Fig. 1.

(A) Population of radar range gates in a slightly supercooled cloud for the following conditions: black, range gate contains cloud droplets; blue, range gate contains small ice particles (and cloud droplets); and red, range gate contains secondary ice particles (and cloud droplets). Small ice particles exist if LDR is at least −16 dB, while secondary ice particles exist if, additionally, the spectral reflectivity is at least −21 dBZ$\cdot$s$\cdot {\mathrm{m}}^{-1}$ (Materials and Methods). Confidence of the existence of secondary ice particles increases with greater reflectivity. The red points represent the spectral reflectivity threshold of −16 dBZ$\cdot$s$\cdot {\mathrm{m}}^{-1}$, while the lower and upper boundaries of the gray shading represent the spectral reflectivity thresholds of −21 and −11 dBZ$\cdot$s$\cdot {\mathrm{m}}^{-1}$. (B) Fraction of range gates containing small ice particles (blue) and secondary ice particles (red) relative to the number of range gates containing cloud droplets (black dots in A). The set of all range gates containing cloud droplets is divided into 10 subsets of equal population, ordered by temperature.