Midlatitude westward propagating disturbances preceding intraseasonal oscillations of convection over the subtropical western North Pacific during summer

Lu, Riyu; Ding, Hui; Ryu, Chan-Su; Lin, Zongkai; Dong, Huafeng

doi:10.1029/2007gl031277

Cited by 27 publications

(15 citation statements)

References 16 publications

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“…1996), a pattern conducive to TC development whose establishment depends on the westward shift of the TUTT axis in late July (Sato et al 2005;Lu et al 2007). The associated subtropical PV streamer frequency reaches its maximum near the date line (Wernli and Sprenger 2007), consistent with the eastward shift of the weak TT development region compared to that of the trough-induced pathway (cf.…”

Section: June 2013 M C T a G G A R T -C O W A N E T A Lmentioning

confidence: 99%

A Global Climatology of Baroclinically Influenced Tropical Cyclogenesis

McTaggart‐Cowan¹,

Galarneau²,

Bosart³

et al. 2013

Monthly Weather Review

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Tropical cyclogenesis is generally considered to occur in regions devoid of baroclinic structures; however, an appreciable number of tropical cyclones (TCs) form in baroclinic environments each year. A global climatology of these baroclinically influenced TC developments is presented in this study. An objective classification strategy is developed that focuses on the characteristics of the environmental state rather than on properties of the vortex, thus allowing for a pointwise ''development pathway'' classification of reanalysis data. The resulting climatology shows that variability within basins arises primarily as a result of local surface thermal contrasts and the positions of time-mean features on the subtropical tropopause. The pathway analyses are sampled to generate a global climatology of 1948-2010 TC developments classified by baroclinic influence: nonbaroclinic (70%), low-level baroclinic (9%), trough induced (5%), weak tropical transition (11%), and strong tropical transition (5%). All basins other than the North Atlantic are dominated by nonbaroclinic events; however, there is extensive interbasin variability in secondary development pathways. Within each basin, subregions and time periods are identified in which the relative importance of the development pathways also differs. The efficiency of tropical cyclogenesis is found to be highly dependent on development pathway. The peak efficiency defined in the classification subspace straddles the nonbaroclinic/ trough-induced boundary, suggesting that the optimal environment for TC development includes a baroclinic contribution from an upper-level disturbance. By assessing the global distribution of baroclinically influenced TC formations, this study identifies regions and pathways whose further study could yield improvements in our understanding of this important subset of TC developments.

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Section: June 2013 M C T a G G A R T -C O W A N E T A Lmentioning

confidence: 99%

A Global Climatology of Baroclinically Influenced Tropical Cyclogenesis

McTaggart‐Cowan¹,

Galarneau²,

Bosart³

et al. 2013

Monthly Weather Review

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“…However, there are some inherent flaws in the statistical methods. Using neural networks as an example, it is difficult to objectively determine the number of hidden-layer neurons and the training process tends to predict a local optimum, which will limit the forecast accuracy (Lu et al 2007). The reliability of these methods is gradually reduced as the forecast time increases, so the credibility of the forecast results becomes very low after about 2 weeks (Zou et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Reconstruction and Forecast Experiments of a Statistical–Dynamical Model of the Western Pacific Subtropical High and East Asian Summer Monsoon Factors

Mei¹,

Dong

Zhang

et al. 2015

Weather and Forecasting

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Abnormal activity of the western Pacific subtropical high (WPSH) may result in extreme weather events in East Asia. However, because the relationship between the WPSH and other components of the East Asian summer monsoon (EASM) system is unknown, it is still difficult to forecast such abnormal activity. The delayrelevant method is used to study 2010 data for abnormal weather and it is concluded that the Indian monsoon latent heat flux, the Somali low-level jet, and the Tibetan high activity index can significantly affect anomalies in the WPSH in the EASM system. By combining genetic algorithms and statistical-dynamical reconstruction theory, a nonlinear statistical-dynamical model of the WPSH and these three influencing factors was objectively reconstructed from actual 2010 data and a dynamically extended forecasting experiment was carried out. To further test the forecasting performance of the reconstructed model, further experiments using data from nine abnormal WPSH years and eight normal WPSH years were performed for comparison. All the results suggest that the forecasts of the subtropical high area index, the Indian monsoon latent heat flux, the Somali low-level jet, and the Tibetan high activity index all have good performance in the short and medium terms (,25 days). Not only is the forecasting trend accurate, but the mean absolute percentage error is #9%. This work suggests new areas of research into the association between the WPSH and EASM systems and provides a new method for the prediction of the WPSH area index.

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“…The differences in landsea distribution (Indian subcontinent, Bay of Bengal, Indochina Peninsula, and South China Sea) lead to large discrepancies of the thermal regime and are responsible for the differences of monsoons in those different regions. In East Asia (EA) and the western North Pacific (WNP, EA-WNP), the summer monsoon proceeds with various stages of surges and breaks associated with the evolution of the North Pacific (NP) high pressure system (NP high), in particular, the western stretch of the high (Lu 2001;Hattori et al 2005;Kim et al 2009). Evolutions of the Asian-Pacific summer monsoon can generally be classified into three phases ).…”

Section: Introductionmentioning

confidence: 99%

Upper-Tropospheric Forcing on Late July Monsoon Transition in East Asia and the Western North Pacific

Chou

2012

J. Climate

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By investigating the large-scale circulation in the upper troposphere, it is demonstrated that the rapid late July summer monsoon transition in the East Asia and western North Pacific (EA-WNP) is associated with a weakened westerly at the exit of the East Asian jet stream (EAJS). Even in a normally stable atmosphere under the influence of the North Pacific (NP) high in late July, convection rapidly develops over the midoceanic region of the western NP (158-258N, 1508-1708E). Prior to the rapid transition, the EAJS weakens and shifts northward, which induces a series of changes in downstream regions; the northeastern stretch of the Asian high weakens, upper-tropospheric divergence in the region southwest of the mid-NP trough increases, and convection is enhanced. At the monsoon transition, upper-level high potential vorticity intrudes southward and westward, convection expand from the mid NP westward to cover the entire subtropical western NP, the lower-tropospheric monsoon trough deepens, surface southwesterly flow strengthens, and the western stretch of the NP high shifts northward ;108 latitude to the south of Japan. This series of changes indicates that the EA-WNP late July monsoon transition is initiated from changes in the upper-tropospheric circulation via the weakening of the EAJS south of ;458N. The weakening of the EAJS south of ;458N is related to a reduced gradient of the geopotential height on the northern flank of the Asian high, which is related to the massive inland heating and weakening of the South Asian monsoon circulation. The exact timing of the monsoon onset might be tied to the hypothesized ''Silk Road pattern'' and/or a strong weakening of the South Asian monsoon circulation.

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Midlatitude westward propagating disturbances preceding intraseasonal oscillations of convection over the subtropical western North Pacific during summer

Cited by 27 publications

References 16 publications

A Global Climatology of Baroclinically Influenced Tropical Cyclogenesis

A Global Climatology of Baroclinically Influenced Tropical Cyclogenesis

Reconstruction and Forecast Experiments of a Statistical–Dynamical Model of the Western Pacific Subtropical High and East Asian Summer Monsoon Factors

Upper-Tropospheric Forcing on Late July Monsoon Transition in East Asia and the Western North Pacific

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