The magnetic measurements from the Mars Global Surveyor satellite are used to study the magnetic field on the Martian dayside, and its variation with the solar wind. Because of the lack of solar wind measurements near Mars, solar wind measurements near Earth during a period centered on a Mars-Earth conjunction are used. Concurrent variations at Mars and Earth related to the interplanetary sector-structure and dynamic pressure variations are demonstrated. The study is confined to the northern hemisphere of Mars in regions where the crustal anomalies are weak. Here we find a close association between the solar wind dynamic pressure and the magnetic pressure in the pile-up region, and also a strong asymmetry with the Interplanetary magnetic field (IMF) By-component, probably related to solar wind pick-up of planetary ions.