[ncl-talk] bandpass filter issue

[Xi Chang]

Hi Maria,

Yes, i actually want to analyze 16-day planetary waves  (k=1) waves using
daily data. But in this case, i dont need to decompose it into eastward and
westward propgating waves. I tried to bandpass filter the data, but since
the frequency bands are too narrow (1/15) and (1/17).. the results are bad.
any suggestion? does it mean that i need higher temporal resolution?
the steps that i do are:
1. filter data using forward and backward fourier to retain k=1
2. bandpass this filtered data to retain only freq at 1/16day

Chang


On Tuesday, 6 October 2015, Maria Gehne - NOAA Affiliate <
maria.gehne at noaa.gov> wrote:

> Can you explain in more detail what you are trying to do? Are you trying
> to only look at phenomena that have a period of 16 days?
>
> Maria
>
> On Tue, Oct 6, 2015 at 12:31 AM, Xi Chang <xi.chang01 at gmail.com> wrote:
>
>> Thanks for the reply. No i dont use it, since what i need is how to
>> extract/filter the daily data having frequency 1/16 day. is it possible to
>> only use bandpass filter?
>>
>>
>>
>>
>> On Tuesday, 6 October 2015, Dennis Shea <shea at ucar.edu> wrote:
>>
>>> Are you looking a 'complex demodulation" ???
>>>
>>> If so, that is in the 6.3.1 release:
>>>   http://www.ncl.ucar.edu/future_release.shtml
>>>
>>> Click 'demod_cmplx'  =>
>>> http://www.ncl.ucar.edu/Document/Functions/Contributed/demod_cmplx.shtml
>>>
>>> See Examples at the bottom of
>>> http://www.ncl.ucar.edu/Applications/spec.shtml
>>>
>>>
>>> On Mon, Oct 5, 2015 at 4:32 PM, Xi Chang <xi.chang01 at gmail.com> wrote:
>>> > Hi NCL,
>>> >
>>> > I have daily data 10 years. I'd like to filter the data at frequency
>>> (1/16)
>>> > day. To do so what the most appropiate  frquency ranges that i have to
>>> use
>>> > ?, is it domething like fa=1/15 and fb=1/17 ?
>>> > I aware if the band is too narrow the filtered signals are fake
>>> /artificial
>>> > (i tesed with ncl butterwooth and the filtered results are weird) ? is
>>> there
>>> > any idea how to do that appropriately? do i need to use hourly data
>>> instead
>>> > of daily?
>>> >
>>> > Thanks
>>> >
>>> > _______________________________________________
>>> > ncl-talk mailing list
>>> > ncl-talk at ucar.edu
>>> > List instructions, subscriber options, unsubscribe:
>>> > http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>> >
>>>
>>
>> _______________________________________________
>> ncl-talk mailing list
>> ncl-talk at ucar.edu
>> List instructions, subscriber options, unsubscribe:
>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>
>>
On Tuesday, 6 October 2015, Maria Gehne - NOAA Affiliate <
maria.gehne at noaa.gov> wrote:

> Can you explain in more detail what you are trying to do? Are you trying
> to only look at phenomena that have a period of 16 days?
>
> Maria
>
> On Tue, Oct 6, 2015 at 12:31 AM, Xi Chang <xi.chang01 at gmail.com
> <javascript:_e(%7B%7D,'cvml','xi.chang01 at gmail.com');>> wrote:
>
>> Thanks for the reply. No i dont use it, since what i need is how to
>> extract/filter the daily data having frequency 1/16 day. is it possible to
>> only use bandpass filter?
>>
>>
>>
>>
>> On Tuesday, 6 October 2015, Dennis Shea <shea at ucar.edu
>> <javascript:_e(%7B%7D,'cvml','shea at ucar.edu');>> wrote:
>>
>>> Are you looking a 'complex demodulation" ???
>>>
>>> If so, that is in the 6.3.1 release:
>>>   http://www.ncl.ucar.edu/future_release.shtml
>>>
>>> Click 'demod_cmplx'  =>
>>> http://www.ncl.ucar.edu/Document/Functions/Contributed/demod_cmplx.shtml
>>>
>>> See Examples at the bottom of
>>> http://www.ncl.ucar.edu/Applications/spec.shtml
>>>
>>>
>>> On Mon, Oct 5, 2015 at 4:32 PM, Xi Chang <xi.chang01 at gmail.com> wrote:
>>> > Hi NCL,
>>> >
>>> > I have daily data 10 years. I'd like to filter the data at frequency
>>> (1/16)
>>> > day. To do so what the most appropiate  frquency ranges that i have to
>>> use
>>> > ?, is it domething like fa=1/15 and fb=1/17 ?
>>> > I aware if the band is too narrow the filtered signals are fake
>>> /artificial
>>> > (i tesed with ncl butterwooth and the filtered results are weird) ? is
>>> there
>>> > any idea how to do that appropriately? do i need to use hourly data
>>> instead
>>> > of daily?
>>> >
>>> > Thanks
>>> >
>>> > _______________________________________________
>>> > ncl-talk mailing list
>>> > ncl-talk at ucar.edu
>>> > List instructions, subscriber options, unsubscribe:
>>> > http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>> >
>>>
>>
>> _______________________________________________
>> ncl-talk mailing list
>> ncl-talk at ucar.edu <javascript:_e(%7B%7D,'cvml','ncl-talk at ucar.edu');>
>> List instructions, subscriber options, unsubscribe:
>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>
>>
>
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