Yohai Kaspi

Thermal tides on Venus have been extensively studied near the cloud tops, where their three‐dimensional structure and contribution to the atmospheric momentum budget have been characterized from temperature and wind fields. However, their downward propagation and influence within the deep atmosphere remain uncertain, and their behavior in the deep atmosphere, particularly near the surface, remains poorly constrained. Using the LMD Venus Planetary Climate Model, we investigate the near‐surface thermal tides and their governing timescales. The simulations show that these tides are generated by heat transfer from the surface to the planetary boundary layer and produce a diurnal pressure response with a phase lag of about corresponding to a radiative adjustment timescale of about 10 Earth days. In addition, a 35‐day oscillation appears within the stably stratified 10–20 km layer, consistent with a planetary‐scale internal gravity wave. These results suggest that coherent oscillations beyond the diurnal tide can develop in the deep atmosphere, with the surface pressure variability dominated by a superposition of three modes: the diurnal and semidiurnal tides and the 35‐day oscillation. Together, these components account for about 70 of the total surface pressure variance, with potential implications for gravity measurements by forthcoming missions such as VERITAS and EnVision.

Thermal tides dominate the dynamics of Venus’ middle atmosphere and are believed to play a major role in maintaining atmospheric superrotation. However, their global three-dimensional structure and associated circulation remain only partially constrained observationally. Previous studies have primarily characterized either temperature variability from radio occultations or horizontal winds near the cloud tops from cloud tracking, leaving the vertical coupling between thermal structure and atmospheric dynamics only partially resolved.Here we analyze more than 1,000 radio-occultation profiles from Venus Express (2006–2014) and Akatsuki (2016–2024), spanning latitudes from 90°S to 90°N and altitudes between 40 and 95 km. Using the combined dataset, we reconstruct the temperature field as a function of latitude, altitude, and local solar time, and decompose it into diurnal and semidiurnal tidal components.The reconstructed temperature field reveals a clear latitudinal transition in the dominant tidal regime: semidiurnal tides dominate at low latitudes, while diurnal tides become increasingly important toward mid and high latitudes. Vertical phase tilts indicate vertically propagating modes originating near the cloud region, consistent with thermal excitation within the main solar-heating layer.Building on the observed thermal structure, we derive the associated three-dimensional tidal circulation using a dynamically consistent inversion based on the linearized momentum, continuity, and thermodynamic equations in the cyclostrophic regime. The diagnosed wind field reveals coherent zonal, meridional, and vertical tidal circulations. Zonal wind perturbations reach amplitudes of ~10–15 m/s, while vertical velocities are of order 0.1 m/s. Comparison with wind measurements near the cloud tops shows good agreement in both magnitude and large-scale structure.These results provide a unified observational view of Venus thermal tides and new constraints on vertical coupling, wave propagation, and the dynamical structure of the Venusian atmosphere.

The giant planets exhibit a fundamental contrast in their equatorial circulation: Jupiter and Saturn are characterized by broad eastward equatorial jets, or superrotation, whereas Uranus and Neptune exhibit strong westward equatorial flow, or subrotation. This dichotomy has often been interpreted as evidence for distinct dynamical regimes on the gas and ice giants. However, here we show that these opposing equatorial states may instead arise from a common dynamical mechanism, with the direction of the equatorial jet determined by the way convection, rotation, and eddy momentum transport interact within the planetary interior and atmosphere.Here we present a unified perspective on the formation of super- and sub-rotating equatorial jets across the giant planets. In deep rotating convection models, columnar convective motions can organize angular momentum in a way that produces either eastward or westward equatorial flow. The two outcomes emerge as separate equilibrated branches of the same dynamical system, implying that the transition from superrotation to subrotation may be understood as a bifurcation rather than as a change in the underlying forcing. Importantly, both regimes are maintained by comparable wave and eddy processes, suggesting that the gas and ice giants need not require fundamentally different explanations for their equatorial jets.This picture connects naturally with idealized atmospheric 3D hydrodynamical simulations of the ice giants, which show that Uranus- and Neptune-like subrotation can be sustained when the modeled circulation extends sufficiently deep and allows eddy momentum fluxes to converge angular momentum away from the equator. Taken together, the two approaches suggest a continuous dynamical pathway linking the deep convective interiors of the gas giants with the deep atmospheric circulation of the ice giants. The observed contrast between superrotation and subrotation may therefore reflect different equilibrated states of a shared convective-eddy system, controlled by planetary parameters such as convective forcing, stratification, rotation rate, and effective dynamical depth.This unified framework provides a basis for interpreting the diversity of zonal winds among the giant planets and offers testable predictions for future observations of Uranus and Neptune, where the depth and maintenance of the equatorial jets remain key open questions.

In rapidly rotating planets, convection driven by residual heat from planetary formation is predicted to organize into columnar circulations aligned with the rotation axis. Such motions have long been proposed to play a central role in giant-planet dynamics, including the maintenance of Jupiter's equatorial superrotation and adjacent westward jets, but their expected depth makes them difficult to observe directly. We analyze microwave brightness-temperature measurements from the Juno Microwave Radiometer (MWR), using multiple channels that probe atmospheric layers down to approximately 100 bar in Jupiter's equatorial region. The data reveal coherent hemispheric asymmetries and characteristic spatial scales consistent with expectations from rapidly rotating deep convection. Comparisons with deep convection simulations reproduce similar signatures and support the interpretation. Cross-depth correlations further suggest axially extended, tilted convective structures. Together, these results provide observational constraints on the geometry and spacing of Jupiter's deep convective motions and their connection to the planet's large-scale atmospheric circulation.

Results from the Juno investigation of Jupiter have challenged our understanding of Jupiter origin and evolution. As the archetype of giant planets, the study of Jupiter provides knowledge needed to understand the origin of our own solar system and the planetary systems being discovered around other stars. Jupiter uniquely informs us about the origin of our own planetary system. The mass of Jupiter’s heavy element core and the abundance of heavy elements in the atmosphere discriminate among models for giant planet formation. Measurements by Juno of Jupiter’s gravity field suggest Jupiter’s core is diffuse, extended and contains compositional gradients. These new results require new models of Jupiter’s formation and evolution. The gravity science results on the measurement of J4 coupled to current estimates on the hydrogen and helium equation of state suggests Jupiter’s interior composition has low metallicity, potentially solar or even sub-solar. This is inconsistent with measurements of the atmosphere by both Juno and the Galileo probe which indicate the atmospheric composition is of higher metallicity (2-4x solar). The combined results from Juno provide new constraints on theories of Jupiter’s formation and evolution and giant planets in general. A summary of Juno’s results relevant to Jupiter’s formation and evolution will be presented along with a discussion of theoretical implications on Jupiter, and giant planets both within our solar system and beyond.

Radio occultation measurements provide a direct way to probe the vertical structure of Jupiter’s atmosphere. As a spacecraft radio signal passes through the planetary limb, it is refracted by the atmosphere, allowing profiles of refractivity, pressure, and temperature to be retrieved at high vertical resolution. The measurements are also used to probe Jupiter’s ionosphere, allowing electron density profiles to be retrieved in the upper atmospheric layers. For ESA’s Jupiter Icy Moons Explorer, JUICE, radio occultation experiments are planned to study the thermal structure and variability of Jupiter’s upper troposphere and lower stratosphere, the structure of the ionosphere, and their connection to broader questions of atmospheric circulation and dynamics. The 3GM radio science experiment on JUICE will enable a new set of radio occultation measurements of Jupiter’s atmosphere using highly stable radio links. Around 100 occultation opportunities are expected during the mission, providing a broad sampling of latitudes and longitude. For the highest-resolution radio occultation experiments, we have developed an accurate varying spacecraft pointing technique during each observation. This approach is expected to allow the radio occultation experiments to penetrate to deep atmospheric levels, down to approximately 1.5 bar. In addition, the presence of an Ultra Stable Oscillator will enable one-way occultation measurements, which are especially valuable for retrieving high-resolution atmospheric profiles. At present, NASA's Juno mission provides the most extended radio occultation dataset of Jupiter's neutral atmosphere. Since July 2023, Juno has obtained the first new measurements of this kind since the Voyager era, sounding the atmosphere down to approximately 0.5 bar. These two-way coherent observations require ray tracing of both the uplink and downlink signals through Jupiter's oblate atmosphere, and have produced pressure-temperature profiles over a growing range of latitudes and longitudes. The analysis now includes measurements in the northern polar region, showing profiles that define the cold northern stratospheric vortex above 65 degrees north. The Juno results have already provided new constraints on Jupiter’s present day thermal structure, meridional variability, and polar dynamics. In this presentation, we use the recent Juno radio occultation results as a foundation for preparing the atmospheric science of JUICE. Juno has already provided a new view of Jupiter’s upper troposphere and lower stratosphere, revealing vertical structure and variability that can guide the next stage of radio occultation studies. Building on these results, JUICE will extend the investigation with improved accuracy, higher vertical resolution, and the potential to sound deeper into the atmosphere than before. Together, these observations will provide a major step toward a more complete three-dimensional view of Jupiter’s thermal structure and atmospheric dynamics.

Since 2023, NASA’s Juno mission has been conducting radio occultations of Jupiter’s atmosphere, ionosphere, and aurorae. Radio occultations are enabled by the natural orbital evolution of the trajectory, placing Jupiter between the Juno spacecraft and Earth. As of September 2026, data from over two dozen occultation pairs have been analyzed to determine atmospheric temperature/pressure profiles and ionosphere electron density profiles over a wide range in latitudes, including the polar regions where auroral activity is present. Measurements of the radio frequencies at X-band (8.4 GHz) and Ka-band (32 GHz) are inverted into refractivity through classical numerical ray tracing techniques. From the refractivity, atmospheric temperature/pressure and ionosphere electron density are derived. These data reveal temperature distribution of Jupiter’s atmosphere in regions never before sampled and provide unique data on the polar structure. Future radio occultation opportunities will continue to probe the northern high latitude and equatorial regions.BackgroundJupiter’s atmosphere was sampled by the Pioneer and Voyager missions in the 1970s through radio occultation and the Galileo probe. Radio occultations are key to providing direct measurement of the temperature structure and electron density measurements. Juno’s extended mission offers dozens of occultation observation opportunities due to the natural orbital evolution of the spacecraft’s trajectory. These observations are distributed over a wide range of latitudes of the planet, from the equatorial regions to the north and south poles. These data are complementary to other data including Juno’s Microwave Radiometer (MWR), plasma wave instrument (Waves), and visible & infrared imaging (from both Juno instruments and ground-based observations).ObservationJuno Gravity Science Instrument (Asmar et. al. 2017) is a radio science instrument which utilizes dual-frequency X-band (8.4 GHz) and Ka-band (32 GHz) radio links between the Juno spacecraft and the Earth-based observing stations of NASA’s Deep Space Network (DSN). Although designed to measure gravity fields, the instrumentation is also excellent for radio occultations (Buccino et. al., 2022). As Juno passes behind Jupiter during closest approach, the received frequency is affected by refraction. The depth the occultation reaches is limited by spacecraft pointing: when the signal refracts outside the main beam of the antenna, the observation is concluded at a depth of approximately ~300 mbar. Although Juno is not capable of limb-tracking maneuvers as was done on Voyager, small offsets to the pointing enable a deeper probe depth than otherwise would be achieved (~500 mbar).Figure 1. Map of the conducted (as of August 2026) and future experiment opportunities for radio occultation locations on Jupiter with the Juno spacecraft. Triangles indicate an ingress occultation, and circles indicate an egress occultation. Overlaid is the magnetic field model (JRM33) and the atmospheric basemap, along with the auroral ovals (white lines).Regions of InterestJuno’s extended mission allowed for probing of the atmosphere and ionosphere at a wide range of latitudes beginning with PJ-53 (July 2023). As the occultation season progresses, the latitude becomes more poleward allowing probing of the circumpolar cyclones. A maximum of 88 N occurred on PJ-86 (August 2026), within the polar cyclone. In the south, a maximum of -88 S was achieved on PJ-83. As occultation season reaches its end on PJ-97 (August 2027), opportunities exist for mid-latitude and equatorial regions, including a near-equatorial occultation on PJ-90 (December 2026).ResultsThe atmosphere and ionosphere perturb the radio link causing measurable changes in frequency. Following the methodology in Schinder et. al. 2015, a numerical ray tracing technique is used to invert these frequency changes, along with the spacecraft’s trajectory and planetary ephemeris, into a refractivity profile. The first set of Jupiter occultations resulted in detailed temperature-pressure profiles from mid-latitude regions to the upper-latitude regions (Caruso et. al., 2025 and Smirnova et. al., 2025). These revealed cooler stratosphere and warmer troposphere at the equator. Further studies (Smirnova et. al., 2026) showed the polar stratospheric vortex is indeed cooler with a sharp temperature change at 65°N. Ionosphere electron density profiles of the same regions (Coffin et. al., 2025) show high variability in electron density layers, suggesting a complex interaction with the magnetosphere.AcknowledgementsThe work of DB, MP, RP, and SL was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Government sponsorship acknowledged. AC, LGC, PT, and MZ are grateful to the Italian Space Agency (ASI) for financial support through Agreement No. 2022-16-HH.0, No. 2023-6-HH.0, and No. 2024-5-HH.0. PS was supported by NASA Contract NNM06AA75C from the Marshall Space Flight Center under subcontract 699054X from Southwest Research Institute.© 2026 California Institute of Technology. Government sponsorship acknowledged.ReferencesAsmar, Sami W., et al. "The Juno gravity science instrument." Space Science Reviews1 (2017): 205-218.Buccino, Dustin, et al. "Planning and execution of Juno radio occultation experiments at Jupiter." 2023 IEEE aerospace conference. IEEE, 2023.Schinder, P. J., et al. "A numerical technique for two-way radio occultations by oblate axisymmetric atmospheres with zonal winds." Radio Science7 (2015): 712-727.Caruso, Andrea, et al. "Probing Jupiter's atmosphere through Juno Radio occultations: Methodology and initial observations." Geophysical Research Letters22 (2025): e2024GL113231.Smirnova, Maria, et al. "Probing Jupiter's atmosphere through Juno radio occultations: Analysis of the atmospheric...

Dynamics in Venus’s massive atmosphere drive large-scale mass redistribution, generating measurable perturbations in the planet's external gravitational field. Future high-precision gravity measurements from upcoming missions will provide new constraints on the planet’s internal structure and atmospheric mass redistribution. While the deep atmosphere is difficult to observe with traditional remote sensing, these gravitational signatures offer a direct probe into near-surface dynamics. In this study, we analyze atmospheric fields from the Venus Planetary Climate Model (VPCM) to evaluate time-varying gravitational harmonics and assess the expected magnitude of the signal relative to the sensitivity of future gravity measurements. Our analysis shows that low-degree harmonics (l≤4) may reach amplitudes large enough to be distinguishable from the static internal gravity field. Spectral analysis of the simulated harmonics reveals a signal dominated by the diurnal thermal tide, with additional contributions from the semi-diurnal tide and a 35-day wave signal. This suggests that time-variable gravity measurements may be sensitive not only to thermally forced tides, but also to atmospheric wave activity in Venus’s deep atmosphere. We show that the dominant tidal and wave frequencies may be detectable in future gravity-tracking observations. Furthermore, we present a series of sensitivity experiments to determine how variations in atmospheric parameters influence the gravity signal amplitude and temporal structure. By identifying which atmospheric properties control these signatures, we demonstrate how future gravity data can be used to retrieve specific characteristics of the Venusian atmosphere.

The unresolved recent multidecadal cooling of the eastern Pacific and its uncertain future remain key puzzles in climate dynamics. We propose the land-sea heating contrast as a potential driver of this phenomenon. To test this, we amplify the land-sea contrast by quadrupling carbon dioxide (CO ₂ ) only over land in a global coupled climate model. We show that this causes a pronounced transient cooling of the eastern and equatorial Pacific. A transient 1%-per-year CO ₂ increase over land produces decadal cooling, suggesting relevance to the observed eastern Pacific cooling. Targeted simulations with locally increased CO ₂ concentrations over different land regions reveal three drivers of this cooling: a northward intertropical convergence zone shift, a westward convection shift over the western Pacific, and strengthened subtropical highs from Rossby waves. These insights recast the commonly used ocean dynamical thermostat mechanism as a feedback rather than a driver of transient cooling and contribute to understanding and predicting Pacific temperature patterns.