The influence of boreal summer intra-seasonal oscillations on Indo-western Pacific Ocean surface waves

Abstract

The present study examines the influence of Boreal Summer Intra-Seasonal Oscillation (BSISO) on Tropical Indian Ocean surface waves using the latest version of ECMWF reanalysis (ERA5) during summer monsoon months June through August (JJA). BSISO is a distinct mode of ISO during JJA having a northward and eastward movement from the equatorial Indian Ocean to the western Pacific Ocean. Composite analysis of anomalies of significant wave heights (SWH), wind sea, swell, and mean wave period for 8 phases of BSISO has been carried out to understand its influence. SWH anomalies in response to BSISO’s are phase-dependent. Negative SWH anomalies are noticed with strong northward and weak eastward propagation during the phases 1–3 in response to the easterly wind anomalies over the north Indian Ocean (NIO). During phases 5–7, high positive SWH anomalies (~ 0.5 m) in response to the westerly wind anomalies with northward and weak eastward propagation over NIO. Phases 4 and 8 behave like transition phases. In addition, enhanced (suppressed) SWH anomalies (~ 0.5 m) are seen during the active (break) spells of BSISO over NIO. Over the southern tip of India, negative (positive) SWH anomalies prevail during the active (break) conditions. This study clearly suggests that the wave forecast advisories during intra-seasonal time scales would be more useful for offshore and coastal activities during the summer monsoon.

Influence of climate variability on wind‐sea and swell wave height extreme over the Indo‐Pacific Ocean

“…A northward arch‐like feature in the pattern of Pmax during DJF reflects a systematic northward penetration of swells arising from the storms in the NP and SO, consistent with previous studies (Chen et al ., 2002; Zhang et al ., 2011). However, regions such as the AS and western TIO tend to experience reduced Pmax, indicative of less swell activity, and possibly due to the mixing of north‐westward swells with northeasterly monsoon winds, thereby mitigating the swell impact (Remya et al ., 2020; Srinivas et al ., 2020). A similar pattern of extreme parameters is evident during MAM, but the latitudinal width of the wind‐wave climate signal contracts in the NP and expands in SO.…”

Impact of leading Indo‐Pacific climatic modes in modulating the wave power variability and their trends in the North Indian Ocean

“…Similar attempt was done by Fu et al (2018) to establish a relationship between the wave climate and different types of IOD events in the North Indian Ocean (NIO) and found the impact of different IOD events on the wave climate variations over the southeastern region of Sri Lanka. Srinivas et al (2020) studied the influence of Boreal Summer Intra‐Seasonal Oscillation on the Tropical IO surface waves during summer monsoon. Remya et al (2020) studied the effect of tropical and extra‐tropical climate modes on wind‐wave climate of the IO.…”

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

“…However, so far global studies of waves showed no significant relation between climate indices such as the ENSO or the Southern Annular Mode (SAM) and the waves over the wSA, when the interannual component is considered (Godoi et al, 2020;Godoi and Torres Júnior, 2020;Reguero et al, 2015). On the other hand, there is a rise of evidence of modulation in intraseasonal timescales of the wave fields by atmospheric processes (e.g., Godoi and Torres Júnior, 2020; Srinivas et al, 2020). As an example, the Boreal Summer Intra-Seasonal Oscillation (BSISO) in the tropical Indian Ocean is part of the summer monsoon and influences the surface winds, consequently modulating the swh anomalies over its different phases (Srinivas et al, 2020).…”

“…On the other hand, there is a rise of evidence of modulation in intraseasonal timescales of the wave fields by atmospheric processes (e.g., Godoi and Torres Júnior, 2020; Srinivas et al, 2020). As an example, the Boreal Summer Intra-Seasonal Oscillation (BSISO) in the tropical Indian Ocean is part of the summer monsoon and influences the surface winds, consequently modulating the swh anomalies over its different phases (Srinivas et al, 2020). Over the Pacific, Atlantic and Indian oceans, Godoi et al (2020) found significant dependences between the increase in austral summer swh anomalies and different ENSO-MJO (Madden-Julian Oscillation) phase combinations.…”