Changes between Version 107 and Version 108 of Documentation/TrunkFunctionality4

Timestamp:

2021-09-28T17:47:45+02:00 (3 years ago)

Author:

luyssaert

Comment:

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Documentation/TrunkFunctionality4

@@ -425 +425 @@
 The Pgap calculation in r7278 was checked line by line by three persons. No obvious problems were found. Why was it checked in the first place? Pgap based veget is higher than Lambert-Beer based veget. Given the differences in definitions/approach this is not really a surprise but it seemed worth to check. This line by line check revealed that the Pgap that goes into the calculation of veget assumes zenith solar angle. We have two options but both might be problematic: (a)assume zenith angle equals to 0 degrees when calculating Pgap. This woul be OK for interception and turbulence but problematic for radiation-processes, and (b) use the zenith angle at noon. This is an OK for radiative processes (but will always overestimate the gap fraction but it is underestimates the gap fraction for interception. A third solution could be to introduce two or more vegets based on different solar angles? Easy to calculate but then the problem might be shifted to sechiba: which veget to use when?
 
-Since r789X the calculation of Pgap was changed such that the total crown volume cannot exceed the entire canopy space. In earlier version this happened quite often but the impact on porosity was rather small. The same version calculates Pgap for the local zenith angle at noon. Canopy shape was made to vary between the tropics, temperate and boreal PFTs.
+Since r789X the calculation of Pgap was changed such that the total crown volume cannot exceed the entire canopy space. In earlier version this happened quite often but the impact on porosity was rather small. The same version calculates Pgap for the local zenith angle at noon. Canopy shape was made to vary between the tropics, temperate and boreal PFTs. Also the parameter '''hack_pgap''' was added. Its default value is FALSE meaning that Pgap (is iused to calculate veget). If set to TRUE, veget will be calculated by making use of Lambert Beer.