Concentric Eyewall Asymmetries in Hurricane Gonzalo (2014) Observed by Airborne Radar

Abstract

Two eyewall replacement cycles were observed in Hurricane Gonzalo by the NOAA P3 Tail (TA) radar and the recently developed NASA High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) radar. These observations captured detailed precipitation and kinematic features of Gonzalo’s concentric eyewalls both before and after the outer eyewall’s winds became the vortex maximum winds. The data were analyzed relative to the deep-layer environmental wind shear vector. During the beginning eyewall replacement cycle stages, the inner and outer eyewalls exhibited different asymmetries. The inner eyewall asymmetry exhibited significant low-level inflow, updrafts, and positive tangential acceleration in the downshear quadrants, consistent with observational and theoretical studies. The outer eyewall asymmetry exhibited these features in the left-of-shear quadrants, further downwind from those of the inner eyewall. It is suggested that the low-level inflow occurring at the outer but not at the inner eyewall in the downwind regions signals a barrier effect that contributes to the eventual decay of the inner eyewall. Toward the later eyewall replacement stages, the outer eyewall asymmetry shifts upwind, becoming more aligned with the asymmetry of the earlier inner eyewall. This upwind shift is consistent with the structural evolution of eyewall replacement as the outer eyewall transitions into the primary eyewall of the storm.

Dynamics of the Transition from Spiral Rainbands to a Secondary Eyewall in Hurricane Earl (2010)

“…Here, isolated or connected convective cells are initiated and form the upwind end of the larger spiral rainband complex (Didlake and Houze 2013a). In the left-of-shear half, stratiform precipitation is predominant in the downwind end of the complex (May and Holland 1999;Didlake and Houze 2013b). The rainband features associated with this downwind region project more strongly onto the axisymmetric structure given both the mesoscale, homogeneous nature of stratiform precipitation and the fact that these features occur at a smaller radius.…”

“…Secondary eyewalls are frequently observed phenomena in intense tropical cyclones (TCs). Many studies show that these features form when convection outside of a preexisting primary eyewall coalesces into a connected ring with a collocated axisymmetric tangential wind maximum (e.g., Willoughby et al 1982;Black and Willoughby 1992;Dodge et al 1999;Houze et al 2007;Didlake and Houze 2011;Bell et al 2012). Once a secondary eyewall forms, characteristic changes in size and intensity usually occur, which makes predicting these inner-core features a high priority for forecasters (Sitkowski et al 2011(Sitkowski et al , 2012Kossin and Sitkowski 2012;Yang et al 2013;Kossin and DeMaria 2016;Zhang et al 2017).…”

“…In an observational study of Hurricane Rita, Didlake and Houze (2013b) found that the downwind stratiform region of the rainband complex exhibited a mesoscale descending inflow jet similar to the rear-to-front jet of leading-line mesoscale convective systems (MCSs;Houze 2004). At the innermost point of the inflow jet, air suddenly plummets from the middle levels into the boundary layer, which then connects to a local enhancement of the boundary layer radial inflow.…”

Distinct Raindrop Size Distributions of Convective Inner‐ and Outer‐Rainband Rain in Typhoon Maria (2018)

“…In contrast, outer (or distant) rainbands occur often outside the inner-core region, far from the intrinsic vortex dynamics of a TC (Houze, 2010;Li & Wang, 2012). Previous studies have indicated that inner and outer rainbands have different kinematic structures and features (Black & Hallett, 1999;Bogner et al, 2000;Hence & Houze, 2008;Li & Wang, 2012;Moon & Nolan, 2010;Montgomery & Kallenbach, 1997;Wang, 2009;Wang, 2012;Willoughby, 1978), leading to different cloud structures and rain microphysics (Didlake et al, 2017;Houze, 2010Houze, , 2014. As a fundamental property of rain microphysics, the raindrop size distribution (RSD) characteristics within the inner and outer rainbands have not yet been well investigated.…”

Validation of an Airborne Doppler Wind Lidar in Tropical Cyclones

“…While meteorological observations have improved in both quality and density, there remain important data-sparse regions in tropical cyclones (TCs). These regions include the boundary layer [1,2,3] and precipitation free areas, such as moats between the eyewall and outer rainbands or the eyewall and secondary eyewall [4]. One priority of the hurricane research community is to understand the physical processes and dynamics in these areas and ultimately to link them to TC genesis and intensification in order to improve TC forecasts [5,6,7].…”