GR2Analyst vs Py-ART velocity values

[Victoria Clear]

Hi all,

I'm currently doing my master's research on supercells where I'm writing the mesocyclone vrot, diameter, and altitude at which these occur. I am looking at NEXRAD radar files. I was doing it in GR2 but felt this process was a time-sink and subjective way to do my research. Since then, I've created a code using Py-ART to grid my radar object on a 500m x 500m x 500m grid using the Barnes2 weighting function and 'dist_beam' ROI.

The problem I'm having is that my vrots for all my storms tend to be 2-6 m/s lower than that on GR2. For example, from one volume scan, GR2 Vrot values I get are:

• 11.28865979 m/s at an avg beam height of  719 m
• 11.03092784 m/s at an avg beam height of  1132 m
• 10.51546392 m/s at an avg beam height of 1583 m

These are the Vrot values I get from Py-ART with *no* gatefilter exclusions and used the region-based dealiasing function (I found that the gatefilter made the discrepancies worse):

• 8.5 m/s at a grid altitude of 500 m
  
• 8 m/s at a grid altitude of 1000 m
  
• 7 m/s at a grid altitude of 1500 m

I found these values by: 1) subtracting the SMV (found from GR2) from the base velocity radar field by the formula SMV = (translational_motion)*np.cos(np.deg2rad((azimuth_2d-SMVangle)%360)), then subtracting this from the dealiased velocity srv=base_vel-SMV; 2) plotting them at altitude = j using contourf and finding the appropriate polygons through lots of loops I will not post here; 3) calculated vrot using the formula vrot = np.abs(outbound_max-inbound_max)/2. 4) do this for every other subsequent altitude until couplet is no more (I use input a lot as well - I'm not a coder/algorithm-maker, but it works well otherwise).

I wanted to pick your brains and see why they are considerably lower than GR2, whether that is just the nature of gridding a radar (especially mapping the gates to the grid - I tried mapping it to the grid and it took 30+ mins), or if dealiasing could also be a problem. I also wanted to see if anyone had any suggestions on how to correct this or if you've also had this problem.

Best,

Tori

[scolli...@gmail.com]

Hey Victoria!

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Send this to our new home:

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for general science questions:

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[Victoria Clear]

This is the volume scan where the values above were pulled. My plot above is at 500 m altitude, and the bottom GR2 photo is the 0.5° SRV tilt using the SMV applied to both. I find it matches very well, yet can't get over the discrepancy. I also wonder if part of it is due to smoothing of the contours where I can't get as high of individual pixels like in GR2.

[Victoria Clear]

Oops! Sorry about that. Will post there.