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Distinct Oceanic Responses at Rapidly Intensified and Weakened Regimes of Tropical Cyclone Ockhi (2017)
Journal article   Peer reviewed

Distinct Oceanic Responses at Rapidly Intensified and Weakened Regimes of Tropical Cyclone Ockhi (2017)

Lingala Jyothi, Sudheer Joseph, Suneetha P, Matthew Huber and Lijo Abraham Joseph
Journal of geophysical research. Oceans, Vol.127(6)
2022
DOI: https://doi.org/10.1029/2021JC018212
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Abstract

mixing ocean stratification rapid intensification rapid weakening salinity tropical cyclone Ockhi
This study analyzed the upper ocean responses to tropical cyclone (TC) Ockhi (2017) from two regions where it underwent (a) rapid intensification (RI) and (b) rapid weakening (RW) using simulations from the high‐resolution HYbrid Coordinate Ocean Model. Pre‐existed oceanic conditions in the RI region were warmer and fresher than in the RW region. Though the translation speed was slower over the RI region, the storm‐induced sea surface temperature cooling was weaker (−0.8°C) while a significant cooling (−1.9°C) was observed at RW. The mixed layer heat budget analysis revealed that the dominant process driving the temperature tendency in the RI and RW regions were surface thermal forcing (−0.01°C h−1) and entrainment (−0.015°C h−1), respectively. The role of entrainment was restrained by a thick barrier layer in the RI region. The TC‐induced mixing over a weakly stratified ocean at RW resulted in a significant drop in dynamic temperature (Tdy) compared to the RI. The cooling differences were attributed to the contrasting salinity stratification at RI and RW regimes which modulated the ocean's negative feedback to TC intensity changes. Further, the difference between the depths of mixing length and 26°C isotherm at RI and RW regimes indicate that 26°C isotherm does not necessarily represent the mixing depth under the influence of TC. Hence, this study suggests Tdy may be a better metric for cyclone intensity changes than heat content above a fixed isotherm, particularly in the salinity stratified regions. Plain Language Summary Strong surface winds accompanying tropical cyclones usually cool the ocean surface by bringing cooler waters from below the surface. The magnitude of this cooling depends on the intensity of the cyclone, its travel speed, and the underlying ocean condition over which the storm moves. This study examined the ocean responses to cyclone Ockhi (2017), which occurred over the Arabian Sea during the November‐December month. In the early stage of Ockhi, where it had rapidly intensified, the storm moved slowly, and the ocean was forced by intense winds. These conditions, in general, lead to significant ocean surface cooling as it gets more time to interact with the TC. However, in the case of Ockhi, a thick barrier layer resulting from freshwater intrusion inhibited the TC‐induced cooling. On the contrary, there was prominent cooling during the rapidly weakening stage of Ockhi due to the absence of a barrier layer as the waters were more saline. The disparity in the cooling between RI and RW stages had provided distinct negative ocean feedback to the cyclone. Key Points Upper ocean responses to cyclone Ockhi are studied using a numerical ocean model (HYbrid Coordinate Ocean Model) in its rapidly intensified and weakened regions Contrasting salinity structure at rapidly intensified (weakened) regions resulted in a negligible (significant) drop in dynamic temperature Analysis of the mixed layer heat budget in the two regions highlighted the role of the barrier layer on entrainment‐based cooling

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Collaboration types
Domestic collaboration
International collaboration
Citation topics
8 Earth Sciences
8.19 Oceanography, Meteorology & Atmospheric Sciences
8.19.113 Weather Forecasting
Web Of Science research areas
Oceanography
ESI research areas
Geosciences
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