Question

let say the air close to the ground is hot. when a light beam is directed horizontally then light beam

Answer 1

As the air close to the ground is hot ,the light passing through this may refract as hot air has lower refractive index w.r.t. cool air.So if the light is emitted from some cooler air ,then it may change its path i.e. it will come closer to the normal of the interface of both the cool and hot media.