System (storm) - relative winds (isentropic analysis) #1976
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I was working on some isentropic maps using the Unidata isentropic example here: I am still learning about isentropic analysis, but one thing I am seeing is that it's helpful to view "system-relative" wind vectors on a theta surface, rather than the "full wind". I think the example above plots "full wind" vectors interpolated to the theta surface. After digging around a bit, it appears GEMPAK might have a function to get this: I also found this lab exercise using GEMPAK from UWyo that has more info on how to generate it in GEMPAK: I tried searching open discussions or issues but didn't come up with anything. Is anyone aware of how to do this currently in MetPy or what might be needed to implement it? Thank you! |
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MetPy doesn't have the concept of a vector quantity (which is what VECN constructs in GEMPAK); instead, you work with the scalar components directly (u and v). The system-relative wind is therefore just a subtraction operation, so it is "too simple" for MetPy to have its own function. Here is an example: usys = (nam_isen['ugrd'] - 14.49*units('m/s')).rename('usys')
vsys = (nam_isen['vgrd'] - 3.88*units('m/s')).rename('vsys')
wind_sys = xr.merge([usys, vsys])where the system motion was hard-coded to have a u component of 14.49 m/s, and a v component of 3.88 m/s, and |
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We've talked about having a helper for vector quantities in #537, but never gotten to something concrete nor has the need been great enough to focus time there. |
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MetPy doesn't have the concept of a vector quantity (which is what VECN constructs in GEMPAK); instead, you work with the scalar components directly (u and v). The system-relative wind is therefore just a subtraction operation, so it is "too simple" for MetPy to have its own function. Here is an example:
where the system motion was hard-coded to have a u component of 14.49 m/s, and a v component of 3.88 m/s, and
nam_isenis the result ofmetpy.calc.isentropic_interpolation_as_dataset, and that dataset happens to have variables in it n…