# [IDV #WYC-198714]: IDV 4.1u1: Vertical cross section plots conforming to variable surface elevation

• Subject: [IDV #WYC-198714]: IDV 4.1u1: Vertical cross section plots conforming to variable surface elevation
• From: "Unidata IDV Support" <address@hidden>
• Date: Mon, 16 Dec 2013 15:32:43 -0700

```>
> On Dec 4, 2013, at 10:55 AM, Unidata IDV Support
>
> One question is, what does the IDV use to determine the vertical coordinate
> of each grid point in the field that it is contouring? If it is the value of
> sigma (between 0 and 1, with 1 at the bottom and 0 at the top of the domain),
> then where does sigma = 1 begin on the plot's vertical scale? (Should it be
> same as z = 0 for the topographic profile?) And why wouldn't the bottom edge
> of the plot be a straight, horizontal line (corresponding to the same value
> of sigma)? (In my plot, the bottom of the vertical cross section is mostly a
> straight, horizontal line, but it indents upward in distinct, rectangular
> steps to stay above the highest terrain.)
>
>

Dave,
I checked with John about the coordinate transfer in the WRF output. The
CDM library uses the formula:
pressure formula", "pressure(x,y,z) = P(x,y,z) + PB(x,y,z), and height(x,y,z) =
(PH(x,y,z) + PHB(x,y,z)) / 9.81")

And I checked the data value of PH and PHB, not seeing many area with the value
of 0.

Another information from MMM WRF support is that we can not compare the
terrain height with the model first level height. And they think the output is
correct.

So I guess there is not much can be explored from the IDV side. You can
verify the first level value of the PH and PHB in the IDV.

Yuan

Ticket Details
===================
Ticket ID: WYC-198714
Department: Support IDV
Priority: Emergency
Status: Closed

```

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