Detection of intraseasonal oscillations in the Bay of Bengal using altimetry. (10th June 2019)

• Record Type: Journal Article
• Authors: Trott, Corinne B.; Subrahmanyam, Bulusu
• Is Part Of: Atmospheric science letters. Volume 20:Number 7(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-06-10
• Subjects: altimetry -- Bay of Bengal -- intraseasonal oscillations -- Madden‐Julian oscillation; Atmospheric physics -- Periodicals; 551
• DOI: 10.1002/asl.920
• Languages: English
• ISSNs: 1530-261X

Abstract

Abstract: Air–sea and mixed layer dynamics in the Bay of Bengal (BoB) respond strongly to Intraseasonal Oscillations (ISOs) that primarily operate on three observed time scales: the 30–90 day Madden‐Julian Oscillation, the 10–20 day quasi‐biweekly oscillation, and the synoptic‐scale 3–7 day oscillation of the monsoon trough. In this research, we focus on local and basin‐wide signals, zonal and meridional propagation, and variability of ISOs with respect to the strength of the summer monsoon season over a multi‐decadal period (1993–2016). For the first time, this study examines the relationship between larger‐ and shorter‐period ISOs in SLA and shows the usefulness of altimetry data in Indian monsoon studies. We compare ISOs in SLA during years with summer monsoons of varying strengths, finding notably stronger circulation and larger amplitude of all ISOs in years with stronger summer monsoons theorized in part to be due to the first‐baroclinic mode forcing from low‐level winds ( R 2 values of 0.61, 0.67, and 0.64 in the northern, central, and southern Bay, respectively), although it is important to note the influence of other local forcings, such as mesoscale eddies and coastal Kelvin waves. We demonstrate that 30–90 day variability of SLA is initially forced by equatorial processes and strengthened by local processes in the BoB, as higher‐amplitude SLA ISOs were consistently observed in the southern and eastern Bay. Local processes like coastal Kelvin waves were found to strongly influence the 10–20 day quasi‐biweekly signal, as was seen in the high‐amplitude 10–20 day SLA ISOs found in the eastern BoB. The synoptic signal also revealed a zonal pattern consistent with coastal Kelvin wave intensification and eddy generation. Abstract : This study for the first time analyzes altimetric‐derived sea level anomalies to observe three periods of monsoon intraseasonal oscillations. Unlike satellite‐derived temperature and salinity, altimeters do not experience contamination from cloud cover and can be used in all weather conditions. Time‐latitude diagrams of daily SLA (cm) for active summer monsoon and break summer monsoon seasons are longitudinally averaged over 85°–95°E and filtered at periods of (a, b) 30–90 day, (c, d) 10–20 day and (e, f) 3–7 day.