Night Side Research Articles

Longitudinal Evolution of the Velocity of Subauroral Polarization Streams (SAPS) in Different Phases of Magnetic Storms: SuperDARN Observations

AbstractInvestigations of the evolution of subauroral polarization streams (SAPS) are important to understand the plasma transport processes in the polar ionosphere. In this article, three cases of SAPS evolution are analyzed using the observations made by the Super Dual Auroral Radar Network mid‐latitude radar chain, Special Sensor Ultraviolet Spectrographic Imagers instrument and Active Magnetosphere and Planetary Electrodynamics Response Experiment. The three cases occur in the main phase, beginning of recovery phase and end of recovery phase of three magnetic storms. The cases last from 1.5 to 2 h during 1800–0300 MLT (magnetic local time). The observations show that the SAPS velocity evolution is strongly controlled by the ring current injection during the storm main phase. The responses of SAPS velocity are prompt and appear first near the dusk side and then expand to the night side. Besides, the SAPS velocity has a good linear correlation (R = −0.85) with SYMH index during the evolution of the magnetic storm. The SAPS velocity also shows dependence on the AE index and interplanetary magnetic field (IMF) Bz. The correlations between SAPS velocity and AE/Bz increase with the decay of the magnetic storm. However, the effect of substorm/IMF on SAPS velocity is not strong compared to that of the magnetic storm.

Ionospheric and Thermospheric Contributions in TIMED/GUVI O 135.6 nm Radiances

AbstractWe developed an empirically determined, data‐driven method to extract the ionospheric and thermospheric contributions in the Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (GUVI) 135.6 nm radiances on dayside to improve the O/N2 product. The technique assumes a reference dayside ratio of 130.4 and 135.6 nm radiances versus solar zenith angle (SZA) established from geomagnetically quiet observations and a fixed night side 130.4–135.6 nm radiance ratio of 1.2. The method effectively separates the ionospheric and thermospheric contributions in the observed 135.6 nm radiance. This not only improves the estimation of the thermospheric O/N2 ratio, (an important space weather parameter), by removing the ionospheric contribution in the GUVI 135.6 nm radiance data, but also provides the ionospheric signature in the 135.6 nm radiance. Comparison between GUVI ionospheric 135.6 nm radiances due to O+ and electron radiative recombination with coincident GPS TEC data shows a similar morphology of equatorial arcs, such as the arc latitude separation and nonmigrating tidal signature, confirming that the method is reliable. When there are no equatorial arcs, the ionospheric contribution is low, also consistent with low TEC data. This method can be applied to DMSP/SSUSI and other far ultraviolet data with simultaneous disk 130.4 and 135.6 nm measurements.

The Acceleration of Outer-Belt Electrons by Localized Electric Fields

To explain the populations of the outer-belt energetic electrons, including relativistic electrons, that sporadically appear in the magnetosphere, a mechanism was proposed long ago for the acceleration of those electrons by short-term bursts of the electric field, which appear on the night side during substorm disturbances (Kropotkin, 1996). This mechanism can be substantially specified if the modern concepts of bursty bulk flows in the geomagnetic tail, the occurrence of dipolarization fronts, and the excitation of localized field-aligned-resonant poloidal Alfvén oscillations involving a strong component of the electric field in the dawn-dusk direction are taken into account.

Fast near-UV radiation pulsations measured by the space telescope TUS in the auroral region

Observations of a faint pulsating UV emission from the atmosphere in the region of auroral oval were made by a highly sensitive satellite telescope TUS with a milliseconds temporal resolution.The TUS detector was launched in April 2016 on board the Lomonosov spacecraft. TUS was designed to register the extensive air shower (EAS) fluorescent signal from ultra-high-energy cosmic rays in the wavelength range 300–400 nm. EAS fluorescence is a weak and rapidly moving signal in the detector's field of view (FOV). Therefore, the TUS detector was equipped with a 2 m2 mirror and high temporal resolution (0.8 μs) photo detector. The FOV of the device is 6400 km2, the angular resolution is 10 mrad, which corresponds to the 5×5 km square on the Earth surface. The Lomonosov satellite has a polar sun-synchronous orbit with an inclination of 97.3∘, which provides measurements up to the high latitudes on the night side of the orbit. The detector electronics implements several operating modes that differ in time resolution (from 0.8 μs to 6.6 ms) and measure optical phenomena of different time scales.We analyze the near-UV glow in the northern polar region (50°–80° N), carried out in a mode with a temporal resolution of 6.6 ms and a waveform duration of 1.7 s. About 2500 observations were analyzed in a wide range of longitudes. A selection of events with the peculiar spatial-temporal dynamics of the signal was made. An analysis of the selected events structure and location relative to the auroral oval shows that fast pulsations are observed during disturbed geomagnetic conditions at the equatorial border of the auroral zone.

Globally Correlated Ground Magnetic Disturbances During Substorms

AbstractWe observationally address substorm‐related ground magnetic disturbances in terms of the substorm current wedge (SCW) system. The study consists of three data analyses, which approach different aspects of this subject. First, by comparing nightside magnetic disturbances below and above the ionosphere, we confirm that substorm‐related midlatitude magnetic disturbances around the edges of the SCW can be attributed to a remote current system (i.e., SCW) rather than to a local ionospheric current. Second, we statistically examine the magnetic local time (MLT) distributions of the correlation between midlatitude magnetic variations and the nightside westward auroral electrojet (AEJ). We confirm that nightside magnetic disturbances are consistent with the SCW, and find that correlated magnetic variations extend to the midday sector. Finally, we introduce midlatitude and high‐latitude geomagnetic indices for each MLT quadrant, and find that their variations are often correlated with the nightside AEJ intensity. From the magnitude of the correlated variations it is inferred that midday magnetic disturbances at both midlatitudes and high latitudes are remote effects of the SCW. In the dawn‐sector and dusk‐sector auroral zone, in contrast, correlated magnetic disturbances can be attributed mostly to the global enhancement of AEJs, which suggests that the global region‐1 system also changes in correlation with the nightside westward AEJ during substorms. These results consistently indicate that ground magnetic disturbances are correlated globally with the substorm westward AEJ. In contrast, the geomagnetic effect of midlatitude ionospheric currents must be relatively small not only on the night side but also on the day side.

TESS unveils the optical phase curve of KELT-1b

We present the detection and analysis of the phase curve of KELT-1b at optical wavelengths, analyzing data taken by the Transiting Exoplanet Survey Satellite (TESS) during cycle 2 and sector 17. With a mass of ~27 MJup, KELT-1b is an example of a low-mass brown dwarf. Due to the high mass and close proximity of its companion, the host star exhibits a TESS light curve that shows clear ellipsoidal variations. We modeled the data with a six-component model: secondary eclipse, phase curve accounting for reflected light and thermal emission, Doppler beaming, ellipsoidal variations, stellar activity, and the primary transit. We determined the secondary eclipse depth in the TESS bandpass to be 304 ± 75 parts-per-million (ppm). In addition, we measured the amplitude of the phase curve to be 128 ± 27 ppm, with a corresponding eastward offset between the region of maximum brightness and the substellar point of 19.2 ± 9.6 degrees, with the latter showing good agreement with Spitzer measurements. We determined a day-side brightness temperature in the TESS bandpass of 3201 ± 147 K that is approximately 200 K higher than the values determined from the Spitzer 3.6 and 4.5 μm data. By combining TESS and Spitzer eclipse depths, we derived a day-side effective temperature of Teff = 3010 ± 78 K. Previously published eclipse depths in the near-infrared suggest a much higher brightness temperature and this discrepancy cannot be explained by spectral models combined with the current data. We attribute those large eclipse depths to unmodeled ellipsoidal variations, which would typically be manifested as a deeper secondary eclipse in observations with insufficient phase coverage. A one-dimensional self-consistent atmospheric model is able to explain the TESS and Spitzer day-side brightness temperatures with thermal emission alone and no reflected light. The difference between the TESS and Spitzer brightness temperatures can be explained via CO absorption due to a non-inverted temperature profile. The night side data fix an upper limit of ~2000 K on the internal temperature of KELT-1 b.

The rotational and divergent components of atmospheric circulation on tidally locked planets

Tidally locked exoplanets likely host global atmospheric circulations with a superrotating equatorial jet, planetary-scale stationary waves, and thermally driven overturning circulation. In this work, we show that each of these features can be separated from the total circulation by using a Helmholtz decomposition, which splits the circulation into rotational (divergence-free) and divergent (vorticity-free) components. This technique is applied to the simulated circulation of a terrestrial planet and a gaseous hot Jupiter. For both planets, the rotational component comprises the equatorial jet and stationary waves, and the divergent component contains the overturning circulation. Separating out each component allows us to evaluate their spatial structure and relative contribution to the total flow. In contrast with previous work, we show that divergent velocities are not negligible when compared with rotational velocities and that divergent, overturning circulation takes the form of a single, roughly isotropic cell that ascends on the day side and descends on the night side. These conclusions are drawn for both the terrestrial case and the hot Jupiter. To illustrate the utility of the Helmholtz decomposition for studying atmospheric processes, we compute the contribution of each of the circulation components to heat transport from day side to night side. Surprisingly, we find that the divergent circulation dominates day-night heat transport in the terrestrial case and accounts for around half of the heat transport for the hot Jupiter. The relative contributions of the rotational and divergent components to day-night heat transport are likely sensitive to multiple planetary parameters and atmospheric processes and merit further study.

Storm-Time Features of the Ionospheric ELF/VLF Waves and Energetic Electron Fluxes Revealed by the China Seismo-Electromagnetic Satellite

This study reports the temporal and spatial distributions of the extremely/very low frequency (ELF/VLF) wave activities and the energetic electron fluxes in the ionosphere during an intense storm (geomagnetic activity index Dst of approximately −174 nT) that occurred on 26 August 2018, based on the observations by a set of detectors onboard the China Seismo-Electromagnetic Satellite (CSES). A good correlation of the ionospheric ELF/VLF wave activities with energetic electron precipitations during the various storm evolution phases was revealed. The strongest ELF/VLF emissions at a broad frequency band extending up to 20 kHz occurred from the near-end main phase to the early recovery phase of the storm, while the wave activities mainly appeared at the frequency range below 6 kHz during other phases. Variations in the precipitating fluxes were also spotted in correspondence with changing geomagnetic activity, with the max values primarily appearing outside of the plasmapause during active conditions. The energetic electrons at energies below 1.5 MeV got strong enhancements during the whole storm time on both the day and night side. Examinations of the half-orbit data showed that under the quiet condition, the CSES was able to depict the outer/inner radiation belt as well as the slot region well, whereas under disturbed conditions, such regions became less sharply defined. The regions poleward from geomagnetic latitudes over 50° were found to host the most robust electron precipitation regardless of the quiet or active conditions, and in the equatorward regions below 30°, flux enhancements were mainly observed during storm time and only occasionally in quiet time. The nightside ionosphere also showed remarkable temporal variability along with the storm evolution process but with relatively weaker wave activities and similar level of fluxes enhancement compared to the ones in the dayside ionosphere. The ELF/VLF whistler-mode waves recorded by the CSES mainly included structure-less VLF waves, structured VLF quasi-periodic emissions, and structure-less ELF hiss waves. A wave vector analysis showed that during storm time, these ELF/VLF whistler-mode waves obliquely propagated, mostly likely from the radiation belt toward the Earth direction. We suggest that energetic electrons in the high latitude ionosphere are most likely transported from the outer radiation belt as a consequence of their interactions with ELF/VLF waves.

Exploiting night-time averaged spectra from PFS/MEX shortwave channel. Part 1: Temperature retrieval from the CO2ν3 band

Nadir remote sensing of the night side of Mars is challenging, mainly due to the low signal-to-noise ratio of such observations. We show in a companion paper that the abundance of carbon monoxide (CO) during night can be retrieved from the observations of the Planetary Fourier Spectrometer (PFS). This requires, however, an accurate knowledge of the temperature profile, and especially of the night-time thermal inversions, to properly model the atmospheric emission. While the temperature profile is usually retrieved from the ν2 band of CO2 (centered at 667 ​cm−1), this work shows that, for averaged night-time PFS observations built from a large ensemble of spectra, the temperature profile can be retrieved from the more saturated ν3 band of CO2 (centered at 2349 ​cm−1). We show especially that, due to IFOV (instantaneous field-of-view) size differences and boresight offset between the longwave and shortwave channels of PFS, the temperature profile retrieved from the ν3 band is more consistent with the emission observed in the 1-0 band of CO (centered at 2143 ​cm−1), which is used in the second part paper. We provide a complete characterization of the retrieved temperature profiles in terms of error and vertical sensitivity. Using this, we show that using the ν3 CO2 band allows to properly constrain and characterize the thermal inversions encountered near the surface for most night-time observations. The resulting set of temperature profiles is essential for the retrieval of the night-time CO abundance that is presented in the companion paper. Beyond their usefulness for the night-time CO retrieval, we suggest with a last example that temperature profiles retrieved from the ν3 band of CO2 could be use more generally to study surface thermal inversions encountered at night.

E‐POP Observations of Suprathermal Electron Bursts in the Ionospheric Alfvén Resonator

AbstractUtilizing the suprathermal electron imager onboard the e‐POP satellite, we performed a statistical study of groups of repetitive suprathermal electron bursts (STEBs) with 52 events (each with ≥3 STEBs) during 21 e‐POP orbits. The STEBs are observed on both the day side and night side, and within a wide range of geomagnetic latitudes, from 64° to 78°. We interpret these data as temporally varying signatures; we suggest the repetition is due to the ionospheric Alfvén resonator (IAR), since the statistical time separation of adjacent STEBs in the satellite frame is 0.5–1.5 s, which is consistent with the characteristic period of the IAR. Furthermore, the STEBs are associated with low‐frequency magnetic field perturbations. The statistical occurrence of repetitive STEBs shows a preference toward postnoon and midnight sectors at high magnetic latitudes. We also present one example event of four successive STEBs associated with auroral rays in conjugate imagery. The repetition period of STEBs is similar to the oscillation period of magnetic fields observed by Enhanced Polar Outflow Probe (e‐POP). One of the STEBs in an example event exhibits “normal” dispersion (high energy particles with field‐aligned pitch angle arriving first) and the adjacent STEB exhibits “inverse” dispersion (low energy particles with broad pitch angles arriving first). With a test particle simulation, we propose one possible explanation of inverse dispersion in terms of a suprathermal electron population and a downward‐propagating parallel electric field.

Escaping Outflows from Disintegrating Exoplanets: Day-side versus Night-side Escape

Abstract Ultrahot disintegrating exoplanets have been detected with tails trailing behind and/or shooting ahead of them. These tails are believed to be made of dust that are formed out of the supersonic escaping flow that emanated from the permanent day side. Conserving angular momentum, this day-side escape flux would lead the planet in orbit. In order to explain the trailing tails in observation, radiation pressure, a repulsive force pushing the escape flow away from the host star, is considered to be necessary. We here investigate whether escape could be deflected to head away from the host star by the pressure gradient force. We demonstrate in an idealized framework that escape flux from the night side can occur, and sometimes, can be even stronger than the escape from the day-side. The night-side escape infers that escape flow could trail behind the planet in orbit by virtue of angular momentum conservation even without radiation pressure. We also find analytical approximations for both day-side and night-side escape fluxes, which may be applied to study planetary evolution of disintegrating planets.

Laboratory predictions for the night-side surface ice glow of Europa

Europa’s surface continuously experiences high fluxes of charged particles due to the presence of Jupiter’s strong magnetic field. These high-energy charged particles, including electrons, interact with the ice- and salt-rich surface, resulting in complex physical and chemical processes. Here, we report that Europa ice analogues emit characteristic spectral signatures in the visible region when exposed to high-energy electron radiation. The strongest emission (ice glow) we observed was centred at ~525 nm. We found that the presence of sodium chloride and carbonate strongly quenched, while epsomite enhanced, the radiation-induced ice glow. These emission characteristics could be used to determine the chemical composition of Europa’s surface during night-time low-altitude fly-bys of spacecraft such as the Europa Clipper. We estimate that the Europa Clipper Wide Angle Camera could record between 500 and 280,000 counts per second through different colour filters, depending on the chemical composition of Europa’s surface. Though we focus here on Europa, our study may be relevant to other bodies exposed to high doses of ionizing radiation, such as Io and Ganymede. With its extreme radiation environment, rich surface geology and compositional diversity, the radiation-induced ice glow on Europa could enable more precise surface characterization and provide unique night-time views. Based on laboratory experiments and predictions, the Europa Clipper mission is expected to detect the surface ices on the night side of Jupiter’s moon Europa glowing in the dark, with an intensity that can be used to determine their composition.

Hurricanes on tidally locked terrestrial planets: fixed surface temperature experiments

Aims.In this work, we study the presence of hurricanes on exoplanets. Tidally locked terrestrial planets around M dwarfs are the main targets of space missions looking to discover habitable exoplanets. The question of whether hurricanes can form on this kind of planet is important for determining their climate and habitability.Methods.Using a high-resolution global atmospheric circulation model, we investigated whether there are hurricanes on tidally locked terrestrial planets under fixed surface temperatures (TS). The relevant effects of the planetary rotation rate, surface temperature, and bulk atmospheric compositions were examined.Results.We find that hurricanes can form on the planets but not on all of them. For planets near the inner edge of the habitable zone of late M dwarfs, there are more numerous and stronger hurricanes on both day and night sides. For planets in the middle and outer ranges of the habitable zone, the possibility of hurricane formation is low or even close to zero, as has been suggested in recent studies. Earth-based hurricane theories are applicable to tidally locked planets only when the atmospheric compositions are similar to that of Earth. However, if the background atmosphere is lighter than H2O, hurricanes can hardly be produced because convection is always inhibited due to the effect of the mean molecular weight, similarly to the case of Saturn. These results have broad implications on the precipitation, ocean mixing, climate, and atmospheric characterization of tidally locked planets. Finally, A test with a coupled slab ocean and an Earth-like atmosphere in a tide-locked orbit of ten Earth days demonstrates that there are also hurricanes present in the experiment.

NLTT5306B: an inflated, weakly irradiated brown dwarf

ABSTRACT We present Spitzer observations at 3.6 and 4.5 µm and a near-infrared IRTF SpeX spectrum of the irradiated brown dwarf NLTT5306B. We determine that the brown dwarf has a spectral type of L5 and is likely inflated, despite the low effective temperature of the white dwarf primary star. We calculate brightness temperatures in the Spitzer wavebands for both the model radius, and Roche Lobe radius of the brown dwarf, and conclude that there is very little day–night side temperature difference. We discuss various mechanisms by which NLTT5306B may be inflated, and determine that while low-mass brown dwarfs (M < 35 MJup) are easily inflated by irradiation from their host star, very few higher mass brown dwarfs are inflated. The higher mass brown dwarfs that are inflated may be inflated by magnetic interactions or may have thicker clouds.

Coupled day–night models of exoplanetary atmospheres

ABSTRACT We provide a new framework to model the day side and night side atmospheres of irradiated exoplanets using 1D radiative transfer by incorporating a self-consistent heat flux carried by circulation currents (winds) between the two sides. The advantages of our model are its physical motivation and computational efficiency, which allows for an exploration of a wide range of atmospheric parameters. We use this forward model to explore the day and night side atmosphere of WASP-76 b, an ultrahot Jupiter which shows evidence for a thermal inversion and Fe condensation, and WASP-43 b, comparing our model against high precision phase curves and general circulation models. We are able to closely match the observations as well as prior theoretical predictions for both of these planets with our model. We also model a range of hot Jupiters with equilibrium temperatures between 1000 and 3000 K and reproduce the observed trend that the day–night temperature contrast increases with equilibrium temperature up to ∼2500 K beyond which the dissociation of H2 becomes significant and the relative temperature difference declines.

Spatial Variations of Low-mass Negative Ions in Titan’s Upper Atmosphere

Abstract Observations with Cassini’s Electron Spectrometer discovered negative ions in Titan’s ionosphere, at altitudes between 1400 and 950 km. Within the broad mass distribution extending up to several thousand amu, two distinct peaks were identified at 25.8–26.0 and 49.0–50.1 amu/q, corresponding to the carbon chain anions CN− and/or for the first peak and C3N− and/or C4H− for the second peak. In this study we present the spatial distribution of these low-mass negative ions from 28 Titan flybys with favorable observations between 2004 October 26 and 2012 May 22. We report a trend of lower densities on the night side and increased densities up to twice as high on the day side at small solar zenith angles. To further understand this trend, we compare the negative ion densities to the total electron density measured by Cassini’s Langmuir Probe. We find the low-mass negative ion density and the electron density to be proportional to each other on the day side but independent of each other on the night side. This indicates photochemical processes and is in agreement with the primary production route for the low-mass negative ions being initiated by dissociative reactions with suprathermal electron populations produced by photoionisation. We also find the ratio of to to be highly constrained on the day side, in agreement with this production channel, but notably displaying large variations on the night side.

Herschel-PACS photometry of the five major moons of Uranus

Aims.We aim to determine far-infrared fluxes at 70, 100, and 160μm for the five major Uranus satellites, Titania, Oberon, Umbriel, Ariel, and Miranda. Our study is based on the available calibration observations at wavelengths taken with the PACS photometer aboard theHerschelSpace Observatory.Methods.The bright image of Uranus was subtracted using a scaled Uranus point spread function (PSF) reference established from all maps of each wavelength in an iterative process removing the superimposed moons. The photometry of the satellites was performed using PSF photometry. Thermophysical models of the icy moons were fitted to the photometry of each measurement epoch and auxiliary data at shorter wavelengths.Results.The best-fit thermophysical models provide constraints for important properties of the moons, such as surface roughness and thermal inertia. We present the first thermal infrared radiometry longward of 50μm for the four largest Uranian moons, Titania, Oberon, Umbriel, and Ariel, at epochs with equator-on illumination. Due to this inclination geometry, heat transport took place to the night side so that thermal inertia played a role, allowing us to constrain that parameter. Also, we found some indication for differences in the thermal properties of leading and trailing hemispheres. The total combined flux contribution of the four major moons relative to Uranus is 5.7 × 10−3, 4.8 × 10−3, and 3.4 × 10−3at 70, 100, and 160μm, respectively. We therefore precisely specify the systematic error of the Uranus flux by its moons when Uranus is used as a far-infrared prime flux calibrator. Miranda is considerably fainter and always close to Uranus, impeding reliable photometry.Conclusions.We successfully demonstrate an image processing technique for PACS photometer data that allows us to remove a bright central source and reconstruct point source fluxes on the order of 10−3of the central source as close as ≈3 × the half width at half maximum of the PSF. We established improved thermophysical models of the five major Uranus satellites. Our derived thermal inertia values resemble those of trans-neptunian object (TNO) dwarf planets, Pluto and Haumea, more than those of smaller TNOs and Centaurs at heliocentric distances of about 30 AU.

Dynamics of Magnetic Structures during a Magnetospheric Substorm

The Earth’s magnetosphere and the ambient interplanetary environment can create favorable conditions for the nonlinear process of energy release in the form of changes in the topology of the magnetic field and current systems, particle acceleration, wave generation, and sharp gradients in the parameters inherent to a substorm phenomenon. Initially, early studies substantiated the role of variations in the solar wind parameters as a key factor responsible for the onset of a magnetospheric substorm; however, this factor was later shown not to be decisive. Over several decades, continuously improving methods for designing measurement tools and analyzing data helped to identify the processes that accompany the substorm phenomenon and describe them both qualitatively and quantitatively. However, there is no consensus in understanding the scenario of substorm development stepwise. The purpose of the research is to determine the propagation and orientation features of transients (fronts) in the current sheet of the Earth’s magnetotail during a substorm. To do this, the magnetic field measurements obtained by the four spacecraft of the Cluster II mission for July 20, 2013, are analyzed. During this event, spacecraft were located on the night side of the Earth’s magnetosphere and recorded changes in the geomagnetic field during the magnetospheric substorm. We used the single-spacecraft method for finding the minimum variance of the magnetic field and multispacecraft timing analysis involving cross-correlation of time series. The first method allows finding the direction of the normal to the structure under study; the second method makes it possible to find the direction and absolute value of its propagation velocity. The results of the study show that, with the development of substorms, the fronts that move towards the Earth exhibit a decrease in the propagation velocity and a significant degree of curvature. The first effect (a decrease in the propagation velocity of the fronts) indicates a decrease in the energy reserve of the current sheet for the generation of such transients, and the second effect (a significant degree of curvature) indicates the azimuthal localization of the front.

Effects of Thermal Emission on the Transmission Spectra of Hot Jupiters

Abstract The atmosphere on the dayside of a highly irradiated close-in gas giant (also known as a hot Jupiter) absorbs a significant part of the incident stellar radiation, which again gets re-emitted in the infrared wavelengths both from the day and the night sides of the planet. The re-emitted thermal radiation from the nightside facing the observers during the transit event of such a planet contributes to the transmitted stellar radiation. We demonstrate that the transit spectra at the infrared region get altered significantly when such re-emitted thermal radiation of the planet is included. We assess the effects of the thermal emission of the hot Jupiters on the transit spectra by simulating observational spectroscopic data with corresponding errors from the different channels of the upcoming James Webb Space Telescope. We find that the effect is statistically significant with respect to the noise levels of those simulated data. Hence, we convey the important message that the planetary thermal re-emission must be taken into consideration in the retrieval models of transit spectra for hot Jupiters for a more accurate interpretation of the observed transit spectra.

Low-altitude frequency-banded equatorial emissions observed below the electron cyclotron frequency

Abstract. The ICE (Instrument Champ Électrique) experiment on board the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite recorded frequency-banded wave emissions below the electron cyclotron frequency, with band spacing ≳ frequency low-hybrid resonance, in the vicinity of the magnetic equatorial plane. Those radiations were observed in the beginning of the year 2010 on the night side of Earth and rarely on the day side. We distinguish two components: one appears as frequency bands continuous in time between a few kilohertz and up to 50 kHz, and the other one is from 50 to 800 kHz. The first component exhibits positive and negative frequency drift rates in the Southern Hemisphere and Northern Hemisphere, at latitudes between 40 and 20∘. The second one displays multiple spaced frequency bands. Such bands mainly occur near the magnetic equatorial plane with a particular enhancement of the power level when the satellite latitude is close to the magnetic equatorial plane. We show in this study the similarities and the discrepancies between the non-free-space DEMETER frequency-banded emissions and the well-known free-space terrestrial kilometric radiation. The hollow cones of the DEMETER frequency-banded wave emissions are oriented towards Earth's ionosphere. We suggest that the source region is localized in regions poleward of the plasmapause where the ratio of the plasma frequency to gyro-frequency is smaller than one.