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

[Nimrod Micael]

I see... so how would the shear from Surface to 1 km AGL be calculated? I
cant find it online.

Thanks!


On Sat, Sep 7, 2013 at 3:45 PM, Jeff Duda <jeffduda319 at gmail.com> wrote:

> 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
>>>>>>
>>>>>> _______________________________________________
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>>>>>> 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
>>>
>>> _______________________________________________
>>> 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
>
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
>
>


-- 
Nimrod Micael
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