Changes in tropical cyclone intensity with translation speed and mixed‐layer depth: idealized WRF‐ROMS coupled model simulations

Abstract

In this study, two components of a coupled Ocean-Atmosphere-Wave-Sediment Transport modelling system, the atmosphere model Weather Research Forecasting (WRF) and the ocean model Regional Ocean Modeling System (ROMS), are used to investigate the relationships between tropical cyclone (TC) intensity changes and ocean mixed-layer depth (MLD) as well as translation speed through a series of idealized experiments. The coupled WRF-ROMS model can well simulate TC intensity changes and sea-surface temperature (SST) cooling induced by the TCs under different ocean MLD and background flow conditions. Surface enthalpy flux is reduced due to the SST decrease, which subsequently inhibits TC development. A smaller MLD and a slower speed produce a more symmetric cold wake under the TC inner core, which can effectively weaken the TC. The SST has a nonlinear decrease with increasing translation speed under the same MLD condition. A heat budget analysis supports that upwelling plays a more important role in changing the temperature within the upper ocean when the TC moves slowly (e.g. 1 m s −1 ). However, upwelling only dominates the subsurface temperature changes when the translation speed increases so that a smaller SST cooling occurs. A translation speed of 3 m s −1 is found to be the optimal speed for TC development when the MLD is thick enough (50 and 100 m in this study). A larger basic flow (>3 m s −1 ) produces a stronger asymmetry in the vertical velocity and results in a weaker secondary circulation, and hence inhibits TC intensification. For a shallow MLD of 20 m, a 5 m s −1 translation speed can mitigate more cooling effect and make it more favourable for TC maintenance. This result suggests the competing effects of atmospheric and oceanic conditions in determining TC intensity.

The Association of Typhoon Intensity Increase with Translation Speed Increase in the South China Sea

“…Compared to the WNP, the mixed layer was thinner and the thermocline was shallower in the SCS. Typhoons over the SCS [5,6,8,9,29,36,37,54] strongly impact the surrounding populations in the Philippines, Taiwan, Hong Kong, Macao, coastal China, Vietnam, and other neighboring regions. If the translation speed of these typhoons over the SCS increases, then, in the context of TC-ocean interaction, there is a possibility to favor TC intensity increase.…”

“…The slowing-down of Uh (e.g., the case of Typhoon Morakot in Taiwan in 2009 and Hurricane Harvey in the US in 2017) can increase hazards over land due to the longer impact time [1][2][3]. Over the ocean, Uh is an important parameter that influences TC-ocean interaction [4][5][6][7][8][9]. The faster the Uh, the smaller the TC-induced ocean cooling effect, and the more air-sea enthalpy flux is available for TC intensification [4,7,[10][11][12][13][14][15][16][17][18].…”

Developing the Coupled CWRF‐FVCOM Modeling System to Understand and Predict Atmosphere‐Watershed Interactions Over the Great Lakes Region

“…In the past two decades, there have been a growing number of attempts to develop regional coupled atmosphere-ocean models for both weather and climate research (Li et al, 2014;Peng et al, 2012;Seo et al, 2007;Turuncoglu et al, 2013;Wei et al, 2014). Recently, the popular Weather Research and Forecasting (WRF) model (Skamarock et al, 2008) has been coupled with various ocean models and implemented in several regions of the globe oceans (Masson et al, 2012;Samala et al, 2013;Warner et al, 2010;Zhao & Chan, 2017). In principle, these regional coupled models can be used to represent lake-atmosphere interactions over large, deep lakes (Anyah et al, 2006;Long et al, 2007;Song et al, 2004;X.…”

Effects of Model Coupling on Typhoon Kalmaegi (2014) Simulation in the South China Sea

“…TC-induced currents were simulated, and findings indicate that the vertical mixing during the forced stage response of the ocean penetrates to depths below the mixed layer [40]. Recently, fully coupled atmosphere-ocean-wave models have emerged as powerful platforms for TC simulations (e.g., [17,41,42]) and have since been increasingly applied in various types of studies such as air-sea interactions [28], impact of surface waves on TC [20,31,43], influence of mixed layer depth (MLD) on TC [44], contribution of non-breaking waves to upper-ocean mixing [24], impact on TC on SST cooling [10], and characteristics of surface waves under a TC [23]. Knowing the paramount importance of these air-sea processes, improving these aspects of simulations may correspondingly lead to substantial improvements in TC intensity forecast.…”