Nonlinear precipitation response to El Niño and global warming in the Indo-Pacific (original) (raw)
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Changes in the observed precipitation and moisture transport induced by anthropogenic forcing and natural variability were investigated. To separate into the anthropogenic and natural modes, the multi-variate EOF (MVEOF) analysis synthesized from three variables includ- ing of precipitation, SST, and moisture ux convergence is used. The precipitation pattern over the tropics has a tri- polar structure in anthropogenic mode but a zonal asym- metric structure near 150°E in natural mode. The patterns of precipitation were determined in the principal modes of moisture ux convergence using MVEOF. Through a moisture budget analysis, the dynamic factor of moisture ux was found to play an important role in the precipita- tion changes. The natural and anthropogenic modes have zonal wave patterns of potential function associated with the dynamic factor: zonal wavenumber 1 and 2 structure, respectively. When the decadal ENSO is in mega-La Niña phase, natural and anthropogenic forcings represent a posi- tive sign of potential function, which means increased pre- cipitation over the tropical western Paci c (WP). In the tropics, anthropogenic forcing slightly strengthens west- erly winds over the Indian Ocean and easterly winds over the WP, while weaken the easterly winds over the eastern Paci c. The natural variability strengthens the Walker cir- culation in La Niña phase. Therefore, during recent three decades, the slightly strengthening of the wind convergence near the WP by anthropogenic forcing and the strengthen- ing of the Walker circulation by natural variability have caused the increasing precipitation over the WP.
El Niño Impacts on Precipitation in the Western North Pacific–East Asian Sector
Journal of Climate, 2009
In this study, the western North Pacific–East Asian (WNP–EA) rainfall anomaly induced by the strong El Niño in 1982–83, 1991–92, and 1997–98, and its association with the mean state, are examined. Over the northern part of the WNP–EA region (north of 20°N), which is dominated by southwest–northeast tilting frontal systems, positive rainfall anomalies from the fall before the El Niño peak phase (year 0) to the first wet period after the peak phase (year 1) are affected by low- and midlevel horizontal moisture convergence anomalies induced by low-level anticyclonic circulation anomalies over the WNP region that are associated with El Niño. Over the southern part of the WNP–EA region (south of 20°N), which is dominated by tropical convection, positive precipitation anomalies in the first and second wet periods of year 0 and negative precipitation anomalies from the fall of year 0 to the second wet period of year 1 are associated with the variation of the net energy into the atmosphere,...
The Impacts of El Niño/Southern Oscillation on Changing Precipitation over the Tropical Pacific
This study employed Sea Surface Temperature (SST) and Precipitation data to investigate the variability in the El Niño/Southern Oscillation, ENSO (La Niña, El Niño) and its impact on the intensity of precipitation over the Tropical Pacific. The recent La Niña and El Niño episodes were compared in the study to establish the relationship between variability in the ENSO and the associated precipitation. The results suggest that an increase in the strength of a La Niña event will tend to reduce the overall amount of rainfall over the Tropical Pacific while the intensity of the precipitation rises as the strength of El Niño event increases in the region. Also, the changes in the precipitation are largest in December – April during which the ENSO events are strongest under the influence of SST, which is highest over the equatorial Pacific during the period. The outcome of this investigative study would help to improve crop yield through reliable forecast of ENSO and that of the precipitat...
The strengthening and westward shift of Paci c Walker Circulation (PWC) is observed during the recent decades. However, the relative roles of global warming and natural variability on the change in PWC unclearly remain. By conducting numerical atmospheric general circulation model (AGCM) experiments using the spatial SST pat- terns in the global warming and natural modes which are obtained by the multi-variate EOF analysis from three variables including precipitation, sea surface temperature (SST), and divergent zonal wind, we indicated that the westward shift and strengthening of PWC are caused by the global warming SST pattern in the global warming mode and the negative Interdecadal Paci c Oscillation-like SST pattern in the natural mode. The SST distribution of the Paci c Ocean (PO) has more in uence on the changes in equatorial zonal circulations and tropical precipitation than that of the Indian Ocean (IO) and Atlantic Ocean (AO). The change in precipitation is also related to the equato- rial zonal circulations variation through the upward and downward motions of the circulations. The IO and AO SST anomalies in the global warming mode can a ect on the changes in equatorial zonal circulations, but the in u- ence of PO SST disturbs the changes in Indian Walker Circulation and Atlantic Walker Circulation which are a ected by the anomalous SST over the IO and AO. The zonal shift of PWC is found to be highly associated with a zonal gradient of SST over the PO through the idealized numerical AGCM experiments and predictions of CMIP5 models.
Underlying mechanisms leading to El Niño-to-La Niña transition are unchanged under global warming
El Niño's transitions play critical roles in modulating severe weather and climate events. Therefore, understanding the dynamic factors leading to El Niño's transitions and its future projection is a great challenge in predicting the diverse socioeconomic influences of El Niño over the globe. This study focuses on two dynamic factors controlling the El Niño-to-La Niña transition from the present climate and to future climate, using the observation, the historical and the RCP8.5 simulations of Coupled Model Intercomparison phase 5 climate models. The first is the inter-basin coupling between the Indian Ocean and the western North Pacific through the subtropical high variability. The second is the enhanced sensitivity between sea surface temperature and a deep tropical convection in the central tropical Pacific during the El Niño's developing phase. We show that the dynamic factors leading to El Niño-to-La Niña transition in the present climate are unchanged in spite of the increase of greenhouse gas concentrations. We argue that the two dynamic factors are strongly constrained by the climato-logical precipitation distribution over the central tropical Pacific and western North Pacific as little changed from the present climate to future climate. This implies that two dynamical processes leading to El Niño-to-La Niña transitions in the present climate will also play a robust role in global warming.