How does the bow shock deflect solar-wind particles around Earth?

The solar wind—a supersonic flow of charged particles, primarily electrons and protons—encounters the Earth's magnetic field as it approaches the planet. Because the Earth’s magnetic field acts as an obstacle to this plasma flow, a shock front known as the bow shock develops on the sunward side of the planet.12

This bow shock serves as the boundary where the supersonic solar wind is slowed and deflected around the magnetosphere, the cavity containing Earth's magnetic field. By creating this shock wave, the geomagnetic field effectively prevents the direct entry of the solar wind into the magnetosphere, confining the planet's magnetic influence and protecting the atmosphere from the full force of the solar-wind particle flux. Beyond this boundary, the solar wind remains undisturbed, while inside, the pressure of the solar wind compresses the magnetic field on the dayside and elongates it into a magnetotail on the nightside.123