Some potential forcing mechanisms of the year-to-year variability of the tropical convection and its intraseasonal (25–70-day) variability

Fink, Andreas H.; Speth, P.

doi:10.1002/(sici)1097-0088(19971130)17:14<1513::aid-joc210>3.0.co;2-u

Cited by 71 publications

(66 citation statements)

References 63 publications

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“…There are significant negative correlations during the northern summer in the 1950-75 period, indicating enhanced MJO activity during La Niña conditions. The correlations during the later 1976-2005 period are much weaker and are not significant at any time of year, consistent with Fink and Speth (1997) and Slingo et al (1999). This change in the ENSO-MJO relationship between winter and summer indicates that the relationship should not be analyzed using year-round data, consistent with recent work by Hendon et al (2007).…”

Section: Decadal Change In the Enso-mjo Behaviorsupporting

confidence: 87%

“…Significantly shorter (longer) lifetimes are found during warm (cold) conditions in the eastern Pacific, consistent with Gray (1988) and Goulet and Duvel (2000). The zonal distance to traverse for convection is higher however, because the MJO signal extends farther east, beyond the date line, when warm conditions occur in the Pacific (Fink and Speth 1997;Vincent et al 1998;Kessler 2001). It is therefore concluded that the phase speed of the MJO is significantly higher during El Niño.…”

Section: Discussionsupporting

confidence: 60%

“…However, the spatial envelope of MJO activity extends farther east than usual during El Niño conditions, beyond the date line into the central Pacific, associated with the warmer sea surface temperatures (SSTs) there (Anyamba and Weare 1995;Fink and Speth 1997;Vincent et al 1998;Kessler 2001). Lagged relationships were also recently discovered between MJO activity in spring and the state of El Niño in subsequent autumn/winter seasons (Hendon et al 2007).…”

Section: Introductionmentioning

confidence: 99%

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Observed Changes in the Lifetime and Amplitude of the Madden–Julian Oscillation Associated with Interannual ENSO Sea Surface Temperature Anomalies

2007

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Observed changes in the life time and amplitude of the maddenjulian oscillation associated with interannual ENSO sea surface temperature anomalies. Journal of Climate, American Meteorological Society, 2007, 20, pp.2659-2674 The analysis is extended back to 1950 by using an alternative definition of the MJO based on just the zonal wind component of the Wheeler and Hendon indices. A rupture in the amplitude of the MJO is found in 1975, which is at the same time as the well-known rupture in the ENSO time series that has been associated with the Pacific decadal oscillation. The mean amplitude of the MJO is 16% larger in the postrupture compared to the prerupture period. Before the 1975 rupture, the amplitude of the MJO is maximum (minimum) under El Niño (La Niña) conditions during northern winter, and minimum (maximum) under El Niño (La Niña) conditions during northern summer. After the rupture, this relationship disappears. When the MJO-ENSO relationship is analyzed using all-year-round data, or a shorter dataset (as in some previous studies), no relationship is found.

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Section: Decadal Change In the Enso-mjo Behaviorsupporting

confidence: 87%

Section: Discussionsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

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Observed Changes in the Lifetime and Amplitude of the Madden–Julian Oscillation Associated with Interannual ENSO Sea Surface Temperature Anomalies

2007

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“…Using OLR data, Anyamba and Weare (1995) reported that during two out of the three warm ENSO events considered, there was more eastward penetration of intraseasonal activity or the MJO envelope over the central Pacific, and the propagation speed is slower. Later studies using OLR data with a longer base period (Fink and Speth 1997;Vincent et al 1998;Hendon et al 1999;Kessler 2001) came to similar conclusions. This east-west dipole-like perturbation of activity is reversed during cold ENSO events.…”

Section: Introductionmentioning

confidence: 74%

Modulation of the Madden-Julian Oscillation by ENSO: Inferences from Observations and GCM Simulations

Tam

Lau

2005

Journal of the Meteorological Society of Japan

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The impact of the El Niñ o-Southern Oscillation (ENSO) on the Madden-Julian Oscillation (MJO) is studied, based on reanalysis data and output from an ensemble general circulation model (GCM) experiment. Observed monthly sea surface temperature variations over the period of 1950-99 are imposed in the deep tropical eastern/central Pacific in the course of the SST experiment. Both GCM, and reanalysis data, indicate that intraseasonal activity of the low-level zonal wind is enhanced (reduced) over the central (western) Pacific during El Niñ o events. The propagation and growth/decay characterisitcis of the MJO in different phases of ENSO is also examined, based on a lag correlation technique. During warm events there is an eastward shift in the locations of strong growth and decay, and the propagation of the MJO becomes slower in the warm ENSO phase. These changes are reversed during La Niñ a epsiodes.Using output from the GCM experiment, the effects of ENSO on the circulation and convection during the MJO lifecycle are studied in detail. Further eastward penetration of MJO-related convection is simulated during warm events over the central Pacific. An instability index related to the vertical gradient of the moist static energy is found to be useful for depicting the onset of MJO convection along the equator. During warm events, the stronger magnitudes of this index over the central Pacific are conducive to more eastward penetration of convective anomalies in the region. These changes are mainly due to the intensified moisture accumulation at low levels. Analysis of the moisture budget suggests that the stronger moisture accumulation can be related to the increased low-level humidity over the central Pacific during warm events.

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“…However, the general consensus is that the major impact of ENSO is confined to the Pacific. The MJO tends to be active over the central Pacific and inactive over the western Pacific during a warm ENSO event (Gutzler, 1991;Fink and Speth, 1997). In addition, Waliser et al (1999) found from model experiments that ISO events are very sensitive to small changes in SST and, from the air-sea-interaction point of view, that ISO events might be associated with ENSO.…”

Section: The Scs Iso During Enso Eventsmentioning

confidence: 98%

Intraseasonal oscillations and the South China Sea summer monsoon onset

2005

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This paper investigates the role of intraseasonal oscillations (ISOs) in the onset of the South China Sea summer monsoon (SCSSM). Two major components of ISO (10-20-day and 30-60-day modes) are identified. The coupling of these two intraseasonal modes during the pre-monsoon period of the SCSSM are investigated by examining the filtered outgoing longwave radiation (OLR), low-level circulation, apparent heat source and apparent moisture sink from October of a previous calendar year to September of a calendar year.The zonal and meridional propagations of the 10-20-day and 30-60-day modes are found to be different, which reflects their different roles in the establishment and development of the SCSSM. The northwestward propagation of the 10-20-day mode is associated with the weakening of the subtropical high over the western Pacific, while the northeastward propagation of the 30-60-day mode originates from convection over the equatorial Indian Ocean. A hypothesis is then proposed to explain the observed variabilities in the SCSSM onset. When the equatorial Indian Ocean exhibits a 30-60-day mode oscillation, an initially weak convection develops into a large convection band (or monsoon trough). Meanwhile, a convective disturbance of the 10-20-day mode is induced when this monsoon trough extends to the western Pacific. These two processes then collaborate to cause a weakening of the subtropical anticyclone over the South China Sea. Because the monsoon trough associated with the 30-60-day mode subsequently propagates northward into the Bay of Bengal (BOB), the induced vortex together with the 10-20-day westward-migrating convection from the equatorial western Pacific will substantially increase the effect of horizontal advection of moisture and heat, thus destabilizing the atmosphere and weakening the subtropical ridge there. Westerlies can then penetrate and prevail over the SCS region, and the SCSSM onset occurs.

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Some potential forcing mechanisms of the year-to-year variability of the tropical convection and its intraseasonal (25–70-day) variability

Cited by 71 publications

References 63 publications

Observed Changes in the Lifetime and Amplitude of the Madden–Julian Oscillation Associated with Interannual ENSO Sea Surface Temperature Anomalies

Observed Changes in the Lifetime and Amplitude of the Madden–Julian Oscillation Associated with Interannual ENSO Sea Surface Temperature Anomalies

Modulation of the Madden-Julian Oscillation by ENSO: Inferences from Observations and GCM Simulations

Intraseasonal oscillations and the South China Sea summer monsoon onset

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