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We analyze data from multiple flybys by the Solar Orbiter, BepiColombo, and Parker Solar Probe (PSP) missions to study the interaction between Venus' plasma environment and the solar wind forming the induced magnetosphere. Through examination of magnetic field and plasma density signatures we characterize the spatial extent and dynamics of Venus' magnetotail, focusing mainly on boundary crossings. Notably, we observe significant differences in boundary crossing location and appearance between flybys, highlighting the dynamic nature of Venus' magnetotail. In particular, during Solar Orbiter's third flyby, extreme solar wind conditions led to significant variations in the magnetosheath plasma density and magnetic field properties, but the increased dynamic pressure did not compress the magnetotail. Instead, it is possible that the increased EUV flux at this time rather caused it to expand in size. Key findings also include the identification of several far downstream bow shock (BS), or bow wave, crossings to at least 60 RV ${\mathrm{R}}_{V}$ (1 RV ${\mathrm{R}}_{V}$ = 6,052 km is the radius of Venus), and the induced magnetospheric boundary to at least ∼ ${\sim} $ 20 RV ${\mathrm{R}}_{V}$. These crossings provide insight into the extent of the induced magnetosphere. Pre‐existing models from Venus Express were only constrained to within ∼ ${\sim} $ 5 RV ${\mathrm{R}}_{V}$ of the planet, and we provide modifications to better fit the far‐downstream crossings. The new model BS is now significantly closer to the central tail than previously suggested, by about 10 RV ${\mathrm{R}}_{V}$ at 60 RV ${\mathrm{R}}_{V}$ downstream. Plain Language Summary: We studied data from the missions Solar Orbiter, BepiColombo, and Parker Solar Probe to understand Venus' magnetotail. We focused on how Venus' magnetic environment interacts with the solar wind to create its magnetosphere. By looking at magnetic fields and plasma density, we figured out the size and movement of Venus' magnetotail, and found where its boundaries are. We noticed that these boundaries change a lot between missions, showing that Venus' magnetotail is very dynamic. Our main discoveries include finding boundary crossings like the bow shock 60 times Venus' radius downstream, and the magnetospheric boundary about 20 times Venus' radius downstream. This helps us understand how far the magnetosphere extends and improve our models of its shape. We also saw that the solar wind affects the magnetotail: during one mission, even though the solar wind was strong, it didn't squish the magnetotail; instead, it made it bigger because of increased solar radiation. Key Points: Venus' magnetotail is observed during nine spacecraft flybys revealing a dynamic structure reaching at least 60 RV downstreamAn improved bow shock model is presented for the deep tail regionThe pre‐existing model of the induced magnetospheric boundary is valid downstream to at least 20 RV [ABSTRACT FROM AUTHOR]

The potential of deep learning for the investigation of medium scale traveling ionospheric disturbances (MSTIDs) has been exploited through the Sodankyla rapid-run ionosonde in this statistical study. The complementing observations of the Sodankyla ionosonde with those of the Sodankyla meteor radar reveals the diurnal and seasonal occurrence rate of high-latitude MSTIDs in the recent low solar activity period, 2018-2020. In our results, the daytime, nighttime and dusk MSTIDs are predominantly identified during winter, summer, and equinoctial months, respectively. The winter daytime higher (lower) occurrence rate is well correlated with the lower (higher) altitude of the height of the F2-layer peak (hmF2), and the low occurrence rate of the summer daytime is well correlated with the mesosphere-lower-thermosphere wind shear and higher gradient of temperature. Relatively high occurrence rate (>0.4) of summer nighttime MSTIDs has a general--but not one-to-one agreement--with post-noon to evening IU (eastward auroral current index) inferred ionospheric conductivity. Rather, we see a one-to-one relationship between the summer nighttime MSTIDs and zonal wind shear suggesting that the wind shear-induced electrodynamic processes could play significant roles for higher occurrence rate of MSTIDs. Furthermore, significant MSTIDs with ~0.4 occurrence rate are so far revealed during spring and autumn transition periods. The enhanced nighttime MSTID amplitudes during the equinox are observed to be well correlated with IL index (westward auroral current indicator) suggesting that the particle precipitation during substorms could be the primary cause. [ABSTRACT FROM AUTHOR]

Despite the growing importance of planetary Space Weather forecasting and radiation protection for science and robotic exploration and the need for accurate Space Weather monitoring and predictions, only a limited number of spacecraft have dedicated instrumentation for this purpose. However, every spacecraft (planetary or astronomical) has hundreds of housekeeping sensors distributed across the spacecraft, some of which can be useful to detect radiation hazards produced by solar particle events. In particular, energetic particles that impact detectors and subsystems on a spacecraft can be identified by certain housekeeping sensors, such as the Error Detection and Correction (EDAC) memory counters, and their effects can be assessed. These counters typically have a sudden large increase in a short time in their error counts that generally match the arrival of energetic particles to the spacecraft. We investigate these engineering datasets for scientific purposes and perform a feasibility study of solar energetic particle event detections using EDAC counters from seven European Space Agency Solar System missions: Venus Express, Mars Express, ExoMars‐Trace Gas Orbiter, Rosetta, BepiColombo, Solar Orbiter, and Gaia. Six cases studies, in which the same event was observed by different missions at different locations in the inner Solar System are analyzed. The results of this study show how engineering sensors, for example, EDAC counters, can be used to infer information about the solar particle environment at each spacecraft location. Therefore, we demonstrate the potential of the various EDAC to provide a network of solar particle detections at locations where no scientific observations of this kind are available. Plain Language Summary: Space Weather is the discipline that aims at understanding and predicting the state of the Sun, interplanetary medium and its impact on planetary environments. One source of Space Weather is Solar Energetic Particles (SEPs), which are emitted by the Sun and enhance the radiation and particles that flow in space. Predicting the motion of these particles is important but difficult as we need good satellite coverage of the entire inner Solar System, and only a limited number of spacecraft have the necessary instrumentation. Thanks to the European Space Agency flotilla, that is, Venus Express, Mars Express, ExoMars‐Trace Gas Orbiter, Rosetta, BepiColombo, Solar Orbiter, and Gaia, we performed a feasibility study of the detection of SEP events using engineering sensors in the main body of the spacecraft that were originally placed there to monitor its health during the mission. We explored how much scientific information we can get from these engineering sensors, such as the timing and duration of an SEP impacting the spacecraft, or the minimum energy of those particles to trigger a detection. The results of this study have the potential of providing a good network of solar particle detections at locations where no scientific observations are available. Key Points: Space weather detections using housekeeping datasets on European Space Agency spacecraftSome engineering datasets on spacecraft have the potential to be used for scienceSame Space Weather events detected with housekeeping data at widely‐spaced locations in the Solar System [ABSTRACT FROM AUTHOR]

This is a two‐spacecraft study, in which we investigate the effects of the upstream solar wind conditions on the Martian induced magnetosphere and upper ionosphere. We use Mars Express (MEX) magnetic field magnitude data together with interplanetary magnetic field (IMF), solar wind density, and velocity measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, from November 2014 to November 2018. We compare simultaneous observations of the magnetic field magnitude in the induced magnetosphere of Mars (|B|IM) with the IMF magnitude (|B|IMF), and we examine variations in the ratio |B|IM/|B|IMF with solar wind dynamic pressure, speed and density. We find that the |B|IM/|B|IMF ratio in the induced magnetosphere generally decreases with increased dynamic pressure and that a more structured interaction is seen when comparing induced fields to the instantaneous IMF, where reductions in the relative fields at the magnetic pile up boundary (MPB) are more evident than in the field strength itself, along with enhancements in the immediate vicinity of the optical shadow of Mars. We interpret these results as evidence that while the induced magnetosphere is indeed compressed and induced field strengths are higher during periods of high dynamic pressure, a relatively larger amount of magnetic flux threads the region compared to that available from the unperturbed IMF during low dynamic pressure intervals. Plain Language Summary: The solar wind input to the Martian system plays a decisive role in formulating the morphology of the near‐Mars plasma environment. Specifically, ion escape rates, the plasma boundary locations around the planet and the structure of the induced magnetosphere in general have been shown by numerous studies to be influenced by the upstream solar wind conditions. In this work, we use simultaneous measurements from MEX and MAVEN to probe the response of the Martian induced magnetosphere and upper ionosphere to different regimes of solar wind dynamic pressure, speed and density. We find that despite the stronger magnetic fields observed in the induced magnetosphere during periods of high solar wind dynamic pressure, when we compare these fields with the interplanetary magnetic field (IMF) measured simultaneously, we see in fact relative enhancements for low solar wind dynamic pressure. Key Points: MEX and MAVEN data are used to examine the response of Mars' induced magnetosphere to the solar windWe find that induced magnetic fields are enhanced relative to the IMF during intervals of lower dynamic pressureComparing induced fields to the instantaneous IMF reveals more structure in the interaction region at high altitudes [ABSTRACT FROM AUTHOR]

We present the first long‐term characterization of ionization layers in the lower ionosphere of Mars (below ∼90 km), a region inaccessible to orbital in‐situ observations, based on an analysis of radar echo blackouts observed on Mars Express and the Mars Reconnaissance Orbiter from 2006 to 2017. A blackout occurs when the expected surface reflection is partly or totally attenuated for portions of an observation. Enhanced ionization at altitudes of 60–90 km, below the main ionospheric electron density peak, leads to increased absorption of the radar signal, resulting in the blackouts. We find that (a) MARSIS, operating at frequencies between 1.8 and 5 MHz, suffered more blackouts than SHARAD, which has a higher carrier frequency (20 MHz), (b) there is a clear correlation of blackout occurrence with solar cycle, (c) there is no apparent relationship between blackout occurrence and crustal magnetic fields, and (d) blackouts occur during both nightside and dayside observations, although the peak occurrence is deep on the nightside. Analysis of Mars Atmosphere and Volatile EvolutioN Solar Energetic Particle electron counts between 20 and 200 keV demonstrates that these electrons are likely responsible for attenuating the radar signals. We investigate the minimum SEP electron fluxes required to ionize the lower atmosphere and produce measurable attenuation. When both radars experience a blackout, the SEP electron fluxes are at their highest. Based on several case studies, we find that the average SEP spectrum responsible for a blackout is particularly enhanced at its higher energy end, that is, above 70 keV. Plain Language Summary: The orbital radars that study the surface and subsurface of Mars can suffer a near‐total loss of received signal during periods when high‐energy electrons from the Sun enter the Martian atmosphere, causing enhanced ionization at altitudes between 60 and 90 km. We have studied these radar blackouts using radars on the Mars Express and Mars Reconnaissance Orbiter spacecraft. The radars on the two spacecraft work at different frequencies, allowing us to test the theory that a larger effect is predicted at lower frequency. Indeed, we do see more blackouts of the radar operating at lower frequency (1.8–5 MHz) than at the higher frequency (20 MHz). We also find that more blackouts occur for both radars during periods of higher solar activity that is, more solar flares and Coronal Mass Ejections. The radar blackouts occur on the nightside and dayside and over all locations on the planet's surface, indicating a global effect of the solar particle events. We have also investigated the electron fluxes measured by the Mars Atmosphere and Volatile EvolutioN spacecraft and find they are higher during blackouts that include the 20 MHz frequency. These observations provide a new window on the levels of ionization at low altitudes. Key Points: First long‐term characterization of the lower ionosphere of Mars with Mars Express, Mars Reconnaissance Orbiter, and Mars Atmosphere and Volatile EvolutioNRadar sounder blackouts caused by energetic electrons occur globally at MarsRadar sounder blackouts correlate with the solar cycle [ABSTRACT FROM AUTHOR]

Thermal and dynamic perturbations in the polar upper stratospheric/mesosphere‐lower thermosphere in the Arctic winter of 2019–2020 as measured by a meteor radar at 67°N, Aura Microwave Limb Sounder and reanalysis are presented. The most severe disturbances occur from late December to mid‐January, while the rest of the winter is relatively stable. Mesospheric winds are dominated by several impulsive increases in the zonal component, an abrupt descent of the wind core and alternating north‐ and south‐ward flow with a period of half a month. Reduced temperature at 90 km height accompanied by thermal inversions is observed in association with upper stratosphere/lower mesosphere warming in the eastern hemisphere. The warming trend is interrupted by a strong cooling in the entire stratosphere‐mesosphere. The upper middle atmosphere appears considerably stratified. High "walls" surround the vortex that is favorable for its stability. Plain Language Summary: If the stratospheric polar vortex is strong, it serves as a stable background for the overlying atmosphere, which remains undisturbed because waves and heat do not penetrate there from below. In the Arctic winter of 2019–2020, although the vortex is evolved into such a configuration and became exceptionally strong in the late winter, during its initial formation, dramatic disturbances occurred in the upper stratosphere and mesosphere. Impulsive strengthening and descending of the zonal winds, shears, alternating north‐ and south‐ward flows, transient upper stratospheric warming and mesospheric cooling, persistent thermal inversions, observed in the first half of the winter, likely indicate a certain degree of decoupling of the atmospheric layers and the role of the high‐altitude atmosphere in the intensification and splitting of the vortex. Key Points: During the formation of the stratospheric polar vortex, the upper‐middle atmosphere is unstableZonal winds amplifications and descending, alternating north/southward flow occur in the stratosphere and mesosphere‐lower thermosphereTransient warming in the upper stratosphere and cooling above, as well as mesospheric thermal inversions are observed [ABSTRACT FROM AUTHOR]

In the middle atmosphere, spring transition is the time period where the zonal circulation reverses from winter westerly to summer easterly which has a strong impact on the vertical wave propagation influencing the ionospheric variability. The spring transition can be rapid in form of a final sudden stratospheric warming (SSW, mainly dynamically driven) or slow (mainly radiatively driven) but also intermediate stages can occur. In most studies spring transitions are classified either by their timing of occurrence or by their vertical structure. However, all these studies focus exclusively on the stratosphere and it is not clear if and how pre‐winter conditions have an impact on when and how spring transitions take place. Here we classify the spring transitions regarding their vertical‐temporal development beginning in January and spanning the whole middle atmosphere in the core region of the polar vortex. This leads to five classes where the timing of the SSW in the preceding winter and a downward propagating Northern Annular Mode plays a crucial role. First, we use Microwave Limb Sounder satellite data to describe the five classes for recent single years, and then we use Modern‐Era Retrospective analysis for Research and Applications Version 2 reanalysis data for a composite analysis. The results show distinctive differences between the five classes in the months before the spring transition especially in the mesosphere. We hypothesize that this will help to improve the prediction of the spring transition. Additionally, meteor radar winds are used to link spring transition effects in the upper mesosphere and lower thermosphere with the stratospheric final warming. Plain Language Summary: Springtime is characterized by a dramatic change in circulation from winter westerly to summer easterly in the Arctic middle atmosphere (20–100 km). The timing and structure of this change process largely varies from year to year. In most studies spring transitions are classified either by their timing of occurrence or, slightly less common, by their vertical structure. However, all these studies focus on the stratosphere (20–50 km) only and do not consider a large part of the spring transitions because they only investigating for example, particularly early or late occurring spring transitions. Here we classify the spring transitions regarding their vertical and temporal development already starting in mid‐winter. This leads to five classes where the timing of large polar vortex disturbances in the preceding winter as well as the vertical structure of the polar vortex plays a crucial role. This allows a certain prediction at least for some of the five spring transition classes. Additionally, the spring transition in the upper mesosphere and lower thermosphere (80–100 km) is investigated regarding the new spring transition classes and its impact on the ionosphere and therefore on our communication and navigation system is discussed. Key Points: There are five new classes of spring transitions in the middle atmosphereThe classification uses the temporal‐vertical structure of zonal wind and Northern Annular Mode starting in JanuaryThe classification enables a better understanding of the timing and type of the spring transition [ABSTRACT FROM AUTHOR]

Dayside cusp aurorae are created from particles precipitating into the cusp, and ionospheric convection is driven by solar wind electric fields. In this study, we coordinated the observations obtained from the all‐sky camera on Svalbard, the Super Dual Auroral Radar Network, SuperMAG magnetometer data, and far ultraviolet imagers on board the Defense Meteorological Satellite Program satellites for the event January 4, 2014 to examine the morphology of aurorae and the patterns of ionospheric convection for radial interplanetary magnetic field (IMF). During the event, a poleward‐moving auroral form and antisunward ionospheric convection were observed when the IMF turned into almost purely radial. Moreover, both types of antisunward and sunward convection were simultaneously observed near the footprint of the cusp at different times during the radial IMF period. The antisunward convection and sunward convection are typically an indicator of the dayside reconnection for the southward IMF and the lobe reconnection for the northward IMF, respectively. All those observations support the concept of low‐latitude dayside and high‐latitude lobe reconnection for the radial IMF. This study further shows that the coexistence of the two types of reconnection for radial IMF, resulting in an interplay of repetitive antisunward and sunward convection. Plain Language Summary: The event for January 4, 2014 enables us to study the features of dayside cusp aurorae and ionospheric convection for the radial IMF. During the event, a poleward‐moving auroral form and antisunward convection were observed near the footprint of the cusp, which provides indirect evidence of the magnetic reconnection that occurs at the dayside magnetopause for the radial IMF. S‐shaped aurorae, named from their morphology, near the cusp were also observed during the event. This type of aurora was possibly created by magnetosheath plasma jets impinging on the surface of the magnetopause or magnetic reconnection occurring locally on the magnetopause. For ionospheric convection, the primary convection pattern for the radial IMF was similar to that for the southward IMF, particularly for antisunward convection near the cusp. However, sunward convection near the cusp was also observed at the same time, indicating the lobe reconnection coexists with the dayside reconnection. In summary, the features of dayside cusp aurorae and ionospheric convection for the northward and southward IMFs can be seen at different times during the radial IMF event. Key Points: A period of almost purely radial interplanetary magnetic field (IMF) (cone angle < 3°) was embedded in the radial IMF event for January 4, 2014IMF By or Bz related poleward‐moving aurora was created by precipitating electrons along the open field lines in the cusp during the periodThe antisunward ionospheric convection became stable and consistent with magnetometer observations when the IMF was almost purely radial [ABSTRACT FROM AUTHOR]

This study assesses under what circumstances the Martian ionopause is formed on the dayside, both in regions where there are strong crustal magnetic fields and areas where these fields are small (<30 nT). Multiple data sets from three MAVEN dayside deep dip campaigns are utilized between periapsis and 600-1,000 km, as well as solar wind observations from Mars Express. The ionopause is identified as a sudden decrease of the electron density with increasing altitude and a simultaneous increase of the electron temperature and variability below 400 km. This is a physically robust approach as the electron temperature is a key parameter in determining the structure of the ionospheric profile, and, therefore, also a strong indicator of the ionopause location. We find that 36% (54%) of the electron density profiles over strong (weak) crustal magnetic field regions had an ionopause event. We also evaluate the roles of ionospheric thermal and magnetic pressures on the ionopause formation as well as the presence of solar wind particles, H+, down to the location of the ionopause. We found that the topside ionosphere is typically magnetized at mostly all altitudes. The ionopause, if formed, occurs where the total ionospheric pressure (magnetic + thermal) equals the upstream solar wind dynamic pressure. Moreover, the lower edge of the ionopause coincides with the altitude where the solar wind flow stops: The thermal pressure suffers a significant reduction with increasing altitude and the solar wind proton density has a prominent increase. [ABSTRACT FROM AUTHOR]

We track a remarkably bright and persistent auroral cusp spot emission in the high‐latitude Northern Hemisphere polar cap, well inside the main auroral oval, for approximately 11 hr on 16 and 17 June 2012. The auroral emissions are presented in both the Lyman‐α and Lyman‐Birge‐Hopfield bands, as observed by the Special Sensor Ultraviolet Spectrographic Imager on board two of the Defense Meteorological Satellite Programme spacecraft, and supported by detections of precipitating particles by the same spacecraft. The auroral observations are accompanied by patterns of field aligned currents, obtained from the Active Magnetosphere and Planetary Electrodynamics Response Experiment, along with ionospheric convection patterns from the Super Dual Auroral Radar Network. These data provide unprecedented coverage of a cusp spot, unusually seen in both electron and proton aurora. The location and movement of the auroral emissions, current systems, and ionospheric convection patterns are extremely distorted under the northward to Y‐component‐dominated interplanetary magnetic field. The cusp spot emission region is associated with the sunward flow region of the ionosphere. Ion dispersion signatures are detected on traversal of the region of brightest proton auroral emissions. Proton‐excited Lyman‐α emissions are most evident following impulses of high solar wind density. The auroral emissions, field‐aligned current patterns, and ionospheric convection are consistent with a model of a compressed magnetosphere under strongly northward interplanetary magnetic field, following an impact of an Interplanetary Coronal Mass Ejection and associated magnetic cloud at the magnetopause, inducing high‐latitude lobe reconnection that progresses increasingly tailward during the presented interval. Key Points: Extreme IMF‐By causes distortions of polar cap aurora and field‐aligned currentsThe study of cusp spots provides a method to remotely investigate reconnection sites at the distant magnetopauseA cusp spot is found in the sunward flow region between cells of FAC under persistent northward IMF [ABSTRACT FROM AUTHOR]

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) onboard Mars Express, which operates between 0.1 and 5.5 MHz, suffered from a complete blackout for 10 days in September 2017 when observing on the nightside (a rare occurrence). Moreover, the Shallow Radar (SHARAD) onboard the Mars Reconnaissance Orbiter, which operates at 20 MHz, also suffered a blackout for three days when operating on both dayside and nightside. We propose that these blackouts are caused by solar energetic particles of few tens of keV and above associated with an extreme space weather event between 10 and 22 September 2017, as recorded by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Numerical simulations of energetic electron precipitation predict that a lower O2+ nighttime ionospheric layer of magnitude ~1010 m−3 peaking at ~90‐km altitude is produced. Consequently, such a layer would absorb radar signals at high frequencies and explain the blackouts. The peak absorption level is found to be at 70‐km altitude. Plain Language Summary: Several instrument operations, as well as communication systems with rovers at the surface, depend on radio signals that propagate throughout the atmosphere of Mars. This is the case also for two radars that are currently working in Mars' orbit, sounding the ionosphere, surface, and subsurface of the planet. In mid‐September 2017, a powerful solar storm hit Mars, producing a large amount of energetic particle precipitation over a 10‐day period. We have found that high‐energy electrons ionized the atmosphere of Mars, creating a dense layer of ions and electrons at ~90 km on the Martian nightside. This layer attenuated radar signals continuously for 10 days, stopping the radars to receive any signal from the planetary surface. In this work, we assess the properties of this layer in order to understand the implications of this kind of phenomenon for radar performance and communications. Key Points: A large space weather event caused negatively impacted radar performance for 10 daysSolar electron precipitation created a low ionospheric layer at ~90 km on the nightsideThe nightside ionization is comparable to dayside values [ABSTRACT FROM AUTHOR]

This paper is a phenomenological description of multispacecraft observations of energetic particles caused by the close flyby of comet C/2013 A1 Siding Spring with Mars on 19 October 2014. This is the first time that cometary energetic particles have been observed at Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN)‐solar energetic particle (SEP) and the Mars Odyssey‐High Energy Neutron Detector (HEND) instruments recorded evidence of precipitating particles, which are likely O+ pickup ions, during the ~10 hr that Mars was within the region of the comet's coma. O+ pickup ions were also detected several hours after, although whether their origin is the comet or space weather is not conclusive. We discuss the possible origin of those particles and also the cause of an additional shower of energetic particles that HEND observed between 22 and 35 hr after the comet's closest approach, which may be related to dust impacts from the comet's dust tail. An O+ pickup ion energy flux simulation is performed with representative solar wind and cometary conditions, together with a simulation of their energy deposition profile in the atmosphere of Mars. Results indicate that the O+ pickup ion fluxes observed by SEP were deposited in the ionosphere around 105 to 120 km altitude, and they are compared with precomet flyby estimations of cometary pickup ions. The comet's flyby deposited a significant fluence of energetic particles into Mars' upper atmosphere, at a similar level to a large space weather event. Plain Language Summary: Comet Siding Spring is a comet from the Oort cloud (a spherical shell of cometary bodies far beyond the solar system) that made a single flyby through the inner solar system in October 2014. It passed very close to Mars on 19 October 2014, at only one third of the Earth‐Moon distance. This is a unique event as a close encounter of this type with Mars is predicted to occur only once in 100,000 years. In this work, we analyze data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) and the Mars Odyssey missions in order to understand how the Martian atmosphere reacts to such an unusual external event. This is done through the study of energetic particles from the comet. These particles are important as they constitute an energy input into Mars' atmosphere and are therefore useful for understanding atmospheric evolution and habitability. We have found several O+ detections from the comet, while Mars was within the comet environment (during ~10 hr). Also, we discuss several other interesting features that occurred after the closest approach, which could be related to comet dust tail impacts between 22 and 35 hr after the comet's closest approach. In general, the comet deposited into Mars' upper atmosphere a similar level of energy to that of a large space weather storm. Key Points: Both MAVEN and Mars Odyssey saw high‐energy O+ ions from comet Siding SpringThe O+ cometary ions deposited significant energy into the upper atmosphereSome effects may have persisted even after Mars left the outer coma of the comet [ABSTRACT FROM AUTHOR]

Meteoroids constantly enter the Earth's atmosphere, collide with atmospheric molecules, and heat and ablate in the sufficiently dense atmospheric layers at heights between 70 and 110 km. It is still a problem to recognize properties of the meteor streams among the sporadic background. The meteor radar observations at Sodankylä Geophysical Observatory (67°22′N, 26°38′E, Finland) during 2008–2017 show that meteoroids of some showers produce ionization trails at altitudes noticeably exceeding those of sporadic meteors. Using the median height of meteor trails and corresponding upper and lower quartiles as a metric, we unambiguously distinguish all northern hemisphere meteor showers with a zenithal hourly rate larger than 12, namely, the Quadrantids, Lyrids, Eta Aquariids, Arietids (or/and Daytime Zeta Perseids), Perseids, Orionids, Leonids, and Geminids. Additionally, signatures of a possible meteor stream during 26–30 January were detected, although identification of this stream is still under question. This new analysis indicates that the origin of the shower meteor trails at higher altitudes is likely due to higher speed and probably lighter or less dense meteoroids belonging to the showers. Plain Language Summary: Sporadic meteors and shower meteors originate from different extraterrestrial bodies and thus have specific properties (composition, size, velocity, and angle at which they enter the atmosphere). Meteor radar is able to detect the meteor showers because the meteors belonging to a particular shower ablate at different altitudes. Key Points: Short‐time (one to few days) elevations of the median and quartiles of the meteor trail height distribution are observed by the Sodankylä meteor radarMeteoroids belonging to the showers produce ionization trails at altitudes noticeably exceeding those of sporadic backgroundThe effect is due to different properties of the sporadic meteoroids and shower members [ABSTRACT FROM AUTHOR]

Abstract: We analyze 10 years of Mars Express total electron content (TEC) data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument. We describe the spatial, seasonal, and solar cycle behavior of the Martian TEC. Due to orbit evolution, data come mainly from the evening, dusk terminator and postdusk nightside. The annual TEC profile shows a peak at Ls = 25–75° which is not related to the solar irradiance variation but instead coincides with an increase in the thermospheric density, possibly linked with variations in the surface pressure produced by atmospheric cycles such as the CO2 or water cycles. With the help of numerical modeling, we explore the contribution of the ion species to the TEC and the coupling between the thermosphere and ionosphere. These are the first observations which show that the TEC is a useful parameter, routinely measured by Mars Express, of the dynamics of the lower‐upper atmospheric coupling and can be used as tracer for the behavior of the thermosphere. [ABSTRACT FROM AUTHOR]

Background: Standard tibial motor nerve conduction measures are established with recording from the abductor hallucis. This technique is often technically challenging and clinicians have difficulty interpreting the information particularly in the short segment needed to assess focal tibial nerve entrapment at the medial ankle as occurs in posterior tarsal tunnel syndrome. The flexor hallucis brevis (FHB) has been described as an alternative site for recording tibial nerve function in those with posterior tarsal tunnel syndrome. Normative data has not been established for this technique. This pilot study describes the technique in detail. In addition we provide reference values for medial and lateral plantar orthodromic sensory measures and assessed intrarater reliability for all measures. Methods: Eighty healthy female participants took part, and 39 returned for serial testing at 4 time points. Mean values ± SD were recorded for nerve conduction measures, and coefficient of variation as well as intraclass correlation coefficients (ICC) were calculated. Results: Motor latency, amplitude and velocity values for the FHB were 4.1 ± 0.9 msec, 8.0 ± 3.0 mV and 45.6 ± 3.4 m/s, respectively. Sensory latencies, amplitudes, and velocities, respectively, were 2.8 ± 0.3 msec, 26.7 ± 10.1 μV, and 41.4 ± 3.5 m/s for the medial plantar nerve and 3.2 ± 0.5 msec, 13.3 ± 4.7 μV, and 44.3 ± 4.0 msec for the lateral plantar nerve. All values demonstrated significant ICC values (P ≤ 0.007). Conclusion: Motor recording from the FHB provides technically clear waveforms that allow for an improved ability to assess tibial nerve function in the short segments used to assess tarsal tunnel syndrome. The reported means will begin to establish normal values for this technique. [ABSTRACT FROM AUTHOR]

On 19 October 2014, Mars experienced a close encounter with Comet C/2013 A1 Siding Spring. Using data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on board Mars Express (MEX), we assess the interaction of the Martian ionosphere with the comet's coma and possibly magnetic tail during the orbit of their closest approach. The topside ionospheric electron density profile is evaluated from the altitude of the peak density of the ionosphere up to the MEX altitude. We find complex and rapid variability in the ionospheric profile along the MEX orbit, not seen even after the impact of a large coronal mass ejection. Before closest approach, large electron density reductions predominate, which could be caused either by comet water damping or comet magnetic field interactions. After closest approach, a substantial electron density rise predominates. Moreover, several extra topside layers are visible along the whole orbit at different altitudes, which could be related to different processes as we discuss. Plain Language Summary: The comet Siding Spring made a single flyby through the solar system in October 2014, passing close to Mars on 19 October 2014, at only one third of the Earth‐Moon distance. For about 10 hr, the Martian ionosphere (upper atmosphere) was in touch with the cometary coma (also called cometary atmosphere). In this work, we use data from the Mars Express mission to evaluate the behavior of the ionosphere of Mars at the comet closest approach. We find that the Martian ionosphere suffered a quick and complex variability with large density increases and decreases every few kilometers. This variability was caused by the presence of the comet, and we discuss different processes that could have occurred. Key Points: Large and rapid Martian ionospheric variability is observed during the closest approach with comet Siding SpringThe Martian topside ionosphere is more variable after the comet Siding Spring flyby than after a coronal mass ejection arrived at MarsCometary water, dust, and comet induced magnetic field seem to be equally responsible for the large ionospheric density variability [ABSTRACT FROM AUTHOR]