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The analysis of observational rainfall shows that the intensity of rainfall intraseasonal oscillation (ISO) and the summer-mean rainfall over the middle-lower reaches of the Yangtze River Basin (YRB) exhibit a significant positive correlation during 1979–2007. A stronger (weaker) ISO variability is often associated with wet (dry) summer in the YRB. The composite ISOs in both the wet and dry summers are further analyzed. In the wet summers, the rainfall ISO in YRB is primarily associated with the northward propagation of a low-level cyclone-anticyclone pair from the tropics. Cyclonic vorticity and associated boundary layer convergence strengthen the rainfall in situ. In contrast, the rainfall ISO in YRB in the dry summers is primarily associated with the westward propagation of an anomalous anticyclone. Southerly flow to the west of the anomalous anticyclone enhances rainfall in YRB through anomalous moisture advection. In addition to the difference in ISO propagation, the background mean state also shows a marked difference. The diagnosis of water vapor flux budget shows that the convergence and advection of seasonal mean moisture play a critical role in maintenance of the intraseasonal rainfall in the YRB. A greater mean ascending motion and associated higher mean moisture in YRB in the wet summers favor greater intraseasonal rainfall variability in situ. The mean state difference is responsible for distinctive vertical structures of boundary layer vertical velocity. A possible feedback of the ISO to the summer-mean rainfall over the YRB is also discussed.

Based on daily precipitation data from the Chinese Meteorological Administration and reanalysis data from the National Centers for Environmental Prediction-Department of Energy, the character of low-frequency precipitation variability during the first rainy season (April–June) over South China and its corresponding atmospheric circulations in the mid-high latitudes are investigated. The results show that the precipitation anomalies during this period exhibit obvious quasi-biweekly oscillation (QBWO) features, with a period of 8–24 days. The influence of wave trains in the mid-high latitudes to low-frequency persistent heavy rain event (PHR-LF event, the 8–24-day filtered precipitation larger than one standard deviation of filtered time series and persisting at least three days over South China) is further discussed. During the first rainy season over South China, there are two low-frequency wave trains in the mid-high latitudes associated with the PHR-LF event—the wave train crossing the Eurasian continent and the wave train along the subtropical westerly jet. Analysis of wave activity flux indicates that the wave energy disperses toward eastern China along these two low-frequency wave trains from north to south and from west to east, and then propagates downward over South China. Accordingly, the disturbance of the relative vorticity of the cyclonic anomalies over eastern China is strengthened, which enhances the meridional gradient of relative vorticity. Owing to the transport of low-frequency relative vorticity and geostrophic vorticity by meridional wind, the ascending motion over South China intensifies and lasts for a long time, triggering a PHR-LF event. In addition, the tropical system is also a key factor to PHR-LF event. The QBWO of the convection over the South China Sea provide moisture for PHR-LF events, maintaining persistent rainfall and vertical ascending motion over South China.

The boreal summer intraseasonal oscillation (BSISO) is simulated by the Climate System Model (CSM) developed at the Chinese Academy of Meteorological Sciences (CAMS), China Meteorological Administration. Firstly, the results indicate that this new model is able to reasonably simulate the annual cycle and seasonal mean of the precipitation, as well as the vertical shear of large-scale zonal wind in the tropics. The model also reproduces the eastward and northward propagating oscillation signals similar to those found in observations. The simulation of BSISO is generally in agreement with the observations in terms of variance center, periodicity, and propagation, with the exception that the magnitude of BSISO anomalous convections are underestimated during both its eastward propagation along the equator and its northward propagation over the Asian–Pacific summer monsoon region. Our preliminary evaluation of the simulated BSISO by CAMS-CSM suggests that this new model has the capability, to a certain extent, to capture the BSISO features, including its propagation zonally along the equator and meridionally over the Asian monsoon region.

Significance Summer rainfall along the Yangtze River in 2020 was the heaviest since 1961, with devastating socioeconomic impacts. While official forecasts based on tropical Pacific state failed, we show that dynamic models, when initialized with ocean observations globally, succeed in predicting the extreme rainfall. Slowly propagating oceanic Rossby waves in the South Indian Ocean are the source of predictability, which are in turn tied to the record-breaking Indian Ocean Dipole in late 2019. The identification of antecedent subsurface conditions of the Indian Ocean as a key predictor represents an important conceptual advance in Asian summer monsoon dynamics, helping improve disaster preparation that saves lives and properties., Heavy monsoon rainfall ravaged a large swath of East Asia in summer 2020. Severe flooding of the Yangtze River displaced millions of residents in the midst of a historic public health crisis. This extreme rainy season was not anticipated from El Niño conditions. Using observations and model experiments, we show that the record strong Indian Ocean Dipole event in 2019 is an important contributor to the extreme Yangtze flooding of 2020. This Indian Ocean mode and a weak El Niño in the Pacific excite downwelling oceanic Rossby waves that propagate slowly westward south of the equator. At a mooring in the Southwest Indian Ocean, the thermocline deepens by a record 70 m in late 2019. The deepened thermocline helps sustain the Indian Ocean warming through the 2020 summer. The Indian Ocean warming forces an anomalous anticyclone in the lower troposphere over the Indo-Northwest Pacific region and intensifies the upper-level westerly jet over East Asia, leading to heavy summer rainfall in the Yangtze Basin. These coupled ocean-atmosphere processes beyond the equatorial Pacific provide predictability. Indeed, dynamic models initialized with observed ocean state predicted the heavy summer rainfall in the Yangtze Basin as early as April 2020.

Meiyu rainfall in June–July of 2020 hit the Yangtze‐Huaihe River basin, and the precipitation at lots of observational stations broke the records, inducing severe disasters there. Tibetan Plateau vortices (TPVs) generated over the Tibetan Plateau are local major rainfall triggers. In previous knowledge, TPVs can affect the rainfall in eastern China, only after emigrating from the Tibetan Plateau. In this work, roles of TPVs in the record Meiyu are revealed, implying that the effects of TPVs may be underestimated previously. Firstly, TPVs dying out over the Tibetan Plateau may be transformed into troughs and continue to move eastward, influencing the rainfall in Yangtze‐Huaihe River basin. Secondly, southwest vortices, the important rainfall producers in China, tend to be generated and maintained when TPVs are located over eastern plateau. The results give extended knowledge on the effects of TPVs, which are beneficial for the rainfall prediction in eastern China.

The variation in the concentrations of ambient PM2.5 (particles with an aerodynamic diameter less than 2.5 μm) generally forms a continuous sawtooth cycle with a recurring smooth increase followed by a sharp decrease. The abrupt decay of pollution episode is mostly meteorological in origin, and is controlled by the passage of synoptic systems. One affordable and effective measure for the quickly reducing PM2.5 concentrations in northern China is to wait for strong wind to arrive. However, it is still unclear how strong the wind needs to be and exactly what kind of synoptic system most effectively results in the rapid decay of air pollution episodes. PM2.5 variations over the 28 pollution channel cities of Beijing are investigated to determine the mechanisms by which synoptic patterns affect the decay processes of pollution episodes. This work shows more obvious day-to-day variations in PM2.5 concentration in winter than in summer, which implies that wintertime PM2.5 variations are more sensitive to meteorological factors. There were 365 decay processes from January 2014 to March 2020, and 97 of them were related to the effective wet deposition. 26 %~43 % of PM2.5 pollutant is removed by the wet deposition in different seasons. Two dominant circulation patterns are identified in summer, and the same three circulation types (CTs) are identified in the other three seasons based on the dry-day cases. The circulation patterns beneficial to the decay processes all exhibit a higher than normal surface wind speed, a negative relative humidity anomaly and positive divergence in the PM2.5 horizontal flux. In addition, CT1 in spring, autumn and winter is controlled by northeasterly wind and features the most significant horizontal net-outflow of air pollutants and effective upward spread of air pollutants to the free atmosphere, which promotes the abrupt reduction of local PM2.5 concentrations. CT2 is the most frequent synoptic pattern leading to decay processes in autumn and winter, and the domain region is located to the east of an anticyclone system. CT2 features a strong northwesterly wind of 2.98~3.88 m/s, the lowest relative humidity and the highest boundary layer height (BLH) among the three CTs, all of which are favorable for the reduction of PM2.5 concentrations. In CT3, a prevailing westerly wind anomaly occurs in the domain, with remarkable zonal divergence in the PM2.5 flux and strong horizontal wind shear in the near-surface under the boundary layer. PM2.5 concentrations show significant decreases of more than 37 %, 41 % and 27 % after the passage of CT1, CT2 and CT3, respectively. A dry air mass with a positive BLH anomaly and the effective horizontal outflow of air pollutants are the main reasons for the abrupt decay phase in summer. PM2.5 concentrations after the decay process show a significant decreasing trend from 2014 to 2020, reflecting successful emission mitigation. Emission reductions have led to a 4.3~5.7 μg/(m3.yr) decrease in PM2.5 concentrations in the 28 pollution channel cities of Beijing.

Lockdown measures are essential to containing the spread of coronavirus disease 2019 (COVID-19), but they will slow down economic growth by reducing industrial and commercial activities. However, the benefits of activity control from containing the pandemic have not been examined and assessed. Here we use daily carbon dioxide (CO2) emission reduction in China estimated from statistical data for energy consumption and satellite data for nitrogen dioxide (NO2) measured by the Ozone Monitoring Instrument (OMI) as an indicator for reduced activities consecutive to a lockdown. We perform a correlation analysis to show that a 1% day−1 decrease in the rate of COVID-19 cases is associated with a reduction in daily CO2 emissions of 0.22% ± 0.02% using statistical data for energy consumption relative to emissions without COVID-19, or 0.20% ± 0.02% using satellite data for atmospheric column NO2. We estimate that swift action in China is effective in limiting the number of COVID-19 cases, Graphical Abstract, Public Summary • Daily CO2 emission reduction is estimated by a geographic model as an indicator for the activity control in China • A 1% day−1 decrease in the rate of COVID-19 cases is associated with daily CO2 emission reduction of 0.22% ± 0.02% using statistical data for energy consumption or 0.20% ± 0.02% using satellite data for nitrogen dioxide • The swift action of China in activity control, indicated by a 23% reduction in CO2 emissions by the end of February 2020, is effective in limiting the number of COVID-19 cases

Improving the nitrogen use efficiency (NUE) may considerably increase maize yield and decrease the use of nitrogen (N) fertilizer. But the genetic basis of NUE in maize is still poorly understood. In this study, an association panel of 139 maize inbred lines genotyped with 50,790 single nucleotide polymorphism (SNP) was used to dissect the genetic basis of NUE-related traits by genome-wide association study (GWAS). NUE, N uptake efficiency (NupE), N utilization efficiency (NutE), grain N concentration (GNC), stover N concentration (SNC) and N harvest index (NHI) were estimated under two N levels. GWAS was performed using a fixed and random model circulating probability unification (FarmCUP) method. In total, 27 and 23 significant SNP-traits association signals were identified under normal and low N levels. In addition, 10 significant association signals were detected based on the traits relative value (normal N supply / low N supply) of two N levels. Further, 60 candidate genes were predicted for these traits base on linkage disequilibrium (LD) and low nitrogen transcriptome analysis of significant SNP regions. Among the candidate genes identified in this study, 66.7% involved in nitrogen compound metabolic process. Zm00001d025831 and Zm00001d004633 encoded ammonium transporter1 and transmembrane amino acid transporter family protein, respectively, may be important candidate genes for NUE. The markers identified in this study maybe has important significance and could be useful in molecular marker assisted selection in breeding of high-NUE maize varieties, and the candidate genes could deepen the understanding of the genetic basis of NUE.

The 2014–2015 “Monster”/“Super” El Niño failed to be predicted one year earlier due to the growing importance of a new type of El Niño, El Niño Modoki, which reportedly has much lower forecast skill with the classical models. In this study, we show that, so far as of today, this new El Niño actually can be mostly predicted at a lead time of more than 10 years. This is achieved through tracing the predictability source with an information flow-based causality analysis, which has been rigorously established from first principles during the past 16 years (e.g., Liang in Phys Rev E 94:052201, 2016). We show that the information flowing from the solar activity 45 years ago to the sea surface temperature results in a causal structure resembling the El Niño Modoki mode. Based on this, a multidimensional system is constructed out of the sunspot number series with time delays of 22–50 years. The first 25 principal components are then taken as the predictors to fulfill the prediction, which through causal AI based on the Liang–Kleeman information flow reproduces rather accurately the events thus far 12 years in advance.

The horizontal wavenumbers and modal depth functions are estimated by block sparse Bayesian learning (BSBL) for broadband signals received by a vertical line array in shallow-water waveguides. The dictionary matrix consists of multi-frequency modal depth functions derived from shooting methods given a large set of hypothetical horizontal wavenumbers. The dispersion relation for multi-frequency horizontal wavenumbers is also taken into account to generate the dictionary. In this dictionary, only a few of the entries are used to describe the pressure field. These entries represent the modal depth functions and associated wavenumbers. With the constraint of block sparsity, the BSBL approach is shown to retrieve the horizontal wavenumbers and corresponding modal depth functions with high precision, while a priori knowledge of sea bottom, moving source, and source locations is not needed. The performance is demonstrated by simulations and experimental data.

The Chinese government has made many efforts to mitigate fine particulate matter (PM2.5) pollution in recent years by taking strict measures on air pollutants reduction, which has generated the nationwide improvements in air quality since 2013. However, under the stringent air pollution controls, how PM2.5 concentration varies and how much the meteorological conditions contribute to the interannual variations in PM2.5 concentrations are still unclear, which is very important for the local government to assess the emission reduction of previous year and adjust mitigation strategies of next year. The effects of atmospheric circulation on the interannual variation in wintertime PM2.5 concentrations over the Beijing-Tianjin-Hebei (BTH) region in the period of 2013–2018 are evaluated in this study. Generally, the transport of clean and dry air masses and unstable boundary layer working with the effective near-surface horizontal divergence or pumping action at the top of the boundary layer benefit for the horizontal or vertical diffusion of surface air pollutants. Instead, the co-occurrence of a stable boundary layer, frequent air stagnation, positive water vapor advection and deep near-surface horizontal convergence exacerbate the air pollution. Favorable circulation conditions lasting for 2~4 days are beneficial for the diffusion of air pollutants, and 3~7 days of unfavorable circulation events exacerbate the accumulation of air pollutants. The occurrence frequency of favorable circulation events is consistent with the interannual variation in seasonal mean PM2.5 concentrations. There is better diffusion ability in the winters of 2014 and 2017 than in other years. A 76.5 % of the observed decrease in PM2.5 concentrations in 2017 over the BTH region could be attributed to the improvement in atmospheric diffusion conditions. It is essential to exclude the contribution of meteorological conditions to the variation in interannual air pollutants when making a quantitative evaluation of emission reduction measurements.

Tibetan Plateau vortices (TPVs) are important rainfall triggers in southwestern and eastern China after they move off the plateau. Characteristics of the moving‐off TPVs derived from two gridded data sets, the final operational global analysis data from the Global Forecasting System of National Centers for Environment Prediction (NCEP‐FNL) and the ERA‐interim data from the European Centre for Medium‐Range Weather Forecasts, are evaluated against the Yearbooks of Tibetan Plateau Vortex and Shear Line (YB). Generally, NCEP‐FNL captures more moving‐off TPVs in YB than ERA‐interim does. Both gridded data sets perform the best in capturing the TPVs in YB in May and the worst in July. Zonal propagation distances of TPVs are apparently better revealed in NCEP‐FNL than in ERA‐interim, and the performances of NCEP‐FNL and ERA‐interim in showing the meridional propagation distances and lifespans are similar. Positional deviations of TPVs in NCEP‐FNL and ERA‐interim reveal that both data sets show good skills in presenting the TPVs locations, and NCEP‐FNL generally performs better than ERA‐interim. In both gridded data sets, positional deviations of TPVs are larger before the TPVs move off the plateau than after moving off, and zonal deviations are always larger than meridional deviations. Before the TPVs move off, NCEP‐FNL shows no specific preference for the directions of positional deviations, whereas ERA‐interim tends to present further west TPVs locations relative to those in YB. After the TPVs move off, TPVs in both gridded data sets are always observed to the west and north of the TPVs in YB, which is more significant in ERA‐interim.

In recent decades, unprecedented extreme summer heat waves have occurred in Europe, and they have exhibited an increasing trend since 1970s. Although previous studies have suggested that these recent hot European summers could have been instigated by the underlying surface thermal conditions, the possible influence of shrinking Arctic sea ice and Eurasian snow cover on heat waves are not well understood. Herein, we present evidence obtained via observational analyses and numerical experiments indicating that the interdecadal increase in European heat waves is closely linked to the reductions in Arctic sea ice concentration (ASIC) and Eurasian snow cover fraction (EASC) across mid–high latitudes via the excitation of the anomalous Eurasian wave train. The combined effects of declined ASIC and EASC, accompanied by the drier soil and the stronger heat flux, tend to weaken the poleward temperature gradient at mid–high latitudes and affect the midlatitude jet stream and transient eddy activities. These dynamic and thermodynamic circulations increase the likelihood of more persistent European blocking events that favor frequent and strengthened heat waves. Further projection analysis of simulations from 13 CMIP5 climate models suggests that Europe may experience more hot summers as the ASIC and EASC continue to decline over the next century.

The ray-based blind deconvolution algorithm can provide an estimate of the channel impulse responses (CIRs) between a shipping source of opportunity and the elements of a receiving array by estimating the unknown phase of this random source through wideband beamforming along a well-resolved ray path. However, due to the shallow effective depth (typically

Additional file 8 Number of SMR in maize, Brachypodium distachyon, barley, millet, sorghum, soybean, Populus trichocarpa, rice, Arabidopsis.

Additional file 6. Overview of conserved motifs of ZmSMR genes identified through MEME analysis.

The modulation of the intensity of nascent Tibetan Plateau vortices (ITPV) by atmospheric quasi-biweekly oscillation (QBWO) is investigated based on final operational global analysis data from the National Centers for Environmental Prediction. The spatial and temporal distributions of the ITPV show distinct features of 10–20-day QBWO. The average ITPV is much higher in the positive phases than in the negative phases, and the number of strong TPVs is much larger in the former, with a peak that appears in phase 3. In addition, the maximum centers of the ITPV stretch eastward in the positive phases, indicating periodic variations in the locations where strong TPVs are generated. The large-scale circulations and related thermodynamic fields are discussed to investigate the mechanism by which the 10–20-day QBWO modulates the ITPV. The atmospheric circulations and heating fields of the 10–20-day QBWO have a major impact on the ITPV. In the positive QBWO phases, the anomalous convergence at 500 hPa and divergence at 200 hPa are conducive to ascending motion. In addition, the convergence centers of the water vapor and the atmospheric unstable stratification are found in the positive QBWO phases and move eastward. Correspondingly, condensational latent heat is released and shifts eastward with the heating centers located at 400 hPa, which favors a higher ITPV by depressing the isobaric surface at 500 hPa. All of the dynamic and thermodynamic conditions in the positive QBWO phases are conducive to the generation of stronger TPVs and their eastward expansion.

Based on the Final operational global analysis data from the Global Forecasting System of the National Centers for Environment Prediction and the radiosonde data, the development and eastward movement mechanisms of 15 Tibetan Plateau vortices (TPVs) after they move off the plateau are investigated. The results show that the convergence to the east of the TPVs at 500 hPa, the divergence associated with the westerly jet stream at 200 hPa, as well as the corresponding ascending motion provide favorable conditions for the development and eastward movement of the TPVs. The spatial structures of the atmospheric apparent heat source (Q1) and the apparent moisture sink (Q2) are studied, showing that the heating centers of Q1 at 400 hPa mainly sourced from the condensation latent heat are beneficial to the eastward movement of the TPVs, while the horizontal distribution of Q1 at 500 hPa goes against that. The development and eastward movement mechanisms of the TPVs after they move off the plateau are further discussed through diagnosing the potential vorticity (PV) tendency equation. It is revealed that the horizontal PV flux convergence to the east of the TPVs related to the convergence at 500 hPa plays as the dominant role, exerting positive contribution to the PV tendency. Meanwhile, the heating fields induce feeble PV tendency, indicating more important effect of the dynamic factor. The development and eastward movement mechanisms of the TPVs after they move off the plateau are different from those before the TPVs move off, and the dynamic effect is vital in the former stage while the effect of Q1 is revealed as the dominant influencing factor in the latter.

The rectification of intraseasonal wind forcing on interannual sea surface temperature anomalies (SSTA) and sea level anomalies (SLA) associated with El Nino–Southern Oscillation (ENSO) during 1993–2016 are investigated using the LICOM ocean general circulation model forced with daily winds. The comparisons of the experiments with and without the intraseasonal wind forcing have shown that the rectified interannual SSTA and SLA by the intraseasonal winds are much weaker than the total interannual SSTA and SLA in the cold tongue, due to the much weaker rectified than the total interannual Kelvin and Rossby waves in the equatorial Pacific Ocean. The dynamics of the rectification are through the nonlinear zonal and vertical advection by the background currents, which produces downwelling equatorial Kelvin waves during El Nino. The meridional advection is much smaller than the zonal and vertical advection, suggesting that the rectification is not induced by the Ekman dynamics or the thermocline rectification. The rectified interannual Kelvin waves are found to be much smaller than reflected at the Pacific western boundary and those forced by the interannual winds, suggesting that the latter two play a much more important role in ENSO dynamics than the intraseasonal winds. The results of this study suggest an unlikely significant role of oceanic nonlinear rectification by intraseasonal winds during the onset and cycling of El Nino.

Based on data diagnoses, in this study the interdecadal changes in asymmetric impacts of ENSO on wintertime East Asian climate are investigated. It is found that the Pacific Decadal Oscillation (PDO) can significantly modulate the asymmetry in the responses of the East Asian climate to El Nino and La Nina events. In positive PDO phase the response is asymmetric with a strong anomalous anticyclone over western North Pacific (WNP) and significant positive rainfall anomalies over southern China during El Nino winters, but a weak anomalous cyclone over WNP and insignificant negative rainfall anomalies over southern China during La Nina winters. However, such asymmetric responses do not appear in negative PDO phase, with comparable amplitudes of anomalous circulations over WNP and rainfall over southern China in El Nino and La Nina winters. Further analyses reveal that the warm background of the tropical Pacific in positive PDO phase causes significant difference in the amplitudes of convection anomalies over tropical western Pacific, resulting in asymmetric responses of the WNP circulation and rainfall over southern China to El Nino and La Nina events. Nevertheless, the cold background in negative PDO phase reduces the amplitude difference between El Nino and La Nina winters. A comparable convection anomalies appear in tropical western Pacific in El Nino and La Nina winters and the asymmetric responses do not occur.

The Sendai Framework for Disaster Risk Reduction 2015–2030 shifts the focus from managing disasters to reducing risks. Such a shift requires a better understanding of risk in all its dimensions of environment, hazards, exposure, and vulnerability; a disaster risk governance that ensures disaster risk is factored into planning and development at all levels across all sectors, as well as into disaster pre-paredness, rehabilitation, recovery, and reconstruction; and cost–benefit analyses to support the prioritization of investments in disaster risk reduction (DRR) for long-term resilience.

Dairy cows with type II ketosis display hepatic fat accumulation and hyperinsulinemia, but the underlying mechanism is not completely clear. This study aimed to clarify the regulation of lipid metabolism by insulin in cow hepatocytes. In vitro, cow hepatocytes were treated with 0, 1, 10, or 100 nm insulin in the presence or absence of AICAR (an AMP-activated protein kinase alpha (AMPKα) activator). The results showed that insulin decreased AMPKα phosphorylation. This inactivation of AMPKα increased the gene and protein expression levels of carbohydrate responsive element-binding protein (ChREBP) and sterol regulatory element-binding protein-1c (SREBP-1c), which downregulated the expression of lipogenic genes, thereby decreasing lipid biosynthesis. Furthermore, AMPKα inactivation decreased the gene and protein expression levels of peroxisome proliferator-activated receptor-α (PPARα), which upregulated the expression of lipid oxidation genes, thereby increasing lipid oxidation. In addition, insulin decreased the very low density lipoprotein (VLDL) assembly. Consequently, triglyceride content was significantly increased in insulin treated hepatocytes. Activation of AMPKα induced by AICAR could reverse the effect of insulin on PPARα, SREBP-1c, and ChREBP, thereby decreasing triglyceride content. These results indicate that insulin inhibits the AMPKα signaling pathway to increase lipid synthesis and decrease lipid oxidation and VLDL assembly in cow hepatocytes, thereby inducing TG accumulation. This mechanism could partly explain the causal relationship between hepatic fat accumulation and hyperinsulinemia in dairy cows with type II ketosis.

After the quick decaying of the 2015 super El Niño, the predicted La Niña unexpectedly failed to materialize to the anticipated standard in 2016. Diagnostic analyses, as well as numerical experiments, showed that this ENSO evolution of the 2015 super El Niño and the hindered 2016 La Niña may be essentially caused by sea surface temperature anomalies (SSTAs) in the subtropical Pacific. The self-sustaining SSTAs in the subtropical Pacific tend to weaken the trade winds during boreal spring–summer, leading to anomalous westerlies along the equatorial region over a period of more than one season. Such long-lasting wind anomalies provide an essential requirement for ENSO formation, particularly before a positive Bjerknes feedback is thoroughly built up between the oceanic and atmospheric states. Besides the 2015 super El Niño and the hindered La Niña in 2016, there were several other El Niño and La Niña events that cannot be explained only by the oceanic heat content in the equatorial Pacific. However, the questions related to those eccentric El Niño and La Niña events can be well explained by suitable SSTAs in the subtropical Pacific. Thus, the leading SSTAs in the subtropical Pacific can be treated as an independent indicator for ENSO prediction, on the basis of the oceanic heat content inherent in the equatorial region. Because ENSO events have become more uncertain under the background of global warming and the Pacific decadal oscillation during recent decades, thorough investigation of the role of the subtropical Pacific in ENSO formation is urgently needed.

The western North Pacific anomalous anticyclone (WNPAC) is an important atmospheric circulation system that conveys El Nino impact on East Asian climate. In this review paper, various theories on the formation and maintenance of the WNPAC, including warm pool atmosphere–ocean interaction, Indian Ocean capacitor, a combination mode that emphasizes nonlinear interaction between ENSO and annual cycle, moist enthalpy advection/Rossby wave modulation, and central Pacific SST forcing, are discussed. It is concluded that local atmosphere–ocean interaction and moist enthalpy advection/Rossby wave modulation mechanisms are essential for the initial development and maintenance of the WNPAC during El Nino mature winter and subsequent spring. The Indian Ocean capacitor mechanism does not contribute to the earlier development but helps maintain the WNPAC in El Nino decaying summer. The cold SST anomaly in the western North Pacific, although damped in the summer, also plays a role. An inter-basin atmosphere–ocean interaction across the Indo-Pacific warm pool emerges as a new mechanism in summer. In addition, the central Pacific cold SST anomaly may induce the WNPAC during rapid El Nino decaying/La Nina developing or La Nina persisting summer. The near-annual periods predicted by the combination mode theory are hardly detected from observations and thus do not contribute to the formation of the WNPAC. The tropical Atlantic may have a capacitor effect similar to the tropical Indian Ocean.

The relation of spring (March–May) to summer (July–August) precipitation in eastern China is examined using observed data. It is found that when spring precipitation from the lower and middle reaches of the Yangtze River valley to northern China (the YRNC region) is higher (lower), more (less) summer precipitation occurs in northeastern China and the lower and middle reaches of the Yangtze River valley, and less (more) in southeastern China. The analysis of physical mechanism showed that higher (lower) spring precipitation in the YRNC region is closely related to wet (dry) spring soil moisture, which decreases (increases) the surface temperature and sensible heat flux in late spring. Because the memory of spring soil moisture in the YRNC region reaches about 2.4 months, the surface thermal anomaly lasts into the subsequent summer, resulting in a weak (strong) East Asian summer monsoon. A weak East Asian summer monsoon corresponds to an anomalous anticyclone and a cyclone over southeastern and northeastern China, respectively, in the lower troposphere. The anomalous anticyclone depresses the summer precipitation in southeastern China, and the anomalous cyclone promotes precipitation over northeastern China. The abnormal northerly and southerly winds associated with the anomalous cyclone and anticyclone, respectively, converge in the lower and middle reaches of the Yangtze River valley, inducing more summer precipitation there.

In this study, the variations of annual land surface air temperature (SAT) over Eurasia and the northern part of Africa (0 degrees-180 degrees E, 0 degrees-90 degrees N) were investigated using monthly SAT data from the Climatic Research Unit, University of East Anglia for 1901-2014 and the simulations from the Geophysical Fluid Dynamics Laboratory coupled model. The observed results suggested that the SAT variations exhibited robust non-uniform spatial features at multi-time scales. For the variations in inter-annual to decadal time scales (IDV), the intensity generally increased from south to north, with the strongest intensity being around Siberia and four times that of the weakest intensity found around China. The IDV leading pattern showed a north-south dipole across 40 degrees N. The simulated results suggested that the north-south dipole and the northwards increase of the IDV were due to internal interactions within the complex nonlinear climate system, but the natural and greenhouse gas forcings could intensify the IDV. The warming trend of the SAT was generally homogeneous, but it showed distinctive multi-decadal fluctuations in different regions. The linear secular trends and robust multi-decadal variation around Siberia and China corresponded to the considerable acceleration and deceleration in the warming over the two regions, respectively. The warming around Siberia was mainly caused by greenhouse gases but its modulation due to natural forcing was also considerable because of the robust multi-decadal variations. Around China, the multi-decadal variation, contributed by the natural forcing, can explain more than half the variances in the warming. The warming trend around central Asia was intense and parabolic, and the multi-decadal variation over there was weak and showed few modulating effects.

Particle-size distribution, granular structure, and composition significantly affect the physicochemical properties, rheological properties, and nutritional function of starch. Flow cytometry and flow sorting are widely considered convenient and efficient ways of classifying and separating natural biological particles or other substances into subpopulations, respectively, based on the differential response of each component to stimulation by a light beam; the results allow for the correlation analysis of parameters. In this study, different types of starches isolated from waxy maize, sweet maize, high-amylose maize, pop maize, and normal maize were initially classified into various subgroups by flow cytometer and then collected through flow sorting to observe their morphology and particle-size distribution. The results showed that a 0.25% Gelzan solution served as an optimal reagent for keeping individual starch particles homogeneously dispersed in suspension for a relatively long time. The bivariate flow cytometric population distributions indicated that the starches of normal maize, sweet maize, and pop maize were divided into two subgroups, whereas high-amylose maize starch had only one subgroup. Waxy maize starch, conversely, showed three subpopulations. The subgroups sorted by flow cytometer were determined and verified in terms of morphology and granule size by scanning electron microscopy and laser particle distribution analyzer. Results showed that flow cytometry can be regarded as a novel method for classifying and sorting starch granules. © 2017 International Society for Advancement of Cytometry

In this study, the year-to-year variability of surface air temperature (SAT) over China in winter was investigated during 1961–2014. The results indicate that the year-to-year SAT variability can explain more than 30% of the SAT variance over most parts of China, with up to 60% variance over southern China, northeastern China and northwestern China. The leading pattern of year-to-year SAT exhibits homogeneous variability over most parts of China, except in small areas over the Tibetan Plateau and southwestern China. The circulation over the northern Pacific is a key factor of this homogeneous variability pattern. An anomalous anticyclonic circulation and weakening midlatitude westerly jet in the middle and high troposphere over the northern Pacific are associated with the homogeneous warmth over China. The second pattern shows a south–north dipole, with variability in northeastern China opposite to that south of 25°N in China and over the Tibetan Plateau. The south–north dipole pattern is part of a global year-to-year SAT anomaly pattern because it exhibits a significant relationship with the year-to-year SAT over large parts north of 50°N over the Eurasian landmass. The north-cold/south-warm pattern is accompanied by a significant weakening of the Arctic Oscillation. In comparison, the atmospheric circulation anomalies associated with the homogeneous variability pattern are much weaker than those with the south–north dipole pattern. The anomalous Indian Ocean dipole in the previous autumn and the snow cover around China in November are the two key causes of the homogeneous variability pattern. Many factors, such as the tropical central Pacific sea surface temperature (SST), stratospheric quasi-biennial oscillation (QBO), Okhotsk sea ice and western Siberia snow cover, can significantly influence the south–north dipole pattern. Compared to the tropical Pacific SST, the impact of the Indian Ocean SST on the winter SAT over China is much more important.

In this study, modulation of the atmospheric quasi-biweekly oscillation (QBWO) on diurnal variation of the occurrence frequency of Tibetan Plateau vortices (TPVs) during May–August of 2000–2009 was investigated. The diurnal variations of the occurrence frequency of the TPVs (OFTPVs) and the related dynamic and thermodynamic features in the positive and negative phases of QBWO were compared. In both the positive and negative phases, the OFTPVs reaches the maximum from evening to midnight (18–00 LT, LT indicates the local time), and minimum from early morning to noon (06–12 LT). At 18 LT, there is strongest convergence at 500 hPa and ascending motion, as well as the most abundant net water vapor budget over the Tibetan Plateau, which is in favor of the precipitation and the related condensation latent heat release, corresponding to the maximum of OFTPVs in 18–00 LT. On the contrary, in the early morning at 06 LT, the conditions are most unfavorable for genesis of TPVs in 06–12 LT. QBWO leads to stronger convergence at 500 hPa, ascending motion as well as more massive water vapor in the positive phases than those in the negative phases, resulting in larger numbers of TPVs occur in all of the four periods of a day (00–06 LT, 06–12 LT, 12–18 LT, and 18–00 LT) in the former. The TPVs generating from the early morning to noon (06–12 LT) are weaker and more sensitive and fragile to the disadvantageous background, while the TPVs occurring from evening to midnight (18–00 LT) are stronger and seem to be well tolerated, leading to more remarkable contrast between the OFTPVs in the negative and positive phases in 06–12 LT than in 18–00 LT.

SWVs are important summer rain-producing systems over southwestern China, and even wider areas in eastern China when they move eastward. Based on the final analyses data (FNL) of the Global Forecasting System of the National Centers for Environment Prediction, the role played by Tibetan Plateau vortices (TPVs) in the genesis processes of vortices in southwest China, referred to as southwest vortices (SWVs) is investigated. Since the TPVs and SWVs are most active in summer, the cases in May-August are studied. It is revealed that the TPVs moving off the Tibetan Plateau (moving-off TPVs) can exert significant effects on the genesis of SWVs through both dynamic and thermodynamic processes. The moving-off TPVs are favorable for the generation of SWVs through strengthening the cyclonic vorticity, convergence and ascending motion. Diagnoses of the potential vorticity budgets reveals that the condensational latent heat has the greatest contribution to the generation of SWVs. Analysis of the water vapor budget indicates that the water vapor is mainly transported from south of the genesis region of SWVs associated with strong southerlies. It is demonstrated that the southerlies and associated water vapor transport are another prominent factor affecting the genesis of the SWVs.

The spring snow water equivalent (SWE) over Eurasia plays an important role in East Asian and Indian monsoon rainfall. This study evaluates the seasonal prediction capability of NCEP Climate Forecast System version 2 (CFSv2) retrospective forecasts (1983–2010) for the Eurasian spring SWE. The results demonstrate that CFSv2 is able to represent the climatological distribution of the observed Eurasian spring SWE with a lead time of 1–3 months, with the maximum SWE occurring over western Siberia and Northeastern Europe. For a longer lead time, the SWE is exaggerated in CFSv2 because the start of snow ablation in CFSv2 lags behind that of the observation, and the simulated snowmelt rate is less than that in the observation. Generally, CFSv2 can simulate the interannual variations of the Eurasian spring SWE 1–5 months ahead of time but with an exaggerated magnitude. Additionally, the downtrend in CFSv2 is also overestimated. Because the initial conditions (ICs) are related to the corresponding simulation results significantly, the robust interannual variability and the downtrend in the ICs are most likely the causes for these biases. Moreover, CFSv2 exhibits a high potential predictability for the Eurasian spring SWE, especially the spring SWE over Siberia, with a lead time of 1–5 months. For forecasts with lead times longer than 5 months, the model predictability gradually decreases mainly due to the rapid decrease in the model signal.

Seasonal prediction of the East Asian (EA) winter monsoon (EAWM) is of great significance yet a challenging issue. In this study, three statistical seasonal prediction models for the EAWM are established using three leading modes of the Eurasian snow cover (ESC), the first leading mode of sea surface temperature (SST) and the four leading modes of the combination of the ESC and SST in preceding autumn, respectively. These leading modes are identified by the partial-least square (PLS) regression. The first PLS (PLS1) mode for the ESC features significantly anomalous snow cover in Siberia and Tibetan Plateau regions. The ESC second PLS (PLS2) mode corresponds to large areas of snow cover anomalies in the central Siberia, whereas the third PLS (PLS3) mode a meridional seesaw pattern of ESC. The SST PLS1 mode basically exhibits an El Nino-Southern Oscillation developing phase in equatorial eastern Pacific and significant SST anomalies in North Atlantic. A strong EAWM tends to emerge in a La Nina year concurrent with cold SST anomalies in the North Atlantic, and vice versa. After a 35-year training period (1967–2001), three PLS seasonal prediction models are constructed and the 11-year hindcast is performed for the period of 2002–2012, respectively. The PLS model based on combination of the autumn ESC and SST exhibits the best hindcast skill among the three models, its correlation coefficient between the observation and the hindcast reaching 0.86. This indicates that this physical-based PLS model may provide another practical tool for the EAWM. In addition, the relative contribution of the ESC and SST is also examined by assessing the hindcast skills of the other two PLS models constructed solely by the ESC or SST. Possible physical mechanisms are also discussed.

The relationship between cross-equatorial flow (CEF) during winter and spring and the South China Sea summer monsoon (SCSSM) onset is investigated by data diagnoses for the period of 1979–2013 and numerical experiments. The SCSSM onset is found to have a significant negative correlation with the CEF nearby the Philippines in preceding January, February and March prior to SCSSM onset. A strong CEF during January, February and March tends to be succeeded by an early onset of SCSSM, whereas a weak CEF is likely to be followed by a late onset. The CEF in preceding months links with the SCSSM onset through the subtropical high over South China Sea and western North Pacific in April. The subtropical high in April is weak and eastward shifted (strong and westward shifted) when the CEF in preceding months is strong (weak). The weak and eastward shifted (strong and westward shifted) subtropical high favours (does not favour) the convection developing (depressing) over South China Sea, resulting in an early (late) onset of SCSSM. The anomalies of CEF nearby the Philippines in preceding months and its close relationship with subsequent subtropical high are caused by the sea surface temperature anomalies (SSTA) and atmospheric heating source over tropical western Pacific. The difference of SSTA between south and north of equator in tropical western Pacific and the corresponding atmospheric diabatic heating result in the anomalies of CEF in January, February and March, and impact the activity of subtropical high in April. The positive SSTA in tropical western Pacific, combining with the wet and warm climatic background over northern South China Sea and coastal areas of Southern China in April are favourable for a cyclonic circulation anomaly occurring over northern South China Sea. As a result, the subtropical high is weak and eastward shifted, and the SCSSM onset is early.

In this study, the relationship between Eurasian spring snow decrement (SSD) and East Asian summer precipitation and related mechanisms were investigated using observational data and the Community Atmospheric Model, version 3.1 (CAM3.1). The results show that a west–east dipole pattern in Eurasian SSD anomalies, with a negative center located in the region between eastern Europe and the West Siberia Plain (EEWSP) and a positive center located around Baikal Lake (BL), is significantly associated with East Asian summer precipitation via triggering an anomalous midlatitude Eurasian wave train. Reduced SSD over EEWSP corresponds to anomalously dry local soil conditions from spring to the following summer, thereby increasing surface heat flux and near-surface temperatures. Similarly, the increase in SSD over BL is accompanied by anomalously low near-surface temperatures. The near-surface thermal anomalies cause an anomalous meridional temperature gradient, which intensifies the lower-level baroclinicity and causes an acceleration of the subtropical westerly jet stream, leading to an enhanced and maintained Eurasian wave train. Additionally, the atmospheric response to changed surface thermal conditions tends to simultaneously increase the local 1000–500-hPa thickness, which further enhances the Eurasian wave train. Consequently, significant wave activity flux anomalies spread from eastern Europe eastward to East Asia and significantly influence the summer precipitation over China, with more rainfall over northeastern China and the Yellow River valley and less rainfall over Inner Mongolia and southern China.

This paper presents a review on the impact of El Nino on the interannual variability of atmospheric circulations over East Asia and rainfall in China through the anomalous anticyclone over western North Pacific (WNPAC). It explains the formation mechanisms of the WNPAC and physical processes by which the WNPAC affects the rainfall in China. During the mature phase of El Nino, the convective cooling anomalies over western tropical Pacific caused by the weakened convections trigger up an atmospheric Rossby wave response, resulting in the generation of the WNPAC. The WNPAC can persist from the winter when the El Nino is in its peak to subsequent summer, which is maintained by multiple factors including the sustained presence of convective cooling anomalies and the local air-sea interaction over western tropical Pacific, and the persistence of sea surface temperature anomalies (SSTA) in tropical Indian and tropical North Atlantic. The WNPAC can influence the atmospheric circulations over East Asia and rainfall in China not only simultaneously, but also in the subsequent summer after an El Nino year, leading to more rainfall over southern China. The current paper also points out that significant anomalies of atmospheric circulations over East Asia and rainfall over southern China occur in El Nino winter but not in La Nina winter, suggesting that El Nino and La Nina have an asymmetric effect. Other issues, including the impact of El Nino diversity and its impact as well as the relations of the factors affecting the persistence of the WNPAC with summer rainfall anomalies in China, are also discussed. At the end of this paper some issues calling for further investigation are discussed.