Add two new ecosystem-level height metrics

[ckoven]

This PR adds two metrics for average canopy height. The first is a crown-area-weighted canopy height for all plants in the canopy. This approach averages in zero height for the unoccupied areas when the canopy is not closed. This is roughly what would be returned as the mean height from lidar returns, and is also close to what FATES is currently doing for aerodynamic roughness height scaling. The second new variable is a basal-area-weighted average height of all trees; this is equivalent to what is called "Lorey's height" in the forestry literature. This variable doesn't take into account canopy strata or canopy closure.

Description:

Collaborators:

email discussion thread with @mpaiao @jkshuman @JessicaNeedham @adamhb @pollybuotte @lmkueppers @XiulinGao

Expectation of Answer Changes:

This also changes two numbers in adjacent lines of code that are very close to pi to just make them pi, so it will be answer changing for the existing basal area calculation as well as the 2 new variables.

Checklist:

• My change requires a change to the documentation.
• I have updated the in-code documentation .AND. (the technical note .OR. the wiki) accordingly.
• I have read the CONTRIBUTING document.
• FATES PASS/FAIL regression tests were run
• If answers were expected to change, evaluation was performed and provided

Test Results:

CTSM (or) E3SM (specify which) test hash-tag:

CTSM (or) E3SM (specify which) baseline hash-tag:

FATES baseline hash-tag:

Test Output:

[glemieux]

Fates test suite run against the fates-sci.1.59.4_api.24.1.0-ctsm5.1.dev106 baseline shows all expected pass, with expected DIFFs in testmods that report FATES_BASALAREA_SZPF. This is due to the update to the pi constant as noted in the PR description.

Tests results here: /glade/u/home/glemieux/scratch/ctsm-tests/tests_pr892

I also ran a quick one year f10 case with the new variables as output to make sure it built and ran successfully.

[glemieux]

Retesting per 82dbd83 update to change all uses of tiny to nearzero.

[glemieux]

Re-test shows the same results as previously found.

/glade/u/home/glemieux/scratch/ctsm-tests/tests_pr892_nearzero