The occurrence of the 2017/2018 La Niña, following a weak‐to‐neutral La Niña in boreal winter 2016/2017, was surprising. Based on observational records and multiple linear regression analysis for the ...Pacific zonal wind tendency (dU/dt), this study investigates possible reasons why the La Niña condition suddenly happened in late 2017. Similar to previous four double‐peaked La Niña events (1983–1985, 1998–2000, 2007–2009, and 2010–2012), we find that the multiyearly persistent easterly anomaly in the central equatorial Pacific is a key condition to the development of the second La Niña. The occurrence of the 2017/2018 La Niña results from large warm sea surface temperature (SST) anomalies in the tropical Indian and Atlantic Oceans that act to force the persistent easterly anomaly in the Pacific via modifying the Walker Circulations. About 24% of the variance of the Pacific dU/dt can be statistically explained by the tropical Indian Ocean and Atlantic SST anomalies.
Plain Language Summary
The 2017/2018 La Niña appears to be surprising, given that an El Niño‐like condition has already developed in the first half of 2017 but actually in opposite to most models' forecasts that issued a false alarm of an El Niño. Previous studies suggested that both the tropical Indian and Atlantic Oceans have exhibited a rapid warming in recent decades, which have caused an easterly trend in the central Pacific. In this study, we examine the possible contributions of the tropical Indian Ocean and Atlantic SSTs to the occurrence of the second La Niña in 2017/2018. Our results highlight the importance of the SST warming in the tropical Indian and Atlantic Oceans for the occurrence of the second La Niña under rapid SST warming in the two basins during recent decades.
Key Points
Persistent easterly anomaly in the central equatorial Pacific is a key condition to the occurrence of the second La Niña
Rapid SST warming in the tropical Indian and Atlantic Oceans acts to strengthen the persistent easterly anomaly
About 24% of the variance of the dU/dt in the central equatorial Pacific during 1980‐2017 can be explained by the IO and AO SSTAs
Currently, the Arctic is undergoing a significant warming, which has exerted widespread impacts on global climate. Although many mechanisms responsible for the Arctic warming have been proposed, the ...impacts of the multi‐decadal change of tropical sea surface temperature receive little attention. Here we use numerical experiments to elucidate that the Indian Ocean (IO) warming may contribute to the Arctic warming. Through enhancing the Atlantic Meridional Overturning Circulation, the IO warming remotely induces more ocean heat transport from the North Atlantic to the Arctic. The resulted upper ocean warming dominates the surface warming in the Arctic. Additionally, despite the net negative contribution of the atmospheric heat transport, more warm air is conveyed into the Kara Seas, North Eurasia, and North America sectors, contributing to the local warming. The results propose a new mechanism to interpret the Arctic warming and indicate the important remote impacts of the tropical IO warming.
Plain Language Summary
The Arctic warming is a significant phenomenon in the context of global warming, which not only impacts the local ecosystem but also influences global climate. Improved understanding of its causes is important to the protection of the Arctic ecosystem and the forecast of global climate. Although many previous studies have proposed various mechanisms to interpret the Arctic warming, its causes are still not fully understood. In this study, we find that the Indian Ocean (IO) warming is also a possible contributor to the Arctic warming. Through enhancing the Atlantic Meridional Overturning Circulation, the IO warming remotely induces more ocean heat transport from the North Atlantic to the Arctic and then contributes to the Arctic warming. Additionally, the southerly winds in the high latitudes in response to the IO warming, transport more warm air into the Kara Seas, North Eurasia and North America and contributes to the local warming. The present study indicates the IO warming may also contribute to the Arctic warming. A better understanding of the remote impacts of tropical oceans may foster the comprehensive understanding of the complicated reasons for the Arctic warming.
Key Points
Rapid warming in the Indian Ocean (IO) may contribute to the Arctic warming through both oceanic and atmospheric pathways
More ocean heat is transported from the North Atlantic to the Arctic due to enhanced Atlantic Meridional Overturning Circulation in response to the IO warming
Southerly winds in the high latitudes in response to the IO warming convey more warm air into parts of the Arctic
Variations in the El Niño/Southern Oscillation (ENSO) are associated with a wide array of regional climate extremes and ecosystem impacts
. Robust, long-lead forecasts would therefore be valuable for ...managing policy responses. But despite decades of effort, forecasting ENSO events at lead times of more than one year remains problematic
. Here we show that a statistical forecast model employing a deep-learning approach produces skilful ENSO forecasts for lead times of up to one and a half years. To circumvent the limited amount of observation data, we use transfer learning to train a convolutional neural network (CNN) first on historical simulations
and subsequently on reanalysis from 1871 to 1973. During the validation period from 1984 to 2017, the all-season correlation skill of the Nino3.4 index of the CNN model is much higher than those of current state-of-the-art dynamical forecast systems. The CNN model is also better at predicting the detailed zonal distribution of sea surface temperatures, overcoming a weakness of dynamical forecast models. A heat map analysis indicates that the CNN model predicts ENSO events using physically reasonable precursors. The CNN model is thus a powerful tool for both the prediction of ENSO events and for the analysis of their associated complex mechanisms.
CRISPR/Cas9 is a valuable tool for both basic and applied research that has been widely applied to different plant species. Nonetheless, a systematical assessment of the efficiency of this method is ...not available for the allotetraploid Brassica napus-an important oilseed crop. In this study, we examined the mutation efficiency of the CRISPR/Cas9 method for 12 genes and also determined the pattern, specificity and heritability of these gene modifications in B. napus. The average mutation frequency for a single-gene targeted sgRNA in the T0 generation is 65.3%. For paralogous genes located in conserved regions that were targeted by sgRNAs, we observed mutation frequencies that ranged from 27.6% to 96.6%. Homozygotes were readily found in T0 plants. A total of 48.2% of the gene mutations, including homozygotes, bi-alleles, and heterozygotes were stably inherited as classic Mendelian alleles in the next generation (T1) without any new mutations or reversions. Moreover, no mutation was found in the putative off-target sites among the examined T0 plants. Collectively, our results demonstrate that CRISPR/Cas9 is an efficient tool for creating targeted genome modifications at multiple loci that are stable and inheritable in B. napus. These findings open many doors for biotechnological applications in oilseed crops.
Enzyme fusion, the fusion of enzymes with different domains to a single protein, has been widely recognized as a promising strategy in the development of biocatalysts. Nature has evolved gene fusion ...to combine different catalytic enzymes to function as a fusion enzyme, and this strategy is utilized in many natural product biosynthetic pathways. Owing to rapid advances in genome sequencing and biosynthetic pathway characterization, there is increasing interest in fusion enzymes from fungal biosynthetic pathways, particularly those involved in tailoring steps. This concept aims to provide an up-to-date overview of fusion enzymes that catalyze tailoring reactions in the biosynthesis of fungal secondary metabolites. Since fungal fusion enzymes are often associated with novel metabolites, this pioneering work may stimulate the exploration of the structural diversity of fungal natural products through genome mining of the untapped biosynthetic pathways involving fusion enzymes.
Motivated by the prevalence of corporate sustainability and the rise of uncertainty at the national level, we investigate the impact of three sources of uncertainty; namely, economic policy, climate ...change, and political instability, on firms' sustainability performance. Using a sample of 6804 firms from 72 countries spanning 15 years, our study revealed that uncertainty due to climate change, economic policy, and political instability negatively affects firms' sustainability performance. This finding is in line with the real options theory that uncertainty in an external environment discourages firms' long-term investment (e.g. investment in corporate sustainability). In addition, the results show that the option for delay in sustainability investment moderated the relation between uncertainty at the national level and firms' sustainability performance. Firms with better sustainability performance had higher firm value when facing uncertainty. Interestingly, firms with higher profitability performed better in sustainability when facing uncertainty at the national level.
•Economic policy uncertainty, political instability and climate change at the national level negatively affects firms' sustainability performance.•The option for delay in sustainability investment affected or moderated the relationship between uncertainty at the national level and firms' sustainability performance.•Firms with better sustainability performance had higher firm value when facing uncertainty.•The findings are robust after controlling for potential endogeneity concerns.
Computation-in-memory (CIM) is a promising candidate to improve the energy efficiency of multiply-and-accumulate (MAC) operations of artificial intelligence (AI) chips. This work presents an static ...random access memory (SRAM) CIM unit-macro using: 1) compact-rule compatible twin-8T (T8T) cells for weighted CIM MAC operations to reduce area overhead and vulnerability to process variation; 2) an even-odd dual-channel (EODC) input mapping scheme to extend input bandwidth; 3) a two's complement weight mapping (C2WM) scheme to enable MAC operations using positive and negative weights within a cell array in order to reduce area overhead and computational latency; and 4) a configurable global-local reference voltage generation (CGLRVG) scheme for kernels of various sizes and bit precision. A 64 × 60 b T8T unit-macro with 1-, 2-, 4-b inputs, 1-, 2-, 5-b weights, and up to 7-b MAC-value (MACV) outputs was fabricated as a test chip using a foundry 55-nm process. The proposed SRAM-CIM unit-macro achieved access times of 5 ns and energy efficiency of 37.5-45.36 TOPS/W under 5-b MACV output.
Herein, we report an efficient photocatalytic strategy for the decarboxylative transformations of redox‐active esters to construct C=C, C(sp3)−N, and C(sp3)−X bonds in a single‐step. This ...operationally simple method provides a straightforward access to a variety of protected alkyl amines, alkyl halides and olefins under mild conditions in the absence of metals and photocatalysts. The method can successfully be applied to primary, secondary, and tertiary aliphatic carboxylic acid derivatives. Mechanistic studies indicate that the charge transfer complex (CTC) was formed by nBu4NI with redox‐active esters, in which the nBu4NI acted as both an iodine source and an efficient electron donor.
Herein, we described a versatile photocatalytic strategy for the decarboxylative transformations of redox‐active esters (RAE) to a variety of alkyl halides, amines, and olefins in the presence of nBu4NI in a single‐step. It is a straightforward method which is applied to the functionalization of a series of primary, secondary, and tertiary aliphatic carboxylic acid derivatives and complex natural products. Mechanistically, a charge transfer complex (CTC) was formed through non‐covalent interaction between RAE and nBu4NI. Upon photoexcitation, the ammonia salt acted as both an efficient electron donor and an iodine source for radical recombination. The mild reaction condition allows this method can be applied for modification of complex natural products and versatile follow‐up transformations.
The interactions between El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are known to have great implications for global climate variability and seasonal climate predictions. ...Observational analysis suggests that the ENSO–IOD inter‐basin connection is time‐varying and related to the Atlantic Multidecadal Oscillation (AMO) with weakened ENSO–IOD relationship corresponding to AMO warm phases. A suite of Atlantic pacemaker simulations successfully reproduces the decadal fluctuations in ENSO–IOD relationship and its link to the AMO. The warm sea surface temperature (SST) anomalies associated with the AMO drive a series of Indo‐Pacific mean climate changes through tropical‐wide teleconnections, including the La Niña‐like mean SST cooling over the central Pacific and the deepening of mean thermocline depth in the eastern Indian Ocean. By modulating ocean–atmosphere feedback strength, those mean state changes decrease both ENSO amplitude and the Indian Ocean sensitivity to ENSO forcing, therefore decoupling the IOD from ENSO.
Plain Language Summary
The El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are two most important interannual climate signals exciting world‐wide climate and socioeconomic impacts. Their interactions are known to have great implications for global climate variability and seasonal climate predictions. However, the ENSO–IOD relationship is time‐varying and show prominent decadal fluctuations. Such changes in ENSO–IOD relationship are associated with the decadal variation in IOD teleconnections and predictability. The prediction skill of IOD is high when the ENSO–IOD relationship is strong, and vice versa. But it remains unknown what controls the decadal modulation of Indo‐Pacific inter‐basin connection. Our findings suggest that the Atlantic Multidecadal Oscillation (AMO) may modulate the ENSO–IOD inter‐basin connection. The AMO sea surface temperature anomalies drive a series of Indo‐Pacific mean climate changes through tropical‐wide teleconnections. Those mean state changes further influence both ENSO amplitude and the Indian Ocean sensitivity to ENSO forcing, thereby modulating the ENSO–IOD relationship. This study advances our understandings on inter‐basin and cross‐scale interactions in the climate system.
Key Points
The inter‐basin connection between El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole is time‐varying and controlled by the remote Atlantic Multidecadal Oscillation (AMO)
The AMO sea surface temperature anomalies drive a series of Indo‐Pacific mean climate changes through tropical‐wide teleconnections
The AMO induced mean state changes influence both ENSO amplitude and the Indian Ocean sensitivity to ENSO forcing
Using both observations and ensemble hindcasts of Nanjing University of Information Science and Technology Climate Forecast System (NUIST‐CFS1.0) for the period of 1983–2020, the leading modes of sea ...surface temperature anomalies (SSTAs) over the tropical Atlantic in boreal spring and summer (March–April–May–June–July–August, MAM‐JJA) and their connections with El Niño‐Southern Oscillation (ENSO) are investigated with Empirical Orthogonal Function (EOF), partial‐correlation, and composite analyses. In both observations and hindcasts, the first EOF mode is characterized by a basin‐wide SSTA pattern, and the second mode features a meridional dipole pattern. The meridional dipole mode cannot trigger ENSO, while the basin‐wide SST warming mode contributes to a subsequent La Niña via both north‐tropical and equatorial pathways. The north‐tropical pathway involves a low‐level anomalous anticyclone over North Pacific as a Matsuno‐Gill‐type response to the basin‐wide SST warming, related to a North Pacific Meridional Mode characterized with a cold SSTA and north‐easterly wind coupling over the northeast tropical Pacific, and finally triggers La Niña via the seasonal footprinting mechanism. This pathway is less important in the hindcasts than in observations. The equatorial pathway is tightly linked to the Kelvin wave, characteristic of an eastward propagation of the coupled pattern of SST and low‐level winds and a wedge‐like 500‐hPa air temperature anomaly over the tropical Indian and western equatorial Pacific Oceans, which is more significant in the hindcasts than in observations. Further composite analyses confirm that, even without the effect of the preceding ENSO, a basin‐wide tropical Atlantic SST warming favours the development of La Niña.
In both observations and the NUIST‐CFS1.0 hindcasts, the first EOF mode is characterized by a basin‐wide SSTA pattern, and the second mode features a meridional dipole pattern. The meridional dipole mode cannot trigger ENSO, while the basin‐wide SST warming mode contributes to a subsequent La Niña via both north‐tropical and equatorial pathways. Composite analyses confirm that, even without the effect of the preceding ENSO, a basin‐wide tropical Atlantic SST warming favours the development of La Niña.
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