The Colorado River is one of the most important rivers in the southwestern U.S., with ~ 90% of the total flow originating from the Upper Colorado River Basin (UCRB). The UCRB April–July streamflow is ...well-correlated to the UCRB spring precipitation. It is known that the UCRB precipitation is linked to an El Niño-like sea surface temperature (SST) pattern, but the causal effect of the tropical Pacific SST on the UCRB spring precipitation is still uncertain. Here, we apply a Granger causality approach to understand the causal effect of the tropical Pacific averaged SST in previous three seasons (winter, fall, and summer) on the UCRB averaged precipitation in spring in observations and two climate models. In observations, only the winter SST has Granger causal effect (with
p
-value ~ 0.05) on spring precipitation, while historical simulations of the two climate models overestimate the causal effect for winter and fall (with
p
-value < 0.01 and < 0.05, respectively) due to model biases. Moreover, future projections of the two climate models show divergent causal effects, especially for the scenario with high anthropogenic emissions. The divergent projections indicate that (1) there are large uncertainties in model projections of the causal effect of the tropical Pacific SST on UCRB spring precipitation and (2) it is uncertain whether climate models can reliably capture changes in such causality. These uncertainties may result in large uncertainties in seasonal forecasts of the UCRB hydroclimate under global climate change.
Walker circulations near East Africa are identified and their influence on the interannual variability of East African rainfall is explored in multiple reanalyses and observational precipitation ...datasets. The robustness of methodology for identifying 2-dimensional overturning circulations in a three-dimensional flow is investigated. Three Walker circulations with potential relevance to East African rainfall are identified, namely, the East African, the Congo Basin, and the Indian Ocean Walker circulations. Consistent anti-correlations across the reanalyses exist for the upward and downward branches of the Indian Ocean Walker Circulation during September–March, with strongest connections during October–December; they do not emerge for the other two Walker circulations. Less (more) precipitation occurs over East Africa in the short-rains season when the Indian Ocean Walker Circulation is anomalously strong (weak). These rainfall variations are associated with anomalous mid-level moisture divergence that primarily results from variations in wind divergence rather than atmospheric moisture. The anomalous horizontal advection of moist static energy can be important in modulating convection, but this argument is not conclusive considering the unclosed budget and the variations within the composites. The associations above do not indicate causality. Caution is advisable when using the concept of Walker circulations because a two-dimensional stream function can over-simplify the complexity of the three-dimensional circulation.
Significant events of East Asian pressure surge are identified based on sea level pressure for boreal winters of the period 1979–2016. These events typically grow from a high pressure anomaly over ...Northern Europe and the northwestern Russia and attain their peak over Siberia around ten days after the initiation. The structure of the pressure surge at its peak intensity mimics that of the semi-permanent Siberian High. With a two-level quasi-geostrophic (QG) model, a nonmodal instability analysis of the winter climatological flow reveals that one of the most rapidly amplifying “optimal disturbances” with an optimization time of 2 days resembles the structure of the East Asian pressure surge. This optimal disturbance originates from small-scale precursor disturbances over Northern Europe and the Barents Sea. Such initial disturbances grow in magnitude via Siberia towards East Asia, forming a low-level ridge extending to around 50° N. The optimal disturbance successfully captures the temporal and spatial scales and the overall structure of the circulation anomaly associated with the pressure surge, albeit with varying degrees of accuracy of the location of individual trough/ridge of the surge anomaly. Additional experiments suggest that (1) adding damping effect to the two-level QG model extends the low-level ridge further south to around 40° N and (2) the upper level wave train feature associated with pressure surge can be captured even in a barotropic model by optimal disturbances with an optimization time of 4 days.
Toxicity and transformation process of polycyclic aromatic hydrocarbons (PAHs) is strongly depended on the interaction between PAHs and dissolved organic matters (DOM). In this study, a 125W ...high-pressure mercury lamp was used to simulate the sunlight experiment to explore the inhibition mechanism of four dissolved organic matters (SRFA, LHA, ESHA, UMRN) on the degradation of anthracene and pyrene in water environment. Results indicated that the photodegradation was the main degradation approach of PAHs, which accorded with the first-order reaction kinetics equation. The extent of degradation of anthracene and pyrene was 36% and 24%, respectively. DOM influence mechanism on PAHs varies depending upon its source. SRFA, LHA and ESHA inhibit the photolysis of anthracene, however, except for SRFA, the other three DOM inhibit the photolysis of pyrene. Fluorescence quenching mechanism is the main inhibiting mechanism, and the binding ability of DOM and PAHs is dominantly correlated with its inhibiting effect. FTIR spectroscopies and UV-Visible were used to analyze the main structural changes of DOM binding PAHs. Generally, the stretching vibration of N-H and C-O of polysaccharide carboxylic acid was the key to affect its binding with anthracene and C-O-C in aliphatic ring participated in the complexation of DOM and pyrene.
In the background environment of the serious problem of high temperature heat damage in deep mining, some mines have complex and interlocking forms of roadway arrangement, with the innovative concept ...of cooling on demand as the principle, this paper develops a mobile ice cooling equipment, and introduces and explains the equipment from the perspective of principle, composition and dimensions. and uses Comsol simulation software to simulate and analyze the main heat exchange process of the mobile ice cooling equipment under the conditions of two cooling sources, obtains quantitative results on the finned tube arrangement parameters and the heat exchange cooling effect of the equipment under ideal conditions, which provides data for the optimization and upgrading of this mobile ice cooling equipment. The results show that the mobile cooling equipment is capable of feeding the desired temperature of the cooling air into deep mine, and with flexible, convenient, efficient, and cost effective. This research and development is a new exploration of deep ventilation and cooling technology and equipment means, puts forward a new concept, accumulates valuable experience, and lays the foundation for the subsequent related research and optimization.
This paper reports a complete diagnosis of energetics of the three representative structurally distinct unstable modes in the Charney problem with a generic stratosphere presented in Mak et al ...(2021). The diagnosis of the vertically-local-energetics of these modes (Charney+ mode, Green mode and Tropopause mode) helps delineate the physical nature of the impacts of a tropopause upon their vertical structures. The total-energetics diagnosis reveals that the computational noise is negligible in the significantly unstable modes, but that in a weakly unstable mode is measurable. Treating the top boundary as a sufficiently high free-surface adequately permits the existence of vertically propagating modes with negligibly small energy passing through it. The analysis of this generalized Charney problem could be relevant to the study of troposphere-stratosphere interaction capable of inducing anomalous tropospheric weather regimes.
In this article, we propose a revocable lattice-based CP-ABE (Ciphertext-Policy Attribute-Based Encryption) scheme (RL-ABE), which is suitable to be applied in the cloud storage. The RL-ABE scheme ...can resist quantum algorithm attack and ensure fine-grained access control to the users' rights in achieving shared data. In addition, our scheme can realize attribute revocation, which can expediently renew users' attributes to grant or revoke their access rights. Then, we formally prove the security of our scheme based on the hardness of Ring Learning with Error problem(R-LWE) to resist quantum algorithm attack, and prove our scheme can solve security threatens to withstand collusion attacks. Finally, the performance analysis shows the high efficiency of our scheme compared with other related schemes.
In this study, the effect of Fe (II) on Anaerobic Ammonium Oxidation (ANAMMOX) process was investigated by step-wise increasing the Fe (II) in influent from 1 to 50 mg L−1. The nitrogen removal, ...biofilm property and the microbial community were analyzed in each phase. Results showed that, the anaerobic ammonia-oxidizing bacteria (AAOB) bioactivity and the nitrogen removal of ANAMMOX system were slightly improved to 0.58 from the initial 0.51 kg m−3 d−1 by Fe (II) in 1–5 mg L−1. The nitrogen removal was suppressed and could recover to the initial level during the same period under 10–20 mg L−1 Fe (II), while it did not recover to the initial level under 30 mg L−1 Fe (II) and showed no recovery performance under 50 mg L−1 Fe (II). The irreversible suppression threshold of Fe (II) was calculated as 50 mg L−1. The iron content in ANAMMOX biofilm presented linear correlation with the influent Fe (II) in 1–20 mg L−1, which then tended to be stable when Fe (II) was higher. Dehydrogenase activity (DHA) showed similar and faster response to Fe (II) than the microbial activity, and it was an effective pre-indicator for the nitrogen removal performance in the ANAMMOX system suffered Fe (II). The Fe (II) feeding firstly led to the relative abundance of AAOB decreased to 11.04% from the initial 35.46%, and finally picked up to 19.39% after the long-term acclimatization.
•Fe (II) in 1–5 mg L−1 effectively improved AAOB bioactivity and nitrogen removal.•Fe (II) in 10–30 mg L−1 performed reversible inhibition on ANAMMOX process.•The irreversible suppression threshold of Fe (II) on ANAMMOX was 50 mg L−1.•DHA was a pre-indicator for nitrogen removal performance of ANAMMOX system suffered Fe (II).•Fe (II) feeding lowered the relative abundance of Candidatus Kuenenia.
Durable and efficient hydrogen evolution reaction (HER) electrocatalysts that can satisfy industrial requirements need to be developed. Platinum (Pt)‐based catalysts represent the benchmark ...performance but are less studied for HER under high current densities in neutral electrolytes due to their high cost, poor stability, and extra water dissociation step. Here a facile and low‐temperature synthesis for constructing “blackberry‐shaped” Pt nanocrystals on copper (Cu) foams with low loading as self‐standing electrodes for HER in neutral media is proposed. Optimized hydrogen adsorption free energy and robust interaction induced by charge density exchange between Pt and Cu ensure the efficient and robust HER, especially under high current densities, which are demonstrated from both experimental and theoretical approaches. The electrode exhibits small overpotentials of 35 and 438 mV to reach current densities of ‐10 and ‐1000 mA cm−2, respectively. Meanwhile the electrode illustrates outstanding stability during chronoamperometry measurement under high current densities (‐100 to ‐400 mA cm−2) and 1000 cycles linear sweep voltammetry tests reaching ‐1000 mA cm−2. This study provides new design strategies for self‐standing electrocatalysts by fabricating robust metal–metal interactions between active materials and current collectors, thus facilitating the stable function of electrodes for HER under technologically relevant high current densities.
The facile in situ growth of blackberry‐shaped Pt nanocrystals on Cu foams as self‐standing hydrogen evolution reaction (HER) electrode is presented. The optimized hydrogen adsorption free energy and robust interaction between active materials and current collectors induced by charge density exchange ensure high efficiency and durability for HER in neutral media under technologically relevant high current densities.
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