The effect of atmosphere–ocean coupling on the prediction of 2016 western North Pacific tropical cyclones

Abstract

We examine the merit of atmosphere-ocean coupled models for tropical cyclone (TC) predictions in the western North Pacific (WNP), where accurate TC predictions remain challenging. The UK Met Office operational atmospheric global numerical weather prediction (NWP) model is compared with two trial coupled configurations, in which the operational atmospheric model is coupled to a one-dimensional mixed-layer ocean model and a three-dimensional dynamical ocean model. Reforecasts for the 2016 TC season show that the coupled models outperform the NWP model for TC location predictions, with a systematic improvement of 50-100 km over the seven-day forecasts, but the coupled models amplify the underestimation of TC intensity in the NWP model. Nearly identical TC predictions (for both location and intensity) are found in the two coupled models, indicating the dominance of thermodynamic processes at the air-sea interface for TC predictions on these timescales. The improved prediction of the TC position in the coupled models is associated with an enhanced Western North Pacific Subtropical High (WNPSH), which introduces an anticyclonic steering flow anomaly that shifts TC tracks further west in the southern part of the region and further east in the northern part. Based on sensitivity experiments, we show that these improvements in the coupled models are due mainly to colder initial sea-surface temperatures (SSTs). Air-sea feedbacks do not change the WNPSH or TC tracks noticeably. Apart from the effect of the initial SSTs, tropical ocean warming due to air-sea interaction in the coupled forecasts can also reduce the predicted TC intensity, presumably due to a stronger regional Hadley circulation with increased subtropical subsidence.

Simulations of Bay of Bengal tropical cyclones in a regional convection-permitting atmosphere–ocean coupled model

“…Cooler SSTs to the right of the TC track drive the TC towards the relatively warmer SSTs to its left. The leftward displacement of TC tracks in CPL agrees with other studies of coupled models (Khain & Ginis, 1991;Wu et al, 2005), although some authors have also found rightward displacement (Bender et al, 1993) or both leftward and rightward 250 displacement (Feng et al, 2019).…”

“…Lewis et al, 2019). Most previous studies show that air-sea coupling reduces TC 70 intensity (Feng et al, 2019;Mogensen et al, 2017;Neetu et al, 2019;Takaya et al, 2010;Zarzycki, 2016; https://doi.org/10.5194/wcd-2021-46 Preprint. Discussion started: 26 July 2021 c Author(s) 2021.…”

The influence of air–sea coupling on forecasts of the 2016 Indian summer monsoon and its intraseasonal variability

“…Further details on these forecasts can be found in Feng et al . (2019), which analysed the same three sets of forecasts for West Pacific tropical cyclones.…”

“…Comparing KPP and ATM shows the effects of thermodynamic air-sea coupling; comparing NEMO and ATM shows the effects of thermodynamic and dynamic coupling (i.e., including the ocean dynamical response); comparing NEMO and KPP shows the effects of ocean dynamics within the coupled system. Further details on these forecasts can be found in Feng et al (2019), which analysed the same three sets of forecasts for West Pacific tropical cyclones.…”

Impact of Tropical Cyclones on Inhabited Areas of the SWIO Basin at Present and Future Horizons. Part 1: Overview and Observing Component of the Research Project RENOVRISK-CYCLONE

“…As highlighted in the latest reports of WMO's International Workshop on Tropical Cyclones (IWTC), research carried out over the last four years has considerably improved our understanding of TC intensification processes [1,2], as well as TC tracking and intensity forecasting [3,4]. The operational implementation of coupled ocean-atmosphere (OA) numerical weather prediction (NWP) systems by many national weather services has, in particular, played a key role in reducing forecasting errors at all space and time scales [5][6][7][8]. Despite these important advances, additional efforts are still needed to accurately predict and characterize the potential impacts of tropical cyclones on a given territory, especially during landfall.…”