A Precursory Signal of the Central Pacific El Niño Event: Eastern Pacific Cooling Mode

In recent decades, the tropical Pacific frequently experiences a new type of El Niño with warming center in the central tropical Pacific (i.e., the CP-El Niño) with distinct global climate effect to the traditional El Niño (i.e., EP-El Niño). Predicting the El Niño diversity is still a huge challenge for climatologists partly due to the precursory signals of El Niño events with different type is unclear. In the present study, a novel precursory signal that presents a negative sea surface temperature anomaly in the eastern tropical Pacific (i.e., EP-cooling mode) is revealed, which tends to evolve into a CP-El Niño event. The transition from the EP-cooling mode to CP-El Niño is explained by the basin-scale air-sea coupling in the tropical Pacific and teleconnections between the tropical and North Pacific. With the EP-cooling mode as a predictor, the forecast skill for the CP-El Niño in hindcast experiments is obviously improved by using regression models. The results in the present study are therefore instructive for promoting a better understanding of El Niño diversity and predictability.

On Abnormally Strong Currents Observed on the Northern Coast of Peru during the 2015-2016 El Niño

The northern coast of Peru is a region that can rapidly detect the impact of an El Niño. To investigate the effects of the 2015-2016 El Niño on the oceanographic environment of the northern coast of Peru, the temperature and current data obtained from moored equipment at an oil platform were analyzed. Strong coastal along-shore currents of more than 0.60 m·s-1 were observed three times, although the mean current speed was 0.10 m·s-1 flowing toward the south-southwest. After the first strong current, the bottom temperature increased and the mixed layer deepened and remained there during the El Niño event. The temperature reached a maximum after the strong coastal current, then decreased gradually. An analysis of wind and sea surface height anomalies revealed that the coastal strong current was caused by Kelvin waves and the deepening of the mixed layer was not related to local winds, but to coastal Kelvin waves from the equator during the El Niño event.

Assessing the seasonal variability of shallow underground waters quality from a volcanic – sedimentary formation during El Niño event in Panama

Providing drinking water to growing populations has become a worldwide concern. Therefore, in many countries some groundwater reserves are now being used to supply drinking water in remote urban areas. The state of these groundwater reserves is strongly influenced by the local geological conditions. Furthermore, climate change has caused a decrease in the periodicity of environmental conditions such as rainfalls, a key driver in replenishing these reserves. In 2019, the weak El Niño event affected the rainfall pattern, as well as physical and chemical quality of shallow ground waters in Panama. Within this study, the northwestern central region of Panama groundwaters have been systematically characterized during El Niño 2018 – 2019 event. Our results indicate that changes in values of physicochemical parameters such as alkalinity, pH and conductivity are related to changes in the amount of rainfall reported in the region starting from dry season (DS) to the rainy season (RS). Chloride was recorded as an indicator of anthropogenic activity and/or the effect of human populations on specific sites in the aquifer recharge zones. Lead (Pb2+), Zinc (Zn2+), Manganese (Mn2+), and Copper (Cu2+) concentrations in the groundwater were evaluated during the DS and RS 2019. Recorded data indicates sub – lethal concentrations of Pb2+, Zn2+, Mn2+ were associated to changes in alkalinity values of groundwater during the DS. While during the RS, a decrease in pH values favored the dissolution of Cu2+ and Zn2+. Our findings suggest that seasonal rainfall deficits modify shallow underground water alkalinity and pH values, inducing the redissolution of Pb2+, Zn2+, Mn2+, Cu 2+and exposing populations to sub – lethal concentrations of those microelements.

Pengaruh El Niño Terhadap Pola Distribusi Klorofil-a dan Pola Arus di Wilayah Perairan Selatan Maluku

El Niño is a phenomenon that can affect changes in weather and climate elements in Indonesia, especially rainfall. During the El Niño events, the rainfall in Maluku region tended to decrease. This condition can indeed cause prolonged drought. However, El Niño events also have a positive impact, especially in water areas. During the El Niño events, the chlorophyll-a concentration in the water will increase. This is due to the upwelling process that removes nutrients from the sea. High chlorophyll-a concentrations will bring pelagic fish species in the waters. The correlation test between sea surface temperature (SST) during El Niño and chlorophyll-a has a value of -0.91. This correlation value indicates that when SST increases, the chlorophyll-a concentration in the waters will decrease, on the other hand, if SST has decreased, the chlorophyll-a concentration in the water will increase. The value of chlorophyll-a concentration in the water during the El Niño event (July - February) showed a significant increase compared to during normal conditions. Of all the El Niño events, 2015 to 2016 was the year with the strongest El Niño events. The chlorophyll-a concentration during El Niño 2015 to 2016 was very high, ranging from 0.2 to 1.0 mg / m3. The results obtained indicate that the El Niño event has a positive correlation with the increase in chlorophyll-a concentration in the water. El Niño merupakan fenomena yang tidak bisa dihindari, kejadian El Niño dapat mengurangi curah hujan seperti di wilayah Maluku. Namun, kejadian El Niño juga mempunyai dampak postif khususnya di wilayah perairan. Pada saat terjadi El Niño maka konsentrasi klorofil-a di perairan akan meningkat. Hal ini disebabkan karena adanya proses upwelling yang mengangkat nutrisi dari dalam laut. Konsentrasi klorofil-a yang tinggi akan mendatangkan jenis ikan pelagis di perairan. Uji korelasi antara suhu permukaan laut (SST) pada saat El Niño dengan klorofil-a memiliki nilai - 0.91. Nilai korelasi ini menunjukkan bahwa pada saat SST mengalami kenaikan maka konsentrasi klorofil di perairan akan menurun, sebaliknya jika SST mengalami penurunan maka konsentrasi klorofil diperairan akan meningkat. Nilai konsentrasi klorofil-a diperairan pada saat kejadian El Niño (Juli - Februari) menunjukkan peningkatan yang cukup signifikan dibandingkan pada saat tidak terjadi El Niño . Dari semua kejadian El Niño , tahun 2015 - 2016 merupakan kejadian dengan El Niño yang sangat kuat. Konsentrasi klorofil-a pada saat El Niño 2015 - 2016 sangat tinggi berkisar 0.2 - 1.0 mg/m3. Dari hasil yang didapatkan menunjukkan bahwa kejadian El Niño dapat mempengaruhi konsentrasi klorofil-a diperairan.

Synergistic Effect of El Niño And The North Pacific Oscillation On Wintertime Precipitation Over Southeastern China And The East China Sea Kuroshio Area

Wintertime precipitation in China is most pronounced over the southeastern area, and the Kuroshio in the East China Sea anchors a prominent precipitation band over the warm side of the sea surface temperature front. Previous studies have suggested that many factors contribute to the interannual variation of the precipitation over southeastern China (SC), whereas less attention has been paid to precipitation variability over the East China Sea Kuroshio (ECSK) area. This study focuses on the interannual variation of wintertime precipitation over the SC and ECSK areas. Empirical orthogonal function analysis reveals a spatially uniform pattern from SC to the ECSK area. Composite analysis shows that an El Niño event intensifies wintertime precipitation over our target region, and this effect is tripled when an El Niño follows a positive North Pacific Oscillation (NPO) event in the previous winter. The positive NPO event in the previous winter intensifies the El Niño event via the Victoria mode ocean bridge and the subsequent Bjerknes feedback. In comparison with single-factor El Niño events, a much weaker Walker cell induced by the joint event induces a much weaker regional Hadley cell through anomalous descending motion over the western tropical Pacific. The weakened regional Hadley circulation over the western Pacific directly enhances the precipitation over the SC and ECSK area. In this study, the synergistic effect of an El Niño event and a positive NPO event indicates that the influence of the El Niño event can be amplified by the positive NPO event in the previous winter.

Resistance of African tropical forests to an extreme climate anomaly

The responses of tropical forests to environmental change are critical uncertainties in predicting the future impacts of climate change. The positive phase of the 2015–2016 El Niño Southern Oscillation resulted in unprecedented heat and low precipitation in the tropics with substantial impacts on the global carbon cycle. The role of African tropical forests is uncertain as their responses to short-term drought and temperature anomalies have yet to be determined using on-the-ground measurements. African tropical forests may be particularly sensitive because they exist in relatively dry conditions compared with Amazonian or Asian forests, or they may be more resistant because of an abundance of drought-adapted species. Here, we report responses of structurally intact old-growth lowland tropical forests inventoried within the African Tropical Rainforest Observatory Network (AfriTRON). We use 100 long-term inventory plots from six countries each measured at least twice prior to and once following the 2015–2016 El Niño event. These plots experienced the highest temperatures and driest conditions on record. The record temperature did not significantly reduce carbon gains from tree growth or significantly increase carbon losses from tree mortality, but the record drought did significantly decrease net carbon uptake. Overall, the long-term biomass increase of these forests was reduced due to the El Niño event, but these plots remained a live biomass carbon sink (0.51 ± 0.40 Mg C ha−1 y−1) despite extreme environmental conditions. Our analyses, while limited to African tropical forests, suggest they may be more resistant to climatic extremes than Amazonian and Asian forests.