• radius =  9 µm
• wavelength = 0.65 µm
• refractive index = 1.3319552
• scattering angle = 178°.

Fig. 1   Intensity as a function of radius

Fig. 1 shows that the scattered intensity varies dramatically with small changes in radius.  In addition to some relatively gradual changes, such as the peaks around 9.005 µm and 9.088 µm for parallel polarisation, there are very sharp "spikes".  It is important to understand that these spikes are extremely narrow: for example the spike near 9.021 µm has a width of 3 x10^-12 m - which is of atomic dimensions!

Fig. 2 shows similar complicated behaviour with small variations in wavelength. Note that varying the wavelength automatically varies the refractive index used in the calculations. 

Fig. 3   Intensity as a function of refractive index

Fig. 3 shows the effect of varying the refractive index whilst keeping the other parameters fixed at their nominal values.
 

Close examination of Figs 1 - 3 suggests that many of the sharp minima for parallel polarisation correspond to sharp maxima for perpendicular polarisation.

Fig. 4 shows scattering of monochromatic red light from drops of radius 9 - 9.1 µm for scattering angles between 170° and  180°.  Strong scattering occurs around 178° for parallel polarisation, with even stronger scattering due to sharp maxima near 180°.  Some "strange" behaviour is also apparent, such as the vertical lines showing that the sharp maxima at 180° correspond with minimal scattering at between 170° and 179°.