Intraseasonal variability of ocean surface wind waves in the western South Atlantic: the role of cyclones and the Pacific South American pattern

Abstract

Abstract. Extratropical cyclones are known to generate extreme significant wave height (swh) values at the ocean surface in the western South Atlantic (wSA), which are highly influenced by intraseasonal scales. This work aims to investigate the importance of intraseasonal timescales (30–180 d) in the regional climatology of waves and its atmospheric forcing. The variability is explained by analyzing the storm track modulation due to westerly winds. These winds present timescales and spatial patterns compatible with the intraseasonal component of the Pacific South American (PSA) patterns. The analyses are made using ECMWF’s ERA5 from 1979 to 2019 and a database of extratropical cyclones based on the same reanalysis. Empirical orthogonal function (EOF) analyses of the 10 m zonal wind and swh are used to assess the regime of westerlies and waves in the wSA. The EOF1 of the 10 m zonal wind (u10) presented a core centered at 45∘ W and 40∘ S, while the EOF2 is represented by two cores organized into a seesaw pattern with a center between 30–40∘ S and another to the south of 40∘ S. Composites of cyclone genesis and track densities as well as swh fields were calculated based on the phases of both EOFs. In short, EOF phases presenting cores with a positive (negative) u10 anomaly provide a favorable (unfavorable) environment for cyclone genesis and track densities and, therefore, positive (negative) swh anomalies. The modulation of the cyclone tracks is significant for extreme values of the swh. The spatial patterns of the EOFs of u10 are physically and statistically consistent with 200 and 850 hPa geopotential height signals from the Pacific, indicating the importance of the remote influence of the PSA patterns over the wSA.

A Comparison of Multiple Approaches to Study the Modulation of Ocean Waves Due To Climate Variability

“…Composite analysis determines the mean values of wave parameters over the years when the climate index anomalies are higher (lower) than plus (minus) 1 standard deviation (Sasaki et al., 2021). Hence, the composite analysis considers the mean values of wave parameters over significant event years.…”

“…Specifically, the wavelet coherence shows the covariability of time series pairs over the time–frequency domain. Wavelet analysis has previously been used to study regional wave variability (Anoop et al., 2015; Castelle et al., 2018; Cromwell, 2006; Sasaki et al., 2021; Scott et al., 2021); however, it has seldom been used to investigate global ocean wave variability. The wavelet codes used are available at https://paos.colorado.edu/research/wavelets.…”

“…In addition, it shows commonalities/differences between the responses for DJF and JJA. Furthermore, following Sasaki et al (2021) and Kumar et al (2016), ±1 standard deviation (dashed lines in Figure 3) was selected as the threshold value of each climate index anomaly to determine the wave parameter composites over significant event years (Figure 5 and Figures S4-S6 in Supporting Information S1). These significant event years are represented by the periods when climate indexes are above (below) the upper (lower) dashed lines in Figure 3.…”

The Effect of Currents on Large Surface Gravity Waves Under Cyclonic Conditions in the South/Southeastern Brazil

“…The southwestern South Atlantic Ocean is regularly traversed by cyclones (e.g., Gozzo et al., 2014; Hoskins & Hodges, 2005; Reboita et al., 2018), which can generate, among other effects, large surface gravity waves driven by the stormy winds (e.g., Da Rocha et al., 2004). In south/southeastern Brazil, there is a high frequency of cold fronts trailing from cyclones (e.g., Reboita et al., 2010; Sasaki et al., 2021), and these frontal systems have been pointed out as the main driver for the development of large wave events (LWEs, e.g., Da Rocha et al., 2004; Gramcianinov et al., 2020; Pianca et al., 2010). Cyclone‐generated waves may be hazardous in this region (e.g., Da Rocha et al., 2004; Innocentini & Neto, 1996), resulting in damage to economic activities such as navigation, harbors, oil/gas exploration, and fishery.…”

Persistent La Niña’s favor joint soybean harvest failures in North and South America

“…Similarly, ENSO can affect extra-tropical sea surface temperature regions (SST) that can subsequently induce atmospheric teleconnections of their own which might impact crops during the summer reproductive period (Anderson et al, 2017b;MacLeod et al, 2021;Vijverberg and Coumou, 2022). Relevant examples are the north pacific SST conditions which can influence boreal summer hot and dry conditions in the US and the south Atlantic SST conditions which can influence austral summer hot and dry conditions in South America (Barros et al, 2000;Cai et al, 2020;Doyle and Barros, 2002;Gelbrecht et al, 2021;Jorgetti et al, 2014;McKinnon et al, 2016;Sasaki et al, 2021;Vijverberg et al, 2020;Vijverberg and Coumou, 2022). Both these patterns are influenced by ENSO teleconnections which highlights a https://doi.org/10.5194/egusphere-2022-960 Preprint.…”