# [IDV #XXB-920520]: formula: Storm relative helicity

• Subject: [IDV #XXB-920520]: formula: Storm relative helicity
• From: "Unidata IDV Support" <address@hidden>
• Date: Thu, 23 Jan 2014 16:42:29 -0700

```> Hi
>
> Thank you very much for the advice. I have edited the portion what gave the
> error by adding "make2D(item)"& i now get a result. The unit is also correct
> (mÂ/sÂ)
>
> Now I would like to ask you one last question on this jython code. perhaps
> you can help me with this one too.
>
> The original formula calculates the Storm relative helicity of a normal storm
> motion
> umotion = 0.75 * umean
> vmotion = 0.75 * vmean
>
> I would now like to do the same jython, but applied to the deviant storm
> motion of a right moving supercel.
> the formula to calculate the deviant storm motion (u & v component) is this
> one:
>
> umotion=((umean+(7.5/(shear))*vshear))
> vmotion=((vmean-(7.5/(shear))*ushear))
>
> so plugged in the full jython it looks like this:
>
> def srh3km(u, v, top, bottom, unit=None):
> u1000=getSliceAtLevel(u, 100000)
> u950=getSliceAtLevel(u, 95000)
> u900=getSliceAtLevel(u, 90000)
> u850=getSliceAtLevel(u, 85000)
> u800=getSliceAtLevel(u, 80000)
> u750=getSliceAtLevel(u, 75000)
> u700=getSliceAtLevel(u, 70000)
> v1000=getSliceAtLevel(v, 100000)
> v950=getSliceAtLevel(v, 95000)
> v900=getSliceAtLevel(v, 90000)
> v850=getSliceAtLevel(v, 85000)
> v800=getSliceAtLevel(v, 80000)
> v750=getSliceAtLevel(v, 75000)
> v700=getSliceAtLevel(v, 70000)
>
> umean=layerAverage(u, bottom, top, unit)
> vmean=layerAverage(v, bottom, top, unit)
>
> ushear=layerDiff(u, 50000, 100000, unit)
> vshear=layerDiff(v, 50000, 100000, unit)
>
> shear=sqrt(ushear*ushear+vshear*vshear)
>
> ******************************************************
> umotion=((umean+(7.5/(shear))*vshear))    <= Problem resides here: "unit
> exception"
> vmotion=((vmean-(7.5/(shear))*ushear))    <= Problem resides here: "unit
> exception"
> ******************************************************
>
> srh1=((make2D(u950)-make2D(umotion))*(make2D(v1000)-make2D(vmotion))-(make2D(u1000)-make2D(umotion))*(make2D(v950)-make2D(vmotion)))
> srh2=((make2D(u900)-make2D(umotion))*(make2D(v950)-make2D(vmotion))-(make2D(u950)-make2D(umotion))*(make2D(v900)-make2D(vmotion)))
> srh3=((make2D(u850)-make2D(umotion))*(make2D(v900)-make2D(vmotion))-(make2D(u900)-make2D(umotion))*(make2D(v850)-make2D(vmotion)))
> srh4=((make2D(u800)-make2D(umotion))*(make2D(v850)-make2D(vmotion))-(make2D(u850)-make2D(umotion))*(make2D(v800)-make2D(vmotion)))
> srh5=((make2D(u750)-make2D(umotion))*(make2D(v800)-make2D(vmotion))-(make2D(u800)-make2D(umotion))*(make2D(v750)-make2D(vmotion)))
> srh6=((make2D(u700)-make2D(umotion))*(make2D(v750)-make2D(vmotion))-(make2D(u750)-make2D(umotion))*(make2D(v700)-make2D(vmotion)))
>
> sreh = srh1 + srh2 + srh3 + srh4 + srh5 + srh6
>
> return sreh
>
> When I run this jython code, the IDV gives me a "unit exception" error (no
> further information).
>
> I tried to insert a "noUnit(shear)" or "noUnit(vshear)" but none of these
> options work because when plugging in a noUnit() the IDV gives me the error
> message "FlatField: RangeUnits must be convertable with RangeType default
> Units".
>

Have you tried to insert noUnit on both shear and vshear?

Yuan
> As you have helped me with the first question, can you provide an explanation
> as to why this piece of jython doesn't work? or maybe edit the 2 lines or
> point me in the right direction?
>
> The whole purpose of these 2 forumulas (helicity of normal storm motion &
> helicity of deviant storm motion) is to compare the 2 quantitatively for a
> talk about supercels & severe weather. I would like to create the 2 maps &
> lay them next to eachother for comparison purposes.
>
> Any help is much appreciated.
>
> Dzengiz
>

Ticket Details
===================
Ticket ID: XXB-920520
Department: Support IDV
Priority: High
Status: Open

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