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I am currently working with RAP analysis data within Metpy to calculate various parameters such as SRH, CAPE, etc. I am wondering if Metpy recognizes when pressure levels are below the ground (will automatically ignore the levels where the data is below ground level, e.g., 'negative' heights). For example, when calculating bunkers storm motion and providing the geopotential height profile, does Metpy recognize the pressure levels that are below ground level as the input fields from the RAP analysis data are on pressure levels (1000 hPa, 950 hPa, etc.). I have tried to determine this but have not been able to with any certainty. In addition, should the data provided for the height profile be height above sea-level or height above ground-level or it does not matter?

#SRH calculations bunk_right,bunk_left,mean_motion=mcalc.bunkers_storm_motion(units.Pa*upd_mask_p1[x,y,:],units.meters/units.second*mask_u_wnd1t[x,y,:],units.meters/units.second*mask_v_wnd1t[x,y,:],units.meter*mask_hgt1t[x,y,:])
njmike
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  • Please provide some code with your post – Risalat Zaman May 22 '21 at 18:34
  • For example here when calculating bunkers storm motion at a point in western Kansas above. The data used in the calculation is pressure level data, so the lowest pressure levels are at negative heights AGL. I do not believe Metpy recognizes and masks the levels that are below ground level. @RisalatZaman – njmike Jun 14 '21 at 16:36

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MetPy does not automatically recognize and ignore negative heights, you'll need to mask out/remove such levels yourself when using calculated heights. (Honestly, I'm not sure this has come up before since so many use cases are using observed soundings.)

Regarding above ground level (AGL) versus above sea level (ASL), that's going to depend on the calculation, though almost every one I can think of is using AGL, especially for the severe weather indices (for instance Bunkers 2000 says "all heights above ground level"). MetPy's calculations currently assume the heights given are appropriate and will use them when calculating layers.

DopplerShift
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