The influences of ocean on intensity of Typhoon Soudelor (2015) as revealed by coupled modeling

Abstract

Typhoon Soudelor (2015) moved northwestward toward Taiwan and passed several mesoscale ocean eddies over the open ocean. A high-resolution air-sea coupled model HWRF is employed to simulate Soudelor. Coupled model with low-or high-resolution ocean conditions can largely reduce the over-intensification of the typhoon from uncoupled modeling. Coupled modeling with a more realistic finer-resolution Hybrid Coordinate Ocean Model (HYCOM) analysis helps better capture the rapid weakening of the super-intense typhoon for the first 2 days and the following re-intensification before 80 hr, due to the initial more realistic ocean conditions. The rapid weakening is related to the existence of initial cold core ocean eddies near the earlier typhoon, while the warm core eddies tend to decrease the typhoon-induced SST cooling and thus induce the re-intensification of the later typhoon. The typhoon boundary layer is shallower at the rear-right quadrant of the moving typhoon than that at other quadrants. The coupled modeling results show that a much shallower boundary layer lower than 200 m is produced at the rearright quadrant for the super-intense typhoon as the typhoon passes over cold core eddies and induces stronger SST cooling. In addition, stronger typhoon cold wake in coupled experiments induces larger inflow angles at lower levels at the rear-right quadrant than other studies. The simulated track near and after landfall at east Taiwan is also improved for the coupled experiment compared to the uncoupled experiment. K E Y W O R D Scold core eddy, typhoon-ocean interaction, Typhoon Soudelor (2015)

Response of a tropical cyclone to a subsurface ocean eddy and the role of boundary layer dynamics

“…Although coupled simulations of tropical cyclones exist with a smaller horizontal grid spacing of 2–3 km, this is the first study of a tropical cyclone simulated in a global domain with no nesting and a grid spacing as low as 5 km for both the atmosphere and the ocean (Chen et al ., 2017; Li and Huang, 2019). Because horizontal diffusion parametrised in boundary‐layer schemes typically scales with the horizontal grid spacing in mesoscale models, simulated tropical cyclone intensity can increase when the horizontal grid spacing is decreased (Rotunno et al ., 2009).…”

“…However, the process by which tropical cyclone intensity changes is far from straightforward. Recent studies using coupled models turn to Emanuel's influential paradigm to explain changes in tropical cyclone intensity due to a cold wake (Emanuel, 1989; 1995; 1997; Lee and Chen, 2014; Chen et al ., 2017; Li and Huang, 2019). However, one shortcoming of this paradigm is that, while considering boundary‐layer thermodynamics, it does not recognise the importance of atmospheric boundary‐layer dynamics to spin up (Montgomery and Smith, 2014).…”

“…Although boundary‐layer dynamics has been shown to play an important role for the radially outward movement of the eyewall updraught in atmosphere‐only simulations, its role has not been examined in coupled simulations. Recent studies of the tropical cyclone cold wake attribute the radially outward movement of the eyewall updraught to decreasing surface latent heat flux and the accompanying weakening deep convection in the eyewall updraught (Chen et al ., 2010; 2017; Li and Huang, 2018; Guo et al ., 2020; Ma, 2020). While these studies do examine the role of boundary‐layer dynamics in determining the moisture transported inwards by the boundary layer, they do not examine the role of boundary‐layer dynamics in determining the inner‐core expansion.…”

Intensification of a distant hurricane by warm‐core eddies in the Gulf Stream in boreal fall

“…A statistical research has reported that the regions where intense TCs are observed correspond to those of active WCEs, and 70% of observed TCs over the Western North Pacific encounter the WCEs at least one time (Ma et al, 2017). Under these backgrounds, a lot of studies regarding the local influence of ocean conditions associated with the WCEs on TC intensity have been conducted for the real TCs such as Hurricane Opal (Shay et al, 2000), Hurricane Katrina (Wu et al, 2007), and Typhoon Soudelor (Li & Huang, 2019) and for the idealized TC (Sun et al, 2020).…”

A coupled model analyses on the interaction between oceanic eddies and tropical cyclones over the Bay of Bengal

“…The oceanic conditions occurring directly below the tropical cyclone, both surface and sub-surface, are often forgotten or not included in the analysis. Hence model studies are required to understand the oceanic processes that happen during the passage of tropical cyclones and how energy is transferred for cyclonic intensifications (Li and Huang 2019;Tada et al 2018). Atmospheric models use the observational SST data as oceanic forcing to simulate the cyclone track and intensity.…”