A study has been carried out to understand the similarities and differences in a pair of developing and a non-developing tropical disturbances using NCMRWF Unified Model (NCUM) and the concepts of marsupial theory of tropical cyclogenesis. We focused on two systems, tropical cyclone (TC) Ockhi that attained Very Severe Cyclonic Storm (VSCS) strength, and another system that attained deep depression state, however, subsequently weakened. As per the first hypothesis of Marsupial Paradigm, genesis of both the systems is found to be associated with a westward moving parent disturbance. The pouch region associated with the parent disturbance is identified as a region of enhanced moisture. The vertical profiles of vorticity and convergence show that the pathway of genesis is bottom-up for both the systems. Further analyses have been carried out to understand why the depression failed to attain tropical cyclone strength. It has been evidenced that the vertical wind shear is too high (> 50 ms− 1) in the premises of the depression core during the post-genesis evolution. At the same time, the center of the depression happened to be in the close proximity of a ridge present over central Indian land mass. Additionally, significant evidence of dry air intrusion into the core of the depression is seen in the Total Precipitable Water (TPW) analysis and HYSPLIT back trajectory analysis. Furthermore, the depression immediately interacts with the colder sea water as it moves northwestward. Though the marsupial paradigm of tropical cyclogenesis is applicable in the North Indian Ocean as well, factors such as SST, wind shear, closeness to the land mass may play a critical role in further development of the system.

中文翻译：

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利用NCUM预报系统研究NIO发展中和非发展中热带系统的气旋成因

使用 NCMRWF 统一模型 (NCUM) 和热带气旋发生有袋动物理论的概念，开展了一项研究，以了解一对发展中和非发展中热带扰动的异同。我们专注于两个系统，热带气旋 (TC) Ockhi 达到了非常强烈的气旋风暴 (VSCS) 强度，另一个系统达到了深低气压，但随后减弱了。根据有袋动物范式的第一个假设，发现这两个系统的起源都与向西移动的亲本扰动有关。与母体干扰相关的小袋区域被识别为水分增加的区域。涡度和收敛的垂直剖面表明两个系统的成因路径都是自下而上的。已经进行了进一步分析，以了解低气压未能达到热带气旋强度的原因。有证据表明，在后成因演化过程中，坳陷核心区的垂直风切变过高（> 50 ms- 1）。与此同时，洼地的中心恰好位于印度中部陆地上空的山脊附近。此外，在总可降水量 (TPW) 分析和 HYSPLIT 反向轨迹分析中可以看到干燥空气侵入洼地核心的重要证据。此外，当低气压向西北移动时，它会立即与较冷的海水相互作用。虽然热带气旋的有袋动物范式也适用于北印度洋，但海温、风切变、