Help with finding appropriate function to model this

[naive summit]

I have this distribution that is popping up in my data and I'd like to generate functions to apporximate it

[calm veldt]

taylor series

[tawny gate]

Huh

[tawny gate]

Your question suggests you want multiple functions (Fourier transform then) but your title suggests you want a specific function (regression then). For regression, it seems like a combination of polynomial and sinusoidal one would do.

Although, the easiest thing to do would be put this through a stochastic gradient descent. If you have the individual data points, then you can also consider interpolation, which is pretty much what gives you the curves joining the points.