Atmospheric Constraints Research Articles

Peering above the clouds of the warm Neptune GJ 436 b with CRIRES+

Context. Exoplanets with masses between Earth and Neptune are amongst the most commonly observed, yet their properties are poorly constrained. Their transmission spectra are often featureless, which indicate either high-altitude clouds or a high atmospheric metallicity. The archetypical warm Neptune GJ 436 b is such a planet showing a flat transmission spectrum in observations with the Hubble Space Telescope (HST). Aims. Ground-based high-resolution spectroscopy (HRS) effectively probes exoplanet atmospheres at higher altitudes and can therefore be more sensitive to absorption coming from above potential cloud decks. In this paper we aim to investigate this for the exoplanet GJ 436b. Methods. We present new CRIRES+ HRS transit data of GJ 436 b. Three transits were observed, but since two were during bad weather conditions, only one transit was analyzed. The radiative transfer code petitRADTRANS was used to create atmospheric models for cross-correlation and signal-injection purposes, including absorption from H2O, CH4, and CO. Results. No transmission signals were detected, but atmospheric constraints can be derived. Injection of artificial transmission signals indicate that if GJ 436 b would have a cloud deck at pressures P > 10 mbar and a <300× solar metallicity, these CRIRES+ observations should have resulted in a detection. Conclusions. We estimate that the constraints presented here from one ground-based HRS transit are slightly better than those obtained with four HST transits. Combining HRS data from multiple transits is an interesting avenue for future studies of exoplanets with high-altitude clouds.

New Insights into the Internal Structure of GJ 1214 b Informed by JWST

Recent JWST observations of the sub-Neptune GJ 1214 b suggest that it hosts a high-metallicity (≳100× solar), hazy atmosphere. Emission spectra of the planet show molecular absorption features, most likely due to atmospheric H2O. In light of this new information, we conduct a thorough reevaluation of the planet’s internal structure. We consider interior models with mixed H/He/H2O envelopes of varying composition, informed by atmospheric constraints from the JWST phase curve, in order to determine possible bulk compositions and internal structures. Self-consistent atmospheric models consistent with the JWST observations are used to set boundary conditions for the interior. We find that a total envelope mass fraction of at least 8.1% is required to explain the planet’s mass and radius. Regardless of H2O content, the maximum H/He mass fraction of the planet is 5.8%. We find that a 1:1 ice-to-rock ratio along with 3.4%–4.8% H/He is also a permissible solution. In addition, we consider a pure H2O (steam) envelope and find that such a scenario is possible, albeit with a high ice-to-rock ratio of at least 3.76:1, which may be unrealistic from a planet formation standpoint. We discuss possible formation pathways for the different internal structures that are consistent with observations. Since our results depend strongly on the atmospheric composition and haze properties, more precise observations of the planet’s atmosphere would allow for further constraints on its internal structure. This type of analysis can be applied to any sub-Neptune with atmospheric constraints to better understand its interior.

Verification of Kastner Visibility of Hilal Observation Results at Condrodipo Rukyat Center in 1444 H

The Kastner Hilal visibility method is one of numerous contemporary observation techniques developed with the objective of monitoring the appearance of Hilal with greater precision. This paper presents a discussion of Hilal observations conducted at the Condrodipo Rukyat Center. The visibility results are analyzed using curve graphs, facilitating the assessment and validation of the observations. The findings demonstrate that employing the Kastner mathematical model can corroborate visibility with a substantial degree of concurrence, regardless of atmospheric constraints and sky conditions. However, the results of observer reports in the field are often inconsistent with model predictions, especially in conditions of low Hilal altitude and naked eye observations. Therefore, more rigorous scientific verification and reliable methodologies are needed to confirm observations for the integrity of the determination of the beginning of the lunar month.

Impact of α enhancement on the asteroseismic age determination of field stars

Aims. We investigated the theoretical biases affecting the asteroseismic grid-based estimates of stellar mass, radius, and age in the presence of a mismatch between the heavy element mixture of observed stars and stellar models. Methods. We performed a controlled simulation adopting a stellar effective temperature, [Fe/H], an average large frequency spacing, and a frequency of maximum oscillation power as observational constraints. Synthetic stars were sampled from grids of stellar models computed with different [α/Fe] values from 0.0 to 0.4. The mass, radius, and age of these objects were then estimated by adopting a grid of models with a fixed [α/Fe] value of 0.0. The experiment was repeated assuming different sets of observational uncertainties. In the reference scenario, we adopted an uncertainty of 1.5% in seismic parameters, 50 K in effective temperature, and 0.05 dex in [Fe/H]. A higher uncertainty in the atmospheric constraints was also adopted in order to explore the impact on the precision of the observations of the estimated stellar parameters. Results. Our Monte Carlo experiment showed that estimated parameters are biased up to 3% in mass, 1.5% in radius, and 4% in age when the reference uncertainty scenario was adopted. These values correspond to 45%, 48%, and 16% of the estimated uncertainty in the stellar parameters. These non-negligible biases in mass and radius disappear when adopting larger observational uncertainties because of the possibility of the fitting algorithm exploring a wider range of possible solutions. However, in this scenario, the age is significantly biased by −8%. Finally, we verified that the stellar mass, radius, and age can be estimated with a high accuracy by adopting a grid with the incorrect value of [α/Fe] if the metallicity [Fe/H] of the target is adjusted to match the Z in the fitting grid. In this scenario, the maximum bias in the age was reduced to 1.5%.

Atmospheric constraints on changing Arctic CH4 emissions

Rapid warming in the Arctic has the potential to release vast reservoirs of carbon into the atmosphere as methane (CH4) resulting in a strong positive climate feedback. This raises the concern that, after a period of near-zero growth in atmospheric CH4 burden from 1999 to 2006, the increase since then may be in part related to increased Arctic emissions. Measurements of CH4 in background air samples provide useful, direct information to determine if Arctic CH4 emissions are increasing. One sensitive first-order indicator for large emission change is the Interpolar Difference, that is the difference in surface atmospheric annual means between polar northern and southern zones (53°–90°), which has varied interannually, but did not increase from 1992 to 2019. The Interpolar Difference has increased moderately during 2020–2022 when the global CH4 burden increased significantly, but not yet to its peak values in the late-1980s. For quantitative assessment of changing Arctic CH4 emissions, the atmospheric measurements must be combined with an atmospheric tracer transport model. Based on multiple studies including some using CH4 isotopes, it is clear that most of the increase in global atmospheric CH4 burden is driven by increased emissions from microbial sources in the tropics, and that Arctic emissions have not increased significantly since the beginning of our measurement record in 1983 through 2022.

Improved atmospheric constraints on Southern Ocean CO2 exchange

We present improved estimates of air-sea CO2 exchange over three latitude bands of the Southern Ocean using atmospheric CO2 measurements from global airborne campaigns and an atmospheric 4-box inverse model based on a mass-indexed isentropic coordinate (Mθe). These flux estimates show two features not clearly resolved in previous estimates based on inverting surface CO2 measurements: a weak winter-time outgassing in the polar region and a sharp phase transition of the seasonal flux cycles between polar/subpolar and subtropical regions. The estimates suggest much stronger summer-time uptake in the polar/subpolar regions than estimates derived through neural-network interpolation of pCO2 data obtained with profiling floats but somewhat weaker uptake than a recent study by Long et al. [Science 374, 1275-1280 (2021)], who used the same airborne data and multiple atmospheric transport models (ATMs) to constrain surface fluxes. Our study also uses moist static energy (MSE) budgets from reanalyses to show that most ATMs tend to have excessive diabatic mixing (transport across moist isentrope, θe, or Mθe surfaces) at high southern latitudes in the austral summer, which leads to biases in estimates of air-sea CO2 exchange. Furthermore, we show that the MSE-based constraint is consistent with an independent constraint on atmospheric mixing based on combining airborne and surface CO2 observations.

First VLTI/GRAVITY Observations of HIP 65426 b: Evidence for a Low or Moderate Orbital Eccentricity

Giant exoplanets have been directly imaged over orders of magnitude of orbital separations, prompting theoretical and observational investigations of their formation pathways. In this paper, we present new VLTI/GRAVITY astrometric data of HIP 65426 b, a cold, giant exoplanet which is a particular challenge for most formation theories at a projected separation of 92 au from its primary. Leveraging GRAVITY’s astrometric precision, we present an updated eccentricity posterior that disfavors large eccentricities. The eccentricity posterior is still prior dependent, and we extensively interpret and discuss the limits of the posterior constraints presented here. We also perform updated spectral comparisons with self-consistent forward-modeled spectra, finding a best-fit ExoREM model with solar metallicity and C/O = 0.6. An important caveat is that it is difficult to estimate robust errors on these values, which are subject to interpolation errors as well as potentially missing model physics. Taken together, the orbital and atmospheric constraints paint a preliminary picture of formation inconsistent with scattering after disk dispersal. Further work is needed to validate this interpretation. Analysis code used to perform this work is available on GitHub: https://github.com/sblunt/hip65426.

Brown Dwarf Retrievals on FIRE!: Atmospheric Constraints and Lessons Learned from High Signal-to-noise Medium-resolution Spectroscopy of a T9 Dwarf

Brown dwarf spectra offer vital testbeds for our understanding of the chemical and physical processes that sculpt substellar atmospheres. Recently, atmospheric retrieval approaches have been successfully applied to low-resolution (R ∼ 100) spectra of L, T, and Y dwarfs, yielding constraints on the chemical abundances and temperature structures of these atmospheres. Medium-resolution (R ∼ 103) spectra of brown dwarfs offer additional insight, as molecular features are more easily disentangled and the thermal structure of the upper atmosphere is better probed. We present results from a GPU-based retrieval analysis of a high signal-to-noise, medium-resolution (R ∼ 6000) FIRE spectrum from 0.85 to 2.5 μm of the T9 dwarf UGPS J072227.51–054031.2. At 60× higher spectral resolution than previous brown dwarf retrievals, a number of novel challenges arise. We examine the effect of different opacity sources, in particular for CH4. Furthermore, we find that flaws in the data like errors from order stitching can bias our constraints. We compare these retrieval results to those for an R ∼ 100 spectrum of the same object, revealing how constraints on atmospheric abundances and temperatures improve by an order of magnitude or more with increased spectral resolution. In particular, we can constrain the abundance of H2S, which is undetectable at lower spectral resolution. While these medium-resolution retrievals offer the potential of precise, stellar-like constraints on atmospheric abundances (∼0.02 dex), our retrieved radius is unphysically small ( R Jup), indicating shortcomings with our modeling framework. This work is an initial investigation into brown dwarf retrievals at medium spectral resolution, offering guidance for future ground-based studies and JWST observations.

Can the Orbital Debris Disease Be Cured Using Lasers?

Ground-based high-power lasers are, in principle, able to de-orbit any kind of space debris object from the low Earth orbit (LEO) by remotely inducing laser-ablative momentum. However, the assessment of efficiency and operational safety depends on many factors, like atmospheric constraints or the risk of debris disintegration during irradiation. We analyze laser momentum for a great variety of target geometries and sizes and—for the first time in a large-scale simulation—include thermal constraints in the laser irradiation configuration. Using a coherently coupled 100 kJ laser system at 1030 nm wavelength and a 5 ns pulse duration in an optimized pointing elevation angle range, the pulse frequency should amount to less than 10 Hz to prevent fragment meltdown. For mechanically intact payloads or rocket bodies, repetition rates should be even lower. Small debris fragments sized between 10 and 40 cm can be de-orbited by employing around 100 to 400 station passes with head-on irradiation, while objects exceeding 2 m typically require far more than 1000 irradiations for de-orbit. Hence, laser-based debris removal cannot be considered a prime space sustainability measure to tackle the highest-risk large debris, yet it can provide the remediation of a multitude of small-sized debris using small networks of globally distributed laser sites.

Early Insights for Atmospheric Retrievals of Exoplanets Using JWST Transit Spectroscopy

We have entered the era of the James Webb Space Telescope (JWST). We use the first JWST transmission spectrum of the hot Saturn-mass exoplanet, WASP-39 b, obtained with the NIRSpec instrument in the 3–5 μm range to investigate (a) what atmospheric constraints are possible with JWST-quality data in this spectral range, (b) requirements for atmospheric models used in retrievals, (c) effect of differences between data reduction pipelines on retrieved atmospheric properties, and (d) complementarity between JWST data in the 3–5 μm range and Hubble Space Telescope (HST) observations at shorter wavelengths. JWST spectra in the 3–5 μm range provide a promising avenue for chemical detections while encompassing a window in cloud opacity for several prominent aerosols. We confirm recent inferences of CO2, SO2, H2O, and CO in WASP-39 b; report tentative evidence for H2S; and retrieve elemental abundances consistent with Saturn’s metallicity. We retrieve molecular abundances with ∼0.3–0.6 dex precision with this relatively limited spectral range. When considering the 3–5 μm data alone, reported differences in spectra with different reduction pipelines can affect abundance estimates by up to ∼1 dex and the detectability of less prominent species. Complementing with data at shorter wavelengths, e.g., with other JWST instruments or HST WFC3 (∼0.8–1.7 μm), can significantly improve the accuracy and precision of the abundance estimates. The high data quality enables constraints on aerosol properties, including their composition, modal size, and extent, motivating their consideration in retrievals. Our results highlight the promise of JWST exoplanet spectroscopy, while underscoring the importance of robust data reduction and atmospheric retrieval approaches in the JWST era.

Using the atmospheric CO2 growth rate to constrain the CO2 flux from land use and land cover change since 1900.

We explore the ability of the atmospheric CO2 record since 1900 to constrain the source of CO2 from land use and land cover change (hereafter "land use"), taking account of uncertainties in other terms in the global carbon budget. We find that the atmospheric constraint favors land use CO2 flux estimates with lower decadal variability and can identify potentially erroneous features, such as emission peaks around 1960 and after 2000, in some published estimates. Furthermore, we resolve an offset in the global carbon budget that is most plausibly attributed to the land use flux. This correction shifts the mean land use flux since 1900 across 20 published estimates down by 0.35 PgC year-1 to 1.04 ± 0.57 PgC year-1 , which is within the range but at the low end of these estimates. We show that the atmospheric CO2 record can provide insights into the time history of the land use flux that may reduce uncertainty in this term and improve current understanding and projections of the global carbon cycle.

What sets aeolian dune height?

Wherever a loose bed of sand is subject to sufficiently strong winds, aeolian dunes form at predictable wavelengths and growth rates. As dunes mature and coarsen, however, their growth trajectories become more idiosyncratic; nonlinear effects, sediment supply, wind variability and geologic constraints become increasingly relevant, resulting in complex and history-dependent dune amalgamations. Here we examine a fundamental question: do aeolian dunes stop growing and, if so, what determines their ultimate size? Earth’s major sand seas are populated by giant sand dunes, evolved over tens of thousands of years. We perform a global analysis of the topography of these giant dunes, and their associated atmospheric forcings and geologic constraints, and we perform numerical experiments to gain insight on temporal evolution of dune growth. We find no evidence of a previously proposed limit to dune size by atmospheric boundary layer height. Rather, our findings indicate that dunes may grow indefinitely in principle; but growth depends on morphology, slows with increasing size, and may ultimately be limited by sand supply.

Unveiling Nongray Surface of Cloudy Exoplanets: The Influence of Wavelength-dependent Surface Albedo and Cloud Scattering Properties on Retrieval Solutions

Direct-imaging spectra hold rich information about a planet’s atmosphere and surface, and several space-based missions aiming at such observations will become a reality in the near future. Previous spectral retrieval works have resulted in key atmospheric constraints under the assumption of a gray surface, but the effect of wavelength-dependent surface albedo on retrieval has not been shown. We explore the influence of the coupling effect of cloud and wavelength-dependent surface albedo on retrieval performance via modeling suites of Earth-like atmospheres with varying cloud and surface albedo parameterizations. Under the assumption of known cloud scattering properties, the surface spectral albedos can be reasonably recovered when the surface cover represents that of Earth-like vegetation or ocean, which may aid in characterizing the planet’s habitability. When the cloud scattering properties cannot be assumed, we show that the degeneracy between the cloud properties and wavelength-dependent surface albedo leads to biased results of atmospheric and cloud properties. The multiepoch visible-band observations offer limited improvement in disentangling this degeneracy. However, the constraints on atmospheric properties from the combination of the UV band (R ∼ 6) + visible band (R ∼ 140) are consistent with input values to within 1σ. If short-bandpass data are not available, an alternative solution to reduce the retrieval uncertainties would be to have the prior constraints on the planetary cloud fraction with less than 20% uncertainty.

Design and Development of a Mobile Robotic System for Aircraft Wing Fuel Tank Inspection

<div class="section abstract"><div class="htmlview paragraph">This paper presents the design concept behind a novel remote visual inspection robotic system for fighter jet aircraft wing fuel tank inspection. This work is part of a larger research project which focuses on design, simulation, physical prototyping and experimental validation of a robotic system. Whereas this paper specifically focuses on the development concept of locomotion design choice for the robot. Therefore without an effective mobility method the robot will not be able to fulfill its purpose to access the hazardous confined spaces of the fuel tank. Aircraft wing fuel tank inspection is a challenging area of maintenance which requires a considerable amount of preparation and involvement of several tasks in order to conduct effective Visual and Non Destructive Inspection. The environment of an aircraft wing fuel tank poses several challenges due to both physical and atmospheric constraints which can be detrimental to human personal. This paper introduces an effective locomotion design which should allow the robot to enter and maneuver within confined spaces. The robot is relatively small, approximately 70mm in height and width yet, flexible enough to move within the restricted spaces of the wing. The mobile robot platform is a combination of small track systems that articulate like a snake. An additional mobile platform deploys an inspection sensor to reach the spaces that are unreachable by the robot body. Like other proposed robotic systems this particular proposal differs as it allows the robot to enter from the root of the wing and reach the narrower spaces towards with the wing tip. This paper highlights the stakeholder requirements to illustrate the foundation of the robotic system design. An overview of current complications of wing fuel tank inspection is presented and the analysis of current proposed robotic systems for wing fuel tank inspection. An engineering design methodology approach is followed for this project. Several locomotion methods are evaluated and an innovative locomotion method is illustrated with the use of CAD models. The desired outcome of this research is to eliminate the entry or close contact with the fuel tank by human personal.</div></div>

Photosynthetic acclimation and sensitivity to short- and long-term environmental changes in a drought-prone forest.

Future climate will be characterized by an increase in frequency and duration of drought and warming that exacerbates atmospheric evaporative demand. How trees acclimate to long-term soil moisture changes and whether these long-term changes alter trees' sensitivity to short-term (day to months) variations of vapor pressure deficit (VPD) and soil moisture is largely unknown. Leaf gas exchange measurements were performed within a long-term (17 years) irrigation experiment in a drought-prone Scots pine-dominated forest in one of Switzerland's driest areas on trees in naturally dry (control), irrigated, and 'irrigation-stop' (after 11 years of irrigation) conditions. Seventeen years of irrigation increased photosynthesis (A) and stomatal conductance (gs) and reduced gs sensitivity to increasing VPD and soil drying. Following irrigation-stop, gas exchange decreased only after 3 years. After 5 years, maximum carboxylation (Vcmax) and electron transport (Jmax) rates in irrigation-stop recovered to similar levels as to before the irrigation-stop. These results suggest that long-term release from soil drought reduces the sensitivity to VPD and that atmospheric constraints may play an increasingly important role in combination with soil drought. Moreover, our study indicates that structural adjustments lead to an attenuation of initially strong leaf-level acclimation to strong multiple-year drought.

HyDRo: atmospheric retrieval of rocky exoplanets in thermal emission

ABSTRACT Emission spectroscopy is a promising technique to observe atmospheres of rocky exoplanets, probing both their chemistry and thermal profiles. We present hydro, an atmospheric retrieval framework for thermal emission spectra of rocky exoplanets. hydro does not make prior assumptions about the background atmospheric composition, and can therefore be used to interpret spectra of secondary atmospheres with unknown compositions. We use hydro to assess the chemical constraints which can be placed on rocky exoplanet atmospheres using JWST. First, we identify the best currently known rocky exoplanet candidates for spectroscopic observations in thermal emission with JWST, finding >30 known rocky exoplanets whose thermal emission will be detectable by JWST/MIRI in fewer than 10 eclipses at R ∼ 10. We then consider the observations required to characterize the atmospheres of three promising rocky exoplanets across the ∼400–800 K equilibrium temperature range: Trappist-1 b, GJ 1132 b, and LHS 3844 b. Considering a range of CO2- to H2O-rich atmospheric compositions, we find that as few as eight eclipses of LHS 3844 b or GJ 1132 b with MIRI LRS will be able to place important constraints on the chemical compositions of their atmospheres. This includes confident detections of CO2 and H2O in the case of a cloud-free CO2-rich composition, besides ruling out a bare rock scenario. Similarly, 30 eclipses of Trappist-1 b with MIRI LRS can allow detections of a cloud-free CO2-rich or CO2-H2O atmosphere. hydro will allow important atmospheric constraints for rocky exoplanets using JWST observations, providing clues about their geochemical environments.

The coupled effect of soil and atmospheric constraints on the vulnerability and water use of two desert riparian ecosystems

Plant response to soil and atmospheric water stresses is the dominant control of Dryland ecosystem functions, affecting water resources, ecosystem stability and biodiversity. The link between water stresses and plant water status is regulated by plant hydraulics, of which the corresponding impact on plant water use and the susceptibility of Dryland ecosystems remains under-explored. We used a plant hydraulic model to describe hydraulic states and water flux of two species (Populus euphratica and Tamarix ramosissima) in desert riparian ecosystems. We optimized hydraulic parameters and tested the model using observed physiological states and ecosystem water flux. The optimized model was used to evaluate plant hydraulic sensitivity, tree mortality risk, and evapotranspiration under a wide range of water stress scenarios. The model captures the observed leaf water potential, sap-flow and ecosystem evapotranspiration. Our scenario analysis demonstrates that hydraulic sensitivities generally reduce as the water stresses intensify. The results highlight a strong coupled impact of the co-occurrence of soil and atmospheric water stresses on restricting ecosystem water flux and intensifying mortality risk. The assessment of multiple aspects of eco-physiological functions and the stress scenario analysis of desert riparian ecosystems will contribute to a better prediction of ecosystem functions and facilitate resource management under future climate.

Performance of Single-Epoch EWL/WL/NL Ambiguity-Fixed Precise Point Positioning with Regional Atmosphere Modelling

Precise point positioning (PPP) with ambiguity resolution (AR) can improve positioning accuracy and reliability. The narrow-lane (NL) AR solution can reach centimeter-level accuracy but there is a certain initialization time. In contrast, extra-wide-lane (EWL) or wide-lane (WL) ambiguity can be fixed instantaneously. However, due to the limited correction accuracy of the empirical atmospheric model, the positioning accuracy is only a few decimeters. In order to further improve the real-time performance of PPP while ensuring accuracy, we developed a multi-system multi-frequency uncombined PPP single-epoch EWL/WL/NL AR method with regional atmosphere modelling. In the proposed method, the precise atmosphere, including zenith wet-troposphere delay (ZWD) and the slant ionosphere, is extracted through multi-frequency stepwise AR, which then is both interpolated and broadcast to users. By adding regional atmosphere constraints, users can achieve single-epoch PPP AR with centimeter-level accuracy. To verify the algorithm, four sets of reference networks with different inter-station distances are used for experiments. With atmosphere constraints, the accuracy of the single-epoch WL solution can be improved from the decimeter level to a few centimeters, with an improvement of more than 90%, and the epoch fix rate can also be improved to varying degrees, especially for the dual-frequency case. Due to the enlarged noise of the EWL combination, its accuracy is at the decimeter level, while the accuracy of the WL/NL solution can reach several centimeters. However, reliable NL ambiguity-fixing tightly relies on atmosphere constraints with sufficiently high accuracy. When the modelling of the atmosphere correction is not accurate enough, the NL AR performance is degraded, although this situation can be improved to a certain extent through the multi-GNSS combination. In contrast, in this case, the WL ambiguity can be successfully fixed and can support the precise positioning with an accuracy of several centimeters.

An Atmospheric Constraint on the Seasonal Air‐Sea Exchange of Oxygen and Heat in the Extratropics

AbstractThe air‐sea exchange of oxygen (O2) is driven by changes in solubility, biological activity, and circulation. The total air‐sea exchange of O2 has been shown to be closely related to the air‐sea exchange of heat on seasonal timescales, with the ratio of the seasonal flux of O2 to heat varying with latitude, being higher in the extratropics and lower in the subtropics. This O2/heat ratio is both a fundamental biogeochemical property of air‐sea exchange and a convenient metric for testing earth system models. Current estimates of the O2/heat flux ratio rely on sparse observations of dissolved O2, leaving it fairly unconstrained. From a model ensemble we show that the ratio of the seasonal amplitude of two atmospheric tracers, atmospheric potential oxygen (APO) and the argon‐to‐nitrogen ratio (Ar/O2), exhibits a close relationship to the O2/heat ratio of the extratropics (40–). The amplitude ratio, /, is relatively constant within the extratropics of each hemisphere due to the zonal mixing of the atmosphere. / is not sensitive to atmospheric transport, as most of the observed spatial variability in the seasonal amplitude of APO is compensated by similar variations in (Ar/). From the relationship between /heat and / in the model ensemble, we determine that the atmospheric observations suggest hemispherically distinct /heat flux ratios of 3.3 0.3 and 4.7 0.8 nmol between 40 and in the Northern and Southern Hemispheres respectively, providing a useful constraint for and heat air‐sea fluxes in earth system models and observation‐based data products.

Differentiating modern and prebiotic Earth scenarios for TRAPPIST-1e: high-resolution transmission spectra and predictions for JWST

ABSTRACT The TRAPPIST-1 system is a priority target for terrestrial exoplanet characterization. TRAPPIST-1e, residing in the habitable zone, will be observed during the James Webb Space Telescope (JWST) GTO Program. Here, we assess the prospects of differentiating between prebiotic and modern Earth scenarios for TRAPPIST-1e via transmission spectroscopy. Using updated TRAPPIST-1 stellar models from the Mega-MUSCLES survey, we compute self-consistent model atmospheres for a 1 bar prebiotic Earth scenario and two modern Earth scenarios (1 and 0.5 bar eroded atmosphere). Our modern and prebiotic high-resolution transmission spectra ($0.4\!-\! 20\, \rm{\mu m}$ at R ∼100 000) are made available online. We conduct a Bayesian atmospheric retrieval analysis to ascertain the molecular detectability, abundance measurements, and temperature constraints achievable for both scenarios with JWST. We demonstrate that JWST can differentiate between our prebiotic and modern Earth scenarios within 20 NIRSpec Prism transits via CH4 abundance measurements. However, JWST will struggle to detect O3 for our modern Earth scenario to $\gt 2\, \sigma$ confidence within the nominal mission lifetime (∼ 80 transits over 5 yr). The agnostic combination of N2O and/or O3 offers better prospects, with a predicted detection significance of $2.7\, \sigma$ with 100 Prism transits. We show that combining MIRI LRS transits with Prism data provides little improvement to atmospheric constraints compared to observing additional Prism transits. Though biosignatures will be challenging to detect for TRAPPIST-1e with JWST, the abundances for several important molecules – CO2, CH4, and H2O – can be measured to a precision of ≲ 0.7 dex (a factor of 5) within a 20 Prism transit JWST program.