Compute MOC south. transport from bottom up

To match changes made in E3SM in
E3SM-Project/E3SM#5170, this merge changes
the transport computation into the southern boundary of an MOC
region to work from the bottom up rather than the top down.

mpas_analysis/ocean/streamfunction_moc.py

@@ -1538,7 +1538,7 @@ def _compute_moc(latBins, nz, latCell, regionCellMask, transportZ,
     """compute meridionally integrated MOC streamfunction"""
 
     mocTop = np.zeros([np.size(latBins), nz + 1])
-    mocTop[0, range(1, nz + 1)] = transportZ.cumsum()
+    mocTop[0, nz-1:-1:-1] = - transportZ[nz-1:-1:-1].cumsum()
     for iLat in range(1, np.size(latBins)):
         indlat = np.logical_and(np.logical_and(
             regionCellMask == 1, latCell >= latBins[iLat - 1]),