# What is this peak's meaning?

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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???

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.

Voss 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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