Interdecadal increase of tropical cyclone genesis frequency over the western north Pacific in May

Intl Journal of Climatology

Huang

et al. 2018

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The weakening in the relationship between the South China Sea summer monsoon onset (SCSSMO) and the low‐level cross‐equatorial flow (CEF) in May is investigated using the ERA‐Interim reanalysis data sets during 1979–2016. The SCSSMO–SCSCEF relationship has experienced a significant inter‐decadal change, and the correlation coefficient becomes weaker after the late 1990s. The correlation has shifted from the significant negative value in the earlier decade to insignificant in the later decade. This inter‐decadal change is robust under several sensitive tests and largely independent of the El Niño‐Southern Oscillation signal. One possible explanation is the change in mechanisms driving the SCSSMO over the course of the two periods. Before the late 1990s, the northwards march of the intertropical convergence zone, which has a close relationship with the SCSCEF, is mainly responsible for the SCSSMO. After the late 1990s, warming of the western North Pacific favours more tropical cyclones and disturbances during May. The westwards movement of these tropical disturbances would affect the SCSSMO and help explain why the SCSSMO–SCSCEF relationship became weaker in the later decade.

Section: Possible Explanation Of This Inter-decadal Changesupporting

confidence: 83%

On the weakening relationship between the South China Sea summer monsoon onset and cross‐equatorial flow after the late 1990s

Intl Journal of Climatology

Huang

et al. 2018

Self Cite

“…In recent years, the interdecadal changes of the WNP TC genesis have been the subject of intense scientific research (Matsuura et al, 2003;Ho et al, 2004;Huangfu et al, 2016). It is well known that the TC activities experienced a shift around the late-1970s, with a subsequent upward trend (Chan and Shi, 1996;Zhang et al, 1997;Chao et al, 2000;Chan, 2005).…”

Section: Introductionmentioning

confidence: 99%

Interdecadal variation of tropical cyclone genesis and its relationship to the monsoon trough over the western North Pacific

Huangfu

Huang

Intl Journal of Climatology

et al. 2016

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Using the European Centre for Medium‐Range Weather Forecasts Interim Reanalysis data set and the tropical cyclone (TC) best track data obtained from the International Best Tracks Archive for Climate Stewardship project from June to November for the epoch of 1979–2013, this study reexamines the recent interdecadal shift in TC genesis over the western North Pacific (WNP) in the late 1990s. An interdecadal decrease in the frequency of the WNP TC genesis was observed during 1998–2013 compared to the period of 1979–1997. The spatial distribution of the interdecadal decrease of the WNP TC genesis running northwest‐southeast, consistent with the monsoon trough (MT) zone. The results imply that the WNP genesis may be closely related to the MT on the interdecadal timescale. After the late 1990s, the intensity of the WNP MT becomes weaker and it extends more westward, thereby providing an unfavourable condition for the TC genesis. Through a diagnosis of the energetics, we suggested that the barotropic energy conversion in the eastern part of the WNP MT tends to be weakened in the late 1990s, hence less energy to support the WNP TC genesis. Both the meridional shear and the convergence of the mean zonal winds over the eastern WNP MT have an important impact on the conversion from mean kinetic energy to eddy kinetic energy, which can be considered as the atmospheric cause of the interdecadal decrease of TC genesis.

“…The onset date of the SCSSM is commonly used to indicate droughts and floods during the first rainy season over South China as well as anomalous precipitation over other regions (Huang et al, 2006;Yuan et al, 2010;He and Zhu, 2015;Gu et al, 2018). Recently, the onset date of the SCSSM has been shown to be related to the tropical cyclone (TC) genesis over the western North Pacific in May (Huangfu et al, 2017a(Huangfu et al, , 2017b(Huangfu et al, , 2017cHuangfu et al, 2018aHuangfu et al, , 2018b. Hence, the onset date of the SCSSM has been intensely studied.…”

Section: Introductionmentioning

confidence: 99%

The role of synoptic‐scale waves in the onset of the South China Sea summer monsoon

Huangfu

Atmospheric Science Letters

Wang

et al. 2018

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The role of premonsoon synoptic‐scale waves (2‐ to 10‐day oscillation) in the onset of the South China Sea summer monsoon (SCSSM) is investigated in this study. The results indicated that the onset date of the SCSSM from 1979–2016 was related to the intensity of premonsoon synoptic‐scale waves. The more active the premonsoon synoptic‐scale waves, the earlier the SCSSM tended to be established. This study focused on the accumulative effects of premonsoon synoptic‐scale waves on the SCSSM onset because active years often included more than one process. According to the regression analysis results, three premonsoon synoptic‐scale waves influenced the onset of the SCSSM. First, waves over the southern Bay of Bengal (BOB) were related to Kelvin waves, which accelerated the intrusion of southwesterly winds over the BOB into the South China Sea (SCS). Second, waves over the eastern SCS were related to tropical depression (TD)‐type waves. Westerly anomalies south of this type of synoptic‐scale wave were favorable for the onset of the SCSSM. Third, waves originating from the north were hypothesized to be related to the mid‐latitude fronts. The mid‐latitude vortex moved northeast of the SCS and induced the intrusion of southwesterlies over the SCS. All three waves continuously enabled the westerly anomalies and affected the SCSSM. In addition, the combined effects of these synoptic‐scale waves were investigated. The results showed that active waves led to significant anomalous westerlies along the boreal tropical region and cyclonic circulation over the Philippine Sea. Anomalous convection was enhanced over the BOB and SCS, and the western Pacific subtropical high was suppressed. The combined intensities of these premonsoon synoptic‐scale waves indicated their potential for use as a new predictor of the onset of the SCSSM.