Mechanisms of Northward Propagation of Boreal Summer Intraseasonal Oscillation Revealed by Climate Model Experiments

Yang, Young‐Min; Wang, Bin; Lee, June‐Yi

doi:10.1029/2018gl081612

Cited by 21 publications

(22 citation statements)

References 41 publications

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“…Previous studies focusing on northward propagation of BSISO convection in the eastern IO have suggested that vorticity anomalies by zonal vertical shear may be the dominant factor for northward propagation of ISO (DeMott et al, 2013; Yang, Wang, & Lee, 2019). We speculate that because much warmer SST and more abundant moisture occur in the WNP compared to those in the eastern IO, convection may be mainly generated due to upward transport of moisture by surface fluxes processes rather than dynamical processes in the WNP.…”

Section: Conclusion and Discussionmentioning

confidence: 98%

“…To obtain the effect of different mean state on BSISO northward propagation, we conduct three experiments: (1) the NESM3.0 with observed orography (TP100); (2) orography reduced by 50% (TP50); and (3) flat orography (TP00) over the TP region (60–110°E, 25–45°N). Figure 1 of Yang, Wang, and Lee (2019) shows a horizontal map of orography over the TP region used in the experiments. We smooth the boundaries of the orographic area based on the method of Cannon et al (2017) to remove undesired numerical noises.…”

Section: The Model and Diagnostic Methodsmentioning

confidence: 99%

“…The change of vertical zonal wind shear can generate a barotropic vorticity anomaly by the coupling of the baroclinic and barotropic modes by mean vertical shear (Wang & Xie, 1997; Xie & Wang, 1996). Yang, Wang, and Lee (2019) demonstrated that the vorticity anomaly under the mean vertical wind shear is the major driver for the BSISO northward propagation over the IO. The lower tropospheric vorticity anomalies regressed on the 20–70 day filtered precipitation averaged over the western Pacific (0–5°N, 125–145°E) are shown in Figure 4b.…”

Section: Causes Of the Changes Of Iso Simulations With Reduced Orographymentioning

confidence: 99%

“…Our previous study demonstrates that the vorticity advection under the mean vertical wind shear is the major driver for BSISO propagation in the IO (Yang, Wang, & Lee, 2019). However, over the WNP, the vertical wind shear is significantly weaker than that over the IO.…”

Section: Introductionmentioning

confidence: 99%

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Dominant Process for Northward Propagation of Boreal Summer Intraseasonal Oscillation Over the Western North Pacific

Yang

Lee

Wang

2020

Geophysical Research Letters

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Northward propagation of boreal summer intraseasonal oscillation (BSISO) over the Western North Pacific (WNP) has significant impacts on extreme events over Asia and Europe. Here we test hypotheses that northward propagation mechanisms over the WNP may differ from those over the Indian Ocean (IO) by performing numerical experiments with changing mean states through lowering the Tibetan Plateau (TP). Our results suggest that air-sea interaction plays a dominant role in the propagation over the WNP, whereas the mean vertical wind shear mechanism is the major driver over the IO. Lowering TP significantly reduces sea surface temperature (SST) anomalies to the north of BSISO center due to the enhanced surface wind and latent heat flux anomalies. This air-sea interaction reduces upward transport of heat and moisture from surface to lower troposphere, weakening the northward propagation over the WNP. This study implies changes in SST patterns under global warming may influence BSISO propagation. Plain Language Summary A heavy rainfall system propagates slowly from the equatorial western Pacific to the south China Sea and north of the Philippine Sea on a 20-70-day time scale. This rainfall system affects the onset of East Asia monsoon and extreme weather including typhoons. Therefore, a better understanding of the dominant processes of the northward propagation of this heavy rainfall system may contribute to reducing its social and economic damage. For this purpose, we performed a set of climate model experiments. We found that lowering the Tibetan Plateau significantly decreases the meridional gradient of the warm SST anomalies associated with the heavy rainfall system, suggesting that the air-sea interaction plays a dominant role in the BSISO northward propagation over the Western North Pacific. In contrast, vertical shear of zonal winds and associated positive vorticity anomalies, the major driver over the Indian Ocean, does not contribute to the northward movement over the Western North Pacific.

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Section: Conclusion and Discussionmentioning

confidence: 98%

Section: The Model and Diagnostic Methodsmentioning

confidence: 99%

Section: Causes Of the Changes Of Iso Simulations With Reduced Orographymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dominant Process for Northward Propagation of Boreal Summer Intraseasonal Oscillation Over the Western North Pacific

Yang

Lee

Wang

2020

Geophysical Research Letters

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“…Several mechanisms have been advanced to explain the NP of BSISO (Wang and Xie 1996;Xie and Wang 1996;Jiang et al 2004;Bellon and Sobel 2008;Zheng and Huang 2019). Jiang et al (2004) proposed the vertical wind shear mechanism for the NP of BSISO, which was further confirmed with numerical simulation studies (Drbohlav and Wang 2005;Yang et al 2019). Under a background state flow with easterly vertical wind shear, the combination of vertical shear flow and meridional gradient of baroclinic divergence could lead to positive barotropic vorticity in the free atmosphere to the north of convection center.…”

Section: Introductionmentioning

confidence: 73%

Influences of ENSO on boreal summer intraseasonal oscillation over the western Pacific in decaying summer

Chen

2020

Clim Dyn

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Characteristics of boreal summer intraseasonal oscillation (BSISO) over the western Pacific in ENSO decaying summer are revealed in this study. BSISO activity over the western Pacific is significantly weakened (strengthened) in El Niño (La Niña) decaying summer. Coherent and robust northward propagation (NP) of BSISO can be observed from the equator to the north of 25° N in La Niña decaying summer, while the intensity of BSISO NP is rapidly weakened to the north of 15° N in El Niño decaying summer. ENSO modulates BSISO activity by regulating circulation and moisture anomalies. Large-scale atmospheric circulation undergoes radical changes between El Niño and La Niña decaying summer. In El Niño (La Niña) decaying summer, anomalous anticyclonic (cyclonic) circulation and descending (ascending) motion are observed over the western Pacific, which provides an unfavorable (favorable) background state for the activity of BSISO. Low-level moistening north of BSISO convection center is crucial to its activity and NP, and the stronger low-level moistening in La Niña decaying summer induces the stronger NP. Differences in moisture variations between El Niño and La Niña decaying summer mainly stem from the meridional moisture advection, especially the meridional advection of intraseasonal moisture caused by lowfrequency background state meridional wind. The stronger air-sea interaction over 15°-25° N in La Niña decaying summer could also promote the stronger NP of BSISO via surface heat fluxes exchanges. Zonal and meridional vertical wind shears can also influence the boundary convergence to the north of BSISO convection center and promote the NP of BSISO via vertical wind shear and vorticity advection mechanisms, but they are not the dominant reasons for the differences in the NP of BSISO between El Niño and La Niña decaying summer.

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Impacts of the boreal summer intraseasonal oscillation on precipitation extremes in Indonesia

Muhammad

Lubis

2022

Intl Journal of Climatology

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The relationship between boreal summer intraseasonal oscillation (BSISO) and precipitation extremes over Indonesia is investigated using observational datasets from 30 years of rain gauge measurements and the gridded Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of Water Resources from 1998 to 2015. The results indicate that the frequency of daily extreme precipitation events in Indonesia (defined as total precipitation above the 95th percentile) during extended boreal summer (May-August) is significantly modulated by BSISO, especially over the western and northern regions. Under the influences of BSISO1, the probability of the precipitation extremes over Sumatra and Borneo increases by 20-120% (relative to the seasonal probability) during phases 1-3 and approximately 50-80% over the eastern part of Borneo and Sulawesi during phase 4. Under BSISO2, the probability of the extremes increases up to 40% over Sumatra during phases 1 and 2 and up to 140% over Borneo and Sulawesi during phases 2 and 3. The increase in the probability of extreme summer precipitation is associated with enhanced large-scale moisture flux convergence and upward moisture transport induced by the active phases of BSISO. These results provide potential information for medium-to extended-range predictions of summer precipitation extremes in Indonesia.

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Mechanisms of Northward Propagation of Boreal Summer Intraseasonal Oscillation Revealed by Climate Model Experiments

Cited by 21 publications

References 41 publications

Dominant Process for Northward Propagation of Boreal Summer Intraseasonal Oscillation Over the Western North Pacific

Dominant Process for Northward Propagation of Boreal Summer Intraseasonal Oscillation Over the Western North Pacific

Influences of ENSO on boreal summer intraseasonal oscillation over the western Pacific in decaying summer

Impacts of the boreal summer intraseasonal oscillation on precipitation extremes in Indonesia

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