What is this peak's meaning?

This graph is amplitude of Fourier transform of rainfalls (total of 14610 days) in frequency domain. In this case, what is this peak meaning???

Answer 1

[dpb]

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.

Answer 2

[Voss]

It means that the magnitude of the Fourier transform of this rainfall data has a local maximum at that frequency.