legacy/src/main/java/ucar/nc2/NetcdfFileWriteable.java
public Attribute addGlobalAttribute(Attribute att) {
    if (!defineMode)
      throw new UnsupportedOperationException("not in define mode");

    if (!N3iosp.isValidNetcdfObjectName(att.getShortName())) {
      String attName = N3iosp.makeValidNetcdfObjectName(att.getShortName());
      log.warn("illegal netCDF-3 attribute name= "+att.getShortName() + " change to "+ attName);
      att = new Attribute(attName, att.getValues());
    }

    return super.addAttribute(null, att);
  }
public Attribute addGlobalAttribute(Attribute att) {
    if (!defineMode)
      throw new UnsupportedOperationException("not in define mode");

    if (!N3iosp.isValidNetcdfObjectName(att.getShortName())) {
      String attName = N3iosp.makeValidNetcdfObjectName(att.getShortName());
      log.warn("illegal netCDF-3 attribute name= "+att.getShortName() + " change to "+ attName);
      att = new Attribute(attName, att.getValues());
    }

    return super.addAttribute(null, att);
  }
Add a Global attribute to the file. Must be in define mode.
@param att the attribute.
@return the created attribute