legacy/src/main/java/ucar/nc2/NetcdfFileWriteable.java
public void addVariableAttribute(String varName, String attName, String value) {
    addVariableAttribute(varName, new Attribute(attName, value));
  }
public void addVariableAttribute(String varName, String attName, String value) {
    addVariableAttribute(varName, new Attribute(attName, value));
  }
Add an attribute of type String to the named Variable. Must be in define mode.

@param varName name of variable. must already have been added to the file.
@param attName name of attribute.
@param value   String value of atribute.