Evolution of brightness temperatures and sub-band differences at the location of the propagating shock wave (location A) between t = 0–500 s. (a) Brightness temperatures of SB3.1, SB3.4, SB6.1, and SB6.4. (b) Brightness temperature differences between the sub-bands ΔT_b|_B3 (T_b|_SB3.1 − T_b|_SB3.4) and ΔT_b|_B6 (T_b|_SB6.1 − T_b|_SB6.4). (c) Time-derivative of the sub-band differences ΔT_b|_B3 and ΔT_b|_B6. In each panel, the time at which the different bands start to sample the shock waves is marked with tick marks t₁ (bands 3 and 6), t₂ (band 6), and t₃ (band 3).