Double Jet Research Articles

High-resolution Radio Study of the Dragonfly Pulsar Wind Nebula Powered by PSR J2021+3651

The Dragonfly Nebula (G75.2+0.1) powered by the young pulsar J2021+3651 is a rare pulsar wind nebula (PWN) that shows double tori and polar jets enclosed by a bow-shock structure in X-rays. We present new radio observations of this source taken with the Very Large Array at 6 GHz. The radio PWN has an overall size about two times as large as the X-ray counterpart, consisting of a bright main-body region in the southwest, a narrow and fainter bridge region in the northeast, and a dark gap in between. The nebula shows a radio spectrum much softer than that of a typical PWN. This could be resulting from compression by the ram pressure as the system travels mildly supersonically in the interstellar medium. Our polarization maps reveal a highly ordered and complex B-field structure. This can be explained by a toroidal field distorted by the pulsar motion.

Analysis of Direct Force Characteristics Based on WENO Method and Numerical Simulation

The direct force active control technology of direct gas composite is an important development direction and key technology of precision guidance weapons, which provides an effective power for the aircraft to carry out great manoeuvrability and agile flight. When the vehicle adopts direct force / aerodynamic composite control, the aerodynamic characteristics and jet characteristics are no longer independent of each other, but form a complex flow field structure, which strongly changes the aerodynamic forces acting on the vehicle. This paper makes the design study of the aerodynamic characteristics and jet characteristics of direct gas composite, establish the aerodynamic model and direct force model that can accurately describe the side jet interference effect. Based on the WENO method, this paper calculates the direct force jet through the grid generation and the setting of initial field and boundary conditions, mainly analyses the operation of double jet at typical altitude and the interaction between jets under different flight conditions or flight conditions. The effective conclusions of the coupling effect of aerodynamic characteristics and jet characteristics under some typical conditions are obtained, which provides a research basis for the analysis of the interaction between multiple jets of direct force aircraft with jet control mode.

Interannual variability of the double easterly jets over the tropical western Pacific and their effects on tropical cyclone genesis

AbstractDifferent from other upper‐tropospheric jet stream that owns the single jet axis, the tropical easterly jet (TEJ) generally splits into two branches over the tropical western Pacific where the TEJ inflows from June to September, with the north branch locating near 20°N and the south branch appearing near the equator. However, how these double easterly jets change from year to year and whether they have effects on the tropical cyclones (TCs) over the tropical western Pacific are still unknown. Observational evidence has demonstrated that the double easterly jets in the TEJ's inflow region exhibit an out‐of‐phase relationship in the interannual time scale and is significantly related to the TCs genesis. Corresponding to a stronger south branch and a weaker north branch, the accelerated (decelerated) easterly wind for the south (north) branch would induce a northerly (southerly) ageostrophic wind, thus triggering an upper‐tropospheric divergence between the double easterly jets. This divergence can further lead to anomalous ascending flows over the western North Pacific, which turns out to be the primary cause that increases the TCs number over there. The results highlight that the out‐of‐phase variation of the double easterly jets could dynamically modulate the occurrence of the TCs over the western North Pacific by inducing the secondary vertical circulation.

439 TRANSIENT SEVERE MITRAL REGURGITATION IN REVERSED TAKOTSUBO SYNDROME

Abstract A 65-years old Caucasian woman was referred to the emergency department for chest pain, dyspnoea and high systolic blood pressure. In the previous days she complained a constant state of anxiety and worries due to family troubles. At the admission 12 – lead EKG showed sinus rhythm, ST-T segment depression >1 mm in the lateral and anterior leads (from V2 to V6). Laboratory exams showed elevated values of high sensivity troponin levels (high-sensitive troponin: 41 pg/mL – maximum laboratory cut off value: 12 pg/mL). Bedside echocardiogram showed an LVEF of 40% due to apical hyperkinesis, akynesis of the basal segments and hypokinesis of the mid segments of the left ventricle; a severe double jet MR (Fig.1); a type II diastolic dysfunction (E/A: 1,5; E/e’: 14). Several B lines (> 3) were present in all pulmonary regions assessed by lung POCUS. Cardiac angiography demonstrated non obstructive coronary artery disease. Left ventriculography showed an hyperdynamic apex and severe basal hypokinesis. Clinical and functional status rapidly improved. Daily EKGs were registered with a progressive resolution of the ST-T segment depression. She was discharged on the 7th days and the TTE in pre-discharge showed an LVEF of 60%, without wall motion abnormalities and complete recovery of mitral regurgitation. We report a case of reversible severe mitral regurgitation in a patient with basal ballooning TTS. Mital regurgitation is generally described in the contest of classical apical TTS. The potential mechanisms for severe MR are similar to those of acute myocardial infarction. Admission and daily echocardiographic evaluation is crucial in this subset of patients, with a tailored therapy following the severity of mitral valve disease. Fig. 1

Grouting Additives and Information-Based Construction of Jet Grouting in the Water-Rich Sand Stratum

The dynamic action of groundwater in the water-rich sand stratum carries away injected cement slurry before it becomes solidified, which seriously affects the determination of the diameter and strength of the column. Grouting additives and information-based construction are two main actions to control the quality of jet grouting construction. This study introduced a solution of grouting additives and information-based construction of jet grouting in the water-rich sand stratum. First, high-polymer cement grout (HPCG), red mud and phosphogypsum cement grout (RPCG) and metakaolin cement grout (MKCG) additives were screened with a series of laboratory tests on solidification time and permeability; moreover, the mix proportion of grouting fluids was developed in order to adapt for water-rich sand strata. Secondly, information-based construction of jet grouting was conducted to control grouting quantity with real-time monitoring of drill rotational velocity, drill lifting speed and injection pressure equipped with the monitoring system on the double fluid jet grouting systems. Lastly, the validity of grouting additives and information-based construction in the water-rich sand stratum was verified via a test pile in situ, and a series of material tests on drilling core samples on permeability with SEM observation. The results indicate that the high polymer is the preferred additive of grouting fluids because the solidification time can be controlled in the range of 10 min to 20 min; the permeability of drilling core samples can reach the order of 10−7, with the mix proportion being A:B = 2:1, high-polymer additive:water > 1:3, with a water-cement ratio of 0.8. The specifications of information-based construction are a drill rotational velocity of 10 r/min, a drill lifting speed of 0.2 m/min, an injection pressure of 20 MPa and a grouting quantity of 40 L/min.

Impact of Single and Duplex Cryogenic Jets on Mechanical and Physical Characteristics in Turning of Titanium Superalloys

This analyses evaluates the cutting force , surface roughness, chip morphology, chip–tool interface temperature, tool life, and Single use of a coated carbide tool and double liquid nitrogen jets for friendly superalloy that is extremely difficult to cut being turned (Ti-6Al4V). The rake face was the only focus of the single jet, while the rake and flank surfaces were concurrently hit by the duplex jets. Liquid nitrogen jets provided the highest machining quality, reducing cutting force , temp, hardness, and, apparently, tool life. When equated to dry and single jet assist, the double liquid nitrogen jets increased life of the tool by 60% and 30%. In spite of this, chip manufacture has not changed. Using duplex liquid nitrogen jets to extend tool life, reduce tool costs, lower temperatures, improve surface quality, and most importantly, promote machinability of Ti-6Al-4V superalloy has been accepted as a sustainably booster.

A close supermassive black hole binary in Centaurus A?

The Event Horizon Telescope (EHT) project has recently published a high-resolution picture of the Centaurus A galaxy core, where a supermassive black hole (SMBH) is supposed to be located. This picture has been accompanied with interpretation difficulties. In particular, the expected central SMBH and its accretion disk are not detected, the conical forward plasma jet seems hollow and its bended shape is difficult to explain. We argue that this image could in fact reveal the existence of two SMBHs, instead of one. Within this alternative interpretation, the black holes and their disks become visible on the image, the curved jet shapes may more easily be explained and the jets display no dark spine. The putative SMBH binary system shows a projected separation distance of ∼0.4-0.7 milliparsec. This is 700 times narrower than the NGC 7674 SMBH binary, so far the visually-identified system with the shortest such distance (0.35 pc). The orbital period can be inferred to lie in the 101 to 10−1 yr magnitude range. The image suggests a double helical jet structure that, if real, would support the lower end of this estimation range. If confirmed by future observations, this close SMBH binary in Centaurus A will be of great interest as a testing ground for SMBH binary dynamics models and plasma jet studies.

Performance analysis of synthetic jet micropump based on double piezoelectric actuators

To alleviate the problem of low flow rates of synthetic jet piezoelectric pumps for liquid medium, a double piezoelectric synthetic jet micropump (DPSJM) is proposed. DPSJM generates pressure change in the pump chamber by the high voltage vibration of the double piezoelectric actuators. Theoretical models are used to analyze the factors affecting the performance of DPSJM. The flow field is analyzed by using the finite element method in the jet chamber, and the prototype is built and tested. The results show that the performance of the DPSJM is best with double piezoelectric actuators with a sine wave drive signal and a pump chamber height of 1 mm. The highest flow rate comes to 22.11 ml min−1 at 175 V, 65 Hz. Moreover, the DPSJM is simple in construction. When compared to other types of valveless piezoelectric pumps, there was no resistance fluid in the pump chamber, which could significantly reduce the damage to the transfer medium.

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.

Nanofluid heat transfer in a microchannel heat sink with multiple synthetic jets and protrusions

This study focuses on the innovative integration of different cooling techniques to maximize the thermal performance in a 3D microchannel heat sink (MCHS). The paper discusses nanofluid flow and thermal fields in the MCHS with protrusions subjected to double synthetic jets (SJs). A validated multiphase mixture model is used to study the effect of Al2O3 particles in water. The effect of particle concentration, orifice spacing, orifice height, oscillation frequency, membrane amplitude, and phase actuation on convective and conductive heat transfer is analyzed. Heat transfer is significantly influenced by the particle concentration in both active and inactive SJs. Overall, 180° out-of-phase jet configurations show better performance in terms of convective heat transfer, while in-phase jet arrangements are more efficient in conductive heat transfer enhancement. In terms of thermal performance, 180° out-of-phase cases show a higher figure of merit (FOM) than in-phase SJs. Increasing the frequency and amplitude enhances the heat transfer. In the case of nanofluids, the maximum degree of convective enhancement of 1.23 demonstrates the effectiveness of SJs and protrusions. However, the maximum degree of overall thermal enhancement of 54% is obtained at in-phase actuation under the same conditions.

Investigation of the effect of turbulence induced by double non-reactive gas jet on the deflagration-to-detonation transition

Jet-in-crossflow (JICF) is proved to be advantageous to accelerate flame propagation and stimulate the deflagration-to-detonation transition (DDT) process in the recent decade. Studies focused on the performance of the jet of combustible mixture or reactive gas on facilitating the DDT process are carried out, and the results show that the combustible JICF can promote the flame transition to detonation efficiently. Although most investigations attribute the ability of the JICF on promoting DDT to the turbulent effect induced by the jet, the combustion-enhancement effect of the jet medium is seldom considered. In our previous work, it is proposed that the non-reactive gas jet in an optimal condition can accelerate flame propagation and promote the precursor shock wave formation. Hence, the performance of the multi-jet of non-reactive gas on facilitating the DDT process is worth investigating. In this paper, three different double jet placement methods are designed: parallel, staggered, and opposite positioned, and their performances on accelerating flame propagation and promoting the DDT process are investigated systematically. The results indicate that the staggered jet can accelerate the flame to detonation within a short run-up distance whereas the parallel jet and the opposite jet can only make the flame accelerate slightly. The schlieren images of flame evolution affected by double jet indicate that the complicated reactivity gradients generate on the flame surface while the flame is disturbed by the double jet. The interaction between the staggered jet and the flame induces local explosions, which results in a prominent increase of the flame area and a large volumetric burning rate. For the opposite jet, its negative effect of combustion-inhibition of the aggregated CO2 overwhelms the positive effect of turbulence-enhancement on the flame acceleration.

Nonlinear propagation effect in x-ray parametric amplification during high harmonic generation

We report the realization and characterization of parametric amplification in high harmonic generation around 100 eV using He gas in a double gas jet arrangement. The delay of the seed extreme ultraviolet (XUV) pulse with respect to the amplifier gas jet was scanned by changing the distance between the gas jets. Experiments and numerical calculations show that parametric amplification occurs within a temporal window of several optical cycles. Strong correlation between the seed and amplifier was observed in a shorter, few optical cycles delay range, which appeared as a modulation of the XUV intensity with an unexpected one optical cycle periodicity instead of half optical cycle. Simulations revealed that the strong correlation and also the unusual periodicity was the consequence of the nonlinear effect produced by plasma dispersion on the parametric amplification process during propagation in the amplifier jet.

Effects of Air Supply Terminal Devices on the Performance of Variable Refrigerant Flow Integrated Stratum Ventilation System: An Experimental Study

A variable refrigerant flow integrated stratum ventilation (VRF-SV) system was proposed as an energy efficient substitute for conventional central cooling systems for buildings. The novel system provided conditioned air to enclosed spaces with high indoor air quality and thermal comfort. This study investigated the effects of different types of ASTDs on the performance of the VRF-SV hybrid system. The performance was experimentally evaluated with five air terminal types, including bar grille, double deflection grille, jet slot, perforated and drum louver diffusers. The evaluation was carried out using standard indices: temperature and velocity distribution, airflow pattern, effective draft temperature (EDT), air distribution performance index (ADPI), thermal sensation vote and comfort feedback survey. The results indicated that the ASTD type had a significant impact on airflow pattern. Furthermore, the bar grille diffuser provided the occupants with greater thermal comfort and acceptable indoor environment. Almost all the EDT values determined in the breathing zone in the case with bar grille diffuser found under the satisfactory range, i.e., −1.2 < K < 1.2. Based on these values, the ADPI for bar grille diffuser was calculated as 92.8%. Thus, the bar grille diffuser is recommended to be installed with the VRF-SV hybrid system in buildings.

High-order compact difference schemes on wide computational stencils with a spectral-like accuracy

In this paper, we propose a generalized framework for the derivation of compact difference schemes for the approximation of an arbitrary order derivative. We formulate a methodology for calculating the approximation coefficients involving a large number of mesh points leading to very high-order formulas, e.g., 20th or 30th order. The main emphasis is on the first and second order derivative occurring in the Navier-Stokes equations governing fluid flow problems. Contrary to most studies on compact schemes in which the computational stencils employed in the discretization are narrow and consist of only a few mesh points K, in the presented paper we consider wide stencils that in practice are limited only by the overall number of the nodes in a computational grid. We analyze the features of such wide stencil based schemes in physical and spectral space. It is shown that the solutions obtained applying the schemes of the same order but involving different number of the mesh points characterize significantly different accuracy. This is presented by direct comparisons of the analytically derived formula for the leading terms of the truncation errors as well as in practical simulations. The test cases include a second order ordinary differential equation with variable coefficients, 1D Burgers equation and three typical benchmark problems used in Computational Fluid Dynamics (CFD), i.e., inviscid vortex advection, convected Taylor-Green vortices and a double jet flow. The obtained results are compared with available analytical solutions and the solutions obtained with the help of a pseudo-spectral method. We found that very high-order compact schemes reach the spectral accuracy characterized by the error decrease proportional to O(hK). In some cases, they show even higher accuracy, and moreover, reaching the limit of the machine precision they are substantially more resistant to the round-off errors.

Numerical Investigation of Single-Row Double-Jet Film Cooling of a Turbine Guide Vane under High-Temperature and High-Pressure Conditions

Single-row double-jet film cooling (DJFC) of a turbine guide vane is numerically investigated in the present study, under a realistic aero-thermal condition. The double-jet units are positioned at specific locations, with 57% axial chord length (Cx) on the suction side or 28% Cx on the pressure side with respect to the leading edge of the guide vane. Three spanwise spacings (Z) in double-jet unit (Z = 0, 0.5d, and 1.0d, here d is the film hole diameter) and four spanwise injection angles (β = 11°, 17°, 23°, and 29°) are considered in the layout design of double jets. The results show that the layout of double jets affects the coupling of adjacent jets and thus subsequently changes the jet-in-crossflow dynamics. Relative to the spanwise injection angle, the spanwise spacing in a double-jet unit is a more important geometric parameter that affects the jet-in-crossflow dynamics in the downstream flowfield. With the increase in the spanwise injection angle and spanwise spacing in the double-jet unit, the film cooling effectiveness is generally improved. On the suction surface, DJFC does not show any benefit on film cooling improvement under smaller blowing ratios. Only under larger blowing ratios does its positive potential for film cooling enhancement start to show. Compared to the suction surface, the positive potential of the DJFC on enhancing film cooling effectiveness behaves more obviously on the pressure surface. In particular, under large blowing ratios, the DJFC plays dual roles in suppressing jet detachment and broadening the coolant jet spread in a spanwise direction. With regard to the DJFC on the suction surface, its main role in film cooling enhancement relies on the improvement of the spanwise film layer coverage on the film-cooled surface.

The influence of a second ground electrode on hydrogen peroxide production from an atmospheric pressure argon plasma jet and correlation to antibacterial efficacy and mammalian cell cytotoxicity

This study investigates how addition of a 2nd ground electrode in an argon plasma jet influences the production of hydrogen peroxide (H2O2) in deionised water (DIW). Briefly, plasma is ignited by purging argon gas through a quartz tube at 1 l min−1 and applying a sinusoidal voltage of 7 kV (peak–peak) at 23.5 kHz to a high voltage stainless steel needle electrode sealed inside the quartz tube surrounded by one or two copper ring(s) that served as the ground electrode(s) situated downstream of the high voltage electrode. The mechanisms of H2O2 production are investigated through the electrical and optical plasma properties and chemical analysis of the treated DIW. We discover that the addition of a 2nd ground electrode results in higher accumulation of charges on the inner wall surface of the quartz tube of the plasma jet assembly resulting in an increase in the discharge current and dissipated power. This further leads to an increase in the electron temperature that more than doubles the H2O2 production through dissociative recombination of water vapour molecules, whilst still maintaining a biological tissue tolerable gas temperature. The double ground electrode plasma jet is shown to be highly effective at reducing the growth of common wound pathogens (Pseudomonas aeruginosa and Staphylococcus aureus) in both planktonic and biofilm states whilst inducing a low level of cytotoxicity in HaCaT keratinocyte skin-like cells under certain conditions. The information provided in this study is useful in understanding the complex physicochemical processes that influence H2O2 production in plasma jets, which is needed to optimise the development of plasma sources for clinical applications.

Numerical simulation of single/double liquid jets in supersonic crossflows

This study investigates the mixing processes of liquid jets in supersonic crossflows at a Mach number of 2.1 by using numerical simulations that employ the Coupled Level-Set/Volume-of-Fluid (CLSVOF) method, which is based on the Delayed Detached Eddy Simulation (DDES). The instantaneous spray morphology from the simulations agreed well with the experimental data. The spray presents the ‘Ω’ shape when viewed from the front, and the maximum error in the penetration depth was 15% from a side perspective. The direction of the air movement determined the shape of the liquid column shearing and breaking. In turn, the breaking process of the liquid jet significantly affects the structure of the air flow. Three-dimensional flow around the liquid column occurred when the supersonic incoming flow impinged on the liquid column, ultimately forming counter-rotating vortex pairs (CVP) in the inner region of the spray. Evolution of the reverse vortex pair accelerated the mixing process of the spray. Single liquid jet was used as a basis to further study double jets in Mach 2.1 airflow. The results show that the breaking length and penetration depth of the downstream jet are significantly improved.

Machine learning regression-CFD models for the nanofluid heat transfer of a microchannel heat sink with double synthetic jets

A comprehensive analysis consisting of computational fluid dynamics (CFD) and machine learning algorithms (MLAs) is conducted to study the effect of geometrical and operational parameters on nanofluid heat transfer in a microchannel heat sink (MCHS) with double synthetic jets (SJs). A parametric CFD study is initially carried out on insert types (dimple/protrusion), insert arrangements (inline/staggered), insert diameters, and jet phase actuation (in-phase/180° out-of-phase actuation). Four popular regression models used to save the computational cost are k-nearest neighbor (k−NN), random forest (RF), Gaussian process regression (GPR), and Multi-layer perceptron (MLP). In the MCHS with inactive jets, the heat transfer coefficient (HTC) is enhanced by 104.8% by adding 5% alumina particles and inline protrusions (D = 0.26 mm). Staggered arrangements also show a higher heat transfer rate and pressure drop ratio. In the case of active jets, adding nanoparticles and staggered dimples significantly reduces the maximum temperature. The k-NN regression model shows more accurate predictions than the other MLAs. The conductive heat transfer rate is maximized by 53.99% in the in-phase actuation cases. The optimum results are obtained at the inline dimple set with D = 0.265 mm in the in-phase actuation case.

Two types of ridging South Atlantic Ocean anticyclones over South Africa and the associated dynamical processes

Using 41 years of ERA5 reanalysis, two types of ridging South Atlantic Ocean high pressure systems were identified in the South African domain. Type-N events have a zonal structure and the ridging component breaks off from the parent South Atlantic Ocean anticyclone, after extending across the South African mainland. Type-S events extend south of the mainland and then break off. The Type-N (Type-S) ridging component is weaker (stronger) leaving behind a stronger (weaker) South Atlantic Ocean high. The two types of ridging events are associated with different configurations of Rossby wave packets that propagate across the South Atlantic Ocean. Surface and upper tropospheric anomalies associated with Type-S wave packets are stronger than those associated with Type-N events and the vertical coupling of the anomalies is much stronger during Type-S events. Type-N events are associated with a double jet streak structure, with the downstream jet contributing to upward motion over the landmass by means of its thermally direct circulation at its jet entrance. The upstream jet during Type-N events induces downward motion over the southern half of South Africa as it propagates eastward. The Type-S upstream jet streak, which only appears during winter, has limited zonal extent and does not induce downward motion over the country. Type-N ridging is associated with stronger ageostrophic moisture fluxes along the southern coast leading to higher moisture content and precipitation along the south eastern and eastern coasts of South Africa.

The impact of deep convection representation in a global atmospheric model on the warm conveyor belt and jet stream during NAWDEX IOP6

Abstract. The effect of parameterized deep convection on warm conveyor belt (WCB) activity and the jet stream is investigated by performing simulations of an explosively developing large-scale cyclone that occurred during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) field campaign using the Météo-France global atmospheric model ARPEGE. Three simulations differing only from their deep convection representation are analysed. The first one was performed with the Bougeault (1985) scheme (B85), the second one with the Prognostic Condensates Microphysics and Transport (PCMT) scheme of Piriou et al. (2007), and the third one without any parameterized deep convection. In the latter simulation, the release of convective instability at the resolved scales of the model generates localized cells marked by strong heating with few degrees extent in longitude and latitude along the fronts. In runs with active parameterized deep convection (B85, PCMT), the heating rate is more homogeneously distributed along fronts as the instability release happens at subgrid scales. This difference leads to more rapid and abrupt ascents in the WCB without parameterized deep convection and more moderate but more sustained ascents with parameterized deep convection. While the number of WCB trajectories does not differ much between the three simulations, the averaged heating rates over the WCB trajectories exhibits distinct behaviour. After 1 d of simulations, the upper-level heating rate is on average larger, with the B85 scheme leading to stronger potential vorticity (PV) destruction. The difference comes from the resolved sensible and latent heating and not the parameterized one. A comparison with (re)analyses and a large variety of airborne observations from the NAWDEX field campaign (Doppler radar, Doppler lidar, dropsondes) made during the coordinated flights of two aircraft in the WCB outflow region shows that B85 performs better in the representation of the double jet structure at 1 d lead time than the other two simulations. That can be attributed to the more active WCB at upper levels. However, this effect is too strong and that simulation becomes less realistic than the other ones at forecast ranges beyond 1.5 d. The simulation with the PCMT scheme has an intermediate behaviour between the one with the B85 scheme and without parameterized deep convection, but its impact on the jet stream is closer to the latter one. Finally, additional numerical experiments show that main differences in the impact on the jet between PCMT and B85 largely come from the chosen closure, with the former being based on CAPE and the latter on moisture convergence.