elementArea field in mesh files has wrong units

[anton-seaice]

It looks like we should be using units of radians^2 for elementArea for in ESMF unstructed mesh files.

e.g.

     double elementArea(elementCount) ;
            elementArea:units = "radians^2" ;
            elementArea:long_name = "area weights" ;

See:

https://earthsystemmodeling.org/docs/release/ESMF_8_0_1/ESMF_refdoc/node3.html#SECTION03028200000000000000

Saying that, we are not currently using this field. e.g.

https://github.com/CICE-Consortium/CICE/blob/3ebdef778bded4b10d628a179ea746d091e21150/cicecore/drivers/nuopc/cmeps/ice_comp_nuopc.F90#L732-L733

would need another argument ( addUserArea = .true. ) to actually load this. (See COSIMA/access-om3#240)

It also looks like the cells at the north poles on the grid, should be using numElementConn = 3 , not 4.

i.e.

elementConn can be either a 2D array or a 1D array. If it is a 2D array, the second dimension of the elementConn variable has to be the size of the largest number of nodes in any element (i.e. maxNodePElement), the actual number of nodes in an element is given by the numElementConn variable.

Presumable the last element in the elementConn field is set the the _FillValue when there are only three corners to an element

 int elementConn(elementCount, maxNodePElement) ;
            elementConn:long_name = "Node Indices that define the element /
                                     connectivity";
            elementConn:_FillValue = -1 ;
            elementConn:start_index = 1 ;