Calculate tunable parameter $m$ defined as the ratio of steady state annual LAI to GPP.

[davidorme]

This is the next step in calculating the LAI phenology - the description is taken from the documented attached to the meta issue #347:

The equation to calculate parameter m is shown in equation 4:

(Eqn 4) $m =(\sigma \cdot GSL \cdot LAI_{max})/ (A_{0sum} \cdot f_{APAR_{max}})$

This shouldn't be too difficult. Apart from $\sigma$, the values are all taken directly from the outputs and inputs to #348

• $GSL$ is the length of the continuous above 0℃ period longer than five days, which is a required input for 348.
• LAImax is annual peak LAI, calculated from Equation 2 in 348.
• A0sum is the annual total potential GPP, from the P Model input to 348.
• fAPARmax is annual peak fAPAR, calculated from Equation 1 in 348.

The parameter $\sigma$ then represents the extent to which seasonal LAI dynamics depart from a “square wave” whereby maximum LAI would be maintained over the whole growing season. IIUC, this is used to effectively round off the shoulders of that square expectation to account for leaf growth and budburst at the start of the season and then also nutrient resorption and leaf senescence processes at the end.