# [ncl-talk] Vertical motion with zonal wind

Adam Phillips asphilli at ucar.edu
Fri Feb 23 13:44:29 MST 2018

```Hi Jenny,
You are reading in OMEGA. Note that OMEGA has opposite signs and different
units from the conventional W variable.

For upward motion:  W is positive and OMEGA is negative
for downward motion: W is negative and OMEGA is positive

A basic, simple relationship
omega = -rho*grav*w              ; Pa/s
Hence:
w          = -omega/(rho*grav)    ; (say) m/s

Note the sign ....
-----
I believe all you have to do is flip the sign of your W variable:
W = in->OMEGA
W = -W
assuming you want upward arrows for upward motion.

Also note that NCL has a omega_to_w function:
https://www.ncl.ucar.edu/Document/Functions/Contributed/omega_to_w.shtml

Hope that all makes sense! If not or if you have further questions please
respond to the ncl-talk email list.

On Fri, Feb 23, 2018 at 1:24 AM, Jenny Taylor <jenny63taylor91 at gmail.com>
wrote:

> Mary,
>
> I was trying with the following attached script. But vertical motion near
> the equator, as well as the 30S and 30N, shows rising motion in the output
> which is not correct in real term. Please kindly look into my script and
> figure and inform me what I am missing or doing any wrong in this.
>
> Data structure is below;
>
> Variable: t
> Type: float
> Total Size: 655360 bytes
>             163840 values
> Number of Dimensions: 4
> Dimensions and sizes:   [time | 1] x [lev_p | 20] x [lat | 64] x [lon |
> 128]
> Coordinates:
>             time: [ 791.. 791]
>             lev_p: [950..50]
>             lat: [-87.8638..87.8638]
>             lon: [ 0..357.1875]
> Number Of Attributes: 1
>   _FillValue :  9.96921e+36
>
> Variable: u
> Type: float
> Total Size: 655360 bytes
>             163840 values
> Number of Dimensions: 4
> Dimensions and sizes:   [time | 1] x [lev_p | 20] x [lat | 64] x [lon |
> 128]
> Coordinates:
>             time: [ 791.. 791]
>             lev_p: [950..50]
>             lat: [-87.8638..87.8638]
>             lon: [ 0..357.1875]
> Number Of Attributes: 1
>   _FillValue :  9.96921e+36
>
> Variable: v
> Type: float
> Total Size: 655360 bytes
>             163840 values
> Number of Dimensions: 4
> Dimensions and sizes:   [time | 1] x [lev_p | 20] x [lat | 64] x [lon |
> 128]
> Coordinates:
>             time: [ 791.. 791]
>             lev_p: [950..50]
>             lat: [-87.8638..87.8638]
>             lon: [ 0..357.1875]
> Number Of Attributes: 1
>   _FillValue :  9.96921e+36
>
> Variable: w
> Type: float
> Total Size: 655360 bytes
>             163840 values
> Number of Dimensions: 4
> Dimensions and sizes:   [time | 1] x [lev_p | 20] x [lat | 64] x [lon |
> 128]
> Coordinates:
>             time: [ 791.. 791]
>             lev_p: [950..50]
>             lat: [-87.8638..87.8638]
>             lon: [ 0..357.1875]
> Number Of Attributes: 1
>   _FillValue :  9.96921e+36
>
>
> Thanking you,
> Jenny
>
>
> On Thu, Feb 22, 2018 at 1:17 AM, Mary Haley <haley at ucar.edu> wrote:
>
>> Jenny,
>>
>> In order to do plot overlays of different variables, you need to use the
>> "overlay" procedure in NCL.
>>
>> ----------------------------------------------------------------
>>
>> The overlay procedure works one of two ways:
>>
>> [1] It overlays data from one plot (called the "overlay" plot) into the
>> data space of another plot (called the "base" plot).
>>
>> The two plots must have intersecting data spaces for this to work. By
>> "data space", I mean the range of the X and Y axes of the two plots must
>> intersect. Otherwise, you will not see the overlay plot at all.
>>
>> For an example, see overlay_8.ncl at:
>>
>> http://www.ncl.ucar.edu/Applications/overlay.shtml#ex8
>>
>> [2] It simply "lines up" the two plots in the same rectangular region and
>> draws them. It's not as common to do overlays this way, because it requires
>> that you do all the work of making sure the two plots are in the same data
>> space.
>>
>> For an example, see overlay_9.ncl at:
>>
>> http://www.ncl.ucar.edu/Applications/overlay.shtml#ex9
>>
>> ----------------------------------------------------------------
>>
>> It doesn't matter whether you are doing contour plots, vector plots, or
>> XY plots: you can overlay any of these on another one using the "overlay"
>> procedure.
>>
>> The "overlay" examples page has several other scripts showing how to use
>> the overlay procedure. In particular, you might want to look at
>> overlay_1.ncl, overlay_6.ncl, and/or wrf_gsn_5.ncl:
>>
>> http://www.ncl.ucar.edu/Applications/overlay.shtml
>>
>> If you continue to have problems, please post back to ncl-talk and
>> include your script and a "printVarSummary" of the data you are trying to
>> plot.
>>
>> Thanks,
>>
>> --Mary
>>
>>
>> On Fri, Feb 16, 2018 at 9:59 AM, Jenny Taylor <jenny63taylor91 at gmail.com>
>> wrote:
>>
>>> Dear NCL Users,
>>>
>>> I am trying to plot vector wind field at different pressure level for
>>> latitute range 40N-40S. I am following the below mention script;
>>> https://www.ncl.ucar.edu/Applications/Scripts/h_lat_7.ncl
>>>
>>> I am trying to overlay vertical motion (rising/sinking) in vector arrows
>>> and zonal wind in color scheme.
>>>
>>> Can anyone suggest me, in that case which funtion I need to use in it?
>>> Any help will be appriciated.
>>>
>>> Thanks,
>>> Jenny
>>>
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>>
>
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