Search Results (5)

Sri Lanka typically experiences anomalously wet conditions during the summer following El Niño events, but this response varies due to El Niño complexity. This study investigates the impact of post-El Niño conditions on Sri Lanka’s Monsoon rainfall, contrasting summers after fast- and slow-decaying El Niño events. Results indicate that fast-decaying El Niño events lead to wet and cool summers while slow-decaying events result in dry and warm summers. These contrasting responses are linked to sea surface temperature (SST) changes in the central to eastern Pacific. During the fast-decaying El Niño, the transition to La Niña generates strong easterlies in the central and eastern Pacific, enhancing moisture convergence, upward motion, and cloud cover, resulting in wetter conditions over Sri Lanka. During the fast-decaying El Niño, enhanced precipitation over the Maritime Continent acts as a diabatic heating source, inducing Gill-type easterly wind anomalies over the tropical Pacific. These winds promote coupled feedbacks that accelerate the transition to La Niña, strengthening moisture convergence and upward motion over Sri Lanka. Conversely, slow-decaying El Niño events are associated with cooling in the western North Pacific and warming in the Indian Ocean, which promotes the development of the western North Pacific anticyclone, suppressing upward motion and reducing cloud cover, leading to conditions over Sri Lanka. Changes in the Walker circulation further contribute to these distinct rainfall patterns, highlighting its influence on regional climate dynamics. These findings enhance our understanding of the seasonal predictability of rainfall in Sri Lanka during post-El Niño Summers. Full article

In this work, we studied the influence of spring (SP) and summer (SU) El Niño events on the landfalling tropical cyclones (TCs) in China. The results showed that compared to SU El Niño years, the average latitude of the landfalling TCs in SP El Niño years shifted significantly southward and that the average TC intensity was significantly stronger, especially in the post-landfall period. Additionally, more severe tropical storm-level TCs generated over the South China Sea made landfall in China. Meanwhile, in SP El Niño years, landfalling TCs in southern China had a greater landfall intensity, but landfalling TCs in eastern China were the opposite. These changes in TC intensity during the SP El Niño years could be attributed to more favorable dynamical and thermodynamical conditions, which are beneficial for maintaining TC intensity and duration after landfall. These results could have important implications for an in-depth understanding of TC activities, as well as TC disaster prevention and mitigation. Full article

El Niño events vary from case to case with different decaying paces. In this study, we demonstrate that the different El Niño decaying paces have distinct impacts on the East Asian monsoon circulation pattern during post-El Niño summers. For fast decaying (FD) El Niño summers, a large-scale anomalous anticyclone dominates over East Asia and the North Pacific from subtropical to mid-latitude; whereas, the East Asian monsoon circulation display a dipole pattern with anomalous northern cyclone and southern anticyclone for slow decaying (SD) El Niño summers. The difference in anomalous East Asian monsoon circulation patterns was closely associated with the sea surface temperature (SST) anomaly patterns in the tropics. In FD El Niño summers, the cold SST anomalies in the tropical central-eastern Pacific and warm SST anomalies in the Maritime Continent induce the anticyclone anomalies over the Northwest Pacific. In contrast, the warm Kelvin wave anchored over the tropical Indian Ocean during SD El Niño summers plays a crucial role in sustaining the anticyclone anomalies over the Northwest Pacific. In particular, the opposite atmospheric circulation anomaly patterns over Northeast Asia and the mid-latitude North Pacific are mainly modulated by the stationary Rossby wave trains triggered by the opposite SST anomalies in the tropical eastern Pacific during FD and SD El Niño summers. Finally, the effect of distinct summer monsoon circulation patterns associated with the El Niño decay pace on the summer climate over East Asia are also discussed. Full article

The traditional view holds that a weakened upwelling has often been observed off the coast of southeast Vietnam during the post-El Niño summer. This study investigated a strong upwelling and concurrent phytoplankton bloom off the coast of southeast Vietnam in August 2016 by comparing it with another case in 1998. Analyses of the upwelling structure and formation mechanisms indicated that the abnormal strong upwelling in August 2016 was attributable to strong wind-driven offshore Ekman transport and Ekman pumping, which were caused by the accompanying southwesterly anomalies south of the anomalous cyclone (AC) over the western North Pacific (WNP), and vice versa in August 1998. This anomalous southwesterly wind associated with the AC over the WNP could not be explained by La Niña, the negative Indian ocean dipole, or the positive Pacific meridional mode events. Further analyses showed that the Madden–Julian oscillation (MJO)-induced westerly winds could have contributed more than 75% of the original zonal winds. Nine tropical cyclones generated over the WNP were favorable for excessive precipitation. The opposite configurations of precipitation patterns over the WNP and the Maritime Continent could have further strengthened the AC via a Gill response. Full article

Climate responses to volcanic eruptions include changes in the distribution of temperature and precipitation such as those associated with El Niño Southern Oscillation (ENSO). Recent studies suggest an ENSO-positive phase after a volcanic eruption. In the Atlantic Basin, a similar mode of variability is referred as the Atlantic Niño, which is related to precipitation variability in West Africa and South America. Both ENSO and Atlantic Niño are characterized in the tropics by conjoined fluctuations in sea surface temperature (SST), zonal winds, and thermocline depth. Here, we examine possible responses of the Tropical Atlantic to last millennium volcanic forcing via SST, zonal winds, and thermocline changes. We used simulation results from the National Center for Atmospheric Research Community Earth System Model Last Millennium Ensemble single-forcing experiment ranging from 850 to 1850 C.E. Our results show an SST cooling in the Tropical Atlantic during the post-eruption year accompanied by differences in the Atlantic Niño associated feedback. However, we found no significant deviations in zonal winds and thermocline depth related to the volcanic forcing in the first 10 years after the eruption. Changes in South America and Africa monsoon precipitation regimes related to the volcanic forcing were detected, as well as in the Intertropical Convergence Zone position and associated precipitation. These precipitation responses derive primarily from Southern and Tropical volcanic eruptions and occur predominantly during the austral summer and autumn of the post-eruption year. Full article