Structure and Origin of the Quasi-Biweekly Oscillation over the Tropical Indian Ocean in Boreal Spring

Wen, Min; Li, Tim; Zhang, Renhe; Qi, Yanjun

doi:10.1175/2009jas3105.1

Cited by 27 publications

(14 citation statements)

References 44 publications

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“…The negative OLR anomaly to the west is stronger than the positive one to the east. Such a zonal dipole pattern is consistent with the fact that BWO has a relatively short zonal wavelength compared to that of ISO (Wen et al 2010). An approximately opposite pattern of the OLR anomaly appears in the inactive MTC composite.…”

Section: B Bwo and Iso Activity Associated With Mtc Active And Inactsupporting

confidence: 84%

Factors Controlling Multiple Tropical Cyclone Events in the Western North Pacific*

Gao¹,

2011

Monthly Weather Review

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The statistical feature of occurrence of multiple tropical cyclone (MTC) events in the western North Pacific (WNP) is examined during summer (June-September) for the period of 1979-2006. The number of MTC events ranged from one to eight per year, experiencing a marked interannual variation. The spatial distance between the TCs associated with MTC events is mostly less than 3000 km, which accounts for 73% of total samples. The longest active phase of an MTC event lasts for nine days, and about 80% of the MTC events last for five days or less. A composite analysis of active and inactive MTC phases reveals that positive low-level (negative upper-level) vorticity anomalies and enhanced convection and midtropospheric relative humidity are the favorable large-scale conditions for MTC genesis. About 77% of the MTC events occurred in the region where either the atmospheric intraseasonal (25-70 day) oscillation (ISO) or biweekly (10-20 day) oscillation (BWO) is in a wet phase. The overall occurrence of the MTC events is greatly regulated by the combined large-scale impact of BWO, ISO, and the lower-frequency (90 days or longer) oscillation. On the interannual time scale, the MTC frequency is closely related to the seasonal mean anomalies of 850-hPa vorticity, outgoing longwave radiation (OLR), and 500-hPa humidity fields. The combined ISO and BWO activity is greatly strengthened (weakened) in the WNP region during the MTC active (inactive) years.

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Section: B Bwo and Iso Activity Associated With Mtc Active And Inactsupporting

confidence: 84%

Factors Controlling Multiple Tropical Cyclone Events in the Western North Pacific*

Gao¹,

2011

Monthly Weather Review

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“…Previously, the 10-30-day ISO is thought to be important mainly for the tropics (e.g., Kikuchi and Wang 2009;Goswami and Mohan 2001;Wen et al 2010;Yang et al 2010;Chen and Sui 2010). To date, the importance of the 10-30-day ISO has also been identified over the TP in boreal summer (e.g., Fujinami and Yasunari 2009;Yang et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Clustering of Tibetan Plateau Vortices by 10–30-Day Intraseasonal Oscillation*

Zhang

et al. 2014

Monthly Weather Review

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Tibetan Plateau (TP) vortices and the related 10-30-day intraseasonal oscillation in May-September 1998 are analyzed using the twice-daily 500-hPa synoptic weather maps, multiple reanalysis datasets, and satelliteretrieved brightness temperature. During the analysis period, distinctively active and suppressed periods of TP vortices genesis are noticed. In 1998, nine active periods of TP vortices occurred, which were largely clustered by the cyclonic circulations associated with the intraseasonal oscillation of 500-hPa relative vorticity. In addition to the well-recognized 30-60-day oscillation, the clustering of TP vorticity in the 1998 summer are more likely modulated by the 10-30-day oscillation, because all active periods of TP vortices fall into the positive phase of the 10-30-day oscillation in 1998. Even in the negative (i.e., anticyclonic) phases of the 30-60-day oscillation, the positive (i.e., cyclonic) 500-hPa 10-30-day oscillation can excite the clustering of TP vortices. This result indicates that the 10-30-day oscillation more directly modulates the activities of TP vortices by providing a favorable (unfavorable) cyclonic (anticyclonic) environment. The analysis of the 10-30-day atmospheric oscillation suggests that the westerly trough disturbances, in conjunction with convective instability due to low-level warm advection from the Indian monsoon region, are important in the clustering of TP vortex activities. In particular, the moisture flux from the southwest boundary of TP is essential to the accumulation of convective energy. Thus, a better understanding and prediction of the 10-30-day intraseasonal oscillation is needed to advance the extended-range forecasting of TP vortices and their downstream impacts on the weather and climate over East Asia.

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“…Compared with the research on disturbances in boreal summer, relatively few studies have examined other seasons. Specifically, Shinoda and Han (2005) and Wen et al (2010) illustrated features of lower tropospheric disturbances in boreal autumn and spring, respectively. However, little work has been done on the disturbances in boreal winter.…”

Section: Introductionmentioning

confidence: 99%

Structure and characteristics of submonthly-scale waves along the Indian Ocean ITCZ

Fukutomi

Yasunari

2012

Clim Dyn

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This study examines wave disturbances on submonthly (6-30-day) timescales over the tropical Indian Ocean during Southern Hemisphere summer using Japanese Reanalysis (JRA25-JCDAS) products and National Oceanic and Atmospheric Administration outgoing longwave radiation data. The analysis period is December-February for the 29 years from 1979/1980 through 2007/2008. An extended empirical orthogonal function (EEOF) analysis of daily 850-hPa meridional wind anomalies reveals a well-organized wave-train pattern as a dominant mode of variability over the tropical Indian Ocean. Daily lagged composite analyses for various atmospheric variables based on the EEOF result show the structure and evolution of a wave train consisting of meridionally elongated troughs and ridges along the Indian Ocean Intertropical Convergence Zone (ITCZ). The wave train is oriented in a northeast-southwest direction from Sumatra toward Madagascar. The waves have zonal wavelengths of about 3,000-5,000 km and exhibit westward and southwestward phase propagation. Individual troughs and ridges as part of the wave train sequentially travel westward and southwestward from the west of Sumatra into Madagascar. Meanwhile, eastward and northeastward amplification of the wave train occurs associated with the successive growth of new troughs and ridges over the equatorial eastern Indian Ocean. This could be induced by eastward and northeastward wave energy dispersion from the southwestern to eastern Indian Ocean along the mean monsoon westerly flow. In addition, the waves modulate the ITCZ convection. Correlation statistics show the average behavior of the wave disturbances over the tropical Indian Ocean. These statistics and other diagnostic measures are used to characterize the waves obtained from the composite analysis. The waves appear to be connected to the monsoon westerly flow. The waves tend to propagate through a band of the large meridional gradient of absolute vorticity produced by the mean monsoon westerly flow. This suggests that the monsoon westerly flow provides favorable background conditions for the propagation and maintenance of the waves and acts as a waveguide over the tropical Indian Ocean. The horizontal structure of the wave train may be interpreted as that of a mixture of equatorial Rossby waves and mixed Rossbygravity wavelike gyres.

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Structure and Origin of the Quasi-Biweekly Oscillation over the Tropical Indian Ocean in Boreal Spring

Cited by 27 publications

References 44 publications

Factors Controlling Multiple Tropical Cyclone Events in the Western North Pacific*

Factors Controlling Multiple Tropical Cyclone Events in the Western North Pacific*

Clustering of Tibetan Plateau Vortices by 10–30-Day Intraseasonal Oscillation*

Structure and characteristics of submonthly-scale waves along the Indian Ocean ITCZ

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