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2.9.5. Canopy scaling¶
When LUNA is on, the \(V_{c\max 25}\) for sun leaves is scaled to the shaded leaves \(J_{\max 25}\), \(T_{p25}\), \(k_{p25}\), and \(R_{d25}\) scale similarly.
(2.9.17)¶\[\begin{split}\begin{array}{rcl} {V_{c\max 25 sha}} & {=} & {V_{c\max 25 sha} \frac{i_{v,sha}}{i_{v,sun}}} \\ {J_{\max 25 sha}} & {=} & {J_{\max 25 sun} \frac{i_{v,sha}}{i_{v,sun}}} \\ {T_{p sha}} & {=} & {T_{p sun} \frac{i_{v,sha}}{i_{v,sun}}} \end{array}\end{split}\]
Where \(i_{v,sun}\) and \(i_{v,sha}\) are the leaf-to-canopy scaling coefficients of the twostream radiation model, calculated as
(2.9.18)¶\[\begin{split}i_{v,sun} = \frac{(1 - e^{-(k_{n,ext}+k_{b,ext})*lai_e)} / (k_{n,ext}+k_{b,ext})}{f_{sun}*lai_e}\\ i_{v,sha} = \frac{(1 - e^{-(k_{n,ext}+k_{b,ext})*lai_e)} / (k_{n,ext}+k_{b,ext})}{(1 - f_{sun})*lai_e}\end{split}\]
k_{n,ext} is the extinction coefficient for N through the canopy (0.3). k_{b,ext} is the direct beam extinction coefficient calculated in the surface albedo routine, and \(f_{sun}\) is the fraction of sunlit leaves, both derived from Chapter 2.3.
When LUNA is off, scaling defaults to the mechanism used in CLM4.5.