Characteristics of convective-scale updrafts in the outer core of numerically simulated tropical cyclones: lower-layer shear versus upper-layer shear

The characteristics of convective-scale updrafts in the outer core of tropical cyclones (TC) simulated under lower- and upper-layer vertical wind shear are compared in this study. The results show that there are quite a few notable differences between the two experiments. More deep updrafts develop up to the tropopause in the lower-layer shear experiment, with their top heights above 12 km. Vertical mass transport, maximum vertical velocity associated with outer-core updrafts are statistically significantly larger in the lower-layer sheared TC than in the upper-layer sheared TC, which is related to larger convective effective potential energy, equivalent temperature and water vapor mixing ratio in the boundary layer. Furthermore, the interaction among the lower-layer vertical wind shear, local wind shear induced by the circulation of TC and surface cold pools is also favorable to the initiation and development of updrafts. The radial tilts of the updrafts is associated with updraft top height and asymmetric radial flows. Updrafts with top heights exceeding 12 km dominates in lower-layer shear experiment, the preferential radial tilt is radially outward induced by upper-level asymmetric radial outflow in downshear quadrants but radially inward induced by upper-level asymmetric radial inflow in upshear quadrants. However, in upper-layer shear experiment, most of updrafts prefer to tilt radially inward in height, the largest proportion of the updrafts originate from in upshear quadrants and downshear right quadrant, another small proportion of updrafts with top heights less than 8 km originates from downshear left quadrant, which induced by asymmetric radial inflow at upper-level of troposphere in upshear quadrants and downshear right quadrant, and asymmetric radial inflow in low-mid troposphere in downshear left quadrant, respectively. In the lower-layer shear experiment, updrafts in all quadrants tended to move radially inward induced by radial inflow in lower levels. However, in the upper-layer shear experiment, updrafts in upshear quadrants tended to move radially outward induced by radial outflow in lower levels, updrafts in downshear quadrants tended to move radially inward induced by radial inflow in lower levels. Most of updrafts in lower-layer shear experiment exhibit larger positive thermal buoyancy and negative dynamic buoyancy, resulting in a negative to positive distribution of total buoyancy. In contrast, in the upper-layer shear experiment, most of the updrafts exhibit smaller positive thermal buoyancy and positive dynamic buoyancy, resulting in positive total buoyancy.