why??

What is wind?
We feel winds because the air around us moves. The smoke from a lighted candle gives a good portray of the wind around us.


Where does wind come from?
When we fan ourselves, we make the air move and it is felt as wind. What makes air move during windy weather? This is because of unequal heating, temperatures at different places are not the same. As the warmer air expands, the density and pressure of air decrease. The surrounding cooler air flows in to fill the void and wind develops.

In Hong Kong, windy weather is usually caused by monsoon or tropical cyclone.

A monsoon is a seasonal wind flow due to the difference in surface pressure caused by the differential heating of seas and lands. The northeast monsoon generally prevails over the coast of southern China in winter while the southwest monsoon dominates in summer.

Tropical cyclone is a high wind speed whirlpool, developed over the warm oceans. It has vertical scale of more than ten kilometres and horizontal dimensions of hundreds of kilometres.

Wind cannot be seen or caught. How do we describe wind?
Wind is described by its direction and speed. Wind direction is the direction from which the wind blows. It is usually expressed in terms of the point of compass. Air moving from east to west is called easterly wind. Wind speed is the speed of the air flow. It is usually expressed in kilometres per hour or as a force on the Beaufort Scale.