Three-jet Research Articles

Propeller-Induced Jet Impact on Vegetated Flow Fields: Complex Coupled Effect towards the Velocity Profile

The failure of swirling ship propellers in marine environments can lead to huge repair costs. One of the main causes of such failure is when propellers tangle with vegetation, especially in shallow flow environments like ports, harbours, or shipyards. In order to understand the above-mentioned issue, this study proposes an analytical approach to explore efficient predictions and provide a flow guideline with respect to the co-existence of vegetation and propeller swirling effects. More specifically, we intend to investigate the full-depth theoretical velocity profile to represent propeller-induced flow under submerged vegetation conditions. This paper first investigates the modified logarithmic law approach to determine its suitability to represent the regional vegetated flow zone before implementing it into a three-layer analytical model. It was found, using the benchmark of literature measurements, that the modified log law improved the near-bed velocity calculation by nearly 70% when compared to an existing model. A propeller jet impact computation coupled into the vegetation analytical model was then investigated in different locations within the vegetated flow, i.e., at free-flow, water–vegetation interface, and vegetation-hindered zones, to study their complex velocity distribution patterns. The results demonstrate adequate validation with the vegetated flow and measured propeller jet data from the literature. This proves the potential of the proposed analytical approach in representing a real-world propeller jet event submerged in water flow with the existence of vegetation. The proposed novel method allows costless computation, i.e., as compared to conventional numerical models, in representing the complex interaction of the propeller jet and vegetated flow.

Scale dependence of the q and T parameters of the Tsallis distribution in the process of jet fragmentation

The dependence of the q and T parameters of the Tsallis-distribution-shaped fragmentation function (FF) on the fragmentation scale (found to be equal to the jet mass) is calculated via the resummation of the branching process of jet fragmentation in the leading-log appriximation (LLA) in the $$\phi ^3$$ theory. Jet and hadron spectra in electron-positron ( $$e^+e^-$$ ) annihilations with 2- and 3-jet final states are calculated using virtual leading partons. It is found that jets, produced earlier in the branching process, are more energetic, and the energy, angle and multiplicity distributions of hadrons stemming from them are broader. It is also found that replacing the LL resummation in the branching process by a single splitting provides good approximation for the jet energy distribution in 2-jet events. Furthermore, a micro-canonical statistical event generator is presented for the event-by-event calculation of hadron momenta in $$e^+e^-$$ annihilations.

The 2013 November 12 Solar Energetic Electron Event Associated with Solar Jets

We investigate the hard X-ray (HXR) flare-associated “prompt” solar energetic electron (SEE) 2013 November 12 event with joint EUV jet observations from Solar Dynamics Observatory/Atmospheric Imaging Assembly and STEREO-A/EUVI. The SEE energy spectrum observed by Wind/3D Plasma and Energetic Particle shows a triple-power-law shape with a low-energy break of 10.0 ± 1.7 keV and a high-energy break of 56.6 ± 8.9 keV, which has never been reported before for jet-related SEE events. Associated HXR emissions observed by RHESSI and FGST/Gamma-ray Burst Monitor show three distinctive peaks with different spectral indices β HPE of HXR-producing electrons (HPEs) derived by means of thick-target bremsstrahlung model. The high-energy spectral index β 3 = 4.63 ± 0.65 of SEE is consistent with the HPE spectral index β HPE derived in HXR peak 1 but different from β HPE of HXR peak 2 and peak 3. The main stream of EUV jets reaches a speed of 370 ± 25 km s−1 after an acceleration of up to 2.9 ± 0.4 km s−2 in a timescale of ∼2 minutes, and the acceleration time coincides with the decay phase of HXR peak 1. EUV observations from two different viewing directions help to reconstruct the jet magnetic configurations. After the investigation on HXR emissions and jet configurations, the interchange-reconnection model triggered by the emerging flux could be a satisfactory explanation for this jet event.

Regionalisation of heat waves in southern South America

This study describes the climatological characteristics of regional heat waves (HWs) over southern South America (SSA) for the warm seasons (October–March) of 1979–2018 based on daily maximum temperature series from 131 weather stations. Clustering of stations with high co-occurrence of simultaneous HW days is employed to identify regional HW events over five homogeneous regions: northern, central-eastern and southern SSA regions, central Argentina, and central Chile. When all regions are considered, we find a mean frequency of ∼4 HWs per year. Transitional regions (northern SSA, central-eastern SSA and central Argentina) are characterised by longer, albeit less intense, HWs than the southernmost region (southern SSA), whereas central Chile events display the lowest duration, intensity and extension. By aggregating these single HW attributes into a combined severity index, a ranking of historical HWs has been obtained, with the March 1980 event standing as the most severe one of SSA. The assessment of long-term changes reveals significant increases in the frequency of regional HW days over central Argentina and central Chile only. Trends in HW characteristics are also region dependent, and the southernmost region is the only one where HW severity has increased significantly.We report similarities and differences in the synoptic circulation patterns associated with regional HW events. Southern SSA HWs have the most distinctive signatures, related to extratropical high-pressure systems blocking the westerly flow. In the remaining regions, HWs are associated with anomalies in the South Atlantic (northern SSA, central-eastern SSA and central Argentina) or South Pacific (central Chile) High, and the intensification of the northerly low-level flow by regional thermal lows and South American Low Level Jet events. Regional HWs often migrate from northern to central-eastern SSA and central Argentina, following the displacement/intensification of the South Atlantic High, which partially explains the similarity of their associated patterns.

Simulation of a Solar Jet Formed from an Untwisting Flux Rope Interacting with a Null Point

Coronal jets are eruptions identified by a collimated, sometimes twisted spire. They are small-scale energetic events compared with flares. Using multiwavelength observations from the Solar Dynamics Observatory/Atmospheric Imaging Assembly and a magnetogram from Hinode/Spectro-Polarimeter (Hinode/SP), we study the formation and evolution of a jet occurring on 2019 March 22 in NOAA Active Region 12736. A zero-β magnetohydrodynamic simulation is conducted to probe the initiation mechanisms and appearance of helical motion during this jet event. As the simulation reveals, there are two pairs of field lines at the jet base, indicating two distinct magnetic structures. One structure outlines a flux rope lying low above the photosphere in the north of a bald patch region, and the other structure shows a null point high in the corona in the south. The untwisting motions of the observed flux rope were recovered by adding an anomalous (artificial) resistivity in the simulation. A reconnection occurs at the bald patch in the flux rope structure, which is moving upward and simultaneously encounters the field lines of the null point structure. The interaction of the two structures results in the jet, while the twist of the flux rope is transferred to the jet by the reconnected field lines. The rotational motion of the flux rope is proposed to be an underlying trigger of this process and responsible for helical motions in the jet spire.

NNLO QCD corrections to event shapes at the LHC

In this work we perform the first ever calculation of jet event shapes at hadron colliders at next-to-next-to leading order (NNLO) in QCD. The inclusion of higher order corrections removes the shape difference observed between data and next-to-leading order predictions. The theory uncertainty at NNLO is comparable to, or slightly larger than, existing measurements. Except for narrow kinematical ranges where all-order resummation becomes important, the NNLO predictions for the event shapes considered in the present work are reliable. As a prime application of the results derived in this work we provide a detailed investigation of the prospects for the precision determination of the strong coupling constant and its running through TeV scales from LHC data.

Experimental verification of two types of gluon jets in QCD

The Abelian decomposition of QCD tells that there are two types of gluons, the color neutral neurons and colored chromons. We propose to confirm the Abelian decomposition testing the existence of two types of gluon jets experimentally. We predict that one quarter of the gluon jet is made of the neurons which has the color factor $3/4$ and the sharpest jet radius and smallest charged particle multiplicity, while the three quarters of the gluon jet are made of the chromons with the color factor $9/4$, which have the broadest jet radius (broader than the quark jet). Moreover, we argue that the neuron jet has a distinct color flow which forms an ideal color dipole, while the quark and chromon jets have distorted dipole pattern. To test the plausibility of this proposal, we suggest to analyze the gluon distribution against the jet shape (the sphericity) and/or particle multiplicity from the existing gluon jet events and look for two distinct peaks in the distribution.

Standard Model Background Analysis for Single Lepton Channel

Since protons are not fundamental particles, they produce very large backgrounds in proton-proton collisions. Therefore, in supersymmetry searches, the main challenge is to differentiate supersymmetric signals from Standard Model background. Hence, extensive background analysis becomes an important probe to obtain information in the direction of supersymmetry searches. Among the variety of signatures in this direction, single lepton channel is one of the effective processes in which Standard Model background is obtained. In this work, starting from the generation of background emerging from various events, basic selections and cuts have been applied to obtain a homogenous and a clean sample. On the other hand, the magnitude of missing transverse energy and scalar sum of all transverse momentums are crucial to detect particles that can escape without leaving trace in the detector. Therefore, all necessary histograms have been plotted. Emerging the leading backgrounds from W-bosons + jets and top quark-antiquark + jets events, almost all energy regions, it is seen that W+jets have greater contribution to background. However, for the collisions that produce high number of jets top quark-antiquark + jets become more dominant. Final step of the work is the application of additional selections and cuts for the isolation of potential supersymmetry signals.

Persistent anomalies of the North Atlantic jet stream and associated surface extremes over Europe

Unusual, persistent configurations of the North Atlantic jet stream affect the weather and climate over Europe. We focus on winter and on intraseasonal and seasonal time scales, and study persistent jet anomalies through the lens of large deviation theory using Coupled Model Intercomparison Project (CMIP6) simulations of the MPI-ESM-LR model and ERA5 reanalysis data. The configurations of interest are defined as long-lasting anomalies of a few months in jet latitude, speed or zonality. Our results show that persistent temperature and precipitation extremes over large European regions are anomalously frequent during the unusual, persistent jet configurations we identify. Furthermore, the relative increase in frequency of surface extremes is larger for more intense surface extremes and/or more extreme jet anomalies. This is relevant in the context of the predictability of these extremes. The highest extreme event frequencies at the surface are observed in case of precipitation over the Mediterranean and Western Europe during anomalously zonal and/or fast jet events, pointing to these jet anomalies matching rather homogeneous large scale atmospheric configurations with a clear surface footprint. Additionally, our results emphasise the usefulness of large deviation rate functions to estimate the frequency of occurrence of persistent jet anomalies. They therefore provide a tool to statistically describe long-lasting anomalies, much like extreme value theory may be used to investigate shorter-lived extreme events.

Characterization of physics events in JET preceding disruptions

Characterization of physics events in JET preceding disruptions

Effects of atmospheric low-level jets on the mixing process of a large tropical reservoir.

Changes in the physical and biogeochemical properties of water columns are frequently associated with cold fronts and mesoscale convective systems due to increased cloud cover. The effects of low-level jet (LLJ) events on thermal stratification and water quality, however, remain undescribed, particularly for tropical reservoirs. Here, water temperature time series are combined with meteorological data, LIDAR observations, ERA5 reanalysis data, and hydrodynamical modeling to investigate the impact of an event of LLJ over the Furnas hydropower reservoir in Brazil. The LLJ event was characterized by dry, intense, and persistent winds (~10 m s-1) blowing for more than 12 hours over the main fetch of the reservoir. In the downwind side of the lake, the surface mixed layer depth increased by 50% during the LLJ event. The changes to the water column were produced by a combination of wind-induced upwelling, shear-driven mixing, and nocturnal convective overturning, different from the heat balance expected during passing cold fronts and mesoscale convective systems. The results suggest that both momentum and heat fluxes during LLJ events need to be accounted for in lake modelings to reproduce the vertical mixing process.

Observation and Large Eddy Simulation of Coastal Winds at Anholt Offshore Wind Farm

LiDAR and wave buoy data from the Anholt offshore wind farm have been analysed to determine the seasonal variability of the coastal winds. The wind shear exponent and turbulence intensity were used to classify the atmospheric stability. The occurrence of a Low- Level Jet (LLJ) event in the offshore environment was also studied. Three different periods that represent near-neutral, unstable, and stable atmospheric stratification were chosen for comparison with Large Eddy Simulation (LES) results. The LiDAR data showed that the atmosphere can be typically classified as unstably stratified in summer, while near-neutral stratification was frequently observed in winter. These resulted in higher mean wind speeds, wind velocity shear and directional shear in winter with lower turbulence intensity (TI). The occurrence of LLJ was found to be highest at a wind speed of 6 m/s at 86 m height, and the most frequent maximum velocity in the LLJ was observed between approximately 126 m and 186 m. For the wave data analysis, sea surface roughness was calculated using the wave steepness method, and it was found to be generally less than 0.4 mm, while the wind and wave misalignment was frequently less than 30°. The LES results matched the LiDAR profiles well for all atmospheric conditions, even though LES slightly underestimated the Turbulent Kinetic Energy (TKE) and directional shear for near-neutral conditions.

Fan-shaped jet close to a light bridge

Aims. On the Sun, jets in light bridges (LBs) are frequently observed with high-resolution instruments. The respective roles played by convection and the magnetic field in triggering such jets are not yet clear. Methods. We report a small fan-shaped jet along a LB observed by the 1.6m Goode Solar Telescope (GST) with the TiO Broadband Filter Imager (BFI), the Visible Imaging Spectrometer (VIS) in Hα, and the Near-InfraRed Imaging Spectropolarimeter (NIRIS), along with the Stokes parameters. The high spatial and temporal resolution of those instruments allowed us to analyze the features identified during the jet event. By constructing the Hα Dopplergrams, we found that the plasma is first moving upward, whereas during the second phase of the jet, the plasma is flowing back. Working with time slice diagrams, we investigated the propagation-projected speed of the fan and its bright base. Results. The fan-shaped jet developed within a few minutes, with diverging beams. At its base, a bright point was slipping along the LB and ultimately invaded the umbra of the sunspot. The Hα profiles of the bright points enhanced the intensity in the wings, similarly to the case of Ellerman bombs. Co-temporally, the extreme ultraviolet (EUV) brightenings developed at the front of the dark material jet and moved at the same speed as the fan, leading us to propose that the fan-shaped jet material compressed and heated the ambient plasma at its extremities in the corona. Conclusions. Our multi-wavelength analysis indicates that the fan-shaped jet could result from magnetic reconnection across the highly diverging field low in the chromosphere, leading to an apparent slipping motion of the jet material along the LB. However, we did not find any opposite magnetic polarity at the jet base, as would typically be expected in such a configuration. We therefore discuss other plausible physical mechanisms, based on waves and convection, that may have triggered the event.

Analysis of the main source regions of moisture transport events with the new ESA CCI/CM‐SAF total column water vapour climate data record (v2)

AbstractThis study makes use of the new total column water vapour data record (CDR‐2 (v2)), developed by the European Space Agency (ESA) in coordination with the Satellite Application Facility on Climate Monitoring (CM SAF), to analyse the adequacy of the integrated vertical water vapour column (IWV) data provided by the European Centre for Medium‐Range Weather Forecasts (ECMWF) ERA5 and ERA‐Interim reanalyses in regions of critical interest for moisture transport mechanisms. This information is critical for the initialization of moisture transport models—both Eulerian and Lagrangian—used to study the main mechanisms and predict the future evolution of moisture transport events. In particular, almost 40,000 atmospheric river (AR) and nocturnal low‐level jet (NLLJ) events identified on a global scale between 2002 and 2017 have been used to study the variability between the cited reanalyses and CDR‐2, in terms of both bias in the observed values of IWV during each particular event and daily temporal correlation fields. Although some notable discrepancies are reported in the main tropical rainforest regions, it is observed that, in regions of high interest for both ARs and NLLJs, the degree of agreement between the reanalyses and CDR‐2 is high. The bias observed in the regions of interest is generally low, and the temporal correlation in the IWV fields is above 0.8 in most areas. ERA5 appears to show slightly better performance than ERA‐Interim when resolving the moisture column, and both show greater similarity to CDR‐2 in the midlatitudes compared with tropical regions. The probability density functions constructed on an event‐to‐event basis reinforce these ideas. We conclude that the evaluations presented here using CDR‐2 serve to strengthen avaliable evidence that the ECMWF reanalyses can safely be used in the initializations of Lagrangian dispersion models and Eulerian moisture tracer simulations—commonly used for the analysis of main advection mechanisms—in the vast majority of regions critical to the study of ARs and LLJs. They can also safely be used for the detection of moisture source–sink regions in the study of the global hydrological cycle in these regions.

Multi-jet merging with TMD parton branching

One of the main theoretical systematic uncertainties in studies of final states with large jet multiplicities at high-energy hadron colliders is associated with the merging of QCD parton showers and hard-scattering matrix elements. We present a method to incorporate the physics of transverse momentum recoils due to initial-state shower evolution into multi-jet merging algorithms by using the concept of transverse momentum dependent (TMD) distributions and the associated parton branching. We investigate the dependence on the merging scale and illustrate the impact of the new method at the level of both exclusive and inclusive final-state observables by studying differential jet rates, transverse momentum spectra and multiplicity distributions, using vector boson + jets events at the LHC as a case study.

High‐resolution climate characteristics of the Arabian Gulf based on a validated regional reanalysis

AbstractThe regional climate of the Arabian Gulf (AG) and its variability are examined based on a 40‐year (1980–2019), 5‐km regional reanalysis of the Arabian Peninsula (AP reanalysis). The AP reanalysis fields were first validated against the available observations over the AG, suggesting that this high‐resolution reanalysis well reproduces the spatio‐temporal features of the AG atmospheric circulations. The validated AP reanalysis fields were then analysed to examine the climatic characteristics over the AG including the monthly mean, maximum and minimum temperatures, and the seasonal variations in winds, relative humidity and rainfall over the AG. The AG climate is mostly dry between May and October, and experiences moderate rainfall between December and January. The higher (lower) pressure difference between the northwest and southeast AG during summer (winter) generates the northwesterly Shamal winds over the north (central) AG. The mean Shamal winds are relatively stronger (weaker) and prolonged (shorter) during summer (winter); however, the short lived Shamal jet events in winter can be occasionally stronger than summer. In terms of interannual variability, the Shamal winds are stronger and more persistent in summer during El Niño years and in winter during La Niña years. These differences are mainly associated with changes in temperature gradients between the eastern AG and northwestern AP.

Back-to-back azimuthal correlations in mathrm {Z} +jet events at high transverse momentum in the TMD parton branching method at next-to-leading order

Azimuthal correlations in mathrm {Z} +jet production at large transverse momenta are computed by matching Parton-Branching (PB) TMD parton distributions and showers with NLO calculations via MCatNLO. The predictions are compared with those for dijet production in the same kinematic range. The azimuthal correlations Delta phi between the Z boson and the leading jet are steeper compared to those in dijet production at transverse momenta mathcal{O}(100) GeV , while they become similar for very high transverse momenta {{mathcal {O}}}(1000) GeV . The different patterns of mathrm {Z} +jet and dijet azimuthal correlations can be used to search for potential factorization-breaking effects in the back-to-back region, which depend on the different color and spin structure of the final states and their interferences with the initial states. In order to investigate these effects experimentally, we propose to measure the ratio of the distributions in Delta phi for mathrm {Z} +jet- and multijet production at low and at high transverse momenta, and compare the results to predictions obtained assuming factorization. We examine the role of theoretical uncertainties by performing variations of the factorization scale, renormalization scale and matching scale. In particular, we present a comparative study of matching scale uncertainties in the cases of PB-TMD and collinear parton showers.

Evaluation of a forest parameterization to improve boundary layer flow simulations over complex terrain. A case study using WRF-LES V4.0.1

Abstract. We evaluate the influence of a forest parametrization on the simulation of the boundary layer flow over moderate complex terrain in the context of the Perdigão 2017 field campaign. The numerical simulations are performed using the Weather Research and Forecasting model in large eddy simulation mode (WRF-LES). The short-term, high-resolution (40 m horizontal grid spacing) and long-term (200 m horizontal grid spacing) WRF-LES are evaluated for an integration time of 12 h and 1.5 months, respectively, with and without forest parameterization. The short-term simulations focus on low-level jet events over the valley, while the long-term simulations cover the whole intensive observation period (IOP) of the field campaign. The results are validated using lidar and meteorological tower observations. The mean diurnal cycle during the IOP shows a significant improvement of the along-valley wind speed and the wind direction when using the forest parametrization. However, the drag imposed by the parametrization results in an underestimation of the cross-valley wind speed, which can be attributed to a poor representation of the land surface characteristics. The evaluation of the high-resolution WRF-LES shows a positive influence of the forest parametrization on the simulated winds in the first 500 m above the surface.

Accelerated western European heatwave trends linked to more-persistent double jets over Eurasia

Persistent heat extremes can have severe impacts on ecosystems and societies, including excess mortality, wildfires, and harvest failures. Here we identify Europe as a heatwave hotspot, exhibiting upward trends that are three-to-four times faster compared to the rest of the northern midlatitudes over the past 42 years. This accelerated trend is linked to atmospheric dynamical changes via an increase in the frequency and persistence of double jet stream states over Eurasia. We find that double jet occurrences are particularly important for western European heatwaves, explaining up to 35% of temperature variability. The upward trend in the persistence of double jet events explains almost all of the accelerated heatwave trend in western Europe, and about 30% of it over the extended European region. Those findings provide evidence that in addition to thermodynamical drivers, atmospheric dynamical changes have contributed to the increased rate of European heatwaves, with implications for risk management and potential adaptation strategies.

Permutationless many-jet event reconstruction with symmetry preserving attention networks

Top quarks, produced in large numbers at the Large Hadron Collider, have a complex detector signature and require special reconstruction techniques. The most common decay mode, the ``all-jet'' channel, results in a 6-jet final-state which is particularly difficult to reconstruct in $pp$ collisions due to the large number of permutations possible. We present a novel approach to this class of problem, based on neural networks using a generalized attention mechanism, that we call symmetry preserving attention networks (spa-net). We train one such network to identify the decay products of each top quark unambiguously and without combinatorial explosion as an example of the power of this technique. This approach significantly outperforms existing state-of-the-art methods, correctly assigning all jets in 80.7% of 6-jet, 66.8% of 7-jet, and 52.3% of $\ensuremath{\ge}8$-jet events respectively.