Monitoring Intraseasonal Oscillations in the Indian Ocean Using Satellite Observations

Roman‐Stork, Heather L.; Subrahmanyam, Bulusu; Trott, Corinne B.

doi:10.1029/2019jc015891

Cited by 16 publications

(31 citation statements)

References 83 publications

(227 reference statements)

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“…These altered CKW patterns are consistent with previous studies (Rao et al, 2010; Roman‐Stork, Subrahmanyam, & Trott, 2019), which suggested that a strong pIOD could weaken the CKWs in the Bay to the point of reversing their sign, as seen in 2019. This has serious implications for freshwater transport into the southeastern Arabian Sea by the EICC, which is typically modulated by the second downwelling Kelvin wave and which is a major contributor to SW monsoon onset (Roman‐Stork, Subrahmanyam, & Trott, 2019; Roman‐Stork, Subrahmanyam, & Trott, 2020). The Rossby waves radiated by these Kelvin waves also work to excite eddying in the western Bay the following season (Chen et al, 2012; Rao et al, 2010; Sreenivas et al, 2012).…”

Section: Resultsmentioning

confidence: 99%

“…The 3-7-day mode, composed of synoptic disturbances and oscillations in the monsoon trough, is a primary contributor to the active and break cycles in the monsoon (Goswami et al, 2003;Subrahmanyam et al, 2020). With the monsoon system being a highly coupled phenomenon, a number of studies have focused on the atmospheric implications of these 3-7-day ISOs (Gadgil & Asha, 1992;Gadgil & Joseph, 2003;Goswami & Ajaya Mohan, 2001;Goswami et al, 2003;Krishnamurti & Bhalme, 1976;Murakami, 1976;Rajeevan et al, 2010;Singh & Nakamura, 2010), and some more recent studies have observed the oceanic response to these oscillations (Goswami et al, 2016;Roman-Stork, Subrahmanyam, & Trott, 2020;Subrahmanyam et al, 2020); however, there remains a gap in the knowledge as to how mesoscale eddies could be in turn influencing these synoptic oscillations.…”

Section: Introductionmentioning

confidence: 99%

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Interactions Between Mesoscale Eddies and Synoptic Oscillations in the Bay of Bengal During the Strong Monsoon of 2019

et al. 2020

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The 2019 southwest monsoon season is the first strong monsoon in the last 25 years and occurred concurrently with a strong positive Indian Ocean Dipole (pIOD). Given these unique circumstances, we examine the mesoscale eddy field in the Bay of Bengal (BoB) during 2019 and the interactions between these eddies and 3-7-day synoptic oscillations and tropical systems, which contribute to monsoon rainfall and modulate the active (wet) and break (dry) phases of the Indian monsoon. We find that there is a drastic difference in eddy characteristics between the western (80-90°E) and eastern (90-100°E) BoB, where eddies in the eastern BoB are dominated by coastal Kelvin wave (CKW) dynamics and topographical influences, and the eddies in the western BoB are more heavily modulated by East India Coastal Current dynamics. We further find that the pIOD increased the overall sea level in the BoB and modified CKW propagation in the BoB such that all eddy types had more positive sea level anomalies. We find that cyclonic eddies vary coherently with both upper ocean heat content and 3-7-day bandpass filtered precipitation and that both the number of cyclonic eddies and eddy amplitude increase in coherence with precipitation and ocean heat content following the passage of a tropical system. These results suggest a strong relationship between cyclonic eddies and 3-7-day atmospheric variability. Plain Language Summary The 2019 southwest monsoon is the first strong monsoon since 1994 and also occurred during a strong positive Indian Ocean Dipole event. We analyze the mesoscale eddy field in the Bay of Bengal during 2019 and investigate the connection between these eddies and 3-7-day synoptic oscillations, which control the active (flood) and break (drought) phases of the monsoon over India. We find that coastal Kelvin waves influence eddies in both the eastern and western Bay, but that ocean bottom topography and the western boundary current dominate each region's dynamics, respectively. The positive Indian Ocean Dipole heavily impacted the coastal Kelvin waves in 2019. 3-7-day synoptic events were most closely associated with cyclonic eddies, especially in the western Bay. The number of eddies and eddy amplitudes both increased following the passage of a tropical system. We also recognized a tendency for the tropical systems in 2019 to pass over cyclonic eddies and intensify afterward. Our results suggest a strong relationship between 3-7-day synoptic-scale variability and cyclonic eddies in the Bay of Bengal.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Interactions Between Mesoscale Eddies and Synoptic Oscillations in the Bay of Bengal During the Strong Monsoon of 2019

et al. 2020

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“…This length scale is crucial, as it means that SMAP, that has a 1,000 km swath, is able to capture the structure of the 3‐7‐day mode. By comparison, altimeters have a much narrower swath and so are not able to capture the signal as clearly (Roman‐Stork et al, 2020b).…”

Section: Resultsmentioning

confidence: 99%

“…There have been a number of studies regarding the active and break phases of the monsoon (Gadgil & Asha, 1992;Gadgil & Joseph, 2003;Goswami & Ajaya Mohan, 2001;Goswami et al, 2003;Krishnamurti & Bhlame, 1976;Murakami, 1976;Rajeevan et al, 2010;Singh & Nakamura, 2010), but most have been focused on the atmospheric aspect, with little, if any, consideration given how this would impact the upper ocean. As the monsoon system is a highly coupled phenomenon, it remains critically important that we understand how these atmospheric processes are translated into the ocean and how the ocean in turn influences these atmospheric processes (Goswami et al, 2016;Roman-Stork et al, 2020b).…”

Section: Introductionmentioning

confidence: 99%

Response of the Bay of Bengal to 3‐7‐Day Synoptic Oscillations During the Southwest Monsoon of 2019

2020

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The satellite‐derived precipitation over central India (73–78°E, 20–25°N) during the 2019 southwest monsoon season reveals that high‐amplitude 3‐7‐day synoptic oscillations dominated the other intraseasonal oscillations and contributed to the excess seasonal monsoon rainfall. In this paper, we address the contribution of 3‐7‐day synoptic oscillations in atmospheric and oceanic parameters during the 2019 southwest monsoon season over the Bay of Bengal (BoB). Our study reveals that both satellite observations and the Nucleus for European Modeling of the Ocean (NEMO) model simulations show high‐amplitude 3‐7‐day synoptic scale events during the 2019 monsoon. The upper 300 m of the water column responds to the basin‐scale 3‐7‐day synoptic oscillations as revealed in the vertical structures of NEMO model simulated temperature, salinity, and currents in the BoB. The synoptic scale wind stress drives strong currents in the shallow mixed layer due to salinity stratification in the northern BoB. The northward propagation of the synoptic scale oscillations is evident across the BoB but is capped to the base of the mixed layer, above which the propagation is affected by wind stress and the spread of freshwater flux. The 3‐7‐day synoptic scale oscillations in NEMO sea surface height appear to be related to synoptic scale wind‐driven convergence and divergence of waters through mesoscale eddy circulations that in turn contribute to thermocline variability, rather than the temperature and salinity in the mixed layer.

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“…The MJO is an eastward-propagating system with a phase speed of roughly 5 m/s that is characterized by alternating bands of suppressed and enhanced convection over the equator [9][10][11][12][13]. While it operates on a 30-90-day timescale, it is closely related to the 30-60-day boreal summer intraseasonal oscillation (BSISO), which is a northward-propagating phenomenon in the northern Indian Ocean that has been known to heavily impact monsoon precipitation and onset [13][14][15][16]. The MJO is the dominant form of intraseasonal variability in the tropics [12,13] and is widely known to impact cyclogenesis on a global scale [5,17,18].…”

Section: Introductionmentioning

confidence: 99%

The Impact of the Madden–Julian Oscillation on Cyclone Amphan (2020) and Southwest Monsoon Onset

Roman‐Stork

Subrahmanyam

2020

Remote Sensing

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Cyclone Amphan was an exceptionally strong tropical cyclone in the Bay of Bengal that achieved a minimum central pressure of 907 mb during its active period in May 2020. In this study, we analyzed the oceanic and surface atmospheric conditions leading up to cyclogenesis, the impact of this storm on the Bay of Bengal, and how the processes that led to cyclogenesis, such as the Madden–Julian Oscillation (MJO) and Amphan itself, in turn impacted southwest monsoon preconditioning and onset. To accomplish this, we took a multiparameter approach using a combination of near real time satellite observations, ocean model forecasts, and reanalysis to better understand the processes involved. We found that the arrival of a second downwelling Kelvin wave in the equatorial Bay of Bengal, coupled with elevated upper ocean heat content and the positioning of the convective phase of the MJO, helped to create the conditions necessary for cyclogenesis, where the northward-propagating branch of the MJO acted as a trigger for cyclogenesis. This same MJO event, in conjunction with Amphan, heavily contributed atmospheric moisture to the southeastern Arabian Sea and established low-level westerlies that allowed for the southwest monsoon to climatologically onset on June 1.

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Monitoring Intraseasonal Oscillations in the Indian Ocean Using Satellite Observations

Cited by 16 publications

References 83 publications

Interactions Between Mesoscale Eddies and Synoptic Oscillations in the Bay of Bengal During the Strong Monsoon of 2019

Interactions Between Mesoscale Eddies and Synoptic Oscillations in the Bay of Bengal During the Strong Monsoon of 2019

Response of the Bay of Bengal to 3‐7‐Day Synoptic Oscillations During the Southwest Monsoon of 2019

The Impact of the Madden–Julian Oscillation on Cyclone Amphan (2020) and Southwest Monsoon Onset

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