How I find Annual and SemiAnnual variation in Data?

I am Stuck at a point....

I am using EOF(Empirical Orthogonal Function) models ,using FoF2 frequency.

After applying model i got Base coefficients A1-A3 ,A1 define Pattern of Cyclic behaviour of Solar Flux ,A2 define Annual behaviour of Solar Flux depending factor of F2F2, A3 define Semi- Annual behaviour of Solar Flux depending factor of FoF2.

My Question is how I detect periodicity by Fourier in A2 and A3.

Kindly help me in this regards.