Changes between Version 29 and Version 30 of Branches/Driver_Improvements

Timestamp:

2016-05-27T18:25:13+02:00 (8 years ago)

Author:

aducharne

Comment:

--

Branches/Driver_Improvements

@@ -28 +28 @@
 - LW should not be interpolated linearly: the mean value over the appropriate interval ([t0,t0+dt] in dim2driver) is the value read at t0+dt ; if we linearly interpolate LW between t0 and t0+dt, the mean value becomes LW(t0)+LW(t0+dt), which is usually different from LW(t0+dt). So if we do a linear interpolation, we change the amount of energy that is received by the surface compared to what is defined in the forcing file. 
 - Apparently, the default behavior in dim2driver is to linearly interpolate LW (using the same interpolation scheme used for the instantaneous variables like Tair). This results from inter_lin=F by default, which induces netrad_cons=F and leads to use a linear interpolation, in contradiction with inter_lin=F. This needs to be double checked by someone, and reported in a ticket if confirmed.
-- The simplest conservative interpolation is to use a uniform function, but it creates "steps". If we wanted to smooth this and remain conservative, we could use a function to constrain the time variations, as it is done with the zenith angle for SW. Based on the physics of LW and the data we have, we could define T4_mean as the mean of Tair^4^  over the 6 (split) dt' in the interpolation period. Then the value of LW(t0+n*dt') = LW(itau_n) * Tair(t0+n*dt')^4^ / T4_mean. I think this is conservative, but it needs to checked.
+- The simplest conservative interpolation is to use a uniform function, but it creates "steps". If we wanted to smooth this and remain conservative, we could use a function to constrain the time variations, as it is done with the zenith angle for SW. Based on the physics of LW and the data we have, we could define T4_mean as the mean of Tair^4^  over the 6 (split) dt' in the interpolation period. Then the value of LW(t0+n*dt') = LW(itau_n) * Tair(t0+n*dt')^4^ / T4_mean. I think this is conservative, but it needs to be checked.
 - Shall we understand that the default spred_prec is one in orchidee_driver ? We recently made a collective choice to take spred_prec=split/2, is it overlooked in orchideedriver?
 - For the SW, what are the low incidence angle problems? It must be kept in mind that there is no particular reason why the diurnal cycle of SW should be either very smooth or well centered at noon. We do not deal with extra-terrestrial radiation, but incident SW  at the surface, and the noise induced by clouds can be very large.
-- Finally, the graphics below remain mysterious to me and I can't see any clear link with the above principles.