On Surface Waves Generated By Extra-Tropical Cyclones. Part I: Multi-Satellite Measurements

Abstract

Surface waves generated by Extra-Tropical Cyclones (ETCs) can significantly affect shipping, fishing, offshore oil and gas production and other marine activities. This paper presents results of satellite-data-based investigation of wind waves generated by two North Atlantic ETCs. These ETCs were fast-moving systems, inhibiting resonance (synchronism) between the group velocity of the generated waves and the ETC translation velocity. For these cases, the wave generation begins when the front-boundary of the storm appears at a given ocean location point. Since developing waves are slow, they move backward relative to the storm, grow in time, and then leave the ETC stormy area through the rear sector. Multi-satellite observations confirm such a paradigm, and reveal that the storm regions is filled up with young developing wind waves which are most developed in the rear-right sector. As observed, the energy of these waves was growing in time during the ETC life span. It is demonstrated that the extended-fetch concept (inherent for Tropical Cyclones) does not apply for ETC. Instead, by analogy, the concept of extended-duration wave growth concept is more relevant. Satellite observations well confirm the validity of duration-laws for waves generated by ETCs, and demonstrate that extended-fetch regime for observing waves can only asymptotically be achieved, - at time intervals exceeding the lifespan of considered ETCs.

On Surface Waves Generated by Extra-Tropical Cyclones—Part II: Simulations

“…The second ETC (ETC#2) originated in about the same area but slightly later, at noon on 12 February 2020. Unlike ETC#1, it moved to the northeast, and when it reached 60°N, adjoining Iceland, at noon on 14 February 2020, it lost its initial shape, turning into an "air jet" along the southeast coast of Greenland (follow the wind fields in Animation 1) or Animation 2, and see Section 2.1 in PART I [38]).…”

“…In addition, more wave data, namely, SWH, spectral peak parameters, and wave spectra, were obtained from the China-France Ocean Satellite for Surface Wave Investigation and Monitoring (CFOSAT-SWIM). In total, 130 altimeter tracks and 37 CFOSAT-SWIM tracks were collected over the study area during the life span of both ETCs (see Figures 3 and 4 in PART I [38], where coverage of the study area by satellite data and the trajectories of ETCs are shown).…”

“…In PART I [38], the satellite measurements of surface waves in the storm area of ETCs were analysed using classical self-similar laws of wave growth within the extended fetch/duration framework. Although the applicability of these simplified laws is limited to spatially uniform and steady wind conditions, they are reported to be capable of reproducing the time evolution of maximal values of SWH and wavelength in the storm area during the ETC lifespan.…”

“…To that end, we compared the simulation results of the 2D model with measurements from all altimeter and CFOSAT-SWIM tracks covering the North Atlantic during the study period. In total, 130 altimeter tracks (see Figure 3 in PART I [38]) and 37 CFOSAT-SWIM tracks (see Figure 4 in PART I [38]) were used to perform this comparison. Figure 1 demonstrates the scatter plots of "observed-vs-modeled" SWH (Hs T ) for all tracks crossing the North Atlantic during the lifespans of ETC#1 and ETC#2.…”

“…Already discussed in the companion paper [38] (hereinafter referred as PART I), wind fields inside ETC cases selected for this study were definitely extremely variable in both time and space. This suggests applying and testing the simulation procedure suggested in [37] to simulate surface wave characteristics induced by ETCs, and the resulting swell systems.…”