For simplicity, let's forget about x and y because you are applying exactly the same calculation at each (x,y) point.
I am attaching an image in which there are four terms that I am trying to compute.
term-1 = d(theta)/d(time) on z depth
term-2 = d(theta)/d(time) on n depth
term-3 = d(z)/d(time) on n depth
term-4 = d(theta)/d(z)
You can calculate terms 1 and 4 on the original z-t grid on Ferret. Between terms 2 and 3, I think term 3 would be easier.
You first 1) calculate the depth of neutral surface, z(n, t), using ZAXREPLACE, 2) calculate ∂z/∂t on the n-t grid, and 3) map this back onto the z-t grid using ZAXREPLACE.
In this way, you'll get terms 1, 3 & 4 on the original z-t grid. Term 2 is just the difference.
In my understanding...
term-1 is the differentiation of theta w.r.t. time and can be calculated as theta[l=@ddc]. However, here I am having confusion that whether the term-1 is a differentiation or linear trend.
or shall I compute the derivatives w.r.t. time and then compute the slope?