Distributions of SEP t-f components. (a)-(c) Distributions of high-energy, middle-energy, and low-energy t-f components in time-frequency-energy space. (d)-(f) Distributions of high-energy, middle-energy, and low-energy t-f components in time-frequency space and peak regions under different values of region threshold. The projections of 3D distributions on time-frequency/time-energy/frequency-energy domains are also illustrated in (a)-(c). The black circles denote the t-f components, and the red triangles indicate the clusters. The blue, red, green lines in (d)-(f) indicate the peak regions when ξ = 0.75, 0.5, and 0.25, respectively.