[gradsusr] Question about srh1km(uVAR,vVAR) function

[Jeff Duda]

Because in areas of elevated terrain, the top of the layer in which the
shear is being computed is much closer to the surface than 1 km.  Said
another way, they use the 900 mb level as a surrogate for the 1 km level.
 If the actual surface pressure is close to 900 mb, however, the vertical
distance between the surface and the surrogate 1 km level is going to be
quite small.  Thus, the computed shear value will be expected to be lower
than if you used the 1 km AGL instead.

Jeff


On Sat, Sep 7, 2013 at 1:47 PM, Nimrod Micael <nmicael at aggies.ncat.edu>wrote:

> @Jeff:
>
> Ok because I find it weird that my 0-1 KM shear values at 16Z in GSO is
> about 1/2 of the value of the observation from a sounding taken at the time
> when using that shr1km(u,v) function. However, when I used Rob Hart's
> plotskew script to plot the sounding...the ERSH matched closer to the
> observation at that time. So I am wondering why such a huge error in that.
>
>
> On Sat, Sep 7, 2013 at 2:08 PM, Jeff Duda <jeffduda319 at gmail.com> wrote:
>
>> If you're calculating 0-1 km SRH over flat terrain near sea level, their
>> computation is within reason.  However, if you're on higher terrain or
>> sloped terrain (e.g., the Plains region of the US), you'll want to use a
>> different method.
>>
>> Jeff
>>
>>
>> On Sat, Sep 7, 2013 at 11:28 AM, Nimrod Micael <nmicael at aggies.ncat.edu>wrote:
>>
>>> He stated it's 1 KM MSL.
>>>
>>>
>>>
>>> "However, the question of AGL or MSL depends on your model data output -
>>> if it compensates the pressure height. GFS IIRC does not do that, so it
>>> would be MSL.
>>>
>>> To understand the calculation, you can check the original math from our
>>> website:
>>> http://www.saakeskus.fi/grads-scripts/63-storm-relative-helicity-0-3km"
>>>
>>> So in order to calculate 0-1 KM shear it has to be 0-1 KM AGL?
>>>
>>>
>>> Thanks.
>>>
>>>
>>>
>>>
>>> On Fri, Sep 6, 2013 at 1:30 PM, Jeff Duda <jeffduda319 at gmail.com> wrote:
>>>
>>>> I don't use openGrads, so there may be some specifics I'm not aware
>>>> of.  uVAR and vVAR are just dummy names for the u- and v-components of the
>>>> wind.  The inaccuracies are probably due to the exact specifics with how
>>>> the 0-1 km shear is computed in the script.  One big question is how is the
>>>> 1 km layer wind field being computed?  Is it just 1 km MSL or 1 km AGL?
>>>> Those are things you need to find out.  I recommend asking the authors
>>>> whose email addresses are given on the linked page.
>>>>
>>>> Jeff
>>>>
>>>>
>>>> On Fri, Sep 6, 2013 at 12:20 PM, Nimrod Micael <nmicael at aggies.ncat.edu
>>>> > wrote:
>>>>
>>>>> *srh1km*(*uVAR,vVAR*)
>>>>> What is uVAR and vVAR?  I dont have those variables.
>>>>>
>>>>> http://opengrads.org/doc/udxt/saakeskus/
>>>>>
>>>>> I tried replacing uVar and vVar with u and v wind but I am getting
>>>>> some inaccuracies with the 0-1 KM shear. Can someone help me out?
>>>>>
>>>>> Thanks.
>>>>>
>>>>> --
>>>>> Nimrod Micael
>>>>>
>>>>> _______________________________________________
>>>>> gradsusr mailing list
>>>>> gradsusr at gradsusr.org
>>>>> http://gradsusr.org/mailman/listinfo/gradsusr
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Jeff Duda
>>>> Graduate research assistant
>>>> University of Oklahoma School of Meteorology
>>>> Center for Analysis and Prediction of Storms
>>>>
>>>> _______________________________________________
>>>> gradsusr mailing list
>>>> gradsusr at gradsusr.org
>>>> http://gradsusr.org/mailman/listinfo/gradsusr
>>>>
>>>>
>>>
>>>
>>> --
>>> Nimrod Micael
>>>
>>> _______________________________________________
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>>> gradsusr at gradsusr.org
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>>>
>>>
>>
>>
>> --
>> Jeff Duda
>> Graduate research assistant
>> University of Oklahoma School of Meteorology
>> Center for Analysis and Prediction of Storms
>>
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>> gradsusr mailing list
>> gradsusr at gradsusr.org
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>>
>>
>
>
> --
> Nimrod Micael
>
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>
>


-- 
Jeff Duda
Graduate research assistant
University of Oklahoma School of Meteorology
Center for Analysis and Prediction of Storms
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