Fix poor assumptions in lfc() logic #1023
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akrherz
reviewed
Mar 30, 2019
metpy/calc/thermo.py
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Well that's good because our docs say:
We support Python >= 3.6 and currently support Python 2.7.
😁
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My world will be so much better when Python 2.7 is just a distant memory.
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Ok, now that #1022 is in, can you rebase so we can see what this looks like? |
dopplershift
added
Area: Calc
Currently, some of the logic in the lfc() function assumes a surface parcel is being considered, but that is no longer necessarily the case. This commit addresses the two places where a surface parcel has been assumed. First, when looking for intersections, the code assumed the first point of the parcel trajectory had an identical temperature to the environment. This is only true if a surface-based parcel is being used. Second, the LCL of the parcel is computed using surface values. This, too, is not appropriate if the parcel is not a surface parcel. The lfc_ml2 testcase was giving wrong results because of the second problem. This commit addresses both problems and corrects the associated testcase.
This test gives 990 hPa for the LFC (the LCL value in this case) if the fix to the find_intersections() call is not present.
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OK, I think it is in good shape now. |
dopplershift
approved these changes
Apr 10, 2019
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This PR depends on #1022 and addresses additional problems with the
lfc()calculation. Parts of the logic inlfc()assume the parcel for which the LFC is desired is the surface parcel. One test case is updated, and another is added to show the differences.The first example:
Because the current code uses the surface parcel when computing the LCL internally, the LFC is determined to be over 1000 mb. However, the LCL of the mixed parcel is under 1000 mb. With this PR, the correct value of 982 mb for the LFC (and LCL) is returned.
The second example:
Without the fixes to the find_intersections() logic that this PR includes, the LFC is computed to be 990 mb (which is the LCL), but the actual value is 983 mb, as indicated in the new test.