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.
Highlights
The active phases of boreal summer intra-seasonal oscillation (BSISO) create significant positive SWH anomaly over NIO during monsoon and the high SWH anomalies are seen over the AS (~ 0.5 m)
During the active phase of BSISO, AS experiences high wave activity and this may have an adverse impact on marine activities especially for navigation
Our analysis reveals that the BSISO mode has a significant influence on the ocean surface wave variability over the Indo-western Pacific Ocean
Summary
The active phases of BSISO create significant positive SWH anomaly over NIO during monsoon and the high SWH anomalies are seen over the AS (~ 0.5 m). During the active phase of BSISO, AS experiences high wave activity and this may have an adverse impact on marine activities especially for navigation.
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