What is the “eye”? How is it formed and maintained? What is the “eyewall”? What are “spiral bands”?
The “eye” is a roughly circular area of comparatively light winds and fair weather found at the centre of a severe tropical cyclone. Although the winds are calm at the axis of rotation, strong winds may extend well into the eye. There is little or no precipitation and sometimes blue sky or stars can be seen. The eye is the region of lowest surface pressure and warmest temperatures aloft – the eye temperature may be 10C warmer or more at an altitude of 12 km than the surrounding environment, but only 0-2C warmer at the surface in the tropical cyclone. Eyes range in size from 8 km to over 200 km across, but most are approximately 30-60 km in diameter. The eye is surrounded by the “eyewall”, the roughly circular ring of deep convection, which is the area of highest surface winds in the tropical cyclone. The eye is composed of air that is slowly sinking and the eyewall has a net upward flow as a result of many moderate – occasionally strong – updrafts and downdrafts.
