name of the AgMERRA file is "AgMERRA_1980_prate.nc4" which is refered to the year of data, name of data and finally, nc4 refers to a type of data in that file. This format of data is readed by MATLAB, ArcGIS, R, Panoply, and Agrimetsoft's products.

For better knowing of the format of data, we should know several tips. NetCDF is a set of software libraries and self-describing, machine-independent data formats for array-oriented scientific data. The first version of the format was developed in the late 1980s at the Unidata Program Center, with the objective of building a file format that would permit sharing of data among atmospheric scientists. It has found use in other scientific communities, with different communities developing discipline-specific conventions. The format was and is designed to be portable, platform-independent, scalable, and appendable. See Notes below for more detail on design objectives.

As of January 2012, there are four variants of the format. The first two, known as Classic and 64-bit Offset, are nearly identical and together are often referred to as netCDF-3. This format description is for netCDF-4, an enhanced format introduced in 2008. Functional shortcomings (significant in some circumstances but not all) of netCDF-3 that led to the development of netCDF-4 include the lack of support for parallel input/output, user-defined data types, or for compression. The "enhanced" netCDF-4 data model is an extension to the classic model (used by netCDF-3). The extension adds more powerful forms of data representation and data types at the expense of some additional complexity. Specifically, it adds six new primitive data types, four kinds of user-defined data types, multiple unlimited dimensions, and groups to organize data hierarchically and provide scopes for names.

NetCDF-4 is a binary format that requires the netCDF or HDF5 software libraries for the data to be accessed and manipulated. However, the ncdump utility that is distributed with the software libraries converts the entire contents of a netCDF-4 file to an ASCII form. NetCDF-4 offers the capability to apply attributes to a file as a whole, to a group within a file, or to any individual variable.


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