Publications

The first orbits around Jupiter of the Juno spacecraft in 2016 revealed a symmetric structure of multiple cyclones that remained stable over the next five years. Trajectories of individual cyclones indicated a consistent westward circumpolar motion around both poles. In this paper, we propose an explanation for this tendency using the concept of beta-drift and a "center-of-mass" approach. We suggest that the motion of these cyclones as a group can be represented by an equivalent sole cyclone, which is continuously pushed by beta-drift poleward and westward, embodying the westward motion of the individual cyclones. We support our hypothesis with 2D model simulations and observational evidence, demonstrating this mechanism for the westward drift. This study joins consistently with previous studies that revealed how aspects of these cyclones result from vorticity-gradient forces, shedding light on the physical nature of Jupiter's polar cyclones.

The North Pacific storm-track activity is suppressed substantially under the excessively strong westerlies to form a distinct minimum in midwinter, which seems inconsistent with linear baroclinic instability theory. This “midwinter minimum” of the storm-track activity has been intensively investigated for decades as a test case for storm-track dynamics. However, the mechanisms controlling it are yet to be fully unveiled and are still under debate. Here we investigate the detailed seasonal evolution of the climatological density of surface migratory anticyclones over the North Pacific, in comparison with its counterpart for cyclones, based on a Lagrangian tracking algorithm. We demonstrate that the frequency of surface cyclones over the North Pacific maximizes in midwinter, whereas that of anticyclones exhibits a distinct midwinter minimum under the upstream influence, especially from the Japan Sea region. In midwinter, it is only on such a rare occasion that prominent weakening of the East Asian winter monsoon allows a migratory surface anticyclone to form over the Japan Sea, despite the unfavorable climatological-mean conditions due to persistent monsoonal cold-air outbreaks and the excessively strong upper-tropospheric westerlies. The midwinter minimum of the North Pacific anticyclone density suggests that anticyclones are likely the key to understanding the midwinter minimum of the North Pacific storm-track activity as measured by Eulerian eddy statistics.

Context . The Juno mission has provided measurements of Jupiter’s gravity field with an outstanding level of accuracy, leading to better constraints on the interior of the planet. Improving our knowledge of the internal structure of Jupiter is key to understanding its formation and evolution but is also important in the framework of exoplanet exploration. Aims . In this study, we investigated the differences between the state-of-the-art equations of state and their impact on the properties of interior models. Accounting for uncertainty on the hydrogen and helium equation of state, we assessed the span of the interior features of Jupiter. Methods . We carried out an extensive exploration of the parameter space and studied a wide range of interior models using Markov chain Monte Carlo simulations. To consider the uncertainty on the equation of state, we allowed for modifications of the equation of state in our calculations. Results . Our models harbour a dilute core and indicate that Jupiter’s internal entropy is higher than what is usually assumed from the Galileo probe measurements. We obtain solutions with extended dilute cores, but contrary to other recent interior models of Jupiter, we also obtain models with small dilute cores. The dilute cores in such solutions extend to ~20% of Jupiter’s mass, leading to better agreement with formation–evolution models. Conclusions . We conclude that the equations of state used in Jupiter models have a crucial effect on the inferred structure and composition. Further explorations of the behaviour of hydrogen–helium mixtures at the pressure and temperature conditions in Jupiter will help to constrain the interior of the planet, and therefore its origin.

Several different factors influence the seasonal cycle of a planet. This study uses a general circulation model and an energy balance model (EBM) to assess the parameters that govern the seasonal cycle. We define two metrics to describe the seasonal cycle, ϕs, the latitudinal shift of the maximum temperature, and ΔT, the maximum seasonal temperature variation amplitude. We show that alongside the expected dependence on the obliquity and orbital period, where seasonality generally strengthens with an increase in these parameters, the seasonality depends in a nontrivial way on the rotation rate. While the seasonal amplitude decreases as the rotation rate slows down, the latitudinal shift, ϕs, shifts poleward. A similar result occurs in a diffusive EBM with increasing diffusivity. These results suggest that the influence of the rotation rate on the seasonal cycle stems from the effect of the rotation rate on the atmospheric heat transport.

Clouds are primary modulators of Earth's energy balance. It is thus important to understand the links connecting variabilities in cloudiness to variabilities in other state variables of the climate system, and also describe how these links would change in a changing climate. A conceptual model of global cloudiness can help elucidate these points. In this work we derive simple representations of cloudiness, that can be useful in creating a theory of global cloudiness. These representations illustrate how both spatial and temporal variability of cloudiness can be expressed in terms of basic state variables. Specifically, cloud albedo is captured by a nonlinear combination of pressure velocity and a measure of the low-level stability, and cloud longwave effect is captured by surface temperature, pressure velocity, and standard deviation of pressure velocity. We conclude with a short discussion on the usefulness of this work in the context of global warming response studies.

The Juno spacecraft measured Jupiter's gravity field and determined the even and odd zonal harmonics, Jn, with unprecedented precision. However, interpreting these observations has been a challenge because it is difficult to reconcile the unexpectedly small magnitudes of the moments J4 and J6 with conventional interior models that assume a large, distinct core of rock and ice. Here we show that the entire set of gravity harmonics can be matched with models that assume an ab initio equation of state, wind profiles, and a dilute core of heavy elements that are distributed as far out as 63% of the planet's radius. In the core region, heavy elements are predicted to be distributed uniformly and make up only 18% by mass because of dilution with hydrogen and helium. Our models are consistent with the existence of primary and secondary dynamo layers that will help explain the complexity of the observed magnetic field.

Polar vortices are common planetary-scale flows that encircle the pole in the middle or high latitudes and are observed in most of the solar system's planetary atmospheres. The polar vortices on Earth, Mars, and Titan are dynamically related to the mean meridional circulation and exhibit a significant seasonal cycle. However, the polar vortex's characteristics vary between the three planets. To understand the mechanisms that influence the polar vortex's dynamics and dependence on planetary parameters, we use an idealized general circulation model with a seasonal cycle in which we vary the obliquity, rotation rate, and orbital period. We find that there are distinct regimes for the polar vortex seasonal cycle across the parameter space. Some regimes have similarities to the observed polar vortices, including a weakening of the polar vortex during midwinter at slow rotation rates, similar to Titan's polar vortex. Other regimes found within the parameter space have no counterpart in the solar system. In addition, we show that for a significant fraction of the parameter space, the vortex's potential vorticity latitudinal structure is annular, similar to the observed structure of the polar vortices on Mars and Titan. We also find a suppression of storm activity during midwinter that resembles the suppression observed on Mars and Earth, which occurs in simulations where the jet velocity is particularly strong. This wide variety of polar vortex dynamical regimes that shares similarities with observed polar vortices, suggests that among exoplanets there can be a wide variability of polar vortices.

The large-scale Hadley circulation is a key element in the global heat and moisture transport. It is traditionally defined as the zonally averaged meridional circulation in the tropics, but was shown to have a strong longitudinal dependence, as seen in a decomposition of the three-dimensional atmospheric flow into spatially dependent meridional and zonal circulations. Recent studies provided a useful analysis of the regional strengthening/weakening of the decomposed circulation but not its patterns. Here, we study the interannual variability of the longitudinally dependent meridional circulation (LMC), with a focus on its spatial patterns. We use hierarchical clustering to objectively determine the four main modes of the LMC interannual variability, and apply a Lagrangian air parcel tracking method to reveal the full circulation patterns. While El Niño and La Niña are found, as in previous studies, to play a role in setting these patterns, we find the patterns are not uniquely characterized by standard El Niño-Southern Oscillation (ENSO) indices (Nino3.4 or Southern Oscillation Index). Instead, ENSO flavors (i.e., East Pacific vs. Central Pacific) have different effects on the LMC. The most prominent interannual variability of the LMC is an east-west shift. Latitudinal shifts, as well as contraction/expansion in both latitude and longitude are also identified. Multiple linear regression analysis shows that while a large fraction of the LMC variance is explained by Sea Surface Temperature, the Madden-Julian Oscillation makes a nonnegligible independent contribution. The clustering patterns are also used to study the remote precipitation and surface air temperature teleconnections.

Juno microwave radiometer (MWR) observations of Jupiter's midlatitudes reveal a strong correlation between brightness temperature contrasts and zonal winds, confirming that the banded structure extends throughout the troposphere. However, the microwave brightness gradient is observed to change sign with depth: the belts are microwave-bright in the p10 bar range. The transition level (which we call the "jovicline") is evident in the MWR 11.5 cm channel, which samples the 5-14 bar range when using the limb-darkening at all emission angles. The transition is located between 4 and 10 bars, and implies that belts change with depth from being NH3-depleted to NH3-enriched, or from physically warm to physically cool, or more likely a combination of both. The change in character occurs near the statically stable layer associated with water condensation. The implications of the transition are discussed in terms of ammonia redistribution via meridional circulation cells with opposing flows above and below the water condensation layer, and in terms of the "mushball" precipitation model, which predicts steeper vertical ammonia gradients in the belts versus the zones. We show via the moist thermal wind equation that both the temperature and ammonia interpretations can lead to vertical shear on the zonal winds, but the shear is similar to 50x weaker if only NH3 gradients are considered. Conversely, if MWR observations are associated with kinetic temperature gradients then it would produce zonal winds that increase in strength down to the "jovicline", consistent with Galileo probe measurements; then decay slowly at higher pressures.

The Juno mission observed that both poles of Jupiter have polar cyclones that are surrounded by a ring of circumpolar cyclones (CPCs). The north pole holds eight CPCs and the south pole possesses five, with both circumpolar rings positioned along latitude ~84° N/S. Here we explain the location, stability and number of the Jovian CPCs by establishing the primary forces that act on them, which develop because of vorticity gradients in the background of a cyclone. In the meridional direction, the background vorticity varies owing to the planetary sphericity and the presence of the polar cyclone. In the zonal direction, the vorticity varies by the presence of adjacent cyclones in the ring. Our analysis successfully predicts the latitude and number of circumpolar cyclones for both poles, according to the size and spin of the respective polar cyclone. Moreover, the analysis successfully predicts that Jupiter can hold circumpolar cyclones, whereas Saturn currently cannot. The match between the theory and observations implies that vortices in the polar regions of the giant planets are largely governed by barotropic dynamics, and that the movement of other vortices at high latitudes is also driven by interaction with the background vorticity.

The observed zonal winds at Jupiter's cloud tops have been shown to be closely linked to the asymmetric part of the planet's measured gravity field. Here we examine to what extent, and at which latitudes, must the flows at depth resemble those at the cloud level in order to match the gravity signal. We show, using both the symmetric and asymmetric parts of the measured gravity field, that the observed cloud‐level wind profile between 25°S and 25°N must extend unaltered to depths of thousands of kilometers. Poleward, the midlatitude deep jets also contribute to the gravity signal, but might differ somewhat from the cloud‐level winds. We analyze the likelihood of this difference and give bounds to its strength. We also find that to match the gravity measurements, the winds must project inward in the direction parallel to Jupiter's spin axis, and decay inward in the radial direction.

The midlatitude storm tracks are of the most prominent features of extratropical climate. Despite the theoretical expectation, based on baroclinic instability theory, that baroclinic eddies strengthen with jet intensification, there is evidence that this relation breaks when the jet is particularly strong. The most known case is the Pacific midwinter minimum in storm track activity. To isolate the effect of jet strength on storm activity, we conduct a series of GCM experiments systematically varying jet intensity. The simulations are analyzed using Lagrangian tracking to understand the response from a single-eddy perspective. The Lagrangian analysis shows that while the response of upper-level eddies is dominated by a reduction in the amount of tracked features, the lower-level eddies’ response is also affected by a reduction in their lifetime. Analyzing the jet strength effect on the pairing between the upper- and lower-level eddies, we find that the jet intensification increases the relative speed of the upper-level eddies, breaking the baroclinic wave structure and limiting its growth. We show that the Lagrangian response correlates with a shift in the midlatitude spectrum to low wavenumbers. The shift settles these results with linear baroclinic instability theory, as under the stronger jet conditions synoptic-scale eddies are predicted to have a sub-optimal growth rate. These results can potentially explain the midwinter suppression of storm activity over the Pacific and the difference from the Atlantic response.

Interior modeling of Jupiter and Saturn has advanced to a state where thousands of models are generated that cover the uncertainty space of many parameters. This approach demands a fast method of computing their gravity field and shape. Moreover, the Cassini mission at Saturn and the ongoing Juno mission delivered gravitational harmonics up to J12. Here we report the expansion of the theory of figures, which is a fast method for gravity field and shape computation, to the seventh order (ToF7), which allows for computation of up to J14. We apply three different codes to compare the accuracy using polytropic models. We apply ToF7 to Jupiter and Saturn interior models in conjunction with CMS-19 H/He equation of state. For Jupiter, we find that J6 is best matched by a transition from an He-depleted to He-enriched envelope at 2–2.5 Mbar. However, the atmospheric metallicity reaches 1 × solar only if the adiabat is perturbed toward lower densities, or if the surface temperature is enhanced by ∼14 K from the Galileo value. Our Saturn models imply a largely homogeneous-in-Z envelope at 1.5–4 × solar atop a small core. Perturbing the adiabat yields metallicity profiles with extended, heavy-element-enriched deep interior (diffuse core) out to 0.4 RSat, as for Jupiter. Classical models with compact, dilute, or no core are possible as long as the deep interior is enriched in heavy elements. Including a thermal wind fitted to the observed wind speeds, representative Jupiter and Saturn models are consistent with all observed Jn values.

Uranus and Neptune are the archetypes of “ice giants”, a class of planets that may be among the most common in the Galaxy. They are the last unexplored planets of the Solar System, yet they hold the keys to understand the atmospheric dynamics and structure of planets with hydrogen atmospheres inside and outside the solar system.

During the past few years, both the Cassini mission at Saturn and the Juno mission at Jupiter provided measurements with unprecedented accuracy of the gravity and magnetic fields of the two gas giants. Using the gravity measurements, it was found that the strong zonal flows observed at the cloud level of the gas giants are likely to extend thousands of kilometres deep into the planetary interior. However, the gravity measurements alone, which are by definition an integrative measure of mass, cannot constrain with high certainty the exact vertical structure of the flow. Taking into account the recent Cassini magnetic field measurements of Saturn, and past secular variations of Jupiter's magnetic field, we obtain an additional physical constraint on the vertical decay profile of the observed zonal flows on these planets. Our combined gravity-magnetic analysis reveals that the cloud-level winds on Saturn (Jupiter) extend with very little decay, i.e. barotropically, down to a depth of around 7000 km (2000 km) and then decay rapidly in the semiconducting region, so that within the next 1000 km (600 km) their value reduces to about 1 per cent of that at the cloud level. These results indicate that there is no significant mechanism acting to decay the flow in the outer neutral region, and that the interaction with the magnetic field in the semiconducting region might play a central role in the decay of the flows.

The Ferrel cell consists of the zonal mean vertical and meridional winds in the midlatitudes. The continuity of the Ferrel circulation and the zonal mean momentum and heat budgets imply a collocation of the eddy-driven jet and poleward eddy heat flux maxima, under certain assumptions, including the negligibility of diabatic heating. The latter assumption is questioned, since midlatitude storms are associated with latent heating in the midtroposphere. In this study, the heat budget of the Ferrel cell in both hemispheres is examined, using the JRA55 reanalysis data set. The diabatic heating rate is significant close to the center of the Ferrel cell during winter and at the ascending branch during summer in both hemispheres. The interannual variability shows a positive correlation between the diabatic heating rate in the midlatitude midtroposphere and the latitudinal separation between the eddy heat flux and the eddy-driven jet maxima during winter in both hemispheres.

The Hadley circulation is a key element of the climate system. It is traditionally defined as the zonally averaged meridional circulation in the tropics, therefore treated as a zonally symmetric phenomenon. However, differences in temperature between land and sea cause zonal asymmetries on Earth, dramatically affecting the circulation. This longitudinal dependence of the meridional circulation evokes questions about where and when the actual large-scale tropical circulation occurs. Here, we look into the connection between the longitudinally dependent meridional circulation, and the actual large-scale transport of air in the tropics using a coupled Eulerian and Lagrangian approach. Decomposing the velocity field into rotational and divergent components, we identify how each component affects the actual circulation. We propose an alternative definition for the circulation, which describes the actual path of air parcels in the tropics, as a tropical atmospheric conveyor belt.

The asymmetric gravity field measured by the Juno spacecraft has allowed the estimation of the depth of Jupiter's zonal jets, showing that the winds extend approximately 3,000 km beneath the cloud level. This estimate was based on an analysis using a combination of all measured odd gravity harmonics, J
3, J
5, J
7, and J
9, but the wind profile's dependence on each of them separately has yet to be investigated. Furthermore, these calculations assumed the meridional profile of the cloud-level wind extends to depth. However, it is possible that the interior jet profile varies somewhat from that of the cloud level. Here we analyze in detail the possible meridional and vertical structure of Jupiter's deep jet streams that can match the gravity measurements. We find that each odd gravity harmonic constrains the flow at a different depth, with J
3 the most dominant at depths below 3,000 km, J
5 the most restrictive overall, whereas J
9 does not add any constraint on the flow if the other odd harmonics are considered. Interior flow profiles constructed from perturbations to the cloud-level winds allow a more extensive range of vertical wind profiles, yet when the meridional profiles differ substantially from the cloud level, the ability to match the gravity data significantly diminishes. Overall, we find that while interior wind profiles that do not resemble the cloud level are possible, they are statistically unlikely. Finally, inspired by the Juno microwave radiometer measurements, assuming the brightness temperature is dominated by the ammonia abundance, we find that depth-dependent flow profiles are still compatible with the gravity measurements.

Superrotation is a dynamical regime where the atmosphere circulates around the planet in the direction of planetary rotation with excess angular momentum in the equatorial region. Superrotation is known to exist in the atmospheres of Venus, Titan, Jupiter, and Saturn in the solar system. Some of the exoplanets also exhibit superrotation. Our understanding of superrotation in a framework of circulation regimes of the atmospheres of terrestrial planets is in progress thanks to the development of numerical models; a global instability involving planetary-scale waves seems to play a key role, and the dynamical state depends on the Rossby number, a measure of the relative importance of the inertial and Coriolis forces, and the thermal inertia of the atmosphere. Recent general circulation models of Venus's and Titan's atmospheres demonstrated the importance of horizontal waves in the angular momentum transport in these atmospheres and also an additional contribution of thermal tides in Venus's atmosphere. The atmospheres of Jupiter and Saturn also exhibit strong superrotation. Recent gravity data suggests that these superrotational flows extend deep into the planet, yet currently no single mechanism has been identified as driving this superrotation. Moreover, atmospheric circulation models of tidally locked, strongly irradiated exoplanets have long predicted the existence of equatorial superrotation in their atmospheres, which has been attributed to the result of the strong day-night thermal forcing. As predicted, recent Doppler observations and infrared phase curves of hot Jupiters appear to confirm the presence of superrotation on these objects.

We evaluate a method for determining the depth of Jupiter's Great Red Spot (GRS) with two Jima overflights dedicated to gravity science. The small-scale, localized nature of the anticyclone requires a detection method where the gravity perturbations are regional. To this end, we model the GRS as a dipole of flat disk mass concentrations (mascons), separated along the radial direction of Jupiter. Thermal wind theory predicts such structure composed of two equal and opposite masses below the visible cloud tops, condition that is used to constrain our estimation algorithm. Furthermore, Juno radiometer observations of the GRS brightness temperature indicate the presence of anomalies of opposite sign at different depths. We present the results of both a covariance and recovery analyses of the simulated data, in terms of accuracy in the estimation of the GRS mass and depth of winds. The analyses are carried out using precise Doppler tracking of the Juno spacecraft and by posing constraints on the interior model of the vortex from theory. We find that, if the surface dynamics extend at least several hundred kilometers below the cloud tops, it is possible to resolve the mass concentrations using both gravity passes, and tie the mass to the vortex's depth through thermal wind.

How deep do Saturn's zonal winds penetrate below the cloud level has been a decades-long question, with important implications not only for the atmospheric dynamics but also for the interior density structure, composition, magnetic field, and core mass. The Cassini Grand Finale gravity experiment enables answering this question for the first time, with the premise that the planet's gravity harmonics are affected not only by the rigid body density structure but also by its flow field. Using a wide range of rigid body interior models and an adjoint based optimization for the flow field using thermal wind balance, we calculate the flow structure below the cloud level and its depth. We find that with a wind profile, largely consistent with the observed winds, when extended to a depth of around 8,800 km, all the gravity harmonics measured by Cassini are explained. This solution is in agreement with considerations of angular momentum conservation and is consistent with magnetohydrodynamics constraints.Plain Language Summary Observations show strong east-west flows at the cloud level of Saturn. These winds are strongest at the equatorial regions, reaching up to 400 m/s, about 4 times stronger than tornado strength winds on Earth. Yet until now we had no knowledge on how deep these winds penetrate into the interior of the gas giant. The gravity experiment executed during the Grand Finale stage (May-August 2017) of the NASA Cassini mission helps answering this question. It is well established that any large-scale motion of the fluid would have a signature in the density distribution and therefore in the planet gravity field. If we can estimate the internal structure and shape of the planet, we might be able to decipher the depth of the winds from its signal in the gravity measurements. Moreover, the rigid-body and flow contribution to gravity field are entangled together, therefore it is necessary to use a wide range of rigid-body models in order to define the wind-induced gravity signal. In this work we propose a solution to the problem. We find that the gravity measurements can be explained with a flow pattern, similar to that observed at the cloud level, penetrating to depths of more than 8,000 km into the planet interior. This has important implications not only for the atmospheric dynamics but also for the interior density structure, composition, magnetic field, and core mass.

The interior structure of Saturn, the depth of its winds, and the mass and age of its rings constrain its formation and evolution. In the final phase of the Cassini mission, the spacecraft dived between the planet and its innermost ring, at altitudes of 2600 to 3900 kilometers above the cloud tops. During six of these crossings, a radio link with Earth was monitored to determine the gravitational field of the planet and the mass of its rings. We find that Saturn’s gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 kilometers. The total mass of the rings is (1.54 ± 0.49) × 10
19 kilograms (0.41 ± 0.13 times that of the moon Mimas), indicating that the rings may have formed 10
7 to 10
8 years ago.

One of Jupiter's most prominent atmospheric features, the Great Red Spot (GRS), has been observed for more than two centuries, yet little is known about its structure and dynamics below its observed cloud level. While its anticyclonic vortex appearance suggests it might be a shallow weather-layer feature, the very long time span for which it was observed implies it is likely deeply rooted, otherwise it would have been sheared apart by Jupiter's turbulent atmosphere. Determining the GRS depth will shed light not only on the processes governing the GRS, but on the dynamics of Jupiter's atmosphere as a whole. The Juno mission single flyby over the GRS (PJ7) discovered using microwave radiometer measurements that the GRS is at least a couple hundred kilometers deep. The next flybys over the GRS (PJ18 and PJ21), will allow high-precision gravity measurements that can be used to estimate how deep the GRS winds penetrate below the cloud level. Here we propose a novel method to determine the depth of the GRS based on the new gravity measurements and a Slepian function approach that enables an effective representation of the wind-induced spatially confined gravity signal, and an efficient determination of the GRS depth given the limited measurements. We show that with this method the gravity signal of the GRS should be detectable for wind depths deeper than 300 km, with reasonable uncertainties that depend on depth (e.g., +/- 100 km for a GRS depth of 1000 km).

Dynamical processes in the atmosphere and ocean are central to determining the large-scale drivers of regional climate change, yet their predictive understanding is poor. Here, we identify three frontline challenges in climate dynamics where significant progress can be made to inform adaptation: response of storms, blocks and jet streams to external forcing; basin-to-basin and tropical-extratropical teleconnections; and the development of non-linear predictive theory. We highlight opportunities and techniques for making immediate progress in these areas, which critically involve the development of high-resolution coupled model simulations, partial coupling or pacemaker experiments, as well as the development and use of dynamical metrics and exploitation of hierarchies of models.

The gravity harmonics of a fluid, rotating planet can be decomposed into static components arising from solid-body rotation and dynamic components arising from flows. In the absence of internal dynamics, the gravity field is axially and hemispherically symmetric and is dominated by even zonal gravity harmonics J 2n that are approximately proportional to q n, where q is the ratio between centrifugal acceleration and gravity at the planet's equator. Any asymmetry in the gravity field is attributed to differential rotation and deep atmospheric flows. The odd harmonics, J 3, J 5, J 7, J 9 and higher, are a measure of the depth of the winds in the different zones of the atmosphere. Here we report measurements of Jupiter's gravity harmonics (both even and odd) through precise Doppler tracking of the Juno spacecraft in its polar orbit around Jupiter. We find a north-south asymmetry, which is a signature of atmospheric and interior flows. Analysis of the harmonics, described in two accompanying papers, provides the vertical profile of the winds and precise constraints for the depth of Jupiter's dynamical atmosphere.

This study relates the occurrence of the midwinter minimum in eddy activity over the North Pacific with the seasonality in jet characteristics. During winter, the Pacific jet core is typically around latitude 32°N and has features of a merged subtropical eddy-driven jet. On the other hand, during transition seasons, the jet is at higher latitudes (≈40°N) and resembles more an eddy-driven jet. We find that these differences in jet characteristics play a role in the occurrence of the midwinter minimum. It is found that a midwinter minimum-like behavior in eddy activity, as observed, is obtained in idealized simulations where zonally symmetric temperature profiles are adjusted to mimic the seasonality of longitudinally averaged temperature observed across the North Pacific. Furthermore, we find in both reanalysis data and the idealized simulations that a poleward shift of the January jet leads to an increase in eddy kinetic energy.

Over the past decade, the Cassini spacecraft has provided an unprecedented observational record of the atmosphere of Saturn, which in many ways now surpasses Jupiter as the best-observed giant planet. These observations, along with data from the Voyager spacecraft and Earth-based telescopes, demonstrate that Saturn, like Jupiter, has an atmospheric circulation dominated by zonal (east-west) jet streams, including a broad, fast eastward equatorial jet and numerous weaker jets at higher latitudes. Imaging from Voyager, Cassini and ground-based telescopes also document a wide range of tropospheric features, including vortices, waves, turbulence and moist convective storms. At large scales, the clouds, ammonia gas and other chemical tracers exhibit a zonally banded pattern whose relationships to the zonal jets remain poorly understood. Infrared observations constrain the stratospheric thermal structure and allow the derivation of stratospheric temperatures; these exhibit not only the expected seasonal changes, but also a wealth of variations that are likely dynamical in origin and highlight dynamical coupling between the stratosphere and the underlying troposphere. In parallel to these observational developments, significant advances in theory and modeling have occurred over the past decade, especially regarding the dynamics of zonal jets, and we survey these new developments in the context of both Jupiter and Saturn. Highly idealized two-dimensional models illuminate the dynamics that give rise to zonal jets in rapidly rotating atmospheres stirred by convection or other processes, while more realistic three-dimensional models of the atmosphere and interior are starting to identify the particular conditions under which Jupiter- and Saturn-like flows – including the fast equatorial superrotation, multiple jets at higher latitudes, storms and vortices – can occur. Future data analysis and models have the potential to greatly increase our understanding over the next decade.

Deciphering the flow below the cloud-level of Jupiter remains a critical milestone in understanding Jupiter's internal structure and dynamics. The expected high-precision Juno measurements of both the gravity field and the magnetic field might help to reach this goal. Here we propose a method that combines both fields to constrain the depth-dependent flow field inside Jupiter. This method is based on a mean-field electrodynamic balance that relates the flow field to the anomalous magnetic field, and geostrophic balance that relates the flow field to the anomalous gravity field. We find that the flow field has two distinct regions of influence: an upper region in which the flow affects mostly the gravity field and a lower region in which the flow affects mostly the magnetic field. An optimization procedure allows to reach a unified flow structure that is consistent with both the gravity and the magnetic fields.

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 2016-2018. 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 baroclinic wind structures to be analysed, but have made simplifying assumptions that neglected several physical effects. These 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 of these neglected terms, but lacked an overall approach that is able to include all effects 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 analysed, and the results are compared in the barotropic limit with 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 yet can affect the gravitational moments to some degree. However, none of these terms is dominant so any approximation attempting to improve over the simplified thermal wind approach needs to include all other terms.

The many recently discovered terrestrial exoplanets are expected to hold a wide range of atmospheric masses. Here the dynamic-thermodynamic effects of atmospheric mass on atmospheric circulation are studied using an idealized global circulation model by systematically varying the atmospheric surface pressure. On an Earth analog planet, an increase in atmospheric mass weakens the Hadley circulation and decreases its latitudinal extent. These changes are found to be related to the reduction of the convective fluxes and net radiative cooling (due to the higher atmospheric heat capacity), which, respectively, cool the upper troposphere at mid-low latitudes and warm the troposphere at high latitudes. These together decrease the meridional temperature gradient, tropopause height and static stability. The reduction of these parameters, which play a key role in affecting the flow properties of the tropical circulation, weakens and contracts the Hadley circulation. The reduction of the meridional temperature gradient also decreases the extraction of mean potential energy to the eddy fields and the mean kinetic energy, which weakens the extratropical circulation. The decrease of the eddy kinetic energy decreases the Rhines wavelength, which is found to follow the meridional jet scale. The contraction of the jet scale in the extratropics results in multiple jets and meridional circulation cells as the atmospheric mass increases.

The close-by orbits of the ongoing Juno mission allow measuring with unprecedented accuracy Jupiter's low-degree even gravity moments J(2), J(4), J(6), and J(8). These can be used to better determine Jupiter's internal density profile and constrain its core mass. Yet the largest unknown on these gravity moments comes from the effect of differential rotation, which gives a degree of freedom unaccounted for by internal structure models. Here considering a wide range of possible internal flow structures and dynamical considerations, we provide upper bounds to the effect of dynamics (differential rotation) on the low-degree gravity moments. In light of the recent Juno gravity measurements and their small uncertainties, this allows differentiating between the various models suggested for Jupiter's internal structure.

Comprehensive models of climate change projections have shown that the latitudinal band of extratropical storms will likely shift poleward under global warming. Here we study this poleward shift from a Lagrangian storm perspective, through simulations with an idealized general circulation model. By employing a feature tracking technique to identify the storms, we demonstrate that the poleward motion of individual cyclones increases with increasing global mean temperature. A potential vorticity tendency analysis of the cyclone composites highlights two leading mechanisms responsible for enhanced poleward motion: nonlinear horizontal advection and diabatic heating associated with latent heat release. Our results imply that for a 4 K rise in the global mean surface temperature, the mean poleward displacement of cyclones increases by about 0.85 degrees of latitude, and this occurs in addition to a poleward shift of about 0.6 degrees in their mean genesis latitude. Changes in cyclone tracks may have a significant impact on midlatitude climate, especially in localized storm tracks such as the Atlantic and Pacific storm tracks, which may exhibit a more poleward deflected shape.

Motivated by the expectation that under global warming upper-level meridional temperature gradients will increase while lower-level temperature gradients will decrease, the relations between the vertical structure of baroclinicity and eddy fields are investigated. The sensitivity of eddies and the relation between the mean available potential energy and eddy quantities are studied for cases where the vertical structure of the lapse rate and meridional temperature gradient are modified. To investigate this systematically, an idealized general circulation model with a Newtonian cooling scheme that has a very short relaxation time for the mean state and a long relaxation time for eddies is used. This scheme allows for any chosen zonally mean state to be obtained with good precision. The results indicate that for similar change in the lapse rate or meridional temperature gradient, eddies are more sensitive to changes in baroclinicity where it is already large. Furthermore, when the vertical structure of the lapse rate or the meridional temperature gradient is modified, there is no universal linear relation between the mean available potential energy and eddy quantities.

This study investigates the occurrence of a midwinter suppression in synoptic eddy activity within the North Atlantic storm track. It is found that eddy kinetic energy over the Atlantic is reduced during winter relative to fall and spring, despite the stronger wintertime jet and enhanced baroclinicity. This behavior is similar to the well-known Pacific midwinter minimum, yet the reduction over the Atlantic is smaller and persists for a shorter period. To examine the conditions favorable for this phenomenon, we present an analysis of years with stronger jet intensity versus years of weaker jets over the Atlantic and Pacific basins. When the wintertime jet is stronger, the midwinter suppression of eddy activity is more pronounced, and the jet is more equatorward. Since the climatological Atlantic jet is weaker relative to the Pacific jet, the conditions for a midwinter suppression in the Atlantic are generally less favorable, yet a midwinter suppression often occurs in years of a strong jet.

Jupiter's Great Red Spot (GRS) is the most dominant and long-lived feature in Jupiter's atmosphere. However, whether this is a shallow atmospheric feature or a deeply rooted vortex has remained an open question. In this study, we assess the possibility of inferring the depth of the GRS by the upcoming Juno gravity experiment. This is achieved by an exploration of the possible gravitational signature of the vortex by systematically extending the surface winds into the interior and analyzing the resulting gravity signal. The gravity anomaly is then compared to the expected accuracy in the retrieval of the surface gravity at the GRS location obtained with numerical simulations of the Doppler data inversion based on the expected trajectory of the spacecraft. Starting from observations of the atmospheric velocity at the cloud level, we project the wind using a decay scale height along coaxial cylinders parallel to the spin axis and explore a wide range of decay scale heights in the radial direction. Assuming the large scale vortex dynamics are geostrophic, and therefore thermal wind balance holds, the density anomaly distribution due to Jupiter's winds can be derived from the velocity maps. The novelty of this approach is in the integration of thermal wind relations over a three-dimensional grid, and in the inclusion of the observed meridional velocity as measured during the Cassini flyby of Jupiter. The perturbations in the mean zonal flow give rise to non zero tesseral spherical harmonics in Jupiter's gravitational potential. We provide an estimate of this asymmetric gravity coefficients for different values of the wind decay scale height. We conclude that the mass -anomaly associated with the GRS is detectable by the Juno gravity experiment if the vortex is deep, characterized by a vertical height larger than 2,000 km below the cloud level of Jupiter, and that the large mass involved with deep winds does not render much the ability to measure the feature. (C) 2015

The relation between the mean meridional temperature gradient and eddy fluxes has been addressed by several eddy flux closure theories. However, these theories give little information on the dependence of eddy fluxes on the vertical structure of the temperature gradient. The response of eddies to changes in the vertical structure of the temperature gradient is especially interesting since global circulation models suggest that as a result of greenhouse warming, the lower-tropospheric temperature gradient will decrease whereas the upper-tropospheric temperature gradient will increase. The effects of the vertical structure of baroclinicity on atmospheric circulation, particularly on the eddy activity, are investigated. An idealized global circulation model with a modified Newtonian relaxation scheme is used. The scheme allows the authors to obtain a heating profile that produces a predetermined mean temperature profile and to study the response of eddy activity to changes in the vertical structure of baroclinicity. The results indicate that eddy activity is more sensitive to temperature gradient changes in the upper troposphere. It is suggested that the larger eddy sensitivity to the upper-tropospheric temperature gradient is a consequence of large baroclinicity concentrated in upper levels. This result is consistent with a 1D Eady-like model with nonuniform shear showing more sensitivity to shear changes in regions of larger baroclinicity. In some cases, an increased temperature gradient at lower-tropospheric levels might decrease the eddy kinetic energy, and it is demonstrated that this might be related to the midwinter minimum in eddy kinetic energy observed above the northern Pacific.

The upcoming Juno and Cassini gravity measurements of Jupiter and Saturn, respectively, will allow probing the internal dynamics of these planets through accurate analysis of their gravity spectra. To date, two general approaches have been suggested for relating the flow velocities and gravity fields. In the first, barotropic potential surface models, which naturally take into account the oblateness of the planet, are used to calculate the gravity field. However, barotropicity restricts the flows to be constant along cylinders parallel to the rotation axis. The second approach, calculated in the reference frame of the rotating planet, assumes that due to the large scale and rapid rotation of these planets, the winds are to leading order in geostrophic balance. Therefore, thermal wind balance relates the wind shear to the density gradients. While this approach can take into account any internal flow structure, it is limited to only calculating the dynamical gravity contributions, and has traditionally assumed spherical symmetry. This study comes to relate the two approaches both from a theoretical perspective, showing that they are analytically identical in the barotropic limit, and numerically, through systematically comparing the different model solutions for the gravity harmonics. For the barotropic potential surface models we employ two independent solution methods - the potential-theory and Maclaurin spheroid methods. We find that despite the sphericity assumption, in the barotropic limit the thermal wind solutions match well the barotropic oblate potential-surface solutions. (C) 2016 Elsevier Inc. All rights reserved.

The midlatitude atmosphere is characterized by turbulent eddies that act to produce a depth-independent (barotropic) mean flow. Using the NCEP (National Centers for Environmental Prediction) Reanalysis 2 data, the latitudinal dependence of barotropic kinetic energy and enstrophy are investigated. Most of the barotropization takes place in the extratropics with a maximum value at midlatitudes, due to the latitudinal variations of the static stability, tropopause height, and sphericity of the planet. Barotropic advection transfers the eddy kinetic energy to the zonal mean flow and thus maintains the barotropic component of the eddy-driven jet. The classic description of geostrophic turbulence exists only at high latitudes, where the quasi-geostrophic flow is supercritical to baroclinic instability; the eddy-eddy interactions carry both the barotropization of eddy kinetic energy upscale to the Rhines scale and the barotropization of eddy potential enstrophy downscale.

Slantwise convection should be ubiquitous in the atmospheres of rapidly rotating fluid planets. We argue that convectively adjusted lapse rates should be interpreted along constant angular momentum surfaces instead of lines parallel to the local gravity vector. Using Cassini wind observations of Jupiter and different lapse rates to construct toy atmospheres, we explore parcel paths in symmetrically stable and unstable weather layers by the numerically modeled insertion of negatively buoyant bubbles. Low-Richardson number atmospheres are very susceptible to transient symmetric instability upon local diabatic forcing, even outside of the tropics. We explore parcel paths in symmetrically stable and unstable weather layer environments, the latter by adding thermal bubbles to the weather layer. Parcels that cool in Jupiter's belt regions have particularly horizontal paths, with implications for jetward angular momentum fluxes. These considerations may be relevant to the interpretation of Juno's ongoing observations of Jupiter's weather layer.

The alignment of Saturn's magnetic pole with its rotation axis precludes the use of magnetic field measurements to determine its rotation period(1). The period was previously determined from radio measurements by the Voyager spacecraft to be 10 h 39 min 22.4s (ref. 2). When the Cassini spacecraft measured a period of 10 h 47 min 6s, which was additionally found to change between sequential measurements(3,4,5), it became clear that the radio period could not be used to determine the bulk planetary rotation period. Estimates based upon Saturn's measured wind fields have increased the uncertainty even more, giving numbers smaller than the Voyager rotation period, and at present Saturn's rotation period is thought to be between 10 h 32 mm and 10 h 47 min, which is unsatisfactory for such a fundamental property. Here we report a period of 10 h 32 mm 45 s 46 s, based upon an optimization approach using Saturn's measured gravitational field and limits on the observed shape and possible internal density profiles. Moreover, even when solely using the constraints from its gravitational field, the rotation period can be inferred with a precision of several minutes. To validate our method, we applied the same procedure to Jupiter and correctly recovered its well-known rotation period.

The recent discoveries of terrestrial exoplanets and super-Earths extending over a broad range of orbital and physical parameters suggest that these planets will span a wide range of climatic regimes. Characterization of the atmospheres of warm super-Earths has already begun and will be extended to smaller and more distant planets over the coming decade. The habitability of these worlds may be strongly affected by their three-dimensional atmospheric circulation regimes, since the global climate feedbacks that control the inner and outer edges of the habitable zone-including transitions to Snowball-like states and runaway-greenhouse feedbacks-depend on the equator-to-pole temperature differences, patterns of relative humidity, and other aspects of the dynamics. Here, using an idealized moist atmospheric general circulation model including a hydrological cycle, we study the dynamical principles governing the atmospheric dynamics on such planets. We show how the planetary rotation rate, stellar flux, atmospheric mass, surface gravity, optical thickness, and planetary radius affect the atmospheric circulation and temperature distribution on such planets. Our simulations demonstrate that equator-to-pole temperature differences, meridional heat transport rates, structure and strength of the winds, and the hydrological cycle vary strongly with these parameters, implying that the sensitivity of the planet to global climate feedbacks will depend significantly on the atmospheric circulation. We elucidate the possible climatic regimes and diagnose the mechanisms controlling the formation of atmospheric jet streams, Hadley and Ferrel cells, and latitudinal temperature differences. Finally, we discuss the implications for understanding how the atmospheric circulation influences the global climate.

The investigation of planets around other stars began with the study of gas giants, but is now extending to the discovery and characterization of super-Earths and terrestrial planets. Motivated by this observational tide, we survey the basic dynamical principles governing the atmospheric circulation of terrestrial exoplanets, and discuss the interaction of their circulation with the hydrological cycle and global-scale climate feedbacks. Terrestrial exoplanets occupy a wide range of physical and dynamical conditions, only a small fraction of which have yet been explored in detail. Our approach is to lay out the fundamental dynamical principles governing the atmospheric circulation on terrestrial planets—broadly defined—and show how they can provide a foundation for understanding the atmospheric behavior of these worlds. We first survey basic atmospheric dynamics, including the role of geostrophy, baroclinic instabilities, and jets in the strongly rotating regime (the “extratropics”) and the role of the Hadley circulation, wave adjustment of the thermal structure, and the tendency toward equatorial superrotation in the slowly rotating regime (the “tropics”). We then survey key elements of the hydrological cycle, including the factors that control precipitation, humidity, and cloudiness. Next, we summarize key mechanisms by which the circulation affects the global-mean climate, and hence planetary habitability. In particular, we discuss the runaway greenhouse, transitions to snowball states, atmospheric collapse, and the links between atmospheric circulation and CO2 weathering rates. We finish by summarizing the key questions and challenges for this emerging field in the future.

Transient and stationary eddies shape the extratropical climate through their transport of heat, moisture, and momentum. In the zonal mean, the transports by transient eddies dominate over those by stationary eddies, but this is not necessarily the case locally. In particular, in storm-track entrance and exit regions during winter, stationary eddies and their interactions with the mean flow dominate the atmospheric energy transport. Here it is shown that stationary eddies can shape storm tracks and control where they terminate by modifying local baroclinicity. Simulations with an idealized aquaplanet GCM show that zonally localized surface heating alone (e.g., ocean heat flux convergence) gives rise to storm tracks, which have a well-defined length scale that is similar to that of Earth's storm tracks. The storm tracks terminate downstream of the surface heating even in the absence of continents, at a distance controlled by the stationary Rossby wavelength scale. Stationary eddies play a dual role: within about half a Rossby wavelength downstream of the heating region, stationary eddy energy fluxes increase the baroclinicity and therefore contribute to energizing the storm track; farther downstream, enhanced poleward and upward energy transport by stationary eddies reduces the baroclinicity by reducing the meridional temperature gradients and enhancing the static stability. Transports both of sensible and latent heat (water vapor) play important roles in determining where storm tracks terminate.

NASA's Juno spacecraft will make microwave and gravity measurements of Jupiter. These can reveal information about the composition of Jupiter's atmosphere and about the temperature and density structure below the visible clouds, which is in balance with the structure of the zonal winds. Here we show that there exist strong physical constraints on the structure of the off-equatorial deep zonal winds, and that these imply dynamical constraints on the thermal and gravitational signals Juno will measure. The constraints derive from the facts that Jupiter is rapidly rotating, has nearly inviscid flow, and has strong intrinsic heat fluxes emanating from the deep interior. Because of the strong intrinsic heat fluxes, Jupiter's interior is convecting, but the rapid rotation and weak viscosity constrain the convective motions away from the equator to occur primarily along cylinders parallel to the planet's spin axis. As a consequence, convection is expected to approximately homogenize entropy along the spin axis, thereby adjusting the interior to a convectively and inertially nearly neutral state. In this state, entropy gradients perpendicular to the spin axis are constant but generally not zero on cylinders concentric with the spin axis. Additionally, thermal wind balance relates entropy gradients perpendicular to the spin axis to the zonal wind shear between the observed cloud-level winds and winds in the deep interior (pressures of order 10(6) bar), which must be much weaker because otherwise the Ohmic energy dissipation produced by the interaction of the zonal winds with the planetary magnetic field would exceed the planetary luminosity. Combining these physical constraints with thermal and electrical properties of the atmosphere, we obtain that zonal winds away from the equator likely extend deeply into Jupiter (to a depth between about 0.84R(J) and 0.94R(J) with Jupiter radius R-J) but have strengths similar to cloud level winds only within the outer few percent of

The low-order even gravity harmonics J(2), J(4), and J(6) are well constrained for Jupiter and Saturn from spacecraft encounters over the past few decades. These gravity harmonics are dominated by the oblate shape and radial density distribution of these gaseous planets. In the lack of any north-south asymmetry, odd gravity harmonics will be zero. However, the winds on these planets are not hemispherically symmetric, and therefore can contribute to the odd gravity harmonics through dynamical variations to the density field. Here it is shown that even relatively shallow winds (reaching similar to 40 bars) can cause considerable odd gravity harmonics that can be detectable by NASA's Juno and Cassini missions to Jupiter and Saturn. Moreover, these measurements will have better sensitivity to the odd harmonics than to the high-order even harmonics, which have been previously proposed as a proxy for deep winds. Determining the odd gravity harmonics will therefore help constrain the depth of the jets on these planets, and may provide valuable information about the planet's core and structure. Citation: Kaspi, Y. (2013), Inferring the depth of the zonal jets on Jupiter and Saturn from odd gravity harmonics, Geophys. Res. Lett., 40, 676-680, doi:10.1029/2012GL053873.

Three dimensional studies of convection in deep spherical shells have been used to test the hypothesis that the strong jet streams on Jupiter, Saturn, Uranus, and Neptune result from convection throughout the molecular envelopes. Due to computational limitations, these simulations must be performed at parameter settings far from jovian values and generally adopt heat fluxes 5-10 orders of magnitude larger than the planetary values. Several numerical investigations have identified trends for how the mean jet speed varies with heat flux and viscosity in these models, but no previous theories have been advanced to explain these trends. Here, we show using simple arguments that if convective release of potential energy pumps the jets and viscosity damps them, the mean jet speeds split into two regimes. When the convection is weakly nonlinear, the equilibrated jet speeds should scale approximately with Fly. where F is the convective heat flux and v is the viscosity. When the convection is strongly nonlinear, the jet speeds are faster and should scale approximately as (F/v)(1/2). We demonstrate how this regime shift can naturally result from a shift in the behavior of the jet-pumping efficiency with heat flux and viscosity. Moreover, both Boussinesq and anelastic simulations hint at the existence of a third regime where, at sufficiently high heat fluxes or sufficiently small viscosities, the jet speed becomes independent of the viscosity. We show based on mixing-length estimates that if such a regime exists, mean jet speeds should scale as heat flux to the 1/4 power. Our scalings provide a good match to the mean jet speeds obtained in previous Boussinesq and anelastic, three-dimensional simulations of convection within giant planets over a broad range of parameters. When extrapolated to the real heat fluxes, these scalings suggest that the mass-weighted jet speeds in the molecular envelopes of the giant planets are much weaker-by an order of magnitude or more-than the speeds measured at cloud level. (C) 2010 Elsevier Inc. All rights reserved.

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.

This thesis studies the dynamics of a rotating compressible gas sphere, driven by internal convection, as a model for the dynamics on the giant planets. We develop a new general circulation model for the Jovian atmosphere, based on the MITgcm dynamical core augmenting the nonhydrostatic model. The grid extends deep into the planet's interior allowing the model to compute the dynamics of a whole sphere of gas rather than a spherical shell (including the strong variations in gravity and the equation of state). Different from most previous 3D convection models, this model is anelastic rather than Boussinesq and thereby incorporates the full density variation of the planet. We show that the density gradients caused by convection drive the system away from an isentropic and therefore barotropic state as previously assumed, leading to significant baroclinic shear. This shear is concentrated mainly in the upper levels and associated with baroclinic compressibility effects. The interior flow organizes in large cyclonically rotating columnar eddies parallel to the rotation axis, which drive upgradient angular momentum eddy fluxes, generating the observed equatorial superrotation. Heat fluxes align with the axis of rotation, contributing to the observed flat meridional emission. We show the transition from weak convection cases with symmetric spiraling columnar modes similar to those found in previous analytic linear theory, to more turbulent cases which exhibit similar, though less regular and solely cyclonic, convection columns which manifest on the surface in the form of waves embedded within the superrotation. We develop a mechanical understanding of this system and scaling laws by studying simpler configurations and the dependence on physical properties such as the rotation period, bottom boundary location and forcing structure. These columnar cyclonic structures propagate eastward, driven by dynamics similar to that of a Rossby wave except that the restoring planetary vorticity gradient is in the opposite direction, due to the spherical geometry in the interior.

We further study these interior dynamics using a simplified barotropic annulus model, which shows that the planetary vorticity radial variation causes the eddy angular momentum flux divergence, which drives the superrotating equatorial flow. In addition we study the interaction of the interior dynamics with a stable exterior weather layer, using a quasigeostrophic two layer channel model on a beta plane, where the columnar interior is therefore represented by a negative beta effect. We find that baroclinic instability of even a weak shear can drive strong, stable multiple zonal jets. For this model we find an analytic nonlinear solution, truncated to one growing mode, that exhibits a multiple jet meridional structure, driven by the nonlinear interaction between the eddies. Finally, given the density field from our 3D convection model we derive the high order gravitational spectra of Jupiter, which is a measurable quantity for the upcoming JUNO mission to Jupiter.

Abrupt, switch-like, changes in sea ice cover are proposed as a mechanism for the large-amplitude abrupt warming that seemed to have occurred after each Heinrich event. Sea ice changes are also used to explain the colder-than-ambient glacial conditions around the time of the glacier discharge. The abrupt warming events occur in this mechanism, owing to rapid sea ice melting which warmed the atmosphere via the strong sea ice albedo and insulating feedbacks. Such abrupt sea ice changes can also account for the warming observed during Dansgaard-Oeschger events. The sea ice changes are caused by a weak (order of 5 Sv) response of the thermohaline circulation (THC) to glacier discharges. The main point of this work is therefore that sea ice may be thought of as a very effective amplifier of a weak THC variability, explaining the abrupt temperature changes over Greenland. Synchronous ice sheet collapses from different ice sheets around the North Atlantic, indicated by some proxy records, are shown to be possible via the weak coupling between the different ice sheets by the atmospheric temperature changes caused by the sea ice changes. This weak coupling can lead to a "nonlinear phase locking'' of the different ice sheets which therefore discharge synchronously. It is shown that the phase locking may also lead to "precursor'' glacier discharge events from smaller ice sheets before the Laurentide Ice Sheet discharges. The precursor events in this mechanism are the result rather than the cause of the major glacier discharges from the Laurentide Ice Sheet.