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1.
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2.
We have measured the internal velocity field in jovian synoptic-scale cyclones and anticyclones by tracking cloud elements in very high spatial resolution images obtained by the Voyager 1 and 2 (in 1979) and Galileo (1996-2000) spacecrafts. In total we have studied 24 different closed vortices (6 cyclones, 18 anticyclones) spanning a latitude range from ∼60° N to 60° S and with East-West sizes larger than ∼2000 km. The tangential component of the velocity as a function of the distance to the vortex center and position angle is used to retrieve the vorticity field. We find that the velocity increases in all the vortices from a nearly quiescent center to a maximum at the vortex periphery, with a record of about 180 m s−1 for the GRS. The vorticity of cyclones and anticyclones increases in general toward their periphery with absolute values in the range from ∼2-14×10−5 s−1. There is a marked tendency to increase the vortices vorticity with their latitude location. However the vorticity does not depend on the vortex size, circulation sense, or ambient background meridional wind shear. The vortex Rossby number ranges from ∼0.2 to 0.5. A study of the interaction between the Great Red Spot with other vortices show that the GRS does not change its vorticity upon their absorption. The two White Ovals mergers showed contradictory results, with greater vorticity in the case of BE, but lower vorticity in the case of BA, although data are poorer for this last case. We present the case of a short lived but large coherent cyclone at −59° that was embedded in a weakly anticyclone wind shear domain. We show that jovian vortices do not follow the simple Kida vortex relationship between vorticity and aspect ratio as it has been previously suggested.  相似文献   

3.
《Icarus》2003,166(1):63-74
Observations of the merger of Jupiter's White Ovals BE and FA show altitude-dependent behavior that we seek to capture in numerical simulations. In particular, it was observed that the upper portions of the vortices orbited each other before merging, but the lower portions translated into each other without orbiting, a phenomenon we term the pair-orbit vertical dichotomy. To reproduce this dichotomy in the EPIC model, it is sufficient to have (i) a decrease with altitude of the background zonal winds above the cloud level with a scale height of ∼2.4, (ii) a height scale of the winds inside the vortices that is the same or larger, and (iii) a maximum tangential velocity in each vortex of ∼100 m s−1 or larger. Condition (i) is expected from thermal-wind analyses, (ii) is consistent with thermal-wind and Shoemaker-Levy 9 debris-trajectory analyses, and (iii) is consistent with cloud-top wind tracking. The model generally does not reproduce the dichotomy for vortices with smaller vertical extent or weaker circulations. Our simulated mergers correctly reproduce the observed ∼9° separation at which vortices start to orbit in the upper layers before they merge and the ∼70% area ratio of the final vortex BA to the sum of BE and FA.  相似文献   

4.
The dynamics of mergers of large circulations in Jupiter's atmosphere may permit different models of the atmosphere to be tested. We report well-resolved observations of such events at visible wavelengths: three anticyclonic and three cyclonic events. A merger of anticyclonic white ovals in the South South Temperate domain (2002 March) is compared with the previously reported merger of ovals BE and FA in the South Temperate domain (2000 March). In each case, the two similar-sized ovals converged rapidly once they were separated by less than the sum of their diameters; they orbited around each other anticyclonically during the merger; the merged oval initially had the same rapid drift as the western parent; and, in an unexpected similarity, a cyclonic oval emerged westward from the point of merger. Evidence suggests that a merger of smaller ovals in the North North Temperate domain (2002 February) had similar dynamics. In contrast, mergers of cyclonic ovals in the North Equatorial Belt (‘barges’: 2001 November, 2005 May) proceeded in a different manner. The two parent barges showed no consistent acceleration towards each other as they converged; on contact there was no obvious sign of mutual circulation, and the low-albedo regions had almost passed each other before they finally merged; and the resulting barge had a drift rate intermediate between the two parents, and a length that was greater than either parent. Again, a third such event involving a smaller barge (2002 December) showed many of the same characteristics. These observations define different dynamical behaviour during anticyclonic and cyclonic mergers.  相似文献   

5.
We present observations and theoretical calculations to derive the vertical structure of and secondary circulation in jovian vortices, a necessary piece of information to ultimately explain the red color in the annular ring inside Jupiter’s Oval BA. The observations were taken with the near-infrared detector NIRC2 coupled to the adaptive optics system on the 10-m W.M. Keck telescope (UT 21 July 2006; UT 11 May 2008) and with the Hubble Space Telescope at visible wavelengths (UT 24 and 25 April 2006 using ACS; UT 9 and 10 May 2008 using WFPC2). The spatial resolution in the near-IR (∼0.1–0.15″ at 1–5 μm) is comparable to that obtained at UV–visible wavelengths (∼0.05–0.1″ at 250–890 nm). At 5 μm we are sensitive to Jupiter’s thermal emission, whereas at shorter wavelengths we view the planet in reflected sunlight. These datasets are complementary, as images at 0.25–1.8 μm provide information on the clouds/hazes in the troposphere–stratosphere, while the 5-μm emission maps yield information on deeper layers in the atmosphere, in regions without clouds. At the latter wavelength numerous tiny ovals can be discerned at latitudes between ∼45°S and 60°S, which show up as rings with diameters ?1000 km surrounding small ovals visible in HST data. Several white ovals at 41°S, as well as a new red oval that was discovered to the west of the GRS, also reveal 5-μm bright rings around their peripheries, which coincide with dark/blue rings at visible wavelengths. Typical brightness temperatures in these 5-μm bright rings are 225–250 K, indicative of regions that are cloud-free down to at least the ∼4 bar level, and perhaps down to 5–7 bar, i.e., well within the water cloud.Radiative transfer modeling of the 1–2 μm observations indicates that all ovals, i.e., including the Great Red Spot (GRS), Red Oval BA, and the white ovals at 41°S, are overall very similar in vertical structure. The main distinction between the ovals is caused by variations in the particle densities in the tropospheric–stratospheric hazes (2–650 mbar). These are 5–8 times higher above the red ovals than above the white ones at 41°S. The combination of the 5-μm rings and the vertical structure derived from near-IR data suggests anticyclones to extend vertically from (at least) the water cloud (∼5 bar) up to the tropopause (∼100–200 mbar), and in some cases into the stratosphere.Based upon our observations, we propose that air is rising along the center of a vortex, and descending around the outer periphery, producing the 5-μm bright rings. Observationally, we constrain the maximum radius of these rings to be less than twice the local Rossby deformation radius, LR. If the radius of the visible oval (i.e., the clouds that make the oval visible) is >3000 km, our observations suggest that the descending part of the secondary circulation must be within these ovals. For the Red Oval BA, we postulate that the return flow is at the location of its red annulus, which has a radius of ∼3000 km.We develop a theory for the secondary circulation, where air is (baroclinically) rising along the center of a vortex in a subadiabatic atmosphere, and descending at a distance not exceeding ∼2× the local Rossby deformation radius. Using this model, we find a timescale for mixing throughout the vortex of order several months, which suggests that the chromophores that are responsible for the red color of Oval BA’s red annulus must be produced locally, at the location of the annulus. This production most likely results from the adiabatic heating in the descending part of the secondary circulation. Such higher-than-ambient temperature causes NH3–ice to sublime, which will expose the condensation nuclei, such as the red chromophores.  相似文献   

6.
This work presents a six-year study aimed at characterizing the morphology and properties of the atmospheric features present in jovian cyclonic regions. It complements our previous analysis for the same period on the anticyclonic vortices (Morales-Juberias et al. 2002, Icarus 157, 76-90). The main difference between cyclonic and anticyclonic regions in Jupiter is that a variety of organized morphologies are present in the cyclonic areas, although they can be grouped consistently into five different types: filamentary turbulence related to the highest speed jets, organized folded filamentary regions, elongated areas with contours closed by a ribbon-like feature, discrete, closed brown cyclones (“barges”), and peculiar transient structures such as short wave trains and cyclonic cells. We present data on their color contrast, size, aspect ratio, distribution, lifetimes, relation to the jet system and to the anticyclones, and motions (global and internal to the features). Most cyclonic features show a rapid evolution, compared to the anticyclones, and tend to be dispersed zonally although some survive for a few years. We used the barges that are the most representative, long-lived, and extended type of cyclonic features to show that there exists a linear relationship between their relative velocity and the mean zonal flow speed, similar to that found in our previous work on the anticyclones. There is also some evidence that the drift rate of barges is related to the planetary minus flow vorticity gradient.  相似文献   

7.
Jon Legarreta 《Icarus》2008,196(1):184-201
Numerical simulations of jovian vortices at tropical and temperate latitudes, under different atmospheric conditions, have been performed using the EPIC code [Dowling, T.E., Fisher, A.S., Gierasch, P.J., Harrington, J., LeBeau, R.P., Santori, C.M., 1998. Icarus 132, 221-238] to simulate the high-resolution observations of motions and of the lifetimes presented in a previous work [Legarreta, J., Sánchez-Lavega, A., 2005. Icarus 174, 178-191] and infer the vertical structure of Jupiter's troposphere. We first find that in order to reproduce the longevity and drift rate of the vortices, the Brunt-Väisälä frequency of the atmosphere in the upper troposphere (pressures P∼1 to 7 bar) should have a lower limit value of 5×10−3 s−1, increasing upward up to 1.25×10−2 s−1 at pressures P∼0.5 bar (latitudes between 15° and 45° in both hemispheres). Second, the vortices drift also depend on the vertical structure of the zonal wind speed in the same range of altitudes. Simulations of the slowly drifting Southern hemisphere vortices (GRS, White Ovals and anticyclones at 40° S) require a vertically-constant zonal-wind with depth, but Northern hemisphere vortices (cyclonic “barges” and anticyclones at 19, 41 and 45° N) require decreasing winds at a rate of ∼5 m s−1 per scale height. However vortices drifting at a high speed, close to or in the peak of East or West jets and in both hemispheres, require the wind speed slightly increasing with depth, as is the case for the anticyclones at 20° S and at 34° N. We deduce that the maximum absolute vertical shear of the zonal wind from P∼1 bar up to P∼7 bar in these jets is ∼15 m s−1 per scale height. Intense vortices with tangential velocity at their periphery ∼100 m s−1 tend to decay asymptotically to velocities ∼40 to 60 m s−1 with a characteristic time that depends on the vortex intensity and static stability of the atmosphere. The vortices adjust their tangential velocity to the averaged peak to peak velocity of the opposed eastward and westward jets at their boundary. We show through our simulations that large-scale and long-lived vortices whose maximum tangential velocity is ∼100 m s−1 can survive by absorbing smaller intense vortices.  相似文献   

8.
The formation of pancake cyclones and anticyclones in the E-region of the Earth's ionosphere is considered. It is shown that the vortices can be maintained by the neutral winds or by chemical reactions including the energy release caused by the triple collisions of atomic oxygen with neutrals. It is found that the variations of the magnetic fields induced by the vortices are not localized and decrease slowly far from the vortex core. They can be easily detected by ground based magnetometers or by facilities on board the low-orbiting satellites.  相似文献   

9.
We combine high-resolution observations of the dynamical behavior of small vortices (diameters ?5000 km) located at latitude 60°N on Jupiter with forward modeling, using the EPIC atmospheric model, to address two open questions: the dependence of the zonal winds with depth, and the strength of vortices that are too small to apply cloud tracking to their internal structure. The observed drift rates of the vortices can only be reproduced in the model when the zonal winds increase slightly with depth below the cloud tops, with a vertical shear that is less than was measured at 7°N at the southern rim of a 5-μm hotspot by the Galileo Probe Doppler Wind Experiment (DWE). This supports the idea that Jupiter's vertical shear may vary significantly with latitude. Our simulations suggest that the morphology of the mergers between vortices mainly depends on their maximum tangential velocities, the best results occurring when the tangential velocity is close to the velocity difference of the alternating jets constraining the zone in which the vortices are embedded. We use this correlation, together with the high-resolution data available for the White Ovals, to derive an empirical relationship between the maximum tangential velocity of a jovian vortex and its size, normalized by the strength and size of the encompassing shear zone. The Great Red Spot stands out as a significant anomaly to this relationship, but interestingly it is becoming less so with time.  相似文献   

10.
Seismology is the best tool for investigating the interior structure of stars and giant planets. This paper deals with a photometric study of jovian global oscillations. The propagation of acoustic waves in the jovian troposphere is revisited in order to estimate their effects on the planetary albedo. According to the standard model of the jovian cloud structure there are three major ice cloud layers (e.g., [Atreya et al., 1999. A comparison of the atmospheres of Jupiter and Saturn: Deep atmospheric composition, cloud structure, vertical mixing, and origin. Planet Space Sci. 47, 1243-1262]). We consider only the highest layers, composed of ammonia ice, in the region where acoustic waves are trapped in Jupiter's atmosphere. For a vertical wave propagating in a plane parallel atmosphere with an ammonia ice cloud layer, we calculate first the relative variations of the reflected solar flux due to the smooth oscillations at about the ppm level. We then determine the phase transitions induced by the seismic waves in the clouds. These phase changes, linked to ice particle growth, are limited by kinetics. A Mie model [Mishchenko et al., 2002. Scattering, Absorption, and Emission of Light by Small Particles. Cambridge Univ. Press, Cambridge, pp. 158-190] coupled with a simple radiation transfer model allows us to estimate that the albedo fluctuations of the cloud perturbed by a seismic wave reach relative variations of 70 ppm for a 3-mHz wave. This albedo fluctuation is amplified by a factor of ∼70 relative to the previously published estimates that exclude the effect of the wave on cloud properties. Our computed amplifications imply that jovian oscillations can be detected with very precise photometry, as proposed by the microsatellite JOVIS project, which is dedicated to photometric seismology [Mosser et al., 2004. JOVIS: A microsatellite dedicated to the seismic analysis of Jupiter. In: Combes, F., Barret, D., Contini, T., Meynadier, F., Pagani, L. (Eds.), SF2A-2004, Semaine de l'Astrophysique Francaise, Les Ulis. In: EdP-Sciences Conference Series, pp. 257-258].  相似文献   

11.
Jupiter's eastward jet at 24° N, which formerly had the fastest winds on the planet, has maintained a less extreme speed of ∼135 m/s since 1991, carrying a series of long-lived vortices at 125 m/s. In 2002-2003, as the albedo of the adjacent North Temperate Belt increased, the tracks of the vortices accelerated slightly, and they had disappeared by 2005. In 2005, small tracers had a mean speed of 146.4 (±0.9) m/s, significantly faster than the previous mean speed of the jet, suggesting that the jet peak itself has accelerated at cloud-top level, and that the jet is beginning to return to the super-fast state. These changes may resemble the even greater transformations occurring in the equatorial jet of Saturn.  相似文献   

12.
Kuiper (1972) had suggested that the Great Red Spot (GRS) of Jupiter is a giant hurricane. We present further arguments in support of this idea and propose that it may also apply to the smaller vortices such as the white and brown ovals (barges). Our estimates indicate that the spin-down time-constants for these Jovian vortices are significantly shorter than the observed lifetimes. Thus, the motions must be sustained through the continued release of internal energy. In analogy with the CISK mechanism for the terrestrial hurricane, transport of water vapor, which is observed on Jupiter, may provide the latent energy to fuel the motions. The energy the planet emits must be transported upwards; therefore its troposphere should be convectively unstable. In such an atmosphere, the proposed solar driven meridional circulation is multicellular, of the Ferrel-Thomson type. If the energy transport from the planetary interior is accelerated by the upward motions in the circulation, eastward zonal jets develop such as observed in the equatorial region. But if the upward flow of energy is impeded by the prevailing downward motions in the meridional circulation (which occur, for example, near 20 latitude), we propose that the convective instability is amplified. The conditions then are more favorable for the development of hurricanes which may appear in the form of the GRS and the white and brown ovals. The GRS with its large size and long life time (indicating that it is very deep) is unique, and we suggest that it may have been induced by meteor impact.  相似文献   

13.
Observations made by the Imaging Science Subsystem (ISS), Visible and Infrared Mapping Spectrometer (VIMS) and the long-wavelength Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft reveal that the large, long-lived cyclonic vortex at Saturn's south pole has a 4200-km-diameter cloud-free nearly circular region. This region has a 4 K warm core extending from the troposphere into the stratosphere, concentric cloud walls extending 20-70 km above the internal clouds, and numerous external clouds whose anticyclonic vorticity suggests a convective origin. The rotation speeds of the vortex reach . The Saturn polar vortex has features in common with terrestrial hurricanes and with the Venus polar vortex. Neptune and other giant planets may also have strong polar vortices.  相似文献   

14.
E. Tikhomolov 《Solar physics》1995,156(2):205-219
A numerical simulation of the process of generation of the magnetic field by Rossby vortices, whose horizontal scale is comparable to the solar radius, has been carried out. Long-lived vortices form global magnetic structures that drift together with vortices. Differential rotation in latitude leads to a longer lifetime of cyclones and corresponding magnetic structures. The cyclone and the magnetic structure travel in longitude with the velocity close to a corresponding differential rotation velocity and drift slowly poleward. The interaction of cyclones located in close latitudes makes one of them move to higher latitudes and the poloidal component of the magnetic field to intensify during the interaction.The formation of large-scale vortices was simulated, when the initial condition was specified by a grid of small-scale vortices with a random amplitude distribution. Merging of vortices of the same sign leads to the formation of large-scale vortices whose size is determined by the geometry of the problem and by the differential rotation profile.  相似文献   

15.
We use the fully coupled, three-dimensional, global circulation Jovian Ionospheric Model (JIM) to calculate the coupling between ions in the jovian auroral ovals and the co-existing neutral atmosphere. The model shows that ions subject to drift motion around the auroral oval, as a result of the E×B coupling between a meridional, equatorward electric field and the jovian magnetic field, generate neutral winds in the planetary frame of reference. Unconstrained by the magnetic field, these neutral winds have a greater latitudinal extent than the corresponding ion drifts. Values of the coupling coefficient, k(h), are presented as a function of altitude and cross-auroral electric field strength, for different incoming electron fluxes and energies. The results show that, with ion velocities of several hundred metres per second to over 1 km s−1, k(h) can attain values greater than 0.5 at the ion production peak. This parameter is key to calculating the effective conductivities required to model magnetosphere-ionosphere coupling correctly. The extent to which angular momentum (and therefore energy) is transported vertically in JIM is much more limited than earlier, one-dimensional, studies have predicted.  相似文献   

16.
Using a three-dimensional, time-dependent, global model, we have simulated the response of the thermosphere to an isolated substorm. The substorm is characterized by a time variance of the high latitude convective electric field with an associated enhancement of auroral E region electron density, from an initially quiet thermosphere. We have simulated such an impulsive energy input with both separated and co-incident geographic and geomagnetic poles and have found that, in both cases, in the lower thermosphere ( ～ 120 km), a long-lived vortex phenomenon is generated. Initially, two contra-rotating vortices are generated by the effects of ion drag during the period of enhanced high latitude energy input centred on the polar cap/auroral oval boundary, one at dusk (18.00 L.T.) and the other at dawn (06.00 L.T.). After the end of the substorm, the cyclonic vortex (dawn) dissipates rapidly while the dusk anti-cyclonic vortex appears virtually self-sustaining and survives many hours after the substorm input has ceased. A theory is derived to explain and interpret the results and it appears that the effect is analogous to a meteorological weather system. In this case, however, the dusk anti-cyclonic vortex has, instead of pressure, the centrifugal acceleration balancing the Coriolis force. The equivalent anti-clockwise dawn vortex, unlike a low pressure system, has no balancing force, since Coriolis and the centrifugal term assist and this vortex rapidly disappears.  相似文献   

17.
The influence of the effect of entrainment of superconducting protons by superfluid neutrons on the distribution of neutron vortices in a rotating neutron star is investigated. It is shown that the proton vortex clusters generated by entrainment currents create the magnetic structure of a neutron vortex. The average magnetic field induction in a neutron vortex is calculated. The presence of the magnetic field of a neutron vortex considerably alters the radius of the vortex zone. The width of the vortex-free zone at the surface of the neutron star’s core increases, reaching macroscopic values on the order of several meters. This result considerably changes earlier concepts of the distribution of neutron vortices in a neutron star. Translated from Astrofizika, Vol. 43, No. 3, pp. 377-386, July–September, 2000.  相似文献   

18.
Physical characteristics of naturally formed convective vortices in the Phoenix Mars lander environment have been investigated on a relatively hot summer Martian arctic day. For this, the NCAR LES has been adapted and developed to conduct three micro-scale simulations of the Martian Convective Boundary Layer (CBL), in situations with and without geostrophic wind, and atmospheric radiative flux divergence. Time series analysis of the vortices’ properties is discussed. The study confirms the decrease of vortex populations in windy conditions and also illustrates that intense but small vortices are expected to be observed in higher geostrophic wind situations. This may lead to more dust migration rather than dust devil formation on windy days. The background (geostrophic) wind causes the vortices to become less cyclostrophically balanced.  相似文献   

19.
We show that the crust–core interface in neutron stars acts as a potential barrier to the peripheral neutron vortices approaching the interface in the model in which these are coupled to the proton vortex clusters. This elementary barrier arises because of the interaction of vortex magnetic flux with the Meissner currents set up by the crustal magnetic field at the interface. The dominant part of the force is derived from the cluster–interface interaction. As a result of the stopping of the continuous neutron vortex current through the interface, angular momentum is stored in the superfluid layers in the vicinity of the crust–core interface during the interglitch period. Discontinuous annihilation of proton vortices at the boundary restores the neutron vortex current and spins up the observable crust on short time-scales, leading to a glitch in the spin characteristics of a pulsar.  相似文献   

20.
The nonstationary dynamics of vortices in conventional type II superconductors and in neutron stars is examined in the Newtonian approximation. A relaxation equation is obtained for vortices approaching an equilibrium distribution after a change in an external magnetic field. The relaxation times are estimated for vortices in low-temperature superconductors and for proton vortices in the superconducting core of a neutron star. It is shown that the proton vortex system created by entrainment currents is rigidly coupled to the neutron vortices. Translated from Astrofizika, Vol. 52, No. 2, pp. 291–300 (May 2009).  相似文献   

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