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Why is Earth’s magnetosphere compressed on the side facing the Sun?

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geomagnetic field The magnetic field of a bar magnet has a simple configuration known as a dipole field. Close to Earth's surface this field is a reasonable approximation of the actual field.

Earth’s magnetosphere is compressed on the side facing the Sun because of the constant pressure exerted by the solar wind—a continuous stream of charged particles, primarily protons and electrons, flowing from the Sun.12

At a distance of approximately 10 Earth radii toward the Sun, the pressure of the solar wind reaches an equilibrium with the pressure of Earth’s geomagnetic field. This boundary, known as the magnetopause, acts as an obstacle that deflects the solar wind plasma around the planet. The interaction creates a current system called the magnetopause current, which effectively confines Earth’s magnetic field within this sunward boundary.123

Without the solar wind, Earth’s magnetic field would expand indefinitely outward as a simple dipole. Instead, the solar wind’s pressure constricts the field on the dayside, while the magnetosphere stretches into an elongated magnetotail on the night side, giving the magnetosphere a characteristic teardrop or comet-like shape.312