Why does tropical cyclone originate over the seas? In which part of the tropical cyclone do torrential rains and high velocity winds blow and why?
Tropical cyclones originate over the seas because they require specific favourable conditions that are available only over warm tropical oceans. These conditions include: large sea surface with temperature higher than 27°C, presence of Coriolis force, small variations in vertical wind speed, a pre-existing weak low-pressure area, and upper divergence above the sea level system.
The energy that intensifies the storm comes from the condensation process in the towering cumulonimbus clouds surrounding the centre of the storm. With continuous supply of moisture from the sea, the storm is further strengthened. On reaching the land, the moisture supply is cut off and the storm dissipates. This is why tropical cyclones originate only over the seas and dissipate on reaching the land.
The torrential rains and high velocity winds blow in the eye wall region of the tropical cyclone. The eye is a region of calm with subsiding air, but around the eye is the eye wall where intense activity occurs.
In the eye wall, there is a strong spiralling ascent of air to greater height reaching the tropopause. The wind reaches maximum velocity in this region, reaching as high as 250 km per hour. Torrential rain occurs here due to the strong upward movement of air and the presence of towering cumulonimbus clouds. From the eye wall, rain bands may radiate and trains of cumulus and cumulonimbus clouds may drift into the outer region.
Explanation
This answer addresses both parts of the question comprehensively. The first part explains why tropical cyclones originate over seas using the five favourable conditions mentioned in the textbook. The second part correctly identifies the 'eye wall' as the region of torrential rains and high velocity winds, explaining the mechanism of strong spiralling ascent of air and condensation in cumulonimbus clouds. The answer uses only facts from the provided context and maintains the word limit appropriate for a 5-mark question.