Moisture dynamics of the northward and eastward propagating boreal summer intraseasonal oscillations: possible role of tropical Indo-west Pacific SST and circulation

Pillai, Prasanth A.; Sahai, A. K.

doi:10.1007/s00382-015-2904-7

Cited by 21 publications

(15 citation statements)

References 36 publications

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“…Such an objective and systematic study has not yet emerged. Previous studies on BSISO diversity are either subjective (e.g., B. Wang & Rui, 1990) or not systematic (e.g., Pillai & Sahai, 2016, in that study the propagation directions are pre‐defined). This work attempts a systematic and objective description of BSISO propagation diversity and an in‐depth grasp of underlying mechanisms.…”

Section: Introductionmentioning

confidence: 99%

“…Tropical intraseasonal oscillation (ISO) exhibits pronounced seasonality (Madden, 1986; B. Wang & Rui, 1990). The boreal summer intraseasonal oscillation (BSISO), active mainly over the Indo‐Pacific warm pool region, is more complicated than its winter counterpart, the Madden‐Julian Oscillation (MJO) (Madden & Julian, 1971, 1972), due to the coexistence of equatorial eastward, off‐equatorial westward, and northward propagating low‐frequency modes and their interactions (Lau & Chan, 1986; Pillai & Sahai, 2016; B. Wang & Xie, 1997).…”

Section: Introductionmentioning

confidence: 99%

“…Wang & Rui, 1990) that have origins over the IO. Besides the canonical propagation form, it was also found that there are independent northward propagating BSISO (Pillai & Sahai, 2016;B. Wang & Rui, 1990).…”

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confidence: 98%

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Diversity of the Boreal Summer Intraseasonal Oscillation

Chen

Wang

2021

JGR Atmospheres

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Tropical intraseasonal oscillation (ISO) exhibits pronounced seasonality (Madden, 1986;B. Wang & Rui, 1990). The boreal summer intraseasonal oscillation (BSISO), active mainly over the Indo-Pacific warm pool region, is more complicated than its winter counterpart, the Madden-Julian Oscillation (MJO) (Madden & Julian, 1971, 1972, due to the coexistence of equatorial eastward, off-equatorial westward, and northward propagating low-frequency modes and their interactions (

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Diversity of the Boreal Summer Intraseasonal Oscillation

Chen

Wang

2021

JGR Atmospheres

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“…To this end, an investigation on the characteristics of ISO over the AS and BoB would provide an insight on the problem. Earlier studies have shown that moisture advection, specifically advection of climatological moisture by the anomalous wind from the northwest Pacific, is the principal factor in initiating the active or break conditions over India (Annamalai, ; Pillai & Sahai, , ; Prasanna & Annamalai, ). Furthermore, moisture advection is found to lead rainfall by 8–9 days, whereas there is no lead‐lag between rainfall and moisture convergence.…”

Section: Introductionmentioning

confidence: 99%

Differences in Northward Propagation of Convection Over the Arabian Sea and Bay of Bengal During Boreal Summer

Karmakar

Misra

2020

JGR Atmospheres

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The governing dynamics that modulate the propagation characteristics of intraseasonal oscillations (ISO) during summer monsoon over the two ocean basins, Bay of Bengal (BoB) and Arabian Sea (AS), are investigated using observational analysis and high-resolution regional coupled ocean-atmosphere climate model simulations. ISO features are extracted over the Indian region using a data-adaptive spectral method called multichannel singular spectrum analysis. ISO exhibits stronger intensity over the BoB than over the AS. But ISO-filtered rainfall propagates at a faster rate (∼1.25 • /day) over AS as compared to BoB (∼.74 • /day), giving rise to a northwest-southeast tilted band of rainfall anomalies. However, the composite diagrams of several atmospheric fields associated with northward propagation like vorticity, low-level convergence, and oceanic variables like sea surface temperature and mixed layer depth do not show this difference in propagation speed and all exhibit a speed of nearly 0.75 • /day in both the ocean basins. The difference in speed of ISO-filtered rainfall is explained through moisture flux convergence. Anomalous horizontal moisture advection plays a major role over AS in preconditioning the atmosphere and making it favorable for convection. Anomalous wind acting on climatological moisture gradient is the dominant term in the moisture advection equation. Easterly wind anomalies associated with a low-level anticyclone over India helps advect moisture from the eastern side of the domain. The northwest-southeast tilt of ISO is dictated by the atmospheric processes of moisture advection with the upper ocean playing a more passive role in causing the tilt. Key Points: • Intraseasonal oscillations (ISO) in rainfall over the Bay of Bengal (BoB) propagate at a slower rate than over the Arabian Sea (AS) • Differential atmospheric moisture flux convergence between BoB and AS determines the tilted structure of ISO • The upper ocean in BoB and AS plays a more passive role in the tilt of the ISO Correspondence to:

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“…Furthermore, possible causes for disparity between northwards propagation of MISO in the AGCMs simulations are considered. Studies (Ajayamohan et al, 2011; Pillai & Sahai 2014, 2016) proposed that the anomalous moisture advection plays a major role in the northwards migration of MISO convection from the equatorial IO to the Indian subcontinent. Hence, 30–60‐day filtered precipitation and horizontal moisture advection at each grid point is correlated at the different time lags with respect to a reference time series created by averaging the 30–60‐day filtered precipitation anomalies averaged over the IO.…”

Section: Discussion and Summarymentioning

confidence: 99%

Simulation of monsoon intra‐seasonal oscillations in Geophysical Fluid Dynamics Laboratory models from Atmospheric Model Intercomparison Project integrations of Coupled Model Intercomparison Project phase 5

Mandke

Pillai

Sahai

2020

Intl Journal of Climatology

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The simulation of the intra‐seasonal variability (ISV), especially the fidelity of monsoon intra‐seasonal oscillations (MISO) over the South Asian summer monsoon (SASM), has been evaluated in Atmospheric Model Intercomparison Project run of three Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric general circulation models (AGCM), participating in Coupled Model Intercomparison Project phase 5. Two of the models, namely, “GFDL‐HIRAM‐C180” and “GFDL‐HIRAM‐C360” are global high‐resolution atmospheric models (HIRAMs), which are same but at different horizontal resolutions. Third model “GFDL‐CM3” is at moderate horizontal resolution, whose atmospheric component differs from HIRAMs. Results have led to the conclusion that simulation of ISV over SASM remains poor in GFDL AGCMs at higher horizontal resolution, except northwards propagation of 30–60‐day mode of MISO by HIRAMs. Our diagnostics revealed resemblance in key characteristics of ISV simulated in two HIRAMs, except spectral peak at lower frequencies (30–60 day), which is captured only by “GFDL‐HIRAM‐C180” over equatorial Indian Ocean. Based on these results, it is conjectured that although high horizontal resolution is crucial for AGCMs to reproduce observed northwards propagation of 30–60‐day mode of MISO, the simulation of nature of ISV over SASM is not influenced by the difference of horizontal resolution in two HIRAMs. Analysis implicates that a reasonable representation of meridional migration of horizontal moisture advection, the meridional gradient of low‐level specific humidity over Indian longitudes and precipitation–SST relationship over north Indian Ocean, the northwestern tropical Pacific Ocean and tropical Indian Ocean assures the northwards propagation of 30–60‐day mode of MISO in HIRAMs.

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Moisture dynamics of the northward and eastward propagating boreal summer intraseasonal oscillations: possible role of tropical Indo-west Pacific SST and circulation

Abstract: centre in other two categories. Thus the present study concludes that the difference in underlying SST and atmospheric circulation in tropical Indo-west Pacific oceanic regions encourage the differential propagation of BSISO convection through moisture dynamics.

Cited by 21 publications

References 36 publications

Diversity of the Boreal Summer Intraseasonal Oscillation

Diversity of the Boreal Summer Intraseasonal Oscillation

Differences in Northward Propagation of Convection Over the Arabian Sea and Bay of Bengal During Boreal Summer

Simulation of monsoon intra‐seasonal oscillations in Geophysical Fluid Dynamics Laboratory models from Atmospheric Model Intercomparison Project integrations of Coupled Model Intercomparison Project phase 5

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