What is a ground wave? Why short wave communication over long distance is not possible via ground waves?

Explanation

The amplitude modulated radiowaves having frequency 530 kHz to 1710 kHz (or wavelength between
175 m to 566 m) which are travelling directly following the surface of earth are known ground waves.
The short wave communication over long distance is only possible via sky waves. It is not possible via
ground waves because the ground waves can bend round the corners of the objects on earth and hence ,
their intensity falls with distance, Moreover the ground waves transmission becomes weaker as frequency
increases.