| Re: AO, SAO [message #70761] |
Thu, 29 April 2010 16:49 |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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On Apr 29, 6:16 pm, kiss <kishore1...@gmail.com> wrote:
> Hi
>
> I have 84 monthly temperature values at each height level. I am
> estimating the trends at each altitude levels using 84 monthly values.
> But I have to remove Annual Oscillation (AO) and Semi annual
> oscillation (SAO) and quasi biannual oscillation (QBO) trend from the
> monthly values.
> How to remove these oscillations from the monthly values.
> If anybody knows the methodology, pl. try to advice me.
First, it sounds like this type of analysis has been done in the past
by people in your field. You should probably talk to them about your
methodology, because you will probably want to use comparable
techniques (or perhaps better if you understand the problem well
enough).
Second, a way to capture such oscillations is with Fourier analysis.
You can do a straight fourier transform, although you have to be
careful if there are non-periodic trends in the data. Or, you could
fit a series like,
Y = A + B*t + $
C*COS(2*!DPI*T/YEAR) + D*SIN(2*!DPI*T/YEAR) + $
E*COS(4*!DPI*T/YEAR) + F*SIN(4*!DPI*T/YEAR) + ...
and so on for higher harmonics. This should be equivalent to fourier
analysis, but the A & B terms could capture a constant+linear trend.
Of course there are an infinite number of variations on this.
I still say you should start with whatever your colleagues use first.
Craig
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| Re: AO, SAO [message #70764 is a reply to message #70761] |
Thu, 29 April 2010 15:59  |
Aram Panasenco
Messages: 41
Registered: April 2010
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Member |
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kiss wrote:
> Hi
>
> I have 84 monthly temperature values at each height level. I am
> estimating the trends at each altitude levels using 84 monthly values.
> But I have to remove Annual Oscillation (AO) and Semi annual
> oscillation (SAO) and quasi biannual oscillation (QBO) trend from the
> monthly values.
> How to remove these oscillations from the monthly values.
> If anybody knows the methodology, pl. try to advice me.
>
> Thanking you,
>
> Kishore
Hey there Kishore,
This sounds like a hard problem. Do you know of any formula to remove
these oscillations from the data? The only information I was able to
find was this wikipedia page:
http://en.wikipedia.org/wiki/Quasi-biennial_oscillation
~Aram Panasenco
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