Northward and Northwestward Propagation of 30-60 Day Oscillation in the Tropical and Extratropical Western North Pacific

This study formulates a synoptic-scale eddy (SSE) kinetic energy equation by partitioning the original field into seasonal mean circulation, intraseasonal oscillation (ISO), and SSEs to examine the multiscale interactions over the western North Pacific (WNP) in autumn. In addition, the relative contribution of synopticmean and synoptic-ISO interactions to SSE kinetic energy was quantitatively estimated by further separating barotropic energy conversion (CK) into synoptic-mean barotropic energy conversion (CK S2M ) and synoptic-ISO barotropic energy conversion (CK S2ISO ) components.The development of tropical SSE in the lower troposphere is mainly attributed to CK associated with multiscale interactions. Mean cyclonic circulation in the lower troposphere consistently provides kinetic energy to SSEs (CK S2M . 0) during the ISO westerly and easterly phases. However, CK S2ISO during the ISO westerly and easterly phases differs considerably. During the ISO westerly phase, the enhanced ISO cyclonic flow converts energy to SSEs (CK S2ISO . 0). The magnitude of the downscale energy conversion from mean and ISO to SSEs is related to the strength of the SSEs. During the ISO westerly phase, a stronger SSE extracts more kinetic energy from mean and ISO circulation. This positive feedback between SSE-mean and SSE-ISO interactions causes further strengthening of SSEs during the ISO westerly phase.By contrast, upscale energy conversion from SSEs to ISO anticyclonic flow (CK S2ISO , 0) was observed during the ISO easterly phase. The weaker SSE activity during the ISO easterly phase occurred because the mean circulation provides less energy to SSEs and, at the same time, SSEs lose energy to ISO during the ISO easterly phase. The two-way interaction between the ISO and SSEs has considerable effects on the development of tropical SSEs over the WNP in autumn.

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“…4a). This feature bears some similarities to the ISO in summer (Hsu and Weng 2001;Tsou et al 2005). However, some discrepancies are identified.…”

Section: Large-scale Circulation and Ts Activity In Autumnmentioning

confidence: 68%

The Role of Multiscale Interaction in Synoptic-Scale Eddy Kinetic Energy over the Western North Pacific in Autumn

Tsou

Hsu

2014

Journal of Climate

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“…The strong moisture flux convergence anomaly related to enhanced deep convection over the western north Pacific (WNP) can explain the emanation of Rossby waves, which is Tsou et al 2005). As a result, this mode has the persistent wavelike structure to explain Rossby wave propagation for large-scale circulation conspicuously.…”

Section: Moisture Transportmentioning

confidence: 99%

Thermodynamic characteristics and responses to ENSO of dominant intraseasonal modes in the East Asian summer monsoon

2014

Clim Dyn

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“…The seasonal cycle was first removed, and anomaly fields were bandpass filtered to retain 30-60 day variability (Lau and Chan, 1986;Tsou et al, 2005). For the regressed dynamic fields, the NCEP-NCAR reanalysis data (Kalnay et al, 1996) and the Hadley Centre Sea Ice and Sea Surface Temperature (HadISST) data set (Rayner et al, 2003) from 1979 to 2010 were used.…”

Section: Datamentioning

confidence: 99%

Variability in the East Asian Monsoon: a review

Heo

Lee

et al. 2012

Meteorological Applications

148

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ABSTRACT:This study presents reviews of recent research on the structure and the multiscale variability in the East Asian monsoon. The boreal summer and winter seasons in the East Asian monsoon region exhibit significant intraseasonal, interannual and interdecadal variabilities. The interannual intensity of the East Asian summer monsoon (EASM) is mainly associated with the position of the centre of the Bonin High, which may be distinguished from the North Pacific anticyclone. The frequencies of heavy rainfall events and associated rainfall amounts increase, and extreme heavy rainfall is higher in August than in July, due to changes that occurred in the August rainfall-El Niño-Southern Oscillation (ENSO) relationship around the mid-1970s. This intraseasonal variability in EASM plays a more important role in the explanations of the interannual variability and climate change than does the annual mean. The interannual variability in the East Asian winter monsoon (EAWM) depends on the behaviour of the Siberian High (SH), Aleutian Low and the subtropical westerly jet stream. An EAWM index that takes into account the meridional shear of a 300 hPa zonal wind is a good indicator to represent the intensity of the EAWM. The Arctic Oscillation has a close relationship with the EAWM intensity on the decadal time scale. Distinct sub-seasonal variability is characterized with northward propagation and is observed in the interdecadal change in the monsoonal intraseasonal oscillation (ISO)-ENSO relationship. The preceding winter ENSO influenced the early summer northward propagating ISO (NPISO) activity before the late 1970s, whereas a strong NPISO-ENSO relationship appeared during the later summer after the late 1970s. The NPISO-ENSO relationship is robust owing to a tropical atmospheric bridge process involving the Walker Circulation and Rossby Wave propagation.

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Northward and Northwestward Propagation of 30-60 Day Oscillation in the Tropical and Extratropical Western North Pacific

Cited by 34 publications

References 28 publications

The Role of Multiscale Interaction in Synoptic-Scale Eddy Kinetic Energy over the Western North Pacific in Autumn

The Role of Multiscale Interaction in Synoptic-Scale Eddy Kinetic Energy over the Western North Pacific in Autumn

Thermodynamic characteristics and responses to ENSO of dominant intraseasonal modes in the East Asian summer monsoon

Variability in the East Asian Monsoon: a review

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