ABSTRACT When an area experiences drought and then floods within a short timeframe, the ‘Drought‐to‐Flood Abrupt Alternation (DtFAA)’ event occurs, which causes severe injuries and huge economic loss, and also greatly increases the risk of secondary geological disasters. Based on multiple observation and reanalysis datasets, this study analyses the characteristics of extreme DtFAA events in the middle‐lower reaches of the Yangtze River (MLYR) in China. The results show that a total of 8 extreme DtFAA events occurred in the MLYR during 1980–2022. The drought periods are mainly in spring, and the critical transition periods from drought to flood predominantly occur in June. Compared with drought periods, the significant increase in 500‐hPa geopotential height over the subtropical region and the pronounced decrease over the middle‐high latitudes of East Asia during the flood period constitute the key circulation factors responsible for the occurrence of DtFAA. In the preceding winter of DtFAA events, a pronounced La Niña‐like SSTA exists in the tropical Pacific, whereas in spring, a ‘+ − +’ tripole SSTA (sea surface temperature anomaly) appears from south to north in the North Atlantic. The winter La Niña‐like and the spring tripole SSTA are mutually independent, and both can induce the 500‐hPa circulation patterns that trigger DtFAA events. Among the 8 extreme DtFAA events, 5 events occur when the winter Niño3.4 index is below 0 and the spring North Atlantic Tripole index exceeds 0. In the other 3 years satisfying these conditions, the DtFAA also occurs in part of the MLYR. Therefore, the winter tropical Pacific La Niña‐like and the spring North Atlantic tripole SSTA jointly lead to the occurrence of DtFAA events in the MLYR. When they are met, the occurrence probability of DtFAA in the MLYR is extremely high.

Understanding trends in hydroclimatic variables is crucial for linking local climatic drivers with regional water use practices, particularly in a vulnerable Haor basin in tropical country like Bangladesh. This study evaluated the spatiotemporal trends in hydroclimatic variables at annual and seasonal scales using advanced statistical methods, including the Modified Mann–Kendall (MK) test, Sen’s slope, Sequential Mann-Kendal, Pettitt test, and linear regression model. Additionally, Detrended Fluctuation Analysis (DFA) and Morlet Wavelet Analysis (MWA) were utilized to analyze historical periodic cycles and predict future trends. Results show a significant decrease in annual and seasonal surface water levels (SWL) and rainfall, except for the monsoon, while both maximum and minimum temperatures simultaneously increased. The decline in annual SWL at a rate of 1.18 m/year was influenced by an increase in maximum temperature at a rate of 0.03 °C/year and a decrease in annual total rainfall at a rate of 5.25 mm/year. DFA analysis suggests long-term correlations among these variables, predicting future increases in temperature but continued decreases in rainfall and SWL. Periodic cycles with various frequencies were observed in rainfall, maximum, and minimum temperatures. ECMWF ERA5 reanalysis datasets attribute these changes to higher pre-monsoon geopotential heights, lower relative humidity, and higher monsoon rainfall associated with lower surface pressure. The findings of the study will help develop targeted climate adaptation strategies to mitigate the adverse effects on agriculture, biodiversity, and freshwater availability in the region. The overall study provides essential data that can inform water resource management strategies.

Based on the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and the Global Precipitation Climatology Project (GPCP) data, this study investigates the meteorological anomalies tied to the interannual variability of the South China Sea summer monsoon onset (SCSSMO), and its relationship with the change of the subtropical westerly jet position (SWJP), and the potential influence of the precursory thermal forcing over the eastern Tibetan Plateau (TP). The results show that during the earlier (later) SCSSMO years, there exist significant cyclonic (anticyclonic) circulation anomalies over the South China Sea (SCS) and its adjoining areas, featuring enhanced (suppressed) precipitation. The earlier SCSSMO years correspond to the southward-shifted upper-level subtropical westerly jet position to the north of the SCS. This favors the occurrence of non-geostrophic southward winds in the upper troposphere, the occurrence of upper-level divergence (convergence) and low-level convergence ascending (divergence) over the SCS and its nearby areas (Yangtze River basin) on the south (north) side of the jet axis, and the strengthening of the meridional circulation anomaly with anomalous ascending over the low-latitude and descending over the middle-latitude East Asia. Further analysis suggests that the anomalous heating over the eastern TP is significantly related to the SCSSMO and the change of SWJP. When the previous first-two-pentad heating anomalies over the eastern TP are positive, an anomalous anticyclonic circulation is formed in the upper troposphere, stimulating an eastward-propagating wave train. This, in turn, generates an anomalous cyclonic circulation downstream of the TP in the upper troposphere. As a result, the subtropical upper-level westerly jet downstream of TP shifts southward, which further affected the variation of atmospheric circulation over East Asia, ultimately leading to the earlier SCSSMO.

The onset of the South China Sea summer monsoon (SCSSM) implies the transition of East Asian monsoon circulation from winter to summer, which affects not only the local weather and climate near the South China Sea (SCS) but also other regions through remote teleconnection. In this paper, the interdecadal variability characteristics of the SCSSM onset are analyzed by using various datasets as well as its possible mechanisms. The results show that there is a significant interdecadal delay in the onset date of the SCSSM after 2010. The onset is early around May 13th during 1994–2009. However, the onset is significantly later during 2010–2020 with an average of May 30th. Besides, the air and ocean conditions in SCS in May also took a significant decadal shift around 2010 and manifested itself in atmospheric forcing on the ocean, thus the SCSSM onset is mainly remotely influenced by the tropical Ocean instead of local SST. It is found that the interdecadal variation of the SCSSM onset is mainly caused by the decadal warming/cooling of the tropical central Pacific SST. The SCSSM onset’s relationship with the tropical central Pacific SST seems more binding and stable relative to that with the tropical eastern Pacific SST. Their correlation is stable and still reaches the significant test in recent years. Therefore, the warming of the tropical central Pacific SST during 2010–2020 tends to postpone the SCSSM onset by means of related anomalous anticyclones and weakened activity of low-frequency Oscillation and tropical cyclones. On the contrary, its cooling led to early SCSSM onset during 1994–2009. Therefore, more and special attention should be paid to the tropical central Pacific SST anomaly, it will help us to monitor and predict the SCSSM onset effectively, and improve the seasonal prediction of East Asia summer monsoon greatly.

The northwestern Pacific monsoon trough (NWPMT) deeply impacts socio-economic development and human security over East Asia by supplying moisture to the summer monsoon rainfall and modulating tropical cyclone activities. However, considerable inter-model spreads in the coupled model inter-comparison project phase 6 models make the future projection of the NWPMT less reliable. Here, we find that the inter-model spread of the NWPMT change is significantly correlated with the central equatorial Pacific sea surface temperature change, and mainly determined by the equatorial thermocline sharpness in the historical simulations. According to the emergent constraint method, the central equatorial Pacific SST would warm up about 6% slower than the multi-model mean with 56% uncertainty reduced. Correspondingly, the NWPMT would slacken westward with 36% uncertainty reduced. Results here emphasize the importance of examining and reducing systematic model biases in simulating thermocline sharpness that have been overlooked in past literatures, before achieving more reliable future projections.

We investigate the dynamic behavior of optical vortices, or phase singularities, in random wavefields and demonstrate the direct experimental observation of the anomalous diffusion of optical vortices. The observed subdiffusion of optical vortices show excellent agreement with the fractional Brownian motion, a Gaussian process. Paradoxically, the vortex displacements are observed exhibiting a non-Gaussian heavy-tailed distribution. We also tune the extent of subdiffusion and non-Gaussianity of optical vortex by varying the viscoelasticity of light scattering media. This complex motion of optical vortices is reminiscent of particles in viscoelastic environments suggesting a vortex tracking based microrheology approach. The fractional Brownian yet non-Gaussian subdiffusion of optical vortices may not only offer insights into the dynamics of phase singularities, but also contribute to the understanding certain general physics, including vortex diffusion in fluids and the decoupling between Brownian and Gaussian.

The microphysical properties of supercooled liquid droplets (SLDs) and ice particles of stratiform mixed-phase clouds over Eastern China are characterized using carefully post-processed airborne data. The majority of sampled clouds were precipitating with ice particles and were frequently mixed with SLDs at cold temperature. While the concentration of large ice crystal (> 600 mu m in diameter, the same below) was low (up to 3 L-1), the concentration of smaller ice particle (> 50 mu m) was high (up to 300 L-1). Such particles with high concentration cannot be a result of the recirculation of pre-existing aged ice and thus secondary ice production (SIP) was likely occurring over the stratiform clouds at temperatures between-16.9 degrees C and-6.4 degrees C. The statistical analyses show that concentrations of tiny, hexagonal and irregular ice crystals were significantly greater in updraft than those in downdraft regions, suggesting that updrafts not only provide a favorable environment for the growth of cloud particles, but also promote the multiplication of the above young-age small ice (50-100 mu m) where SIP is commonly occurring. Since the criteria for the other SIP mechanisms are difficult to meet for this light-riming stratiform without deep convections, this analysis indicates that shattering during droplet freezing might thus be an important SIP source at temperatures between-15 degrees C and-9 degrees C. This study should provide a precise opportunity for parameterizations of mixed-phase stratiform clouds associated with the SIP processes and effects of updraft and temperature.

As a result of global warming, drought, flooding, change in the rainfall pattern, etc. occur frequently. All these natural disasters could cause serious damage to the food security. Soybean is one of the most important oil crops in China. In recent years, the changing climate has brought many uncertain risks to the growth and production of soybean. In this study, based on the local meteorological, soil, and soybean growth-related experimental data, the effects of high temperature and drought stress on soybean were tested. The test parameters were leaf area index (LAI) and dry matter weight, while the analytical tool used was World Food Studies Model crop model. The research was carried out in Hailun City, Heilongjiang Province, China. The results showed that warming stress shortened the growth period of soybean and reduced the LAI and dry matter accumulation. On the other hand, drought stress also showed a significant impact on the growth period as well as reduced LAI and dry matter accumulation. Comparing the whole growth as well as the flowering-stage to seed-filling-stage treatments of soybean, the results were found very similar. It indicated that the soybean growth from flowering to seed-filling stage was strongly affected by the external environmental factors. The high temperature and drought disasters in the fruiting stages would have a greater impact on the growth and production of soybean crop.

Rice (Oryza sativa) resistance is its ability to resist various stresses, the changes of which have important impacts on O. sativa yield security. However, the responses of O. sativa stress resistance to elevated atmospheric CO2 concentration and temperature are poorly understood. We conducted a field open top-chamber experiment with O. sativa (Nanjing 9108 and Jinxiangyu I) based on the CO2 and temperature automatic control platform. The experimental treatments included ambient CO2 concentration and temperature treatment (CK, control), elevated CO2 concentration treatment (C, CO2 concentration increase of 200 μmol·mol-1 above CK), elevated temperature treatment (T, temperature increase of 2 ℃ above CK) and elevated CO2 concentration and temperature (CT, CO2 concentration increase of 200 μmol·mol-1 and temperature increase of 2 ℃ above CK). At the critical growth stages of O. sativa, we measured superoxide dismutase activity, silica content, total flavanol content, malondialdehyde content, soluble sugar content, proline content, and soluble protein content by cutting the uppermost functional leaves. We obtained the rice stress resistance index (RSRI) by principal component analysis to analyze the differences in the composition of stress resistance indicators under different treatments. Considering the disease resistance of O. sativa, the spike neck blast disease was counted to verify the expression level of RSRI for O. sativa stress resistance at maturity stage. Results showed that at the elongation-booting stage, C and CT treatments significantly reduced the RSRI of Jinxiangyu I by 36.5% and 41.1%, respectively, compared with CK. T treatment significantly decreased the RSRI of the two varieties by 44.9% and 33.8%, respectively. The RSRI explained 71.9%-74.3% of the variation in the spike neck blast disease. Overall, the stress resistance of two O. sativa varieties were adversely affected by elevated temperature at the elongation-booting stage. There was an interactive effect of CO2 concentration and temperature on O. sativa stress resistance. Compared with Nanjing 9108, the stress resistance of Jinxiangyu I was more sensitive to elevated CO2 concentration.

It is well known that the El Niño-Southern Oscillation (ENSO) could affect the precipitation anomalies in the central-western Indian Ocean (CWIP) through modifying the Walker circulation, with an El Niño generally accompanied by an enhanced CWIP. In this study, we find that this positive association is modulated by the Atlantic Multidecadal Oscillation (AMO). When ENSO and AMO are out-of-phase combinations (i.e., AMO-/El Niño and AMO+/La Niña), the CWIP is significantly stronger than that when they are in-phase cooperated. It is suggested that the AMO’s modulating effect mainly comprises two pathways that influence ENSO’s linkage with the CWIP. On one hand, AMO could modulate the SST variability in the central-eastern tropical Pacific with a stronger ENSO SST amplitude during its negative phase, thus influencing the ENSO-CWIP relationship. On the other hand, AMO is associated with a multidecadal atmospheric variation in the Walker circulation. The weakened circulation during the negative AMO phase favors an anomalous ascending flow over the central-western Indian Ocean, thereby favoring an enhanced CWIP there. Therefore, El Niño is accompanied by a more pronounced CWIP during the negative AMO phase compared to that during a positive AMO phase. For La Niña episodes, however, these two pathways have opposite modulation effects. Although AMO+/La Niña is weaker than AMO-/La Niña, the accompanied CWIP is relatively stronger as an multidecadal dry background induced by the Atlantic warming reinforces the negative CWIP anomaly generated by La Niña. We here highlight that the AMO decadal forcing needs to be considered when investigating the Indian Ocean atmospheric variabilities during ENSO events.

Previous studies have demonstrated that the Atlantic multidecadal oscillation (AMO) could affect El Nino-Southern Oscillation (ENSO) through thermocline adjustment, with a stronger ENSO sea surface temperature (SST) amplitude during a negative AMO phase than during a positive phase. In this study, we find that the ENSO atmospheric anomaly amplitudes in the tropical Pacific during different AMO phases are not necessarily consistent with these ENSO SST changes. For El Nino episodes, the low-level wind and precipitation anomalies over the tropical Pacific in the boreal winter are more pronounced during the negative AMO phase than during the positive phase, corresponding well to the stronger SST anomalies. However, La Nina events during the negative AMO phase are accompanied by weaker atmospheric anomalies in the tropical Pacific, although their SST anomalies are stronger than those during the positive phase. We suggest that this mismatch between La Nina SST and atmospheric anomalies can be largely attributed to AMO decadal modulation. A positive AMO favors intensified trade winds and weakened precipitation in the central tropical Pacific by modifying Walker circulation. Therefore, when La Nina coincides with a positive AMO, the low-level easterly and negative precipitation anomalies are superimposed, which gives rise to stronger atmospheric perturbations. In contrast, under a negative AMO background, the atmospheric anomalies induced by La Nina anomalous SST are partly counteracted by the AMO remote decadal modulation, thereby resulting in weaker anomaly amplitudes. Here, we highlight that AMO decadal forcing needs to be considered when investigating ENSO atmospheric variabilities and related regional climate impacts.

Lightning-generated nitrogen oxides (LNO x ) have a major influence on the atmosphere and global climate change. Therefore, it is of great importance to obtain a more accurate estimation of LNO x . The aim of this study is to provide a reference for the accurate estimation of the total LNO x in the mainland of China based on cloud-to-ground lightning (CG) location data from 2014 to 2018. The energy of each CG flash was based on the number of return strokes per CG flash, the peak current of each return stroke, and the assumed CG breakdown voltage. The energy of intracloud lightning (IC) was based on the estimated frequencies of IC and the assumed energy of each IC flash. Combining the energy of lightning and the number of nitric oxide (NO) molecules produced by unit energy ( ρ no ), the total LNO x production in the mainland of China was determined. The LNO x in the mainland of China estimated in this study is in the range (0.157–0.321) × 10 9 kg per year [Tg(N) yr −1 ], which is on the high end of other scholars’ works. Negative cloud-to-ground lightning (NCG) flashes produce the most moles of NO x , while positive cloud-to-ground lightning (PCG) flashes produce the least total moles of NO x . The breakdown voltage of PCG is greater than that of IC or NCG, while the latter has a greater output of LNO x .

The present study investigates the decadal shift of the interannual relationship between the South China Sea (SCS) monsoon trough (MT) and the genesis frequency of tropical cyclone (TC) over the western North Pacific during June–October 1949–2015. Significant change was found around the 1980s. The weak TC (categories 1–3) number has a decreasing relationship with the SCS MT. Their correlation coefficients are statistically remarkable during 1949–1978 but reduce to around 0.1. In contrast, the connection between strong TC (categories 4–5) number and SCS MT is strengthened after 1980s with correlation reaching up to 0.7. Such a shift can be explained by the changes in large‐scale environmental factors associated with MT movement. After 1980s, when the SCS MT extends southeastward, there exits enhanced cyclonic relative vorticity in lower level, increased moisture in middle level, reduced vertical wind shear and intensified divergence in upper level. These conditions are favourable for weak TC intensifying and developing into strong TC. In addition, more strong TC occurred in the southwest quadrant of WNP after 1980s; thus, the SCS MT would affect the TC for a longer time. Therefore, the genesis frequency of weak TCs has diminished, while more strong TCs are formed along with the SCS MT extending southeastward, leading to their strengthened interannual relationship.

利用美国NOAA海表温度资料,重点分析了北太平洋海温异常EOF第二模态Victoria模态(VM)与ENSO年际关系的非对称特征.研究发现,VM和ENSO在年代际尺度上相关性较弱,而在年际尺度上有很好的相关关系,两者同期为负相关,VM超前1 a为正相关.然而,正负VM事件与ENSO冷暖位相在年际尺度上的联系存在着一定的非对称性.正VM事件与同年冬季热带中东太平洋海温异常的联系较弱,但次年常有厄尔尼诺事件发生;相比较而言,负VM事件在同年一般都有厄尔尼诺事件伴随发生,而与次年冬季热带中东太平洋海温没有显著联系,且很少有ENSO事件发生.由此可见,正VM事件对次年厄尔尼诺的发生发展似乎有促进作用,可作为ENSO前期预报因子之一,而负VM事件不能作为ENSO的前期预报因子.

The multivariate empirical orthogonal function (MV-EOF) method is conducted on June 500 hPa geopotential height and air temperature over the active region of the Northeast China cold vortex (NCCV). Two leading modes are identified. The second leading mode effectively characterizes the different positions of the NCCV while the first leading mode represents the NCCV intensity on monthly time scale. Noticeable NCCV is observed in relative southern region with the second mode in its positive phase (the southward NCCV mode, SCVM), the precipitation in June and July both significantly increases in the middle and lower reaches of the Yangtze River but decreases from the Korean Peninsula to southern Japan. The NCCV locates north of 60°N with the negative phase (the northward NCCV mode, NCVM), the precipitation is suppressed from the lower reaches of the Yangtze River to the Japan Island but excessive from the Bohai Bay to the Korean Peninsula. Monthly precipitation forecast is greatly improved when the NCCV position is additionally considered. For SCVM, approximately 50

By use of observational reanalysis data and the CMIP5 data, the relationships of the Central Pacific (CP) El Niño and the Victoria Mode (VM)/North Pacific Oscillation (NPO) are compared. The VM/NPO and the CP El Niño are physically related via negative feedback process of air–sea interaction. The VM/NPO has a delay effect on the CP ENSO in the subsequent winter. Nevertheless, the impact of VM on the CP El Niño is more effective relative to the NPO. When the conventional ENSO (hereafter as ENSO) own cycle is removed, the former's correlation with the EMI (El Niño Modoki index) in the Dec(+1) only decreases from 0.48 to 0.31, which is still significant. But the latter's correlation dose not reach 95% confidence level. Composition analysis also shows that during the D(+1)JF(+2), very few SST anomalies could be found over 95% significant level whether in positive or negative NPO phase. While for the VM cases, a large area of the CP ENSO‐like SST anomalies is observed significantly in the tropical Pacific. Especially, for non‐ENSO year, CP El Niño occurs in 50% positive VM cases' following winter. Although in previous studies, the VM is only considered as a transition stage during the process of NPO affecting the CP El Niño, the regression analysis shows that the VM is a partly natural mode, most of its variation is contributed by its internal evolution. The CP El Niño would still occur during positive VM cases even when NPO phase is negative. Their relationship remains stable in the CMIP5 RCP8.5 simulations, that is, the global warming does not interfere with the impact of positive VM on the CP El Niño. In conclusion, the VM may be a more effective prediction signal for the CP El Niño than the NPO.

青藏高原东南侧存在一个特殊区域,它常年维持南风,与东亚季风紧密联系,强度变异也将对下游天气气候造成明显影响.该区域南风对全球变暖背景下青藏高原的快速增暖十分敏感.文中利用国际耦合模式比较计划第5阶段(CMIP5)中13个模式的多情景预估结果,分析了全球变暖1.5℃、2℃和3℃下常年南风区南风强度的变异特征.结果表明,13个模式中仅BCC-CSM1.1、GFDL-CM3和MIROC5模式能够较好地模拟常年南风区的范围,以及其独特的"双峰型"季节演变特征.然而,对南风的预估,模式间存在较大差异.MIROC5模式预估南风将明显加强,尤其6月之后,并持续至12月,但BCC-CSM1.1和GFDL-CM3模式预估南风在秋季后将明显减弱.进一步分析发现,各模式预估的差异主要源于它们对青藏高原及东亚地区之间温差的模拟存在显著差异.MIROC5模式模拟的青藏高原升温幅度高于周边区域,其与东亚平原之间的温度梯度将使常年南风区南风增强.因此,模式未来改进中应特别关注对青藏高原与其周边热力梯度的合理模拟,这对青藏高原区及东亚季风气候的正确模拟至关重要.

Agricultural drought (AGD) is one of the most impactful natural disasters for rain-fed agricultural regions worldwide, including those in China. Spatiotemporal characteristics of the winter wheat drought season on the Huang-Huai-Hai (HHH) Plain, China, were studied by employing the Penman-Monteith (P-M) equation and a crop coefficient model based on daily meteorological datasets from 57 stations from 1980 to 2011. The crop water deficit index (CWDI) was employed as an index of AGD appraisal to depict the spatiotemporal changes in drought during the winter wheat growth stages in the HHH Plain, China. Besides, this study also intends to develop a drought disaster risk index (DDRI) of winter wheat for various growth stages based on risk formation theory. The spatial distribution patterns indicated higher CWDI values in the northern and middle parts of the HHH Plain and lower in the southern region throughout the wheat growth stages. Of the winter wheat growth stages on the northern HHH Plain, the drought frequency was the highest during the heading-mature stage, when it reached up to 80–100%. The high drought hazard was obvious during the heading-mature growth stage, with a more severe high drought hazard in the northern region of the HHH Plain than in the southern region. Spatially, the high DDRI values were distributed in the northern and central regions of the HHH Plain. The outcomes suggest that the DDRI model provides accurate spatiotemporal appraisals in both temporal and spatial scales, and these findings are important for enhancing the adaptability and mitigation ability of AGD risk on the HHH Plain.

Agricultural drought risk analysis is useful for reducing probable drought risk in the background of global warming. This study aims to identify spatiotemporal characteristics of drought and drought disaster risk in the summer maize growth period under climate change condition. In this research, we use daily datasets from 79 meteorological stations and the maize yield data in the Huang-Huai-Hai (HHH) plain, eastern China during the period 1960–2015. The drought disaster risk index (DDRI) model was applied to assess the drought disaster risk. The maize drought disaster risk maps were drawn under current and future climate change conditions. The results showed that the high DDRI was distributed in northern region and low DDRI was distributed in most of southern region in the HHH plain. During the summer maize growth period, the DDRI decreased gradually from the northern to southern region. The results also exhibited that under the RCP4.5 (Representative Concentration Pathway 4.5) scenario, about one half of the HHH plain belonged to the slight and sub-slight DDRI region in the future 80 years. Overall, our results demonstrated that the DDRI model provided an accurate assessment in both spatial and temporal scales and had a theoretical guidance for improving the adaptation of crop production. Elevating maize drought risk management helps to lessen the anticipated risk to crop production in the HHH plain under the context of climate change.