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

[Nimrod Micael]

Just change it to height coordinates from that script?


On Sat, Sep 7, 2013 at 4:49 PM, Nimrod Micael <nmicael at aggies.ncat.edu>wrote:

> 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
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> 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
>>>>>
>>>>> _______________________________________________
>>>>> 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
>>>
>>> _______________________________________________
>>> 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
>



-- 
Nimrod Micael
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