New function WeightCells

Hi @nperez

I open this issue for the new function WeightCells() that we talked about a while ago. @erifarov will be in charge of creating this function but I'd like to confirm some details with you first to see if I understand everything correctly.

• The function aims to apply weights to the spatial data, and the weights are calculated from latitude. So, the minimum requirements of the inputs are: (1) data has lat dimension (2) lat should be a vector providing the latitude value (3) lat_dim specifies the lat dim name.

• Is the weight formula wt <- sqrt(cos(lat * pi/180)) (lat is degree)? This is what used in s2dv::ACC and mentioned in the ref* below. I see that in WeightedMean(), the weight is calculated by dlon * dlat * cosphi (line133) I'm not quite sure about the physical meaning of these two methods.

• Is it suitable to have one argument weights to let users put in a prepared weight array?

*ref: https://www.ncl.ucar.edu/Document/Functions/Built-in/eofcov.shtml: "Most frequently, the square root of the cosine of the latitude is used to compute the area weight." wgt = sqrt(cos(lat)) (lat is radian)

Thanks in advance,
An-Chi