Remote Ocean Response to the Madden–Julian Oscillation during the DYNAMO Field Campaign: Impact on Somali Current System and the Seychelles–Chagos Thermocline Ridge

Shinoda, Toshiaki; Han, Weiqing; Zamudio, Luis; Lien, Ren‐Chieh; Katsumata, Masaki

doi:10.3390/atmos8090171

Cited by 12 publications

(9 citation statements)

References 50 publications

(63 reference statements)

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“…Most off-equatorial maxima of intraseasonal OHC variance are characterized by westward propagation. These are also well-known regions of westward propagating equatorial Rossby waves linked to the ISO (Jensen et al, 2015;Shinoda et al, 2013Shinoda et al, , 2017Webber et al, 2010;West et al, 2018). High percentages in the northern hemisphere of the western Indian Ocean are likely related to variability that anticyclonically orbits the Great Whirl (e.g., Melzer et al, 2019;Schott et al, 1990).…”

Section: Resultsmentioning

confidence: 99%

Ocean Heat Content and the Intraseasonal Oscillation

Rydbeck

Jensen

Smith

et al. 2019

Geophysical Research Letters

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Intraseasonal sea surface temperature anomalies generally cool during the convectively active phase of the intraseasonal oscillation in the Indian Ocean, but the behavior of intraseasonal ocean heat content anomalies is quite different. This is demonstrated using satellite observations and ocean reanalysis data. Ocean heat content anomalies increase during the convectively active phase of the intraseasonal oscillation and decrease during the convectively suppressed phase. Much of the intraseasonal variability of ocean heat content is westward propagating, moving in the opposite direction of the intraseasonal oscillation's convective envelope. While sea surface temperature anomalies are strongly regulated by variations in surface fluxes, their out of phase relationship with ocean heat content suggests that different processes are modulating the reservoir of warm water in the upper ocean. We hypothesize that oceanic equatorial waves are the primary forcing of intraseasonal ocean heat content anomalies during intraseasonal oscillation events. Plain Language SummaryThe intraseasonal oscillation organizes rainfall in the tropics and often initiates over the Indian Ocean. It is associated with strong surface winds and widespread cloudiness, which decreases incoming solar radiation, resulting in a cooling of the sea surface. We observe that while the sea surface cools, the reservoir of warm water in the upper Indian Ocean actually increases. This seeming contradiction between the behavior of the sea surface temperature and the ocean heat content is explained by oceanic equatorial wave dynamics. Much of the ocean heat content variability moves westward along lines of latitude that are just poleward of the equator, consistent with the location, timing, and direction of equatorial Rossby wave propagation. By increasing the ocean heat content, these waves are hypothesized to reduce the amount of sea surface cooling produced by the intraseasonal oscillation.

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Section: Resultsmentioning

confidence: 99%

Ocean Heat Content and the Intraseasonal Oscillation

Rydbeck

Jensen

Smith

et al. 2019

Geophysical Research Letters

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“…Further quantitative examination, however, is required in order to prove this assertion. Since the IOD and El Niño-Southern Oscillation (ENSO) have significant influence on interannual variability and the EUC (e.g., Chen et al 2015a), and the IOD also modulates atmospheric ISOs (Shinoda and Han 2005), they may also affect intraseasonal variability of the EUC. How they influence intraseasonal EUC, however, remains unclear, and it will be a good topic for future research.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…12)-although these waves contribute significantly to the western basin intraseasonal current at the surface (Fig. 9d) and to the Somali Current near the equator (Shinoda et al 2017).…”

Section: ) Processes: Western Basinmentioning

confidence: 97%

Intraseasonal Variability of the Equatorial Undercurrent in the Indian Ocean

Chen

Han

et al. 2019

Journal of Physical Oceanography

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By analyzing in situ observations and conducting a series of ocean general circulation model experiments, this study investigates the physical processes controlling intraseasonal variability (ISV) of the Equatorial Undercurrent (EUC) of the Indian Ocean. ISV of the EUC leads to time-varying water exchanges between the western and eastern equatorial Indian Ocean. For the 2001–14 period, standard deviations of the EUC transport variability are 1.92 and 1.77 Sv (1 Sv ≡ 106 m3 s−1) in the eastern and western basins, respectively. The ISV of the EUC is predominantly caused by the wind forcing effect of atmospheric intraseasonal oscillations (ISOs) but through dramatically different ocean dynamical processes in the eastern and western basins. The stronger ISV in the eastern basin is dominated by the reflected Rossby waves associated with intraseasonal equatorial zonal wind forcing. It takes 20–30 days to set up an intraseasonal EUC anomaly through the Kelvin and Rossby waves associated with the first and second baroclinic modes. In the western basin, the peak intraseasonal EUC anomaly is generated by the zonal pressure gradient force, which is set up by radiating equatorial Kelvin and Rossby waves induced by the equatorial wind stress. Directly forced and reflected Rossby waves from the eastern basin propagate westward, contributing to intraseasonal zonal current near the surface but having weak impact on the peak ISV of the EUC.

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“…The HYCOM ocean reanalysis has been extensively validated in the last few years 25,26 . Because of the high resolution of the model, it is able to resolve upper ocean structure near the boundary including the narrow boundary currents 27 , which are difficult to monitor by satellite observations only. The HYCOM reanalysis is available at https://hycom.org/dataserver/gofs-3pt1/reanalysis.…”

Section: Methodsmentioning

confidence: 99%

Ocean variability and air-sea fluxes produced by atmospheric rivers

Shinoda

Zamudio

Guo

et al. 2019

Sci Rep

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Atmospheric rivers (ARs) cause heavy precipitation and flooding in the coastal areas of many mid-latitude continents, and thus the atmospheric processes associated with the AR have been intensively studied in recent years. However, AR-associated ocean variability and air-sea fluxes have received little attention because of the lack of high-resolution ocean data until recently. Here we demonstrate that typical ARs can generate strong upper ocean response and substantial air-sea fluxes using a high-resolution (1/12°) ocean reanalysis. AR events observed during the CalWater 2015 field campaign generate large-scale on-shore currents that hit the coast, generating strong narrow northward jets along the west coast of North America, in association with a substantial rise of sea level at the coast. In the open ocean, the AR generates prominent changes of mixed layer depth, especially south of 30°N due to the strong surface winds and air-sea heat fluxes. The prominent cooling of SST is observed only in the vicinity of AR upstream areas primarily due to the large latent heat flux. Using a long-term AR dataset, composite structure and variations of upper ocean and air-sea fluxes are presented, which are consistent with those found in the events during CalWater 2015.

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Remote Ocean Response to the Madden–Julian Oscillation during the DYNAMO Field Campaign: Impact on Somali Current System and the Seychelles–Chagos Thermocline Ridge

Cited by 12 publications

References 50 publications

Ocean Heat Content and the Intraseasonal Oscillation

Ocean Heat Content and the Intraseasonal Oscillation

Intraseasonal Variability of the Equatorial Undercurrent in the Indian Ocean

Ocean variability and air-sea fluxes produced by atmospheric rivers

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