An Observational Analysis of Ocean Surface Waves in Tropical Cyclones in the Western North Pacific Ocean

Abstract

Knowledge of ocean surface waves in tropical cyclones (TCs) is necessary to calculate air-sea exchanges of momentum and enthalpy for improved TC predictions. Here we use 24 years of TC and significant wave height (SWH) observations in the western North Pacific to analyze storm-following waves within the TC. The SWH was composited according to the TC translation speed, U h , and TC intensity based on V m , the maximum 10-m wind speed. The results show that SWH is largely symmetrical for slow-moving TCs when U h is less than 3 m/s and is asymmetric for faster-moving storms with larger waves in the right-front quadrant referenced to the TC heading. For a class of TCs translating at a medium U h between 3 and 7 m/s, a little less than the waves' group speed, near resonance leads to strong asymmetry with over 50% of waves with SWH exceeding 7-8 m on the right-front quadrant. As V m intensifies to 50 m/s and greater, extreme waves develop and become saturated: SWH ≈ 10-11 m, corresponding to when, as shown in previous studies, the momentum exchange coefficient C D levels off while the enthalpy exchange coefficient C k may increase. Over 80% of the saturated waves then reside in the right-front quadrant, indicating the quadrant's dominant influence on C D and C k . The medium-translating TCs were found to have a greater propensity for intensification than other types of TCs. Our results suggest a link between TC intensity, translation, and wave saturation and asymmetry in the right-front quadrant.Plain Language Summary Tropical cyclones-hurricanes and/or typhoons-are among the most spectacular yet destructive natural phenomena on Earth. Knowledge of ocean surface waves produced by tropical cyclones is necessary to improve the estimates of heat and momentum exchanges between the storm and the sea, which in turn can lead to improved storm predictions. Here we analyzed observations of tropical cyclone tracks, winds, and significant wave heights in the western North Pacific from 1992 to 2015, by following each storm to study wave patterns and properties within a few hundred kilometer radius of the cyclone's center. Our results show that the development of extreme waves 10-11 m on the right-front portion of the storm is related to a class of cyclones that move over the ocean surface neither too slowly nor too quickly and that are also more prone to intensification.Previous observational and modeling studies have yielded insights into how ocean surface waves evolve under TCs Holthuijsen et al., 2012;Hwang & Walsh, 2016;Wright et al., 2001). Under a translating TC, ocean surface waves develop asymmetric patterns with highest significant wave height (SWH; H s ) in the anticyclonic-front quadrant referenced to the TC heading (i.e., right-front (RF) quadrant in the Northern Hemisphere, and left-front (LF) quadrant in the Southern Hemisphere; Bowyer & MacAfee, 2005; Fan et al., ZHANG AND OEY 184

Tropical Cyclone Cold Wake Size and Its Applications to Power Dissipation and Ocean Heat Uptake Estimates

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Forecasting Hurricane-forced Significant Wave Heights using the Long Short-Term Memory Network in the Caribbean Sea

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