Spiral Rainbands in a Numerical Simulation of Hurricane Bill (2009) Spiral Rainbands in a Numerical Simulation of Hurricane Bill (2009). Part I: Structures and Comparisons to Observations Yumin Moon and David S. Nolan 2014 Rainband Classification Data & Methodology Four types of rainbands: primary, secondary, distant, and inner Simulation of Hurricane Bill 2009 was done using the WRF 3.2.1 over a 3 day period of max intensity from 1200 UTC 18 August to 1200 UTC 21 August -Primary and secondary are very similar except with primary being more stationary -Distant has convection similar to squall lines -Inner, not shown in the diagram, are found in closer proximity to the eyewall than the secondary Graphs are radius-height cross sectional averages for each rainband Houze(2010) Principal Rainband Secondary Rainband Updraft Updraft 1.Radial tilt outwards 2. Overturning secondary circulation 3. Enhanced tangential velocity on radial outward side 4. Higher theta-e in updraft Downdraft 1.Radial tilt outwards 2. More mature convection with higher vertical extent found on downwind side 3. Overturning circulation on radial outward side Radial inflow from outward side z=2-4km that descends to surface or Indirect overturning circulation on inward side called inner-edge downdraft (IED) Downdraft Left side displays descending midlevel radial flow and right side is indirect overturning circulation on inward side Stratiform 1. Found on downwind sector of band 2. Radial tilt outwards with bright band at 5 km Distant Rainband Inner Rainband 1.Radial tilt inwards 2. Updraft on radial outward side 3. Strong horizontal convergence at base of updraft and divergence above 4. Structure similar to squall lines 1. Shallow convection below 5 km 2. Reflectivity above 7km is condensates from eyewall convection 3. Hypothesized to form close to the eyewall and propagate outwards