In February, 1982, The Journal of the Atmospheric Sciences published a ground-breaking study by Hugh Willoughby, Jean Clos, and Mohammed Shoreibah on what became to be known as the eyewall replacement cycle. Using data obtained from NOAA P3 flights into very intense Hurricanes Anita, David and Allen, they found that a common feature of intense tropical cyclones was a second ring of convection around the primary eyewall and that this second ring also had a wind-speed maximum. This second ring contracts while starving the inner ring of moisture and energy, so the second ring eventually replaces the first one as the eyewall, and the process can repeat. They also found that the appearance of the second ring marks the end of a period of intensification, enabling improved intensity forecasts.
This historic paper can be found at http://journals.ametsoc.org/doi/pdf/10.1175/1520-0469%281982%29039%3C0395%3ACEWSWM%3E2.0.CO%3B2.