Data from: The role of outflow-layer inertial stability in governing the radial location of secondary eyewall formation in tropical cyclones

Secondary eyewall formation (SEF) in tropical cyclones (TCs) emerges from
a complex interplay of internal dynamics and environmental influences.
Motivated by observations linking low inertial stability in the TC outflow
layer to eyewall replacement cycles, we investigate how variations in
outflow‐layer inertial stability control both the initiation and radial
position of SEF. Idealized simulations reveal that reduced outflow‐layer
inertial stability enhances upper‐level divergence and updraft in the TC
outer core, fostering the growth of stratiform rainbands. By averaging
secondary circulation over the domain grids featuring stratiform
precipitation, it is explicitly shown that the strength of the mesoscale
descending inflow (MDI) is greater within the widespread and more
developed stratiform clouds. Such stratiform‐induced MDI can dynamically
and thermodynamically broaden the tangential wind field in the lower
altitudes. As a result, the ensuing increase in boundary‐layer inertial
stability and inflow supplies greater absolute vorticity influx in the
outer‐core region, making the tangential wind tendency peaks and the
secondary eyewall intensifies at a larger radius. This study highlights
the role of MDI in the coupling between the upper‐ and lower‐tropospheric
dynamics.

热带气旋（tropical cyclones, TCs）中的二次眼墙形成（secondary eyewall formation, SEF）源于内部动力过程与环境影响间的复杂相互作用。受“热带气旋流出层低惯性稳定性（inertial stability）与眼墙置换循环（eyewall replacement cycles）存在关联”的观测结果启发，本研究探讨了流出层惯性稳定性变化对二次眼墙形成起始过程与径向位置的调控作用。理想数值模拟（idealized simulations）结果显示，减弱的流出层惯性稳定性会增强热带气旋外核区（outer core）的高层辐散（upper-level divergence）与上升气流（updraft），进而促进层状雨带（stratiform rainbands）的发展。通过对包含层状降水（stratiform precipitation）的计算域网格内的次级环流（secondary circulation）进行平均分析，本研究明确证实：在分布范围更广、发展更成熟的层状云团内部，中尺度下沉入流（mesoscale descending inflow, MDI）的强度更强。这类由层状云诱发的中尺度下沉入流，可通过动力与热力过程拓宽低层切向风场（tangential wind field）。由此引发的边界层惯性稳定性（boundary-layer inertial stability）增强与入流过程，将为外核区提供更多的绝对涡度输入（absolute vorticity influx），使得切向风倾向峰值出现在更大半径处，同时二次眼墙也会在更大半径处增强。本研究阐明了中尺度下沉入流在对流层上下层动力学（upper- and lower-tropospheric dynamics）耦合过程中的关键作用。