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Various SST indices in the Indo-Pacific region have been proposed in the literature in light of a long-range seasonal forecasting of the Indian Summer Monsoon (ISM). However, the dynamics associated with these different indices have never been compared in detail. To this end, the present work re-examines the variabilities of ISM rainfall, onset and withdrawal dates at interannual timescales and explores their relationships with El Ni?o-Southern Oscillation (ENSO) and various modes of coupled variability in the Indian Ocean. Based on recent findings in the literature, five SST indices are considered here: Ni?o3.4 SST index in December?CJanuary both preceding [Nino(?1)] and following the ISM [Nino(0)], South East Indian Ocean (SEIO) SST in February?CMarch, the Indian Ocean Basin (IOB) mode in April?CMay and, finally, the Indian Ocean Dipole (IOD) averaged from September to November, also, both preceding [IOD(?1)] and following the ISM [IOD(0)]. The respective merits and associated dynamics of the selected indices are compared through various correlation and regression analyses. Our first result is a deceptive one: the statistical relationships with the ISM rainfall at the continental and seasonal scales are modest and only barely significant, particularly for the IOD, IOB and Nino(?1) indices. However, a detailed analysis shows that statistical relationships with the ISM rainfall time series are statistically biased as the ISM rainfall seems to be shaped by much intraseasonal variability, linked in particular to the timing of the onset and withdrawal of the ISM. Surprisingly, analysis within the ISM season shows that Nino(?1), IOB and SEIO indices give rise to prospects of comparatively higher ISM previsibility for both the ISM onset and the amount of rainfall during the second half of the ISM season. The IOD seems to play only a secondary role. Moreover, our work shows that these indices are associated with distinct processes occurring within the Indian Ocean from late boreal winter or early spring onwards. The regression analyses also illustrate that these (local) mechanisms are dynamically and remotely linked to different phases of ENSO in the equatorial Pacific, a result which may have useful implications in terms of forecasting strategies since the choice of the better indices then hinges on the concurrent phasing of the ENSO cycle. 相似文献
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Modified three‐dimensional seismic assessment method for buildings based on ambient vibration tests: extrapolation to higher shaking levels and measuring the dynamic amplification portion of natural torsion 
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下载免费PDF全文 This paper presents applications of the modified 3D‐SAM approach, a three‐dimensional seismic assessment methodology for buildings directly based on in situ experimental modal tests to calculate global seismic demands and the dynamic amplification portion of natural torsion. Considering that the building modal properties change from weak to strong motion levels, appropriate modification factors are proposed to extend the application of the method to stronger earthquakes. The proposed approach is consistent with the performance‐based seismic assessment approach, which entails the prediction of seismic displacements and drift ratios that are related to the damage condition and therefore the functionality of the building. The modified 3D‐SAM is especially practical for structures that are expected to experience slight to moderate damage levels and in particular for post‐disaster buildings that are expected to remain functional after an earthquake. In the last section of this paper, 16 low to mid‐rise irregular buildings located in Montreal, Canada, and that have been tested under ambient vibrations are analyzed with the method, and the dynamic amplification portion of natural torsion of the dataset is reported and discussed. The proposed methodology is appropriate for large‐scale assessments of existing buildings and is applicable to any seismic region of the world. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Robustness of SST teleconnections and precursory patterns associated with the Indian summer monsoon 总被引：2，自引：2，他引：0
This work attempts to reconcile in a common and comprehensive framework the various conflicting results found in the literature regarding Indian Summer Monsoon (ISM) rainfall-Sea Surface Temperature (SST) relationships, especially the links with El-Ni?o Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). To do so, we first examine the linear relationships between ISM rainfall and global SST anomalies during 1950–1976 and 1979–2006 periods. Our results highlight the existence of significant modulations in SST teleconnections and precursory patterns between the first (June–July, JJ) and second part (August–September, AS) of the monsoon. This JJ–AS rainfall dichotomy is more pronounced after the 1976–1977 climate regime shift and tends to blur the global ISM-ENSO signal during the recent period, leading to an apparent weakening of this relationship at the seasonal time scale. Although ISM rainfall in JJ and AS is still strongly linked to ENSO over both periods, the lead-lag relationships between ENSO and AS Indian rainfall have changed during recent decades. Indeed, ENSO variability in the preceding boreal winter has now a significant impact on rainfall variability during the second half of ISM. To evaluate in more details the impact of this JJ-AS dichotomy on the ISM-ENSO-IOD relationships, ISM correlations are also examined separately during El Ni?o and La Ni?a years. Results indicate that the early onset of El Ni?o during boreal spring causes deficient monsoon rainfall in JJ. In response to weaker monsoon winds, warm SST anomalies appear in the west equatorial IO, generating favorable conditions for the development of a positive IOD in AS. Local air-sea processes triggered by the SST anomalies in the eastern node of IOD seem, in turn, to have a more active role on AS rainfall variability, as they may counteract the negative effect of El Ni?o on ISM rainfall via a modulation of the local Hadley circulation in the eastern IO. The JJ–AS rainfall dichotomy and its recent amplification may then result from an enhancement of these IO feedbacks during recent El Ni?o years. This explains why, although El Ni?o events are stronger, a weakening of the ISM-ENSO relationship is observed at the seasonal scale after 1979. Results during La Ni?a years are consistent with this hypothesis although local processes in the southeast IO now play a more prominent role and act to further modulate ISM rainfall in AS. Finally, our results highlight the existence of a biennal rhythm of the IOD-ENSO-ISM system during the recent period, according to which co-occurring El Ni?o and positive IOD events tend to be followed by a warming of the IO, a wet ISM during summer and, finally, a La Ni?a event during the following boreal winter. 相似文献
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