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R Hueso - One of the best experts on this subject based on the ideXlab platform.

  • saturn atmospheric dynamics one year after cassini long lived features and time variations in the drift of the hexagon
    Icarus, 2020
    Co-Authors: R Hueso, A Sanchezlavega, J F Rojas, A A Simon, T Barry, T Del Riogaztelurrutia, A Antunano, Kunio M Sayanagi, M Delcroix, L N Fletcher
    Abstract:

    Abstract We examine Saturn’s atmospheric dynamics with observations in the visible range from ground-based telescopes and Hubble Space Telescope (HST). We present a detailed analysis of observations acquired during 2018 obtaining drift rates of major meteorological systems from the equator to the North polar hexagon. A system of polar storms that appeared in the planet in March 2018 and remained active with a complex phenomenology at least until September is analyzed elsewhere [Sanchez-Lavega et al., A complex storm system and a planetary-scale disturbance in Saturn’s north polar atmosphere in 2018, Nat. Ast., submitted, 2019]. Many of the regular Cloud features visible in 2018 are long-lived and can be identified in Saturn images in 2017, and in some cases, for up to a decade using also Cassini ISS images. Without considering the polar storms, the most interesting long-lived Cloud systems are: i) A bright white spot in the Equatorial Zone that can be tracked continuously since 2014 with minimal changes in its zonal velocity, which was 444.3±3.1 ms−1 in 2014 and 452.4±1.7 ms−1 in 2018. This velocity is remarkably different from the zonal winds at the Cloud Level at its latitude during the Cassini mission, and is closer to zonal winds obtained at the time of the Voyagers flybys and to zonal winds from Cassini VIMS infrared images of the lower atmosphere. ii) A large long-lived Anticyclone Vortex, here AV, that formed after the Great White Spot of 2010-2011. This vortex has changed significantly in visual contrast, drift rate and latitude with minor changes in size over the last years. iii) A system of subpolar vortices at latitudes 60-65°N present at least since 2011. These vortices and additional atmospheric features here studied follow drift rates consistent with zonal winds obtained by Cassini. We also present a study of the positions of the vertices of Saturn’s North polar hexagon from 2015 to 2018. These measurements are compared with previous analyses during the Cassini mission (2007-2014), observations with HST in the 90s, and data from the Voyagers in 1980-1981 to explore the long-term variability of the hexagon’s drift rate. We find variations in the drift rate of the hexagon through these epochs that can not be fit by seasonal changes in the polar area. Instead, the different drift rates reinforce the role of the North Polar Spot that was present in the Voyager epoch and in the early 90s to cause a faster drift rate of the hexagon at that time compared with the current slower one.

  • six years of venus winds at the upper Cloud Level from uv visible and near infrared observations from virtis on venus express
    Planetary and Space Science, 2015
    Co-Authors: R Hueso, J Peralta, I Garatelopez, T V Bandos, A Sanchezlavega
    Abstract:

    Abstract The Venus Express mission has provided a long-term monitoring of Venus atmosphere including the morphology and motions of its upper Clouds. Several works have focused on the dynamics of the upper Cloud visible on the day-side in ultraviolet images sensitive to the 65–70 km altitude and in the lower Cloud Level (50 km height) observable in the night-side of the planet in the 1.74 μm spectral window. Here we use VIRTIS-M spectral images in nearby wavelengths to study the upper Cloud layer in three channels: ultraviolet (360–400 nm), visible (570–680 nm) and near infrared (900–955 nm) extending in time the previous analysis of VIRTIS-M data. The ultraviolet images show relatively well contrasted Cloud features at the Cloud top. Cloud features in the visible and near infrared images lie a few kilometers below the upper Cloud top, have very low contrast and are distinct to the features observed in the ultraviolet. Wind measurements were obtained on 118 orbits covering the Southern hemisphere over a six-year period and using a semi-automatic Cloud correlation algorithm. Results for the upper Cloud from VIRTIS-M ultraviolet data confirm previous analysis based on images obtained by the Venus Monitoring Camera ( Khatuntsev et al. (2013) ). At the Cloud top the mean zonal and meridional winds vary with local time accelerating towards the local afternoon. The upper branch of the Hadley cell circulation reaches maximum velocities at 45° latitude and local times of 14–16 h. The mean zonal winds in the ultraviolet Cloud layer accelerated in the course of the 2006–2012 period at least 15 m s −1 . The near infrared and visible images show a more constant circulation without significant time variability or longitudinal variations. The meridional circulation is absent or slightly reversed in near infrared and visible images indicating that, either the Hadley-cell circulation in Venus atmosphere is shallow, or the returning branch of the meridional circulation extends to Levels below the Cloud Level sensed in near infrared images. At subpolar to polar latitudes the three wavelength ranges show similar features and motions which is a signature of small vertical wind shear and may be affected by vertical convergence of both layers. At the clod top Level observed in UV images there are signatures of a long-term acceleration of the zonal winds at afternoon hours when comparing zonal winds from the first years of Venus Express observations (2006–2008) to later dates (2009–2012) with a mean acceleration of zonal winds of 17±6 m s −1 between both time periods.

  • assessing the long term variability of venus winds at Cloud Level from virtis venus express
    Icarus, 2012
    Co-Authors: R Hueso, J Peralta, A Sanchezlavega
    Abstract:

    Abstract The Venus Express (VEX) mission has been in orbit to Venus for more than 4 years now. The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument onboard VEX observes Venus in two channels (visible and infrared) obtaining spectra and multi-wavelength images of the planet that can be used to sample the atmosphere at different altitudes. Day-side images in the ultraviolet range (380 nm) are used to study the dynamics of the upper Cloud at 66–72 km while night-side images in the near infrared (1.74 μm) map the opacity of the lower Cloud deck at 44–48 km. Here we present a long-term analysis of the global atmospheric dynamics at these Levels using a large selection of orbits from the VIRTIS-M dataset covering 860 Earth days that extends our previous work (Sanchez-Lavega, A. et al. [2008]. Geophys. Res. Lett. 35, L13204) and allows studying the variability of the global circulation at the two altitude Levels. The atmospheric superrotation is evident with equatorial to mid-latitudes westward velocities of 100 and 60 m s −1 in the upper and lower Cloud layers. These zonal velocities are almost constant in latitude from the equator to 50°S. From 50°S to 90°S the zonal winds at both Cloud layers decrease steadily to zero at the pole. Individual Cloud tracked winds have errors of 3–10 m s −1 with a mean of 5 m s −1 and the standard deviations for a given latitude of our zonal and meridional winds are 9 m s −1 . The zonal winds in the upper Cloud change with the local time in a way that can be interpreted in terms of a solar tide. The zonal winds in the lower Cloud are stable at mid-latitudes to the tropics and present variability at subpolar latitudes apparently linked to the activity of the South polar vortex. While the upper Cloud presents a net meridional motion consistent with the upper branch of a Hadley cell with peak velocity v  = 10 m s −1 at 50°S, the lower Cloud meridional motions are less organized with some Cloud features moving with intense northwards and southwards motions up to v  = ±15 m s −1 but, on average, with almost null global meridional motions at all latitudes. We also examine the long-term behavior of the winds at these two vertical layers by comparing our extended wind tracked data with results from previous missions.

  • the jovian anticyclone ba i motions and interaction with the grs from observations and non linear simulations
    Icarus, 2009
    Co-Authors: E Garciamelendo, R Hueso, A Sanchezlavega, J Legarreta, S Perezhoyos, J Gonzalez, J M Gomezforrellad
    Abstract:

    Abstract A study of the dynamics of the second largest anticyclone in Jupiter, Oval BA, and its red colour change that occurred in late 2005 is presented in a three part study. The first part, this paper, deals with its long-term kinematical and dynamical behaviour monitored since its formation in 2000 to September 2008 using ground-based observations archived at the public International Outer Planet Watch (IOPW) database. The vortex changed its zonal drift velocity from 1.8 m s −1 in the period 2000–2002 to 0.8 m s −1 in 2002–2003, and to 2.5 m s −1 since late 2003. It also migrated southwards by 1.0 ± 0.5° in latitude between 2000 and 2004, remaining afterwards at an almost fixed latitude position. During the period 2000–2007, the oval also changed its triangular-like shape to a more symmetrical one. No latitudinal change was found in the months before the development of a red annulus in its interior. The colour change took place in less than 5 months in 2005–2006 and no red colour feature was observed to have been present or entrained by BA months before the annulus development. After detailed examination of the four encounters between BA and GRS that took place during this 9 year period, we did not detect any noticeable change in its drift rate or in apparent structure associated with the encounters at Cloud Level. Also, the area of BA did not significantly change in this period. Additionally, we found that BA displays a long-term oscillation of ∼160 days in its longitude position with peak to peak amplitude of 1.2°. Numerical experiments using the global circulation model EPIC reproduce accurately the shape, connecting it to its latitude migration, and morphology of the oval and confirm that no strong interaction between BA and the GRS is possible at least in the current situation.

  • numerical models of saturn s long lived anticyclones
    Icarus, 2007
    Co-Authors: E Garciamelendo, A Sanchezlavega, R Hueso
    Abstract:

    Abstract New measurements of the dynamical properties of the long-lived Saturn's anticyclonic vortex known as “Brown Spot” (BS), discovered during the Voyager 1 and 2 flybys in 1980–1981 at latitude 43.1° N, and model simulations using the EPIC code, have allowed us to constrain the vertical wind shear and static stability in Saturn's atmosphere (vertically from pressure Levels from 10 mbar to 10 bars) at this latitude. BS dynamical parameters from Voyager images include its size as derived from Cloud albedo gradient (6100 km East–West times 4300 km North–South), mean tangential velocity ( 45 ± 11 m s −1 at 2400 km from center) and mean vorticity ( 4.0 ± 1.5 × 10 −5 s −1 ) , lifetime >1 year, drift velocity ( 5.3 ± 0.1 m s −1 ) relative to Voyager's System III rotation rate, mean meridional atmospheric wind profile at Cloud Level at its latitude and interactions with nearby vortices (pair orbiting and merging). An extensive set of numerical experiments have been performed to try to reproduce this single vortex properties and its observed mergers with smaller anticyclones by varying the vertical structure of the zonal wind and adjusting the static stability of the lower stratosphere and upper troposphere. Within the context of the EPIC model atmosphere, our simulations indicate that BS's drift velocity, longevity and merging behavior are very sensitive to these two atmospheric properties. The best results at the BS latitude occur for static stability conditions that use a Brunt–Vaisala frequency constant in the upper troposphere (from 0.5 to 10 bar) above 3.2 × 10 −3 s −1 and suggest that the wind speed slightly decays below the visible Cloud deck from ∼0.5 to 10 bar at a rate ∂ u / ∂ z ∼ 2 – 6 m s −1 per scale height. Changing the vortex latitude within the band domain introduces latitude oscillations in the vortex but not a significant meridional migration. Simulated mergers always showed orbiting movements with a typical merging time of about three days, very close to the time-span observed in the interaction of real vortices. Although these results are not unique in view of the unknowns of Saturn's deep atmosphere, they serve to constrain realistically its structure for ongoing Cassini observations.

A Sanchezlavega - One of the best experts on this subject based on the ideXlab platform.

  • saturn atmospheric dynamics one year after cassini long lived features and time variations in the drift of the hexagon
    Icarus, 2020
    Co-Authors: R Hueso, A Sanchezlavega, J F Rojas, A A Simon, T Barry, T Del Riogaztelurrutia, A Antunano, Kunio M Sayanagi, M Delcroix, L N Fletcher
    Abstract:

    Abstract We examine Saturn’s atmospheric dynamics with observations in the visible range from ground-based telescopes and Hubble Space Telescope (HST). We present a detailed analysis of observations acquired during 2018 obtaining drift rates of major meteorological systems from the equator to the North polar hexagon. A system of polar storms that appeared in the planet in March 2018 and remained active with a complex phenomenology at least until September is analyzed elsewhere [Sanchez-Lavega et al., A complex storm system and a planetary-scale disturbance in Saturn’s north polar atmosphere in 2018, Nat. Ast., submitted, 2019]. Many of the regular Cloud features visible in 2018 are long-lived and can be identified in Saturn images in 2017, and in some cases, for up to a decade using also Cassini ISS images. Without considering the polar storms, the most interesting long-lived Cloud systems are: i) A bright white spot in the Equatorial Zone that can be tracked continuously since 2014 with minimal changes in its zonal velocity, which was 444.3±3.1 ms−1 in 2014 and 452.4±1.7 ms−1 in 2018. This velocity is remarkably different from the zonal winds at the Cloud Level at its latitude during the Cassini mission, and is closer to zonal winds obtained at the time of the Voyagers flybys and to zonal winds from Cassini VIMS infrared images of the lower atmosphere. ii) A large long-lived Anticyclone Vortex, here AV, that formed after the Great White Spot of 2010-2011. This vortex has changed significantly in visual contrast, drift rate and latitude with minor changes in size over the last years. iii) A system of subpolar vortices at latitudes 60-65°N present at least since 2011. These vortices and additional atmospheric features here studied follow drift rates consistent with zonal winds obtained by Cassini. We also present a study of the positions of the vertices of Saturn’s North polar hexagon from 2015 to 2018. These measurements are compared with previous analyses during the Cassini mission (2007-2014), observations with HST in the 90s, and data from the Voyagers in 1980-1981 to explore the long-term variability of the hexagon’s drift rate. We find variations in the drift rate of the hexagon through these epochs that can not be fit by seasonal changes in the polar area. Instead, the different drift rates reinforce the role of the North Polar Spot that was present in the Voyager epoch and in the early 90s to cause a faster drift rate of the hexagon at that time compared with the current slower one.

  • six years of venus winds at the upper Cloud Level from uv visible and near infrared observations from virtis on venus express
    Planetary and Space Science, 2015
    Co-Authors: R Hueso, J Peralta, I Garatelopez, T V Bandos, A Sanchezlavega
    Abstract:

    Abstract The Venus Express mission has provided a long-term monitoring of Venus atmosphere including the morphology and motions of its upper Clouds. Several works have focused on the dynamics of the upper Cloud visible on the day-side in ultraviolet images sensitive to the 65–70 km altitude and in the lower Cloud Level (50 km height) observable in the night-side of the planet in the 1.74 μm spectral window. Here we use VIRTIS-M spectral images in nearby wavelengths to study the upper Cloud layer in three channels: ultraviolet (360–400 nm), visible (570–680 nm) and near infrared (900–955 nm) extending in time the previous analysis of VIRTIS-M data. The ultraviolet images show relatively well contrasted Cloud features at the Cloud top. Cloud features in the visible and near infrared images lie a few kilometers below the upper Cloud top, have very low contrast and are distinct to the features observed in the ultraviolet. Wind measurements were obtained on 118 orbits covering the Southern hemisphere over a six-year period and using a semi-automatic Cloud correlation algorithm. Results for the upper Cloud from VIRTIS-M ultraviolet data confirm previous analysis based on images obtained by the Venus Monitoring Camera ( Khatuntsev et al. (2013) ). At the Cloud top the mean zonal and meridional winds vary with local time accelerating towards the local afternoon. The upper branch of the Hadley cell circulation reaches maximum velocities at 45° latitude and local times of 14–16 h. The mean zonal winds in the ultraviolet Cloud layer accelerated in the course of the 2006–2012 period at least 15 m s −1 . The near infrared and visible images show a more constant circulation without significant time variability or longitudinal variations. The meridional circulation is absent or slightly reversed in near infrared and visible images indicating that, either the Hadley-cell circulation in Venus atmosphere is shallow, or the returning branch of the meridional circulation extends to Levels below the Cloud Level sensed in near infrared images. At subpolar to polar latitudes the three wavelength ranges show similar features and motions which is a signature of small vertical wind shear and may be affected by vertical convergence of both layers. At the clod top Level observed in UV images there are signatures of a long-term acceleration of the zonal winds at afternoon hours when comparing zonal winds from the first years of Venus Express observations (2006–2008) to later dates (2009–2012) with a mean acceleration of zonal winds of 17±6 m s −1 between both time periods.

  • assessing the long term variability of venus winds at Cloud Level from virtis venus express
    Icarus, 2012
    Co-Authors: R Hueso, J Peralta, A Sanchezlavega
    Abstract:

    Abstract The Venus Express (VEX) mission has been in orbit to Venus for more than 4 years now. The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument onboard VEX observes Venus in two channels (visible and infrared) obtaining spectra and multi-wavelength images of the planet that can be used to sample the atmosphere at different altitudes. Day-side images in the ultraviolet range (380 nm) are used to study the dynamics of the upper Cloud at 66–72 km while night-side images in the near infrared (1.74 μm) map the opacity of the lower Cloud deck at 44–48 km. Here we present a long-term analysis of the global atmospheric dynamics at these Levels using a large selection of orbits from the VIRTIS-M dataset covering 860 Earth days that extends our previous work (Sanchez-Lavega, A. et al. [2008]. Geophys. Res. Lett. 35, L13204) and allows studying the variability of the global circulation at the two altitude Levels. The atmospheric superrotation is evident with equatorial to mid-latitudes westward velocities of 100 and 60 m s −1 in the upper and lower Cloud layers. These zonal velocities are almost constant in latitude from the equator to 50°S. From 50°S to 90°S the zonal winds at both Cloud layers decrease steadily to zero at the pole. Individual Cloud tracked winds have errors of 3–10 m s −1 with a mean of 5 m s −1 and the standard deviations for a given latitude of our zonal and meridional winds are 9 m s −1 . The zonal winds in the upper Cloud change with the local time in a way that can be interpreted in terms of a solar tide. The zonal winds in the lower Cloud are stable at mid-latitudes to the tropics and present variability at subpolar latitudes apparently linked to the activity of the South polar vortex. While the upper Cloud presents a net meridional motion consistent with the upper branch of a Hadley cell with peak velocity v  = 10 m s −1 at 50°S, the lower Cloud meridional motions are less organized with some Cloud features moving with intense northwards and southwards motions up to v  = ±15 m s −1 but, on average, with almost null global meridional motions at all latitudes. We also examine the long-term behavior of the winds at these two vertical layers by comparing our extended wind tracked data with results from previous missions.

  • the jovian anticyclone ba i motions and interaction with the grs from observations and non linear simulations
    Icarus, 2009
    Co-Authors: E Garciamelendo, R Hueso, A Sanchezlavega, J Legarreta, S Perezhoyos, J Gonzalez, J M Gomezforrellad
    Abstract:

    Abstract A study of the dynamics of the second largest anticyclone in Jupiter, Oval BA, and its red colour change that occurred in late 2005 is presented in a three part study. The first part, this paper, deals with its long-term kinematical and dynamical behaviour monitored since its formation in 2000 to September 2008 using ground-based observations archived at the public International Outer Planet Watch (IOPW) database. The vortex changed its zonal drift velocity from 1.8 m s −1 in the period 2000–2002 to 0.8 m s −1 in 2002–2003, and to 2.5 m s −1 since late 2003. It also migrated southwards by 1.0 ± 0.5° in latitude between 2000 and 2004, remaining afterwards at an almost fixed latitude position. During the period 2000–2007, the oval also changed its triangular-like shape to a more symmetrical one. No latitudinal change was found in the months before the development of a red annulus in its interior. The colour change took place in less than 5 months in 2005–2006 and no red colour feature was observed to have been present or entrained by BA months before the annulus development. After detailed examination of the four encounters between BA and GRS that took place during this 9 year period, we did not detect any noticeable change in its drift rate or in apparent structure associated with the encounters at Cloud Level. Also, the area of BA did not significantly change in this period. Additionally, we found that BA displays a long-term oscillation of ∼160 days in its longitude position with peak to peak amplitude of 1.2°. Numerical experiments using the global circulation model EPIC reproduce accurately the shape, connecting it to its latitude migration, and morphology of the oval and confirm that no strong interaction between BA and the GRS is possible at least in the current situation.

  • numerical models of saturn s long lived anticyclones
    Icarus, 2007
    Co-Authors: E Garciamelendo, A Sanchezlavega, R Hueso
    Abstract:

    Abstract New measurements of the dynamical properties of the long-lived Saturn's anticyclonic vortex known as “Brown Spot” (BS), discovered during the Voyager 1 and 2 flybys in 1980–1981 at latitude 43.1° N, and model simulations using the EPIC code, have allowed us to constrain the vertical wind shear and static stability in Saturn's atmosphere (vertically from pressure Levels from 10 mbar to 10 bars) at this latitude. BS dynamical parameters from Voyager images include its size as derived from Cloud albedo gradient (6100 km East–West times 4300 km North–South), mean tangential velocity ( 45 ± 11 m s −1 at 2400 km from center) and mean vorticity ( 4.0 ± 1.5 × 10 −5 s −1 ) , lifetime >1 year, drift velocity ( 5.3 ± 0.1 m s −1 ) relative to Voyager's System III rotation rate, mean meridional atmospheric wind profile at Cloud Level at its latitude and interactions with nearby vortices (pair orbiting and merging). An extensive set of numerical experiments have been performed to try to reproduce this single vortex properties and its observed mergers with smaller anticyclones by varying the vertical structure of the zonal wind and adjusting the static stability of the lower stratosphere and upper troposphere. Within the context of the EPIC model atmosphere, our simulations indicate that BS's drift velocity, longevity and merging behavior are very sensitive to these two atmospheric properties. The best results at the BS latitude occur for static stability conditions that use a Brunt–Vaisala frequency constant in the upper troposphere (from 0.5 to 10 bar) above 3.2 × 10 −3 s −1 and suggest that the wind speed slightly decays below the visible Cloud deck from ∼0.5 to 10 bar at a rate ∂ u / ∂ z ∼ 2 – 6 m s −1 per scale height. Changing the vortex latitude within the band domain introduces latitude oscillations in the vortex but not a significant meridional migration. Simulated mergers always showed orbiting movements with a typical merging time of about three days, very close to the time-span observed in the interaction of real vortices. Although these results are not unique in view of the unknowns of Saturn's deep atmosphere, they serve to constrain realistically its structure for ongoing Cassini observations.

Adam P Showman - One of the best experts on this subject based on the ideXlab platform.

  • how well do we understand the belt zone circulation of giant planet atmospheres
    Space Science Reviews, 2020
    Co-Authors: Leigh N Fletcher, T Guillot, Yohai Kaspi, Adam P Showman
    Abstract:

    The atmospheres of the four giant planets of our Solar System share a common and well-observed characteristic: they each display patterns of planetary banding, with regions of different temperatures, composition, aerosol properties and dynamics separated by strong meridional and vertical gradients in the zonal (i.e., east-west) winds. Remote sensing observations, from both visiting spacecraft and Earth-based astronomical facilities, have revealed the significant variation in environmental conditions from one band to the next. On Jupiter, the reflective white bands of low temperatures, elevated aerosol opacities, and enhancements of quasi-conserved chemical tracers are referred to as ‘zones.’ Conversely, the darker bands of warmer temperatures, depleted aerosols, and reductions of chemical tracers are known as ‘belts.’ On Saturn, we define cyclonic belts and anticyclonic zones via their temperature and wind characteristics, although their relation to Saturn’s albedo is not as clear as on Jupiter. On distant Uranus and Neptune, the exact relationships between the banded albedo contrasts and the environmental properties is a topic of active study. This review is an attempt to reconcile the observed properties of belts and zones with (i) the meridional overturning inferred from the convergence of eddy angular momentum into the eastward zonal jets at the Cloud Level on Jupiter and Saturn and the prevalence of moist convective activity in belts; and (ii) the opposing meridional motions inferred from the upper tropospheric temperature structure, which implies decay and dissipation of the zonal jets with altitude above the Clouds. These two scenarios suggest meridional circulations in opposing directions, the former suggesting upwelling in belts, the latter suggesting upwelling in zones. Numerical simulations successfully reproduce the former, whereas there is a wealth of observational evidence in support of the latter. This presents an unresolved paradox for our current understanding of the banded structure of giant planet atmospheres, that could be addressed via a multi-tiered vertical structure of “stacked circulation cells,” with a natural transition from zonal jet pumping to dissipation as we move from the convectively-unstable mid-troposphere into the stably-stratified upper troposphere.

  • how well do we understand the belt zone circulation of giant planet atmospheres
    arXiv: Earth and Planetary Astrophysics, 2019
    Co-Authors: Leigh N Fletcher, T Guillot, Yohai Kaspi, Adam P Showman
    Abstract:

    The atmospheres of the four giant planets of our Solar System share a common and well-observed characteristic: they each display patterns of planetary banding, with regions of different temperatures, composition, aerosol properties and dynamics separated by strong meridional and vertical gradients in the zonal (i.e., east-west) winds. On Jupiter, the reflective white bands of low temperatures, elevated aerosol opacities, and enhancements of quasi-conserved chemical tracers are referred to as 'zones.' Conversely, the darker bands of warmer temperatures, depleted aerosols, and reductions of chemical tracers are known as `belts.' On Saturn, we define cyclonic belts and anticyclonic zones via their temperature and wind characteristics, although their relation to Saturn's albedo is not as clear as on Jupiter. On distant Uranus and Neptune, the exact relationships between the banded albedo contrasts and the environmental properties is a topic of active study. This review is an attempt to reconcile the observed properties of belts and zones with (i) the meridional overturning inferred from the convergence of eddy angular momentum into the eastward zonal jets at the Cloud Level on Jupiter and Saturn and the prevalence of moist convective activity in belts; and (ii) the opposing meridional motions inferred from the upper tropospheric temperature structure, which implies decay and dissipation of the zonal jets with altitude above the Clouds. These two scenarios suggest meridional circulations in opposing directions, the former suggesting upwelling in belts, the latter suggesting upwelling in zones. This presents an unresolved paradox for our current understanding of the banded structure of giant planet atmospheres, that could be addressed via a multi-tiered vertical structure of 'stacked circulation cells.' [Abridged]

  • atmospheric confinement of jet streams on uranus and neptune
    DPS, 2013
    Co-Authors: Yohai Kaspi, W B Hubbard, Adam P Showman, Oded Aharonson, Ravit Helled
    Abstract:

    The observed Cloud-Level atmospheric circulation on the outer planets of the Solar System is dominated by strong east–west jet streams. The depth of these winds is a crucial unknown in constraining their overall dynamics, energetics and internal structures. There are two approaches to explaining the existence of these strong winds. The first suggests that the jets are driven by shallow atmospheric processes near the surface, whereas the second suggests that the atmospheric dynamics extend deeply into the planetary interiors. Here we report that on Uranus and Neptune the depth of the atmospheric dynamics can be revealed by the planets’ respective gravity fields. We show that the measured fourth-order gravity harmonic, J_4, constrains the dynamics to the outermost 0.15 per cent of the total mass of Uranus and the outermost 0.2 per cent of the total mass of Neptune. This provides a stronger limit to the depth of the dynamical atmosphere than previously suggested, and shows that the dynamics are confined to a thin weather layer no more than about 1,000 kilometres deep on both planets.

  • gravitational signature of jupiter s internal dynamics
    Geophysical Research Letters, 2010
    Co-Authors: Yohai Kaspi, W B Hubbard, Adam P Showman, Glenn R Flierl
    Abstract:

    Telescopic observations and space missions to Jupiter have provided vast information about Jupiter's Cloud Level winds, but the depth to which these winds penetrate has remained an ongoing mystery. Scheduled to be launched in 2011, the Jupiter orbiter Juno will make high-resolution observations of Jupiter's gravity field. In this paper we show that these measurements are sensitive to the depth of the internal winds. We use dynamical models ranging from an idealized thermal wind balance analysis, using the observed Cloud-top winds, to a full general circulation model (GCM). We relate the depth of the dynamics to the external gravity spectrum for different internal wind structure scenarios. In particular, we predict that substantial Jovian winds below a depth of 500 km would lead to detectable (milligal-Level) gravity anomalies with respect to the expected gravity for a planet in solid body rotation.

  • jovian atmospheric dynamics an update after galileo and cassini
    Reports on Progress in Physics, 2005
    Co-Authors: A R Vasavada, Adam P Showman
    Abstract:

    The Galileo and Cassini spacecrafts have greatly enhanced the observational record of Jupiter's tropospheric dynamics, particularly through returning high spatial resolution, multi-spectral and global imaging data with episodic coverage over periods of months to years. These data, along with those from Earth-based telescopes, have revealed the stability of Jupiter's zonal jets, captured the evolution of vortices and equatorial waves, and mapped the distributions of lightning and moist convection. Because no observations of Jupiter's interior exist, a forward modelling approach has been used to relate observations at Cloud Level to models of shallow or deep jet structure, shallow or deep jet forcing and energy transfer between turbulence, vortices and jets. A range of observed phenomena can be reproduced in shallow models, though the Galileo probe winds and jet stability arguments hint at the presence of deep jets. Many deep models, however, fail to reproduce Jupiter-like non-zonal features (e.g. vortices). Jupiter's dynamics likely include both deep and shallow processes, requiring an integrated approach to future modelling—an important goal for the post-Galileo and Cassini era.

Yohai Kaspi - One of the best experts on this subject based on the ideXlab platform.

  • how well do we understand the belt zone circulation of giant planet atmospheres
    Space Science Reviews, 2020
    Co-Authors: Leigh N Fletcher, T Guillot, Yohai Kaspi, Adam P Showman
    Abstract:

    The atmospheres of the four giant planets of our Solar System share a common and well-observed characteristic: they each display patterns of planetary banding, with regions of different temperatures, composition, aerosol properties and dynamics separated by strong meridional and vertical gradients in the zonal (i.e., east-west) winds. Remote sensing observations, from both visiting spacecraft and Earth-based astronomical facilities, have revealed the significant variation in environmental conditions from one band to the next. On Jupiter, the reflective white bands of low temperatures, elevated aerosol opacities, and enhancements of quasi-conserved chemical tracers are referred to as ‘zones.’ Conversely, the darker bands of warmer temperatures, depleted aerosols, and reductions of chemical tracers are known as ‘belts.’ On Saturn, we define cyclonic belts and anticyclonic zones via their temperature and wind characteristics, although their relation to Saturn’s albedo is not as clear as on Jupiter. On distant Uranus and Neptune, the exact relationships between the banded albedo contrasts and the environmental properties is a topic of active study. This review is an attempt to reconcile the observed properties of belts and zones with (i) the meridional overturning inferred from the convergence of eddy angular momentum into the eastward zonal jets at the Cloud Level on Jupiter and Saturn and the prevalence of moist convective activity in belts; and (ii) the opposing meridional motions inferred from the upper tropospheric temperature structure, which implies decay and dissipation of the zonal jets with altitude above the Clouds. These two scenarios suggest meridional circulations in opposing directions, the former suggesting upwelling in belts, the latter suggesting upwelling in zones. Numerical simulations successfully reproduce the former, whereas there is a wealth of observational evidence in support of the latter. This presents an unresolved paradox for our current understanding of the banded structure of giant planet atmospheres, that could be addressed via a multi-tiered vertical structure of “stacked circulation cells,” with a natural transition from zonal jet pumping to dissipation as we move from the convectively-unstable mid-troposphere into the stably-stratified upper troposphere.

  • how well do we understand the belt zone circulation of giant planet atmospheres
    arXiv: Earth and Planetary Astrophysics, 2019
    Co-Authors: Leigh N Fletcher, T Guillot, Yohai Kaspi, Adam P Showman
    Abstract:

    The atmospheres of the four giant planets of our Solar System share a common and well-observed characteristic: they each display patterns of planetary banding, with regions of different temperatures, composition, aerosol properties and dynamics separated by strong meridional and vertical gradients in the zonal (i.e., east-west) winds. On Jupiter, the reflective white bands of low temperatures, elevated aerosol opacities, and enhancements of quasi-conserved chemical tracers are referred to as 'zones.' Conversely, the darker bands of warmer temperatures, depleted aerosols, and reductions of chemical tracers are known as `belts.' On Saturn, we define cyclonic belts and anticyclonic zones via their temperature and wind characteristics, although their relation to Saturn's albedo is not as clear as on Jupiter. On distant Uranus and Neptune, the exact relationships between the banded albedo contrasts and the environmental properties is a topic of active study. This review is an attempt to reconcile the observed properties of belts and zones with (i) the meridional overturning inferred from the convergence of eddy angular momentum into the eastward zonal jets at the Cloud Level on Jupiter and Saturn and the prevalence of moist convective activity in belts; and (ii) the opposing meridional motions inferred from the upper tropospheric temperature structure, which implies decay and dissipation of the zonal jets with altitude above the Clouds. These two scenarios suggest meridional circulations in opposing directions, the former suggesting upwelling in belts, the latter suggesting upwelling in zones. This presents an unresolved paradox for our current understanding of the banded structure of giant planet atmospheres, that could be addressed via a multi-tiered vertical structure of 'stacked circulation cells.' [Abridged]

  • jupiter s atmospheric jet streams extend thousands of kilometres deep
    Nature, 2018
    Co-Authors: Yohai Kaspi, T Guillot, Sj Bolton, Eli Galanti, W B Hubbard, D J Stevenson, L Iess, Jeremy Bloxham, J E P Connerney, Hao Cao
    Abstract:

    The depth to which Jupiter’s observed east–west jet streams extend has been a long-standing question. Resolving this puzzle has been a primary goal for the Juno spacecraft, which has been in orbit around the gas giant since July 2016. Juno’s gravitational measurements have revealed that Jupiter’s gravitational field is north–south asymmetric, which is a signature of the planet’s atmospheric and interior flows. Here we report that the measured odd gravitational harmonics J_3, J_5, J_7 and J_9 indicate that the observed jet streams, as they appear at the Cloud Level, extend down to depths of thousands of kilometres beneath the Cloud Level, probably to the region of magnetic dissipation at a depth of about 3,000  kilometres. By inverting the measured gravity values into a wind field, we calculate the most likely vertical profile of the deep atmospheric and interior flow, and the latitudinal dependence of its depth. Furthermore, the even gravity harmonics J_8 and J_(10) resulting from this flow profile also match the measurements, when taking into account the contribution of the interior structure. These results indicate that the mass of the dynamical atmosphere is about one per cent of Jupiter’s total mass.

  • a full self consistent treatment of thermal wind balance on oblate fluid planets
    Journal of Fluid Mechanics, 2017
    Co-Authors: Eli Galanti, Yohai Kaspi, Eli Tziperman
    Abstract:

    The nature of the flow below the Cloud Level on Jupiter and Saturn is still unknown. Relating the flow on these planets to perturbations in their density field is key to the analysis of the gravity measurements expected from both the Juno (Jupiter) and Cassini (Saturn) spacecrafts during 2016-17. Both missions will provide latitude-dependent gravity fields, which in principle could be inverted to calculate the vertical structure of the observed Cloud-Level zonal flow on these planets. Theories to date connecting the gravity field and the flow structure have been limited to potential theories under a barotropic assumption, or estimates based on thermal wind balance that allow analyzing baroclinic wind structures, but have made simplifying assumptions. Those include the effects of the deviations from spherical symmetry, the centrifugal force due to density perturbations, and self-gravitational effects of the density perturbations. Recent studies attempted to include some effects but not in a self-consistent manner. The present study introduces such a self-consistent perturbation approach to the thermal wind balance that incorporates all physical effects, and applies it to several example wind structures, both barotropic and baroclinic. The contribution of each term is analyzed, and the results are compared in the barotropic limit to those of potential theory. It is found that the dominant balance involves the original simplified thermal wind approach. This balance produces a good order-of-magnitude estimate of the gravitational moments, and is able, therefore, to address the order one question of how deep the flows are given measurements of gravitational moments. The additional terms are significantly smaller and none of these terms is dominant, so any approximation attempting to improve over the simplified thermal wind approach needs to include all other terms.

  • atmospheric confinement of jet streams on uranus and neptune
    DPS, 2013
    Co-Authors: Yohai Kaspi, W B Hubbard, Adam P Showman, Oded Aharonson, Ravit Helled
    Abstract:

    The observed Cloud-Level atmospheric circulation on the outer planets of the Solar System is dominated by strong east–west jet streams. The depth of these winds is a crucial unknown in constraining their overall dynamics, energetics and internal structures. There are two approaches to explaining the existence of these strong winds. The first suggests that the jets are driven by shallow atmospheric processes near the surface, whereas the second suggests that the atmospheric dynamics extend deeply into the planetary interiors. Here we report that on Uranus and Neptune the depth of the atmospheric dynamics can be revealed by the planets’ respective gravity fields. We show that the measured fourth-order gravity harmonic, J_4, constrains the dynamics to the outermost 0.15 per cent of the total mass of Uranus and the outermost 0.2 per cent of the total mass of Neptune. This provides a stronger limit to the depth of the dynamical atmosphere than previously suggested, and shows that the dynamics are confined to a thin weather layer no more than about 1,000 kilometres deep on both planets.

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  • gravitational tides in the outer planets i implications of classical tidal theory ii interior calculations and estimation of the tidal dissipation factor
    The Astrophysical Journal, 1993
    Co-Authors: Petros J Ioannou, Richard S Lindze
    Abstract:

    Classical tidal theory is applied to the gravitational excitation of the atmospheres of the gaseous planets. The only departure made from classical theory is the retention of the effects of nonhdrostaticity which are important in the deeper atmosphere or wherever one expects extremely small static stability. The meridional structure of the tidal response is shown to depend only on the ratio of the period of gravitational forcing to the period of rotation of the planet. Forcing by the low-inclination orbits of the satellites of Jupiter, Saturn, and Uranus excites primarily symmetric Hough modes. Consideration of the vertical structure equation shows that altho4gh the gravitational tidal forcing is proportional to the first symmetric spherical harmonic with zonal wavenumber 2, the tidal response will be concentrated in higher order meridional structures confined equatorward of 50° N on Jupiter, 76° N on Saturn, and 45° N on Uranus. The meridional structure of these modes resembles the visible banding on these planets. The excitation of the tides depends on the distribution of static stability in the interior. Estimates are made showing that observation of the tidal response of the planets at the visible Cloud Level may be within reach of current observational capability. Detection of this signal is shown to provide information about the thermodynamic structure of the interior. A primary purpose of the present paper, in addition to the above, is the presentation of computational results concerning the eigenvalues and eigenfunctions relevant to gravitational tides in the outer planets. Subject headings: planets and satellites: general

  • gravitational tides in the outer planets ii interior calculations and estimation of the tidal dissipation factor
    The Astrophysical Journal, 1993
    Co-Authors: Petros J Ioannou, Richard S Lindze
    Abstract:

    The theory of excitation of tidal oscillations in a fluid planetary body is formulated, and separable equa­ tions are derived that extend the results of the classical theory of tides to the nonhydrostatic interiors of planets. The theory is applied to the example of the gravitational tidal response of Jupiter to forcing by lo. The tidal response is found to crucially depend on the static stability in the interior of the planet, the response of the planet being as much as two to three orders of magnitude greater than the response with a neutral interior. The tidal dissipation factor Q is calculated for Jupiter and found to agree with the values required by the astronomical arguments only if the interior has finite (though small static stability. We are led to the conclusion that the interior of Jupiter must have regions which are stably stratified. Subject headings: planets and satellites: individual (Jupiter) Jupiter has a rotational period of 9.92 hr and a radius approximately 10 times greater than Earth's and 10 times smaller than the Sun's. The main constituents of the plant, hydrogen (90% by mass) and helium (10%), do not solidify, and because of the low density the mass of the planet is only 318 times greater than Earth's. The planet is primarily made up of a highly compressed but relatively cold liquid, with an inte­ rior core at probably 0.1 of the planetary radius. The visible atmospheric envelope is approximately at a pressure of 1 bar and a temperature of 150 K, while the pressure at the core is approximately 40 Mbar at a temperature of nearly 20,000 K (Stevenson 1978). Observations on the thermal emission revealed the existence of an interior heat source which accounts for around 35°/o of the 14 W m- 2 emitted to space. While much progress has been made in our understanding of the general structure of the planet (cf. Stevenson 1978), most of the meteorologically relevant information is limited to the region above the visible Clouds of the planet. The data for the meteorology of the planet is still scant, making the theories for the observed Cloud Level circulations speculative (Ingersoll