# [gradsusr] Finding zonal wind core value, and its position

Jeff Duda jeffduda319 at gmail.com
Wed Dec 12 22:37:29 EST 2012

```Perhaps look for both maxima and just automatically reject the one that is
more poleward.  You can use the cdiff function to compute derivatives and
run the first derivative test to find maxima.

Jeff

On Wed, Dec 12, 2012 at 8:38 PM, Muhammad Yunus Ahmad Mazuki <
ukm.yunus at gmail.com> wrote:

> Well, I'm also looking into other ways in doing this, other than scripting
> in GrADS. There are two jet stream, subtropical and polar front, and I want
> to track the subtropical jet even when it is weak in strength. I'm also
> looking at how to search it degree by degree (or rather y and z point in
> GrADS), with some rules. This is because when there is a need to introduce
> some events in a model that literally wrecks the usual pattern of the
> subtropical jet stream, I need to be sure that my calculation is tracking
> purely subtropical jet stream.
>
>
> On Wed, Dec 12, 2012 at 1:44 AM, Jeff Duda <jeffduda319 at gmail.com> wrote:
>
>> This is hard to get around given the rules you've set forth.  If you
>> can't restrict your search box yet you don't want the maxima that occur at
>> certain spots, how can you tell a script to make that distinction?  What is
>> it about the one jet core that makes it the one you want?  When you can
>> core you want.
>>
>> Jeff Duda
>>
>> On Tue, Dec 11, 2012 at 1:18 AM, Muhammad Yunus Ahmad Mazuki <
>> ukm.yunus at gmail.com> wrote:
>>
>>> Hello,
>>>
>>> The picture attached is a slice of longitude 180E, from 40 S to 20S. As
>>> you can see, the core that I wanted is at the 23S with wind speed of 18. I
>>> have tried using maximum value function in grads, as well as maximum
>>> location, but it would give me 39S corresponding to a core below 40S, which
>>> I do not want. I would like to request suggestion on solving this problem.
>>> Changing the latitude range to less than 40S however is not acceptable, as
>>> at certain condition the core can be at 38 S.
>>>
>>> Sincerely,
>>>
>>> _______________________________________________
>>>
>>>
>>
>>
>> --
>> Jeff Duda
>> University of Oklahoma School of Meteorology
>> Center for Analysis and Prediction of Storms
>>
>>
>> _______________________________________________
>>
>>
>
> _______________________________________________
>
>

--
Jeff Duda