Exploring hail and lightning diagnostics over the Alpine-Adriatic region in a km-scale climate model

The north and south of the Alps, as well as the eastern shores of the Adriatic Sea, are hot spots of severe convective storms, including hail and lightning associated with deep convection. With advancements in computing power, it has become feasible to simulate deep convection explicitly in climate models by decreasing the horizontal grid spacing to less than 4 km. These kilometer-scale models improve the representation of orography and reduce uncertainties associated with the use of deep convection parameterizations. In this study, we perform km-scale simulations for eight observed cases of severe convective storms (seven with and one without observed hail) over the Alpine-Adriatic region. The simulations are performed with the climate version of the regional model Consortium for Small-scale Modeling (COSMO) that runs on graphics processing units (GPUs) at a horizontal grid spacing of 2.2 km. To analyze hail and lightning we have explored the hail growth model (HAILCAST) and lightning potential index (LPI) diagnostics integrated with the COSMO-crCLIM model. Comparison with available high-resolution observations reveals good performance of the model in simulating total precipitation, hail, and lightning. By performing a detailed analysis of three of the case studies, we identified the importance of significant meteorological factors for heavy thunderstorms that were reproduced by the model. Among these are the moist unstable boundary layer and dry mid-level air, the topographic barrier, as well as an approaching upper-level trough and cold front. Although COSMO HAILCAST tends to underestimate the hail size on the ground, the results indicate that both HAILCAST and LPI are promising candidates for future climate research.</p

Mean and extreme precipitation over European river basins better simulated in a 25km AGCM

Limited spatial resolution is one of the factors that may hamper applications of global climate models (GCMs), in particular over Europe with its complex coastline and orography. In this study, the representation of European mean and extreme precipitation is evaluated in simulations with an atmospheric GCM (AGCM) at different resolutions between about 135 and 25km grid spacing in the mid-latitudes. The continent-wide root-mean-square error in mean precipitation in the 25km model is about 25% smaller than in the 135km model in winter. Clear improvements are also seen in autumn and spring, whereas the model's sensitivity to resolution is very small in summer. Extreme precipitation is evaluated by estimating generalised extreme value distributions (GEVs) of daily precipitation aggregated over river basins whose surface area is greater than 50000km2. GEV location and scale parameters are measures of the typical magnitude and of the interannual variability of extremes, respectively. Median model biases in both these parameters are around 10% in summer and around 20% in the other seasons. For some river basins, however, these biases can be much larger and take values between 50% and 100%. Extreme precipitation is better simulated in the 25km model, especially during autumn when the median GEV parameter biases are more than halved, and in the North European Plains, from the Loire in the west to the Vistula in the east. A sensitivity experiment is conducted showing that these resolution sensitivities in both mean and extreme precipitation are in many areas primarily due to the increase in resolution of the model orography. The findings of this study illustrate the improved capability of a global high-resolution model in simulating European mean and extreme precipitation

Ground-based follow-up observations of TRAPPIST-1 transits in the near-infrared

The TRAPPIST-1 planetary system is a favorable target for the atmospheric characterization of temperate earth-sized exoplanets by means of transmission spectroscopy with the forthcoming James Webb Space Telescope (JWST). A possible obstacle to this technique could come from the photospheric heterogeneity of the host star that could affect planetary signatures in the transit transmission spectra. To constrain further this possibility, we gathered an extensive photometric data set of 25 TRAPPIST-1 transits observed in the near-IR J band (1.2 $\mu$m) with the UKIRT and the AAT, and in the NB2090 band (2.1 $\mu$m) with the VLT during the period 2015-2018. In our analysis of these data, we used a special strategy aiming to ensure uniformity in our measurements and robustness in our conclusions. We reach a photometric precision of $\sim0.003$ (RMS of the residuals), and we detect no significant temporal variations of transit depths of TRAPPIST-1 b, c, e, and g over the period of three years. The few transit depths measured for planets d and f hint towards some level of variability, but more measurements will be required for confirmation. Our depth measurements for planets b and c disagree with the stellar contamination spectra originating from the possible existence of bright spots of temperature 4500 K. We report updated transmission spectra for the six inner planets of the system which are globally flat for planets b and g and some structures are seen for planets c, d, e, and f.Comment: accepted for publication in MNRA

Weak evidence for variable occultation depth of 55 Cnc e with TESS

55 Cnc e is in a 0.73 day orbit transiting a Sun-like star. It has been observed that the occultation depth of this Super-Earth, with a mass of 8$M_{\bigoplus}$ and radius of 2$R_{\bigoplus}$, changes significantly over time at mid-infrared wavelengths. Observations with Spitzer measured a change in its day-side brightness temperature of 1200 K, possibly driven by volcanic activity, magnetic star-planet interaction, or the presence of a circumstellar torus of dust. Previous evidence for the variability in occultation was in the infrared range. Here we aim to explore if the variability exists also in the optical. TESS observed 55 Cnc during sectors 21, 44 and 46. We carefully detrend the data and fit a transit and occultation model for each sector in a Markov Chain Monte Carlo routine. In a later stage we use the Leave-One-Out Cross-Validation statistic to compare with a model of constant occultation for the complete set and a model with no occultation. We report an occultation depth of 8$\pm$2.5 ppm for the complete set of TESS observations. In particular, we measured a depth of 15$\pm$4 ppm for sector 21, while for sector 44 we detect no occultation. In sector 46 we measure a weak occultation of 8$\pm$5 ppm. The occultation depth varies from one sector to the next between 1.6 and 3.4 $\sigma$ significance. We derive the possible contribution on reflected light and thermal emission, setting an upper limit on the geometric albedo. Based on our model comparison the presence of an occultation is favoured considerably over no occultation, where the model with varying occultation across sectors takes most of the statistical weight. Our analysis confirms a detection of the occultation in TESS. Moreover, our results weakly lean towards a varying occultation depth between each sector, while the transit depth is constant across visits.Comment: 9 pages, 9 figures, accepted for publication on A&

Rock magnetic investigation of possible sources of the Bangui magnetic anomaly

International audienceThe Bangui magnetic anomaly (BMA) is the largest lithospheric magnetic field anomaly on Earth at low latitudes. Previous studies investigated its geological source using constraints from satellite and ground magnetic field measurements, as well as from surface magnetic susceptibility measurements on rocks from the Panafrican Mobile Belt Zone (PMBZ). Here we combine magnetic field data modelling and rock magnetic property measurements (susceptibility and natural remanent magnetization, NRM) on many samples from this PMBZ and the surrounding formations. It reveals that NRM is a significant component of the total magnetization (Mt) of the BMA source, which reaches 4.3 A/m with maximum thicknesses of 38 and 54 km beneath the western and eastern parts of the BMA. Only the isolated and relatively thin banded iron formations and some migmatites show such Mt values. Thus we suggest that the thick BMA source may be composed either by overlapped slices of such metamorphic rocks, or by an iron-rich mafic source, or by a combination of these two geological structures

The stable climate of KELT-9b

Even among the most irradiated gas giants, so-called ultra-hot Jupiters, KELT-9b stands out as the hottest planet thus far discovered with a dayside temperature of over 4500 K. At these extreme irradiation levels, we expect an increase in heat redistribution efficiency and a low Bond albedo owed to an extended atmosphere with molecular hydrogen dissociation occurring on the planetary dayside. We present new photometric observations of the KELT-9 system throughout 4 full orbits and 9 separate occultations obtained by the 30 cm space telescope CHEOPS. The CHEOPS bandpass, located at optical wavelengths, captures the peak of the thermal emission spectrum of KELT-9b. In this work we simultaneously analyse CHEOPS phase curves along with public phase curves from TESS and Spitzer to infer joint constraints on the phase curve variation, gravity-darkened transits, and occultation depth in three bandpasses, as well as derive 2D temperature maps of the atmosphere at three different depths. We find a day-night heat redistribution efficiency of ~0.3 which confirms expectations of enhanced energy transfer to the planetary nightside due to dissociation and recombination of molecular hydrogen. We also calculate a Bond albedo consistent with zero. We find no evidence of variability of the brightness temperature of the planet, excluding variability greater than 1

The TRAPPIST survey of southern transiting planets. I. Thirty eclipses of the ultra-short period planet WASP-43 b

We present twenty-three transit light curves and seven occultation light curves for the ultra-short period planet WASP-43 b, in addition to eight new measurements of the radial velocity of the star. Thanks to this extensive data set, we improve significantly the parameters of the system. Notably, the largely improved precision on the stellar density (2.41+-0.08 rho_sun) combined with constraining the age to be younger than a Hubble time allows us to break the degeneracy of the stellar solution mentioned in the discovery paper. The resulting stellar mass and size are 0.717+-0.025 M_sun and 0.667+-0.011 R_sun. Our deduced physical parameters for the planet are 2.034+-0.052 M_jup and 1.036+-0.019 R_jup. Taking into account its level of irradiation, the high density of the planet favors an old age and a massive core. Our deduced orbital eccentricity, 0.0035(-0.0025,+0.0060), is consistent with a fully circularized orbit. We detect the emission of the planet at 2.09 microns at better than 11-sigma, the deduced occultation depth being 1560+-140 ppm. Our detection of the occultation at 1.19 microns is marginal (790+-320 ppm) and more observations are needed to confirm it. We place a 3-sigma upper limit of 850 ppm on the depth of the occultation at ~0.9 microns. Together, these results strongly favor a poor redistribution of the heat to the night-side of the planet, and marginally favor a model with no day-side temperature inversion.Comment: 14 pages, 6 tables, 11 figures. Accepted for publication in A&

Transit timing variation and transmission spectroscopy analyses of the hot Neptune GJ3470b

GJ3470b is a hot Neptune exoplanet orbiting an M dwarf and the first sub-Jovian planet to exhibit Rayleigh scattering. We present transit timing variation (TTV) and transmission spectroscopy analyses of multiwavelength optical photometry from 2.4-m and 0.5-m telescopes at the Thai National Observatory, and the 0.6-m PROMPT-8 telescope in Chile. Our TTV analysis allows us to place an upper mass limit for a second planet in the system. The presence of a hot Jupiter with a period of less than 10 d or a planet with an orbital period between 2.5 and 4.0 d are excluded. Combined optical and near-infrared transmission spectroscopy favour an H/He-dominated haze (mean molecular weight 1.08 ± 0.20) with high particle abundance at high altitude. We also argue that previous near-infrared data favour the presence of methane in the atmosphere of GJ3470b

TRAPPIST-1: Global results of the Spitzer Exploration Science Program Red Worlds

With more than 1000 hours of observation from Feb 2016 to Oct 2019, the Spitzer Exploration Program Red Worlds (ID: 13067, 13175 and 14223) exclusively targeted TRAPPIST-1, a nearby (12pc) ultracool dwarf star orbited by seven transiting Earth-sized planets, all well-suited for a detailed atmospheric characterization with the upcoming JWST. In this paper, we present the global results of the project. We analyzed 88 new transits and combined them with 100 previously analyzed transits, for a total of 188 transits observed at 3.6 or 4.5 $\mu$m. We also analyzed 29 occultations (secondary eclipses) of planet b and eight occultations of planet c observed at 4.5 $\mu$m to constrain the brightness temperatures of their daysides. We identify several orphan transit-like structures in our Spitzer photometry, but all of them are of low significance. We do not confirm any new transiting planets. We estimate for TRAPPIST-1 transit depth measurements mean noise floors of $\sim$35 and 25 ppm in channels 1 and 2 of Spitzer/IRAC, respectively. most of this noise floor is of instrumental origins and due to the large inter-pixel inhomogeneity of IRAC InSb arrays, and that the much better interpixel homogeneity of JWST instruments should result in noise floors as low as 10ppm, which is low enough to enable the atmospheric characterization of the planets by transit transmission spectroscopy. We construct updated broadband transmission spectra for all seven planets which show consistent transit depths between the two Spitzer channels. We identify and model five distinct high energy flares in the whole dataset, and discuss our results in the context of habitability. Finally, we fail to detect occultation signals of planets b and c at 4.5 $\mu$m, and can only set 3$\sigma$ upper limits on their dayside brightness temperatures (611K for b 586K for c)