The correct answer is option 3 - Rotation of the Earth.
In the southern hemisphere, wind is deflected towards the left due to the rotation of the Earth, a phenomenon known as the Coriolis effect. The Coriolis effect is caused by the rotation of the Earth on its axis, which makes points on the Earth`s surface move faster near the equator and slower near the poles.
As the Earth rotates, objects, including air masses, tend to keep their original momentum. This means that they appear to curve when viewed from a rotating reference frame. In the southern hemisphere, the Coriolis effect causes wind to deflect towards the left. This is because when air moves from high pressure to low pressure, it gets deflected by the rotation of the Earth.
The other options given are not the correct explanations for why wind is deflected towards the left in the southern hemisphere. Atmospheric temperature does not directly influence the direction of wind deflection, and neither does Earth`s magnetic field. Atmospheric pressure, although it can affect wind patterns, does not explain the specific deflection towards the left in the southern hemisphere.