Rapid Decay of Slowly Moving Typhoon Soulik (2018) due to Interactions With the Strongly Stratified Northern East China Sea

Abstract

Typhoon Soulik decayed rapidly via two-way interaction with the northern East China Sea, the extratropical shelf region, before landing on the Korean Peninsula on 23 August 2018. In the northern East China Sea, where the water column is strongly stratified with warm surface and cold subsurface waters, a large cold wake emerged with intense sea surface cooling, which is primarily caused by vertical mixing in the water column. This abrupt sea surface cooling rapidly increased the downward enthalpy flux, mostly in the form of latent heat flux. The slow translation speed of Typhoon Soulik and strong thermal stratification in the region transferred its energy into the ocean, as the typhoon had a long residence time over the wake, and consequently led to rapid decay with energy loss to typhoon intensity ratio of −4.4 ± 1.0 hPa (kJ cm −2 ) −1 . Plain Language SummaryUnderstanding and predicting tropical cyclones, including typhoons, are very important for reducing and preventing damages to life and property. In August of 2018, Typhoon Soulik was predicted to make landfall on the Korean Peninsula as a strong cyclone with high winds. However, the typhoon rapidly weakened over the northern East China Sea before making landfall-a failed prediction. This study reveals that the rapid decay was caused by two-way interactions between the typhoon and the ocean on the continental shelf. Strong mixing with cold subsurface water due to the high winds associated with the slowly moving typhoon significantly lowered the sea surface temperature, leading to energy loss into the ocean for a sufficiently long period of time to cause rapid decay. These results provide quantitative evidence of energy exchange between the typhoon and the ocean, which can help to improve forecasts of tropical cyclone intensity particularly in the stratified shelf region. Key Points:• Two-way interactions between stratified ocean and a slowly translating (~2 m s −1 ) tropical cyclone yields rapid decay • Severe (>8°C) sea surface cooling is primarily caused by vertical mixing with cold subsurface water on the extratropical shelf • Rapid decay is driven by downward energy transfer enhanced by Soulik's long (~15-hr) residence time over a large cold wake

Compounding impact of severe weather events fuels marine heatwave in the coastal ocean

“…These constraints can influence the way sea surface temperature (SST), the critical thermodynamic interface for ocean–storm interaction, evolves and thus modifies storm intensity 9 . Several studies have shown that the presence of stratification prior to storm arrival can significantly reduce the intensity of impending storms, via ahead-of-eye SST cooling 7 , 8 , 10 , 11 . Conversely, other studies have suggested or shown that anomalously warm conditions on shelves have contributed to the intensification of hurricanes through landfall 6 , 12 – 14 .…”

Tropical cyclone response to anthropogenic warming as simulated by a mesoscale-resolving global coupled earth system model

“…Previous studies (2,4,39) have emphasized the need to use coupled mesoscaleresolving global atmosphere/ocean models in projecting the sensitivity of TCs to future climate change. Our results which are based on one of the highest-resolution coupled global model simulations of long-term future climate change conducted so far, provide new insights into the robustness of previously identified mechanisms.…”

“…TCs are detected and tracked by adopting (with some minor adjustments) a recently proposed method 4 . For our detection we use 6-hourly instantaneous surface pressure, 10-m wind speed, and surface vorticity.…”

“…A recent study(1) reveals consistent patterns in observed changes in TC occurrence and those simulated by climate models, leading to the conclusion that greenhouse warming may have already altered the statistics of TCs beyond the level of natural variability. However, there still remain major uncertainties in model-based projections of TCs, in part due to the effects of horizontal resolution (2,3), atmosphere-ocean coupling (4,5), the choice of physical parameterizations (6) and discretization of the underlying physical equations (7).…”

Characteristics of Satellite-Based Ocean Turbulent Heat Flux around the Korean Peninsula and Relationship with Changes in Typhoon Intensity

“…By 22 August, the intensity of Soulik had reached a stage of "very strong (wind speed of 44-54 m/s)", according to the typhoon intensity criteria of KMA, with a central pressure of 950 hPa and maximum wind speed of 43 m s −1 . Soulik weakened rapidly after the maximum stage, with the maximum wind speed decreasing to 12 m s −1 within 30 h [28]. Typhoon Francisco began to develop on 2 August 2019, over the ocean~1120 km northeast of Guam.…”