ABSTRACT Giant planets can clear deep gaps when embedded in 2D (razor-thin) viscous circumstellar disks. We show by direct simulation that giant planets are just as capable of carving out gaps in 3D. ...Surface density maps are similar between 2D and 3D, even in detail. In particular, the scaling of gap surface density with planet mass, derived from a global "zero-dimensional" balance of Lindblad and viscous torques, applies equally well to results obtained at higher dimensions. Our 3D simulations reveal extensive, near-sonic, meridional flows both inside and outside the gaps; these large-scale circulations might bear on disk compositional gradients, in dust or other chemical species. At high planet mass, gap edges are mildly Rayleigh unstable and intermittently shed streams of material into the gap-less so in 3D than in 2D.
Formation of Giant Planet Satellites Batygin, Konstantin; Morbidelli, Alessandro
The Astrophysical journal,
05/2020, Letnik:
894, Številka:
2
Journal Article
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Recent analyses have shown that the concluding stages of giant planet formation are accompanied by the development of a large-scale meridional flow of gas inside the planetary Hill sphere. This ...circulation feeds a circumplanetary disk that viscously expels gaseous material back into the parent nebula, maintaining the system in a quasi-steady state. Here, we investigate the formation of natural satellites of Jupiter and Saturn within the framework of this newly outlined picture. We begin by considering the long-term evolution of solid material, and demonstrate that the circumplanetary disk can act as a global dust trap, where s ∼ 0.1-10 mm grains achieve a hydrodynamical equilibrium, facilitated by a balance between radial updraft and aerodynamic drag. This process leads to a gradual increase in the system's metallicity, and eventually culminates in the gravitational fragmentation of the outer regions of the solid subdisk into km satellitesimals. Subsequently, satellite conglomeration ensues via pair-wise collisions but is terminated when disk-driven orbital migration removes the growing objects from the satellitesimal feeding zone. The resulting satellite formation cycle can repeat multiple times, until it is brought to an end by photoevaporation of the parent nebula. Numerical simulations of the envisioned formation scenario yield satisfactory agreement between our model and the known properties of the Jovian and Saturnian moons.
We seek to characterize how the change of global rotation rate influences the overall dynamics and large-scale flows arising in the convective envelopes of stars covering stellar spectral types from ...early G to late K. We do so through numerical simulations with the ASH code, where we consider stellar convective envelopes coupled to a radiative interior with various global properties. As solar-like stars spin down over the course of their main sequence evolution, such a change must have a direct impact on their dynamics and rotation state. We indeed find that three main states of rotation may exist for a given star: anti-solar-like (fast poles, slow equator), solar-like (fast equator, slow poles), or a cylindrical rotation profile. Under increasingly strict rotational constraints, the last profile can further evolve into a Jupiter-like profile, with alternating prograde and retrograde zonal jets. We have further assessed how far the convection and meridional flows overshoot into the radiative zone and investigated the morphology of the established tachocline. Using simple mixing length arguments, we are able to construct a scaling of the fluid Rossby number , which we calibrate based on our 3D ASH simulations. We can use this scaling to map the behavior of differential rotation versus the global parameters of stellar mass and rotation rate. Finally, we isolate a region on this map (Rof 1.5-2) where we posit that stars with an anti-solar differential rotation may exist in order to encourage observers to hunt for such targets.
New metrics and evidence are presented that support a linkage between rapid Arctic warming, relative to Northern hemisphere mid-latitudes, and more frequent high-amplitude (wavy) jet-stream ...configurations that favor persistent weather patterns. We find robust relationships among seasonal and regional patterns of weaker poleward thickness gradients, weaker zonal upper-level winds, and a more meridional flow direction. These results suggest that as the Arctic continues to warm faster than elsewhere in response to rising greenhouse-gas concentrations, the frequency of extreme weather events caused by persistent jet-stream patterns will increase.
We have analyzed the Ca-K images obtained at Kodaikanal Observatory as a function of latitude and time for the period of 1913 – 2004 covering Solar Cycles 15 to 23. We have classified the ...chromospheric activity into plage, Enhanced Network (EN), Active Network (AN), and Quiet Network (QN) areas to differentiate between large strong active and small weak active regions. The strong active regions represent toroidal and weak active regions poloidal component of the magnetic field. We find that plage areas mostly up to
50
∘
latitude belt vary with about 11-year solar cycle. We also find that a weak activity represented by EN, AN and QN varies with about 11-year with significant amplitude up to about
50
∘
latitude in both hemispheres. The amplitude of the variation is minimum around
50
∘
latitude and again increases by a small amount in the polar region. In addition, the plots of plages, EN, AN and QN as functions of time indicate the maximum of activity at different latitude occur at different epoch. To determine the phase difference for the different latitude belts, we have computed the cross-correlation coefficients of other latitude belts with the
35
∘
latitude belt. We find that the activity shifts from mid-latitude belts towards equatorial belts at high speed at the beginning of a solar cycle and at lower speed as the cycle progresses. The speed of the shift varies between
≈
19
and
3
m
s
−
1
considering all the data for the observed period. This speed can be linked with the speed of meridional flows, believed to occur between convection zone and the surface of the Sun.
Evidence strongly indicates that the strength of the Sun's polar fields near the time of a sunspot cycle minimum determines the strength of the following solar activity cycle. We use our Advective ...Flux Transport code, with flows well constrained by observations, to simulate the evolution of the Sun's polar magnetic fields from early 2016 to the end of 2019—near the expected time of cycle 24/25 minimum. We run a series of simulations in which the uncertain conditions (convective motion details, active region tilt, and meridional flow profile) are varied within expected ranges. We find that the average strength of the polar fields near the end of cycle 24 will be similar to that measured near the end of cycle 23, indicating that cycle 25 will be similar in strength to the current cycle. In all cases the polar fields are asymmetric with fields in the south stronger than those in the north. This asymmetry would be more pronounced if not for the predicted weakening of the southern polar fields in late 2016 and through 2017. After just 4 years of simulation the variability across our ensemble indicates an accumulated uncertainty of about 15%. This accumulated uncertainty arises from stochastic variations in the convective motion details, the active region tilt, and changes in the meridional flow profile. These variations limit the ultimate predictability of the solar cycle.
Key Points
Cycle 25 will be similar in size to cycle 24
Cycle 25 will have a more active Southern Hemisphere
Stochastic variations in the convective flows and active region characteristics limit predictability
Abstract
The disk around HD 169142 has been suggested to host multiple embedded planets due to the range of structures observed in the dust distributions. We analyze archival Atacama Large (sub-) ...Millimetre Array observations of
12
CO (2–1),
13
CO (2–1), and C
18
O (2–1) to search for large-scale kinematic structures associated with other embedded planets in the outer disk. At 125 au, we identify a coherent flow from the disk surface to the midplane, traced by all three CO isotopologues, and interpret it as a meridional flow potentially driven by an embedded planet. We use changes in the rotation speed of the gas to characterize the physical structure across this region, finding that at 125 au the CO emission traces regions of increased gas pressure, despite being at a surface density minimum. Developing a simple analytical model, we demonstrate that the physical structure of the gap can have non-trivial responses to changes in the surface density, consistent both with previous thermo-chemical models and the conditions inferred observationally. Applying this technique to a range of sources will allow us to directly confront theoretical models of gap-opening in protoplanetary disks.
While designing the stages of a centrifugal pump, there is an important and difficult task of impeller blade design. This article deals with an approach to impeller blade design that is based on ...analytical choice of dependency of flow change along the streamline. The given approach is implemented at JSC "VNIIAEN" in form of custom software which lets the user build a line drawing based on given parameters in normal duty of intermediate stage by designing the blade and calculating the geometrical dimensions of the impeller. The given method has been tested and proven with a physics experiment.
Abstract
We analyze the simulation result shown in Hotta & Kusano (2021) in which the solar-like differential rotation is reproduced. The Sun is rotating differentially with the fast equator and the ...slow pole. It is widely thought that the thermal convection maintains the differential rotation, but recent high-resolution simulations tend to fail to reproduce the fast equator. This fact is an aspect of one of the biggest problems in solar physics called the convective conundrum. Hotta & Kusano succeed in reproducing the solar-like differential rotation without using any manipulation with an unprecedentedly high-resolution simulation. In this study, we analyze the simulation data to understand the maintenance mechanism of the fast equator. Our analyses lead to conclusions that are summarized as follows. (1) The superequipatition magnetic field is generated by the compression, which can indirectly convert the massive internal energy to magnetic energy. (2) The efficient small-scale energy transport suppresses large-scale convection energy. (3) Non-Taylor–Proudman differential rotation is maintained by the entropy gradient caused by the anisotropic latitudinal energy transport enhanced by the magnetic field. (4) The fast equator is maintained by the meridional flow mainly caused by the Maxwell stress. The Maxwell stress itself also has a role in the angular momentum transport for the fast near-surface equator (we call it the
P
unching ball
effect). The fast equator in the simulation is reproduced not due to the low Rossby number regime but due to the strong magnetic field. This study newly finds the role of the magnetic field in the maintenance of differential rotation.
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