Generation of Quasi‐Biweekly Yanai Waves in the Equatorial Indian Ocean. Issue 16 (21st August 2020)

• Record Type: Journal Article
• Authors: Arzeno, Isabella B.; Giddings, Sarah N.; Pawlak, Geno; Pinkel, Robert
• Is Part Of: Geophysical research letters. Volume 47:Issue 16(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-21
• Subjects: equatorial -- Yanai waves -- mixed Rossby‐gravity waves -- satellite -- sea surface height -- monsoon; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL088915
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The spatial and temporal structure of quasi‐biweekly Yanai waves in the Indian Ocean and their relationship to wind stress are uniquely described using satellite observations of sea level anomalies and wind velocities, previously approximated only using theory, numerical models, and discrete mooring observations. Yanai waves represent a significant contribution to equatorial antisymmetric sea level anomaly variability in the 10–20 day band. Robust climatologies produced using 17 years of data (spanning 45–95°E and 10°S to 10°N) reveal a clear spatiotemporal pattern and are consistent with Yanai wave generation in the western equatorial Indian Ocean during monsoon seasons. Spectral and correlation analyses imply that Yanai waves are linearly forced by wind stress patterns with similar wavelengths. A new method of assembling data composites shows the first full structure of a vertical mode‐2 Yanai wave moving across the equatorial Indian Ocean under westward propagating wind vortices. Plain Language Summary: We use sea surface height (SSH) and wind velocity data gathered by satellites to study a large‐scale wave in the Indian Ocean (known as a Yanai wave) that has previously only been understood using theory, numerical models, and limited data. Yanai waves account for a significant portion of the 10–20 day variability in the equatorial Indian Ocean SSH. After analyzing 17 years of satellite data (spanning 45–95°E and 10°S to 10°N), we deduce that Yanai waves with a period of around 14 days are generated, primarily, in the western part of the equatorial Indian Ocean during the summer and winter monsoons. We find that the wind structure driving these Yanai waves is a set of vortices with a similar scale as the wave itself. Finally, we come up with a method that allows us to visualize, for the first time in the literature, the full Yanai wave propagating across the equatorial Indian Ocean. Key Points: Satellite data capture the signal of quasi‐biweekly oceanic Yanai waves and their associated wind structure Meridional wind stress drives quasi‐biweekly Yanai waves in the western Indian Ocean during monsoon seasons Composites defined using an HEOF‐based phase estimate show a synoptic vertical mode‐2 Yanai wave structure