Fig. 3
OMNI data of a the solar wind speed, b the solar wind dynamic pressure, c the cone angle (θXB), and d the magnitude of the interplanetary magnetic field (BT) at the Earth’s bow shock nose, as well as e estimated frequency of upstream waves (fU) for 02:00–09:30 UT on 12 September 2017. fU is estimated from empirical equations by Gul’elmi (1974) (blue curve) and Takahashi et al. (1984) (red curve) only when θXB ≤ 30°. Vertical dotted lines delineate the time interval of 02:30–03:15 UT when a transverse Pc3–4 wave with the frequency of ~ 20 mHz was observed by Probe B