The upper atmospheres of temperate sub-Neptunes are strongly influenced by atmospheric dynamics due to their cool equilibrium temperature and thereby longer chemical time-scales than the atmospheric dynamical time-scales. In this study, we used a three-dimensional (3D) general circulation model to investigate the transport-induced disequilibrium chemistry and vertical mixing on temperate gas-rich mini-Neptunes, using K2-18b as an example. We model K2-18b assuming 180 times solar metallicity and consider it as either a synchronous or an asynchronous rotator, exploring spin-orbit resonances of 2:1, 6:1, and 10:1. We find that the vertical transport affects the chemical structure significantly, making CO2 and CO more abundant (similar to 10(-3)) in the upper atmosphere compared to the chemical equilibrium abundance ( <10-15), and horizontal winds further homogenize the chemical composition zonally in this region. Molecular abundances in the photosphere generally agree across different rotation periods. We employ a passive tracer in the model to estimate the one-dimensional (1D) equivalent eddy-diffusion coefficient (K-zz) of K2-18b, providing a parameter useful for future 1D atmospheric models. Additionally, synthetic transmission spectra generated from our model are compared with the James Webb Space Telescope observations, and we find that our model can provide a comparable fit to the observations. This work offers a 3D perspective on transport-induced chemistry on a temperate sub-Neptune and derives vertical mixing parameters to support 1D modelling.

Extensive studies have consistently demonstrated the widening and weakening of the Hadley circulation (HC) under increasing greenhouse gas concentrations in modern and projected future climates. However, systematic investigations of HC behavior in deep-time paleoclimates remain lacking. Such an investigation would provide us with insights into how the HC evolves under different climate states. Here, we analyze variations of the winter HC over the past 250 million years, using a large set of climate simulations. This period witnessed overall much warmer climates compared to the pre-industrial (PI), associated with temperature fluctuations and substantial paleogeography reorganizations. Our results show that the winter HC intensified and contracted during prolonged cooling periods (250–170 million years ago (Ma), 80 Ma–PI), whereas it weakened and expanded during the warming interval (170–80 Ma). In general, the winter HC in these warmer periods was systematically weaker and wider relative to the PI, with maximum changes reaching a latitudinal expansion of ∼3.2° and a strength weakening of 54%. An exception occurred during the Pangea supercontinent era, when the Northern Hemispheric winter HC was stronger than that of the PI. These indicate that changes in HC strength and width are jointly influenced by global mean surface temperature (or CO2 concentrations) and paleogeography. These findings offer important insights for understanding changes in the HC and associated mechanisms in warm climates, as well as climate evolution throughout geological history.

Tidally locked lava planets are hot, rocky worlds on close-in orbits with a permanent molten dayside. With JWST, their surfaces and atmospheres are beginning to be revealed. This work investigates three-dimensional (3D) magma ocean dynamics, derives scaling laws for the resulting ocean heat transport, and predicts its detectability. For the first time, the ocean circulation driven by the intense momentum and mass exchanges with the supersonic atmosphere is considered in addition to that by thermal forcing. The wind forcing turns out to overwhelmingly dominate the other two mechanisms, driving ocean currents reaching similar to 100 m s-1 and greatly expanding the latitudinal extent of the Matsuno-Gill response. Despite these extreme flow speeds, scaling analysis and 3D simulations consistently demonstrate that magma ocean circulation alone does not produce an observable hot-spot offset. This inefficiency arises because basin geometry and circulation structure fundamentally constrain zonal heat redistribution, suppressing large-scale longitudinal transport even under vigorous flow.

Bauxites and kaolinites, products of intense chemical weathering, are commonly considered as qualitative indicators of warm and humid environmental conditions in paleoclimate studies. Despite their recognized significance, a comprehensive quantitative analysis of the relationship between the formation of bauxites and kaolinites in the geological past and climatic factors remains lacking. Here, we integrate geological records with climate simulations to establish quantitative relationships between bauxite and kaolinite occurrences and temperature-precipitation patterns over the Phanerozoic. Bauxites and kaolinites were mainly located in the tropics in the Paleozoic. They shifted to the subtropics for much of the Mesozoic and Cenozoic. Our findings reveal that bauxites formed with annual mean temperature (AMT) of 26.7 degrees C and annual mean precipitation (AMP) of 1725 mm y(-1) before 250 Ma, and the median AMT and AMP decreased to 24.3 degrees C and 982 mm y(-1) after 250 Ma. Kaolinites formed with medium AMT and AMP of 25.1 degrees C and 1427 mm y(-1) in the Paleozoic, respectively. Then, they decreased to a 20.5 degrees C and 1122 mm y(-1) in the Mesozoic and Cenozoic. The variations in latitudes, temperatures and precipitation of bauxites and kaolinites are attributed to global land distributions and climate states. These results enhance our understanding of the weathering processes of the metallogenesis of bauxites and kaolinites.

Context. More than 200 moons exist in our Solar System, yet no exomoon has been confirmed to date. While the innermost two planets of the Solar System lack natural satellites and most studies favour the existence of exomoons around long-period planets, some theoretical studies that take tidal dissipation, orbital decay, and migration processes into account suggest that exomoons may survive around short-period exoplanets. Aims. We investigated the impact of exomoons on planetary thermal phase curves and assessed their detectability within a theoretical framework. Methods. We simulated the thermal phase curves of exomoon-exoplanet systems, including mutual transits and occultations, and explored their dependence on planetary orbital periods across a wide range of systems. Results. Close-in airless exomoons maintain large day-night temperature contrasts, amplifying the thermal phase-curve signal of the system. When the exomoon transits or is occulted by the exoplanet, the transit depth varies with the planetary phase, and the occultation depth varies with the exomoon's phase. The maximum occultation depth can reach similar to 20 ppm for long-period systems. For short-period planets, the signal can reach up to similar to 100 ppm, although such configurations may not be dynamically stable over long timescales. Conclusions. If exomoons are not accounted for, the planetary temperature distribution retrieved from observed thermal phase curves may overestimate the planetary day-night temperature contrast and underestimate the planetary horizontal heat transport. In principle, the periodic exomoon-exoplanet mutual occultation signal could be extracted using methods such as box-fitting least squares, providing a framework for future observational studies and instrument planning.

Answering the question "Are we alone?" requires atmospheric spectroscopy of nearby terrestrial planets. For an Earth–Sun analog, even the strongest transmission signals are expected to be of order 1 part per million (ppm). Unlike short-period planets, Earth 2.0 planets transit only about once per year, so single-transit sensitivity, rather than stacking repeated observations, is the fundamental design driver. Life 2.0 is a scalable space-mission concept linking Earth 2.0 candidates discovered by PLATO and the Earth 2.0 (ET) mission with atmospheric characterization and biosignature assessment. The baseline architecture comprises 900 one-meter space telescopes, each equipped with a high-throughput Waveguide Integrated Miniature Spectrograph and an ultra-low-read-noise CMOS detector. After independent calibration, spectra acquired simultaneously during a transit are combined, providing the photon-collecting capability of an approximately 30-m aperture at the selected spectral resolution while retaining a modular architecture. The baseline 0.2–1.05 μm range covers O_3, O_2, H_2O, Rayleigh scattering, and other diagnostics, with extension into the infrared as detector technologies mature. Prototype Waveguide Spectral Lens devices have demonstrated 40–66% throughput at resolving powers from R ∼ 200 to R ∼ 20,000. Lightweight silicon-carbide mirrors and sub-electron-noise CMOS detectors support replicated production. Life 2.0 must address detector systematics, instrument stability, and stellar variability; rather than assuming these limitations disappear, it builds on calibration, detector-characterization, and data-analysis techniques advanced during the JWST era. The concept offers a scalable alternative to a monolithic 30-m-class space telescope and a staged pathway toward biosignature spectroscopy of nearby Earth-like planets.

Terrestrial planets within the Venus zone surrounding M-dwarf stars can retain surface ice caps on the perpetual dark side if atmospheric heat transport is inefficient, as suggested by previous global climate simulations. This condition is proposed to play a role in the potential regional habitability of these planets. However, the amount of surface ice may be limited by considering the water condensed from the steam atmosphere in a runaway greenhouse state, and the physical mechanism for triggering the condensation process is not clear. Here, we use a two-column moist radiative–convective–subsiding model to investigate the water condensation process on tidally locked planets from the runaway greenhouse state. We find that the water condensation process is characterized by two distinct equilibrium states under the same incoming stellar flux. The initiation of condensation corresponds to a warm, unstable state exhibiting positive Planck feedback, whereas the termination phase corresponds to a cold, stable state exhibiting negative Planck feedback. We further show that the surface water mass in the collapsed state decreases with the incoming stellar flux, background surface pressure, and optical thickness of noncondensable greenhouse gases, with a global equivalent depth of less than ∼20 cm. Our two-column approach provides a straightforward way to understand the water evolution on Venus zone planets around M dwarfs.

The North Atlantic Oscillation (NAO), the dominant mode of atmospheric variability in the North Atlantic region, plays a crucial role in weather and climate. Here, to investigate when the NAO emerged and how it evolved over geological timescales, we analyzed time-slice paleoclimate simulations during the breakup of the supercontinent Pangea, starting 160 million years ago (Ma). Our findings indicate that a present-day-like NAO mode gradually formed between 80 Ma and 60 Ma, driven by the expansion of the North Atlantic Ocean and the enhanced land-ocean contrast. This expansion led to a regime transition in Northern Hemisphere winter circulation, characterized by a westward shift of the North Atlantic jet, a strengthening of the North Atlantic high pressure and storm track, and the emergence of NAO-like variability. The confluence of orographic effects of the Rocky Mountains also contributed to the strengthening of the NAO. This study depicts the evolutionary history of the NAO over geological time and reveals its coherent relationship with the evolution of continents and orography. This study reveals how the North Atlantic Oscillation emerged and evolved over 160 million years, highlighting the role of continental drift, land-ocean contrast, and orography in shaping modern atmospheric variability.

The middle Miocene represents a significant climatic transition period within the Cenozoic era. However, ocean redox conditions during this period remain poorly understood. Here, we present Fe speciation and redox-sensitive element enrichment factors (EF) for bulk sediments from Site 1146 in the northern South China Sea (SCS) to constrain deep-water redox changes in the region during the middle Miocene. From the Miocene Climatic Optimum (MCO) to the Middle Miocene Climate Transition (MMCT), MnEF was consistently greater than 1 and gradually increased, while UEF remained less than 1 and showed a decreasing trend. These results indicate that deep water in the northern SCS contained dissolved oxygen and the degree of oxygenation increased throughout the middle Miocene. In addition, the ratio of high reactive Fe to total Fe (FeHR/FeT) was consistently lower than the mean value of oxic continental margin sediments (0.28) and gradually increased from the MCO to the MMCT, while the ratio of pyrite Fe to high reactive Fe (Fepy/FeHR) gradually decreased. This result indicates that the reductive mobilization of sedimentary Fe was weakened and the deep water changed from a dysoxic condition to an oxic condition. The increased oxygenation of deep water in the SCS during the cooler MMCT compared to the warmer MCO is not only related to the reduced oxygen consumption for organic matter remineralization, but is also influenced by the increased oxygen supply associated with the enhancement of Antarctic Circumpolar Deep Water.

This study investigated high-frequency gravity waves (HFGWs) with periods below 20 min observed by the Zhurong/Tianwen-1 and Perseverance/Mars 2020 rovers between local time 09:00 and 11:00, from Ls 140 degrees-165 degrees in Mars Year 36. By analyzing the eccentricity of monochromatic wind perturbations in the horizontal wind data, HFGWs were identified via their predominantly linear characteristics in hodographs. The propagation directions of these waves were determined using polarization relationships from the linear theory of HFGWs. The occurrence of HFGWs doubled following the onset of a regional dust storm in the Utopia Planitia where the Zhurong rover landed. The HFGWs observed by Zhurong predominantly propagated in a north-south direction before the dust storm and then shifted into an east-west direction afterward. In this study, the temperature and wind simulations from the Mars Planetary Climate Model were used to estimate atmospheric instability by calculating the Richardson number before and after the dust storm in the locations of both rovers. As the dust storm developed, intensified dust fronts moved northward from the tropical region and modulated atmospheric instability to the south of Zhurong, which may be responsible for the decrease in wave propagation along the north-south direction.

Compared to the well-known polar amplification in a warmer or cooler world, the trend of tropical surface air temperature gradient is frequently overlooked. Through analyzing various observations, assimilation data, proxy data, and modeling, here we show that annual- and zonal-mean tropical (30oS-30oN) meridional surface air temperature gradient (TMSTG) exhibits small changes in a wide range of climates from extremely cold to extremely hot. This phenomenon is robust to CO2 concentration, solar constant, land-sea configuration, vegetation coverage, heat transport, and cloud parameterization. The quasi-invariance of the TMSTG is maintained by the small gradient of incoming solar radiation and by the dynamics of horizontal weak temperature gradient (WTG) and convective moist adiabat (CMA) in the tropics. When planetary obliquity or rotation period is increased, the quasi-invariant region becomes larger. TMSTG's quasi-invariance is a fundamental and useful law that can be used to reconstruct or predict Earth's tropical climate in the past and future.

Hydrologic cycle has wide impacts on the ecosystem, atmospheric circulation, ocean salinity and circulation, and carbon and nitrogen cycles. Under anthropogenic global warming, previous studies showed that the intensification of the hydrologic cycle is a robust feature. Whether this trend persists in hothouse climates, however, is unknown. Here we show that mean precipitation first increases with surface temperature, but it decreases with surface warming when the surface is hotter than ~320-330 K. This non-monotonic phenomenon is robust to the warming trigger, convection scheme, ocean dynamics, atmospheric mass, planetary rotation, gravity, and stellar spectrum. The weakening is because of the existence of an upper limitation of outgoing longwave emission and the continuously increasing shortwave absorption by H2O, and is consistent with the strong increase of atmospheric stratification and dramatic reduction of convective mass flux. Our results have wide implications for the climates and evolutions of Earth, Venus, and potentially habitable exoplanets.

The long-term evolution of climate during the Holocene remains controversial, as proxy and model data, and multiple proxies, show diverging temperature trends between the different reconstructions. Here, we compile sea surface temperature (SST) from multiple marine sediment records in the South China Sea (SCS) and Indo-Pacific over the Holocene, which reveal a phase difference in the precession band of different marine sediment records. Peak identification was performed on the data from each site, and the sea surface temperature anomalies (SSTA) was simply divided into two modes, the Early Holocene (EH-peak) and Middle Holocene (MH-peak), based on the timing of the first maximum peak, using 9 ka as the boundary. The phase difference between the two modes is ∼3 ka in the precession band. We suggest that the phase difference corresponds to the shifts in the mean latitudinal position of the Intertropical Convergence Zone (ITCZ) driven by the Northern Hemisphere Summer Insolation (NHSI). Two modes indicate the warming of the SSTA during the late Holocene, which may be attributed to rising pCO2, a strengthening El Niño, and a weakening of the East Asian winter monsoon (EAWM). Furthermore, we observe a partial overlap between the site distribution of the MH-peak and the modern monsoon precipitation domains, which may indicate the shift in the mean latitudinal position of the ITCZ and the dynamics of the monsoon precipitation domains.

During the Cryogenian Period, Earth may have experienced two global‐scale glaciations in ∼720–635 million years ago (Ma), referred to the Sturtian and Marinoan Glaciations, known as the “snowball Earth”. During the snowball Earth, continental dust emissions from unglaciated regions were hypothesized to have played a pivotal role in the snowball Earth climate. Using an atmospheric general circulation model with an interactive dust module and an ice sheet model, we explicitly simulate continental dust emission on a hard snowball Earth. We find that the strength of continental dust emissions is within 494–3,051 Tg yr −1 , which is comparable to or even less than the modern Earth (2,566 1,966 Tg yr −1 ) and is about one order less than previous estimations. Compared with the present Earth, the main factors for the limited dust emission during the snowball Earth are extended ice sheet cover, seasonal snow cover, and frozen soil, which strongly suppress dust emission from the land surface.

A hothouse climate may develop throughout Earth’s history and its warming future, and on potentially habitable exoplanets near the inner edge of the habitable zone. Previous studies have suggested that near-surface atmospheric inversion (NAIV), with the planetary boundary air temperature being higher than the air temperature adjacent to the surface, is a pronounced phenomenon in hothouse climates. However, the underlying mechanisms are unclear. Here, we show that lower-tropospheric radiative heating is necessary but not independently sufficient in forming the NAIV. Instead, the dynamic heating induced by large-scale subsidence is essential. With the prescribed reasonable large-scale subsidence, NAIV appears in small-domain cloud-resolving simulations, which was not observed in previous studies. Surface evaporative cooling also contributes to the formation of the NAIV. Besides NAIV, we find that surface inversion (SIV), with the air adjacent to the surface being warmer than the underlying sea surface, is also a distinct phenomenon in hothouse climates. SIV is caused by strong surface evaporative cooling and large atmospheric shortwave absorption. These two types of inversion strongly stabilize the atmosphere, weaken atmospheric circulation, dry the free troposphere, and suppress the hydrological cycle.

Magma ocean is expected to exist on the dayside surface of tide-locked planets if surface temperature exceeds the melting temperature of typical crust. The strength of ocean circulation is important for horizontal heat transport that may could be observed by JWST. In most previous studies of lava planets, the system is typically assumed to be vigorously convecting and isentropic. This implies a magma ocean depth reaching 10-100 km, determined by adiabat and melting curves. However, ocean circulation was not included in the previous studies. In this study, we simulate ocean circulation on tidally locked lava worlds using more realistic 2D and 3D models developed by ourselves. Our simulation results show that under small internal heat source, the maximum zonal current speed ranges from 0.1 to 1.0 m/s and the magma ocean depth is 100-1000 m, being more than 100 times shallower than that predicted in a fully convecting system. The ocean depth is mainly determined by global ocean circulation rather than by the adiabat and melting curves. We further demonstrate that ocean heat transport strength is consistently smaller than the stellar insolation by 1–2 orders of magnitude. Consequently, the impact of ocean circulation on the thermal phase curve of tide-locked lava worlds should be small in observations.

Tide-locked lava worlds are surface-melted rocky planets under a 1:1 tidally locked orbit (i.e., synchronously rotating) with orbital period being equal to rotation period and with permanent hot dayside and cold nightside. Previous studies on this type of planets employed scaling analyses and two-dimensional (2D) simulations. This work is a continuation of the previous research but including the effect of the Coriolis force, and the simulation domain is extended to a 3D global sphere. We find that under the condition with thermal-only forcing (without surface wind stresses), the area-mean ocean depth is about 50–300 m (depending on vertical diffusivity) and the area-mean effect of horizontal ocean heat transport (in the order of 10 ^3 –10 ^4 W m ^−2 ) is significantly smaller than stellar radiation (in the order of 10 ^6 W m ^−2 at the substellar region), being consistent with previous results. Different from 2D results, due to the effect of the Coriolis force, large-scale horizontal gyres form on the dayside; ocean currents near the west boundaries are much stronger than those near the east boundaries (called “western intensification”); the deepest ocean is not right at the substellar point but in the middle latitudes as the vertical diffusivity is moderate or large; and meanwhile, there exists significant asymmetry between the west and the east of the substellar point. These results establish the first picture of the 3D thermal-driven ocean circulation and confirm that the lava ocean should be shallow on tide-locked lava worlds.

The low equilibrium temperatures of temperate sub-Neptunes lead to extremely long chemical time-scales in their upper atmospheres, causing the abundances of chemical species to be strongly shaped by atmospheric transport. Here, we used a three-dimensional (3D) general circulation model involving a passive tracer to investigate the atmospheric circulation and 3D transport of temperate gas-rich sub-Neptunes, using K2-18b as an example. We model K2-18b as a synchronous or asynchronous rotator, exploring spin-orbit resonances (SOR) of 2:1, 6:1, and 10:1. We find that the strong absorption of CO2 and CH4 induces a detached convective zone between 1 and 5 bar, resulting in strong vertical mixing at these levels. The upper atmosphere is dominated by eastward winds (an equatorial superrotating jet present in all simulations), leading to warmer evening terminators and approximately 20 per cent higher passive tracer mass mixing ratios compared to the morning terminators. Rotation rates have minimal impact on the strength of global mean vertical mixing, but significantly influence the latitudinal distribution of passive tracers. For synchronous, 2:1 SOR, and 6:1 SOR simulations, passive tracers are more abundant in the upwelling branches at latitudes within 60(degrees), while for the 10:1 SOR simulation, strong transient eddies at high latitudes (>70(degrees)) between 0.1 to 1 bar can transport passive tracers upward from the deep atmosphere, making them more abundant there, despite their alignment with the downwelling branch of the large-scale circulation. This study focuses on the atmospheric dynamics and its influence on passive tracer transport, while a follow-up paper will incorporate active chemical species.

Earth's hydrological cycle has undergone significant change during geological periods. While it is known that the global‐mean surface temperature (GMST) is the first‐order controlling factor, there are other factors less studied. We performed paleoclimate simulations to examine the evolution of global‐mean precipitation (GMP) from 540 million years ago to today. The GMP primarily varies with GMST, however, change in the low‐latitude land fraction is also important. An increase in land fraction can directly reduce GMP by reducing latent heat and increasing sensible heat. Furthermore, the weakened greenhouse gas effect of the drier atmosphere further amplify the direct impact by approximately 44%. A simple model of GMP as a function of GMST and land area fraction is developed, which effectively reproduces the simulation results throughout the Phanerozoic Eon. Our results clearly separate the effects of climate change and continental evolution on hydrological change over geological time and elucidate the functional mechanism.

In the geological past, terrestrial aridity had critical influences on the evolution of life and ecosystems. Here, we combine climate simulations and geological records to investigate the evolution of terrestrial aridity since Pangea. Throughout this geological epoch, tectonics had led to the breakup and reassembly of landmasses, alongside climatic oscillations between hothouse and icehouse conditions. Our findings reveal a dynamic landscape of dryland coverage, encompassing approximately 56% of global land during Pangea, diminishing to about 32% in the Cretaceous, and subsequently rising to around 40% in the Cenozoic era. We identify continental configurations and surface temperatures as pivotal determinants of dryland distribution. Our analysis indicates that the evolution of dryland areas is predominantly influenced by the subtropical land area (79.5%) and global mean surface temperature (15.4%). Furthermore, our study highlights a significant expansion of the dryland area, particularly within semi-arid regions, during periods of carbon dioxide-induced warming, attributed chiefly to increased potential evapotranspiration.