What is this peak's meaning?

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James James
James James on 9 Nov 2021
Answered: dpb on 9 Nov 2021
This graph is amplitude of Fourier transform of rainfalls (total of 14610 days) in frequency domain. In this case, what is this peak meaning???

Accepted Answer

dpb
dpb on 9 Nov 2021
Or, it's just random noise or other non-meaningful artifact; we don't know for sure...
How was the frequency axis created to get the range shown?
If I just assume (risky, granted) a Fs of 1 sample/day, the number of observations turns out to be
>> 14610/365.25
ans =
40
>>
which would mean 40 years of observations.
If I use Fs=1 and compute f=Fs*(0:(L/2))/L, on that basis, 0.00273785 day(^-1) --> 365.25 days.
That implies a fairly strong annual frequency to the accumulation data; this should be confirmable by time series evaluation and a high likelihood of being able to fit a decent ARIMA model with an annual component.

More Answers (1)

_
_ on 9 Nov 2021
It means that the magnitude of the Fourier transform of this rainfall data has a local maximum at that frequency.

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