Changes between Version 14 and Version 15 of Branches/Driver_Improvements

Timestamp:

2016-05-27T08:46:13+02:00 (8 years ago)

Author:

jpolcher

Comment:

--

Branches/Driver_Improvements

@@ -35 +35 @@
 === Jan's understanding of the working of dim2driver (Jan 26/05/2016) ===
 
+It is important to understand that readim2.f90 is written in time steps and not physical time. There are 2 time stepping in the driver :
+- n : is the list of indices of the time axis in the forcing file and readdim2.f90 will step from n-1 to n.
+- itau : is the time stepping of ORCHIDEE and takes 'split' values between n-1 and n.
+
+The readdim2.f90 will then interpolate using values at n-1 and n to obtain the forcing at itauin, which is the current time step of ORCHIDEE. Once itau has stepped through split values the forcing values of n will be copied to n-1 and the new values for n will be read from the netCDF file.
+
+All this is done independently from the physical time for which the values of the forcing at n-1 and n are valid over. This poses no problem for instantaneous variables in the forcing file as then the indexing space (n) and the physical time are identical.
+
+The issue becomes more complicated when we consider fluxes which are averaged over an interval. We can only make the assumption that the time corresponding to index n is within the time interval of the average. But we in readim2.f90 we have no way of knowing if it is at the start, end or anywhere else.
+
 The graphic below explains probably better the above description.
 
 [[Image(Interpolation_dim2driver.jpeg, width=50%)]]
 
-The following changes in nomenclature are used in the figure : t has become Tf and thus the forcing considered is between Tf and Tf+1 for the interpolation toward t'.
 
-The figure is especially meant to illustrate that the interpolation for fluxes assumes that the interval of validity of the fluxes is assumed to be between Tf-1/2 and Tf+1/2 or, t-dt/2 and t+dt/2.
+The figure is especially meant to illustrate that the interpolation for fluxes assumes that the interval of validity of the fluxes at index n is assumed implicitly by readim2.f90 to be between n-1/2 and n+1/2.
 
 == Add an explicit time information within the forcing files ==