title: units for fft of temperature time series
body: <p>I have a time series of air temperatures, that are measured in degrees C and the frequency of the signal is monthly. I compute the power spectra of the time series as:</p>
  
  <pre><code>L = length(temp);
  NFFT = 2^nextpow2(L); % Next power of 2 from length of y
  Y = fft(temp,NFFT)/L;
  Fs = 1; % one sample per month
  f = Fs/2*linspace(0,1,NFFT/2+1); % frequency 
  Pxx = 2*abs(Y(1:NFFT/2+1)); % power
  
  % Plot single-sided amplitude spectrum.
  plot(f,Pxx,'-k'); 
  xlabel('Frequency (c/month)'); % cycles per unit time
  </code></pre>
  
  <p>which results in the following plot.</p>
  
  <p><a href="https://i.stack.imgur.com/YL0kd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/YL0kd.png" alt="enter image description here"></a></p>
  
  <p>What should the units be for the yaxis? Should it be ^{o}C?</p>
  
  <p>The range of the time series is approx 20, so I guess 10 would work as the amplitude...</p>