Q.How are the ground waves polarized?

In surface-wave (ground-wave) propagation, the radio wave hugs the Earth's curved surface, diffracting around it, but loses energy to the ground as it travels.

Surface wave (ground wave) propagation: When a radio wave is radiated from a transmitting antenna close to the ground, it can travel along the surface of the Earth, guided by the boundary between the Earth (a partial conductor) and the atmosphere. This mode of propagation is called surface-wave or ground-wave propagation, and is one of the three principal modes of electromagnetic wave propagation (the others being sky wave and space wave).

The wave follows the curvature of the Earth to some extent because of diffraction — the ground effectively acts as a wave-guide. However, the conducting Earth absorbs energy from the wave as it travels (induced currents dissipate energy as heat in the ground), so the wave is progressively attenuated; the attenuation increases rapidly with frequency, which is why this mode is practical mainly at low and medium frequencies (below a few MHz, roughly up to the MF/AM broadcast band).

Ground-wave propagation is affected by the electrical conductivity of the terrain it passes over — it travels farther over highly conducting surfaces like sea water than over poorly conducting ground like dry, rocky soil. It is used mainly for local and regional AM radio broadcasting, and for maritime and navigational communication, where reliable coverage over a few hundred kilometres is needed regardless of atmospheric/ionospheric conditions.