Purdue University, Department of Earth, Atmospheric and Planetary Sciences, West Lafayette, 47906, USA.
Indian Institute of Technology Bhubaneshwar, Bhubaneshwar, India.
Sci Rep. 2019 Mar 4;9(1):3382. doi: 10.1038/s41598-019-40332-z.
We present a numerical investigation of the processes that influenced the contrasting rapid intensity changes in Tropical Cyclones (TC) Phailin and Lehar (2013) over the Bay of Bengal. Our emphasis is on the significant differences in the environments experienced by the TCs within a few weeks and the consequent differences in their organization of vortex-scale convection that resulted in their different rapid intensity changes. The storm-relative proximity, intensity, and depth of the subtropical ridge resulted in the establishment of a low-sheared environment for Phailin and a high-sheared environment for Lehar. Our primary finding here is that in Lehar's sheared vortex, the juxtaposition in the azimuthal phasing of the asymmetrically distributed downward eddy flux of moist-entropy through the top of the boundary layer, and the radial eddy flux of moist-entropy within the boundary layer in the upshear left-quadrant of Lehar (40-80 km radius) establishes a pathway for the low moist-entropy air to intrude into the vortex from the environment. Conversely, when the azimuthal variations in boundary layer moist-entropy, inflow, and convection are weak in Phailin's low-sheared environment, the inflow magnitude and radial location of boundary layer convergence relative to the radius of maximum wind dictated the rapid intensification.
我们对影响孟加拉湾热带气旋（TC）法利纳和勒哈尔（2013 年）强度急剧变化的过程进行了数值研究。我们的重点是在几周内 TC 经历的环境的显著差异，以及由此导致的涡旋尺度对流组织的差异，从而导致它们的强度急剧变化不同。风暴相对接近度、强度和亚热带脊的深度导致法利纳处于低切变环境，而勒哈尔处于高切变环境。我们的主要发现是，在勒哈尔的切变涡旋中，通过边界层顶部向下的涡旋通量的不对称分布的湿熵与边界层内的湿熵径向涡旋通量在勒哈尔的上风左侧象限（40-80 公里半径）中的方位角相位排列，为低湿熵空气从环境侵入涡旋建立了一条途径。相反，当法利纳的低切变环境中边界层湿熵、流入和对流的方位变化较弱时，流入量大小和边界层收敛相对于最大风速半径的径向位置决定了快速增强。
