A Satellite and Radar Climatology of Tropical Cyclone Principal Rainbands

Secondary eyewall formation typically occurs through the development and “wrapping up” of a principal spiral rainband. It is unclear however what effect environmental conditions have on principal rainband structure and how the initial structure of the principal rainband influences the transition to a secondary eyewall.
We address these questions using a climatology of the formation and structure of principal rainbands in tropical cyclones, and the effect of principal rainband structure on secondary eyewall formation. Here, 85GHz microwave imagery from 1997-2017 is used to objectively identify principal rainbands and secondary eyewalls. We discuss the influence of environmental conditions on both principal rainband formation and subsequent evolution of rainband parameters including crossing angle and band length. We then discuss the effect of these rainband parameters on both the probability of secondary eyewall formation and the structure of the secondary eyewall.
The evolution of the kinematic and reflectivity structure of the principal rainband is then investigated using data from NOAA’s P3 Tail radar. Composites of reflectivity, three-dimensional wind and vorticity are created at different stages of principal rainband formation and transition to a secondary eyewall using observations from 24 North Atlantic tropical cyclones. We will discuss these observations, with a focus on the relationship between principal rainband structure and subsequent secondary eyewall structure, and interpret the results in relation to previously proposed hypotheses of secondary eyewall formation.