Large-scale Cyclone Research Articles

Convective storms in closed cyclones in Jupiter: (II) numerical modeling

On May 31, 2020 a convective storm appeared in one small cyclone in the South Temperate Belt (STB) of Jupiter. The storm, nicknamed as Clyde's Spot, had an explosive start and quickly diminished in activity in a few days. However, it left a highly turbulent cyclone as a remnant that evolved to become a turbulent segment of the STB in a time-scale of one year. A very similar storm erupted on August 7, 2021 in another cyclone of the STB with a similar initial phenomenology. In both cases, the outbreaks started in cyclones that were the result of the merger of pre-existing vortices. In a previous paper we presented an observational study of these storms compared with a similar cyclonic convective system observed during the Voyager 2 flyby [Hueso et al., Convective storms in closed cyclones in Jupiter's South Temperate Belt: (I) Observations, Icarus, 380, 2022]. Here we present numerical simulations of these vortices and storms with the Explicit Planetary Isentropic-Coordinate (EPIC) numerical model. We simulate mergers of cyclones in Jupiter's STB and investigate the deep structure of the resulting cyclone and its capability to uplift material from the water condensation level. Convection is introduced in the model imposing heating sources whose vertical extent, horizontal size and duration are free parameters that we explore. Our simulations reproduce the cloud field of both storms after short episodes of a few hours of intense convection. The evolution of the morphology of the convective cyclone after the convective pulse stopped shows a strong relation between the convective energy released and the initial vorticity in the cyclone. Similar results are obtained for the cyclonic storm observed during the Voyager 2 flyby. We also compare our simulations of these storms with numerical simulations of a storm that developed in the STB in 2018 inside an elongated cyclone known as the South Temperate Belt Ghost [Iñurrigarro et al., Observations and numerical modelling of a convective disturbance in a large-scale cyclone in Jupiter's South Temperate Belt, Icarus, 336, 2020]. In addition, we also simulate one of the large-scale storms that develop in the South Equatorial Belt comparing our simulations with Voyager 1 observations of one of those events. From these simulations, we establish a relative scale of energies associated to these convective storms. As coherent cyclones isolate the local atmosphere from their surroundings, we propose that the availability of condensables inside closed cyclones limits the duration of active convection, allowing larger convective outbursts in larger cyclones. Our simulations of the short and intense convective pulse associated to the 2020 and 2021 STB suggest a minimum local water abundance of 1.0–1.2 times solar at the location of the storms. The lower number considers a significant contribution of ammonia condensation, and the larger number considers only water moist convection with a negligible role of ammonia.

Large-scale Vortices in Rapidly Rotating Rayleigh–Bénard Convection at Small Prandtl number

Abstract One prominent feature in the atmospheres of Jupiter and Saturn is the appearance of large-scale vortices (LSVs). However, the mechanism that sustains these LSVs remains unclear. One possible mechanism is that these LSVs are driven by rotating convection. Here, we present numerical simulation results on a rapidly rotating Rayleigh–Bénard convection at a small Prandtl number Pr = 0.1 (close to the turbulent Prandtl numbers of Jupiter and Saturn). We identified four flow regimes in our simulation: multiple small vortices, a coexisting large-scale cyclone and anticyclone, large-scale cyclone, and turbulence. The formation of LSVs requires that two conditions be satisfied: the vertical Reynolds number is large ( Re z ≥ 400 ), and the Rossby number is small (Ro ≤ 0.4). A large-scale cyclone first appears when Ro decreases to be smaller than 0.4. When Ro further decreases to be smaller than 0.1, a coexisting large-scale cyclone and anticyclone emerges. We have studied the heat transfer in rapidly rotating convection. The result reveals that the heat transfer is more efficient in the anticyclonic region than in the cyclonic region. Besides, we find that the 2D effect increases and the 3D effect decreases in transporting convective flux as the rotation rate increases. We find that aspect ratio has an effect on the critical Rossby number in the emergence of LSVs. Our results provide helpful insights into understanding the dynamics of LSVs in gas giants.

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.

Performance evaluation of industrial large-scale cyclone separator with novel vortex finder

This paper presents an experimental and numerical study on an industrial large-scale tangential-inlet cyclone separator with a novel and easy-to-implement vortex finder. The vortex finder was designed with slots on the side wall to improve cyclone performance. The collection efficiency, pressure drop, and interior flow field were analyzed. The proposed device provides an effective gas flow pathway and a coupled swirl-inertia separation mechanism, which eliminates short circuit flows under the bottom inlet of the slotted vortex finder to reduce the swirling intensity and minimize the flow instability in the separator. The pressure drop was reduced up to 27.9% compared to the conventional separator and the maximal increase in collection efficiency was 5.45%. The results presented here may provide a workable reference regarding the effects of vortex finders on improving flow fields and corresponding performance in industrial large-scale cyclone separators.

Observations and numerical modelling of a convective disturbance in a large-scale cyclone in Jupiter’s South Temperate Belt

Moist convective storms in Jupiter develop frequently and can trigger atmospheric activity of different scales, from localized storms to planetary-scale disturbances including convective activity confined inside a larger meteorological system. In February 2018 a series of convective storms erupted in Jupiter’s South Temperate Belt (STB) (planetocentric latitudes from −23° to −29.5°). This occurred inside an elongated cyclonic region known popularly as the STB Ghost, close to the large anticyclone Oval BA, resulting in the clouds from the storms being confined to the cyclone. The initial storms lasted only a few days but they generated abundant enduring turbulence. They also produced dark features, possibly partially devoid of clouds, that circulated around the cyclone over the first week. The subsequent activity developed over months and resulted in two main structures, one of them closely interacting with Oval BA and the other one being expelled to the west. Here we present a study of this meteorological activity based on daily observations provided by the amateur community, complemented by observations obtained from PlanetCam UPV/EHU at Calar Alto Observatory, the Hubble Space Telescope and by JunoCam on the Juno spacecraft. We also perform numerical simulations with the EPIC General Circulation Model to reproduce the phenomenology observed. The successful simulations require a complex interplay between the Ghost, the convective eruptions and Oval, and they demonstrate that water moist convection was the source of the initial storms. A simple scale comparison with other moist convective storms that can be observed in the planet in visible and methane absorption band images strongly suggests that most of these storms are powered by water condensation instead of ammonia.

Analysis of the pressure fluctuation in the flow field of a large-scale cyclone separator

Flow field in a cyclone separator is not stable and show complex dynamic properties. Dynamic pressure signals were measured at different positions in a large-scale gas-solid cyclone separator such as the vortex finder, outer vortex and inner vortex, using a micro-differential pressure transmitter with different inlet gas velocities and inlet particle concentrations. Power spectral density (PSD) and fast Fourier transform (FFT) were used to analyze the characteristics of these dynamic pressure signals. The results showed that the PSD of the outer vortex was divided into two parts: part 1 in a low frequency region (0–n Hz) with high magnitude and part 2 in a high frequency region (n–50 Hz) with low magnitude. The dominant frequency region was related to outer vortex, and its range and magnitude increased with increased inlet gas velocity. There was a dominant frequency in the vortex finder of the cyclone separator, which was related to inner vortex rotation. The dominant frequency increased with increased inlet gas velocity and decreased with increased particle concentration. Using data processing methods, including an FFT filter and standard deviation, particle effects were found to be focused in lower frequency region parts, while the effects were not linearly depend on the particle concentration. Furthermore, there were special pressure transfer characteristics in the cyclone separator, which resulted in forming the pressure fluctuation. Through PSDs and the coherence analysis of the dynamic pressure in two positions in the vortex space of the cyclone separator, the outer vortex was found to induce a low frequency range pressure fluctuation with high magnitude and the inner vortex induced a new main frequency because of the periodically-rotating flow behavior. Considering the resonance phenomenon, the natural frequency of cyclone separator should be kept away from the frequency of pressure fluctuation, which concentrated below 50 Hz.

Study of the performance, simplification and characteristics of SNCR de-NOx in large-scale cyclone separator

CHMKIN software was used to optimize the mechanism of SNCR reaction. Then the optimized 18-element mechanism and CFD software were combined to simulate the process of SNCR de-NOx and meanwhile the gas–solid characteristics in a cyclone separator of a supercritical CFB boiler were studied. The gas–solid characteristics and SNCR characteristics of the large-scale cyclone separator were obtained. The total pressure difference of the cyclone separator increases with the inlet velocity, and the rate of increase increases gradually. When the inlet velocity is 20m/s, the total pressure difference is 1987.6Pa. The classification efficiency of the cyclone separator increases with the inlet velocity, but the rate of increase decreases gradually. When the inlet velocity is 20m/s, the classification efficiency is 66.74%. The window of the reaction temperature for the SNCR process is in the range of 1123–1323K. The de-NOx efficiency first increases and then decreases with the increase of temperature, reaching a peak at 1223K. At low temperature, improving the NSR has little effect on the de-NOx efficiency. When the reaction temperature is in the temperature window, improving the NSR can effectively enhance the de-NOx efficiency. But after increasing the NSR to a certain extent, the de-NOx efficiency increase will slow down. Setting NSR=1.5 is suitable.

The Drying of Sludge in a Cyclone Dryer Using Computational Fluid Dynamics

A control volume-based technique implemented in FLUENT (ANSYS Inc., Canonsburg, PA) computational fluid dynamics (CFD) package was applied along with the kinetic theory of granular flow (KTGF) to simulate the flow pattern and heat and mass transfer processes for sludge material in a large-scale cyclone dryer. The drying characteristics of sludge at the dryer inlet were obtained from a previous study on the drying of sludge in a large-scale pneumatic dryer. User-defined subroutines were added to extend FLUENT's capability to account for mixture properties and to simulate the constant and falling rate drying periods. The convective heat and mass transfer coefficients were modeled using published correlations for Nusselt and Sherwood numbers. Sensitivity analysis was conducted to determine the effect of gas-phase velocity and temperature on the final product outcome. Numerical predictions for the multiphase flow hydrodynamics showed a highly diluted region in the dryer core and a higher concentration of particles close to the wall region, an indication of nonuniform distribution of particles at a cross-sectional area. The numerical predictions for the hydrodynamic profiles qualitatively depicted the flow behavior natural to these designs. The work demonstrated the successful application of CFD in the design stage of a combined pneumatic-cyclone dryer model.

Nippon Shokubai 1H 2008: segment summary: environment & catalysts business

CHMKIN software was used to optimize the mechanism of SNCR reaction. Then the optimized 18-element mechanism and CFD software were combined to simulate the process of SNCR de-NOx and meanwhile the gas–solid characteristics in a cyclone separator of a supercritical CFB boiler were studied. The gas–solid characteristics and SNCR characteristics of the large-scale cyclone separator were obtained. The total pressure difference of the cyclone separator increases with the inlet velocity, and the rate of increase increases gradually. When the inlet velocity is 20 m/s, the total pressure difference is 1987.6 Pa. The classification efficiency of the cyclone separator increases with the inlet velocity, but the rate of increase decreases gradually. When the inlet velocity is 20 m/s, the classification efficiency is 66.74%. The window of the reaction temperature for the SNCR process is in the range of 1123–1323 K. The de-NOx efficiency first increases and then decreases with the increase of temperature, reaching a peak at 1223 K. At low temperature, improving the NSR has little effect on the de-NOx efficiency. When the reaction temperature is in the temperature window, improving the NSR can effectively enhance the de-NOx efficiency. But after increasing the NSR to a certain extent, the de-NOx efficiency increase will slow down. Setting NSR = 1.5 is suitable.

Synoptic–Dynamic Climatology of Large-Scale Cyclones in the North Pacific

Abstract A climatology of large-scale, persistent cyclonic flow anomalies over the North Pacific was constructed using the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) global reanalysis data for the cold season (November–March) for 1977–2003. These large-scale cyclone (LSC) events were identified as those periods for which the filtered geopotential height anomaly at a given analysis point was at least 100 m below its average for the date for at least 10 days. This study identifies a region of maximum frequency of LSC events at 45°N, 160°W [key point 1 (KP1)] for the entire period. This point is somewhat to the east of regions of maximum height variability noted in previous studies. A second key point (37.5°N, 162.5°W) was defined as the maximum in LSC frequency for the period after November 1988. The authors show that the difference in location of maximum LSC frequency is linked to a climate regime shift at about that time. LSC events occur with a maximum frequency in the period from November through January. A composite 500-hPa synoptic evolution, constructed relative to the event onset, suggests that the upper-tropospheric precursor for LSC events emerges from a quasi-stationary long-wave trough positioned off the east coast of Asia. In the middle and lower troposphere, the events are accompanied by cold thickness advection from a thermal trough over northeastern Asia. The composite mean sea level evolution reveals a cyclone that deepens while moving from the coast of Asia into the central Pacific. As the cyclone amplifies, it slows down in the central Pacific and becomes nearly stationary within a day of onset. Following onset, at 500 hPa, a stationary wave pattern, resembling the Pacific–North American teleconnection pattern, emerges with a ridge immediately downstream (over western North America) and a trough farther downstream (from the southeast coast of the United States into the western North Atlantic). The implications for the resulting sensible weather and predictability of the flow are discussed. An adjoint-derived sensitivity study was conducted for one of the KP1 cases identified in the climatology. The results provide dynamical confirmation of the LSC precursor identification for the events. The upper-tropospheric precursor is seen to play a key role not only in the onset of the lower-tropospheric height falls and concomitant circulation increases, but also in the eastward extension of the polar jet across the Pacific. The evolution of the forecast sensitivities suggest that LSC events are not a manifestation of a modal instability of the time mean flow, but rather the growth of a favorably configured perturbation on the flow.

Low-level jet simulation over the Southern Ocean in Antarctica

We have examined the dynamical characteristics of an intense topographic low level jet (LLJ) that develops in high-resolution numerical simulations of airflow in the Antarctic region. The jet forms off Cape Adare (Victoria Land) over the Southern Ocean, when a large scale cyclone is present in the region of the Ross Sea and adjacent ocean. A low level easterly airflow is directed towards the portion of Transantarctic Mountains located along the west coast of the Ross Sea, inducing a barrier wind airflow which is locally parallel to the topographic barrier. By means of numerical experiments and model output diagnostics, we have investigated the time evolution of different meteorological parameters, and in particular those relevant for the vorticity budget, associated with the LLJ formation. The vertical component of relative vorticity, locally generated mainly by tilting above the boundary layer, is advected downstream creating vorticity streaks extending to the north over the Southern Ocean. The emerging picture is generally consistent with low Froude number regimes of flow over topography. However, complexities in topography geometry and in the large scale flow configuration do not allow direct comparison with existing theories based on simplified models.