Trace spectra of magnetic field fluctuations and magnetic compressibility. In the same format as Fig. 6, but for Wind observations upstream and downstream of the shock. Vertical dashed lines in the top panel indicate the proton cyclotron frequency in the plasma frame upstream f_cu and downstream f_cd and in the spacecraft frame upstream and downstream , respectively. Black solid lines in the top panel show the power-law fits. The power spectra and compressibility C_B are calculated within a 40-min interval.