The Stationary Banding Complex and Secondary Eyewall Formation in Tropical Cyclones

Abstract

89 GHz passive microwave satellite data are used to develop a five year climatology of the incidence and morphology of the stationary banding complex in tropical cyclones and quantify changes in convective morphology prior to secondary eyewall formation. The stationary banding complex is shown to be present in 39% of passive microwave overpasses. Morphology varies substantially between tropical cyclones, with crossing angles ranging from 0.19° to 61.78° and azimuthal extents from 0.29 π to 4.02 π radians. Variations in the incidence and geometry of the stationary banding complex are observed in different environmental conditions and geographic locations. For 84 secondary eyewall formation events included in the sample, a stationary banding complex is observed within 6 hr of the secondary eyewall developing in 79% of cases. Within 12 hr prior to secondary eyewall formation, the crossing angle is significantly lower than its sample median, while the azimuthal extent is higher than its sample median. These results demonstrate that secondary eyewall formation is (most) often preceded by the formation and axisymmetrization of a stationary banding complex.

Stronger Vertical Shear Leads to Earlier Secondary Eyewall Formation in Idealized Numerical Simulations

“…This result is seemingly inconsistent with Vaughan et al. (2020), which found that the VWS is significantly lower in the SBC group. Indeed, Vaughan et al.…”

“…Similar results were also evidenced in an observational study by Vaughan et al. (2020) in which a stationary banding complex (SBC) in TC's outer core was seen within 6 hr before SEF in about 80% concentric eyewall cases. Vaughan et al.…”

“…The continuous downward development of the outer rainbands combined with the boundary layer response-produced SEF. Similar results were also evidenced in an observational study by Vaughan et al (2020) in which a stationary banding complex (SBC) in TC's outer core was seen within 6 hr before SEF in about 80% concentric eyewall cases. Vaughan et al (2020) further documented that although the median VWS is generally lower in the SBC group than in the non-SBC group, relatively higher VWS is also observed in the SBC group.…”

“…This result is seemingly inconsistent with Vaughan et al (2020), which found that the VWS is significantly lower in the SBC group. Indeed, Vaughan et al (2020) also pointed out thatSBC cases can occur in a wide range of shear values. Therefore, those SBC events in shear of >10 m s −1 in Vaughan et al (2020) likely correspond with the SEF experiments in the current study.…”

“…Indeed, Vaughan et al. (2020) also pointed out thatSBC cases can occur in a wide range of shear values. Therefore, those SBC events in shear of >10 m s −1 in Vaughan et al.…”