In 1973, the launch of Skylab created a ~50% depletion in the daytime ionosphere over the N. Atlantic Ocean that lasted for hours. This effect was discovered in the data being routinely gathered by radio receivers monitoring the Total Electron Content (TEC) using the Faraday rotation of a signal from the ATS-3 geostationary satellite. This “ionospheric hole” was created by the H2O and H2 in the rocket exhaust reacting with the ambient O+ in the F region. This reaction is ~2 orders of magnitude faster than the “normal” reaction between O+ and the ambient O2. Subsequent rocket launches were studied to confirm this process. Dedicated rocket launches were also used to create steep density gradients to study ionospheric instabilities near the magnetic equator. Today, rockets are being launched at an ever increasing rate (~2 launches/week), some of them causing ionospheric holes. The launches of Starlink group 6 from Florida de-orbit over the McDonald Observatory where Boston University has an All-sky Imager (ASI) dedicated to observing the optical emissions from the ionosphere. The de-orbit burns release H2O and CO2, both of which create an ionospheric hole with a concurrent burst of 630.0nm airglow. This airglow is bright enough (~ 10kR) to be seen with the unaided eye, and has been documented by citizen scientists. The resulting hole is also seen on GPS TEC maps of the region. Several examples of the de-orbit burns observed with the ASI at McDonald are shown.

Two quasi‐orthogonal nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) were observed by conjugate midlatitude all‐sky imagers in Sutherland (32.4S, 20.8E; magnetic latitude: −40.9) and Asiago (45.87N, 11.53E; magnetic latitude: ) on 4 October 2018. These MSTIDs had fronts elongated quasi‐orthogonally to one another as observed from each location. The first MSTID was aligned northeast‐southwest (NE‐SW) in the Southern Hemisphere (SH) and northwest‐southeast (NW‐SE) in the Northern Hemisphere (NH) and propagated equator‐westwards. These properties are typically attributed to MSTIDs generated through the coupled Perkins and sporadic E instabilities. This is supported by observed conditions in both hemispheres indicating the presence of sporadic E layers and reasonable Perkins instability growth rates. The second MSTID was aligned NW‐SE (SH) and NE‐SW (NH) and propagated equator‐eastwards and represents the first optical observations of conjugate equator‐eastward propagating MSTIDs. A possible linkage to gravity wave‐induced polarization electric fields in the NH (and mapped to the SH) is presented, as significant gravity wave activity was observed in OH and OI greenline observations by the Asiago imager. Their equator‐eastward propagation direction was favored by background winds at the hemisphere of origin, as determined from global model observations.

This work explores the capabilities of our two methods for the determination of cloudless conditions from All-Sky Imager (ASI) data. For the first time, it was demonstrated that the combination of a well-established traditional computer vision technique based on the calculation of a Clearness index and a new data-driven method, that utilizes Convolutional Neural Networks, leverages the benefits of both methods and suppresses their individual disadvantages. The developed tool is reliable and efficient, allowing us to study the occurrence of clear sky conditions over an excellent astronomical location at El Leoncito Observatory in Argentina throughout the years 2006–2023. It was found that seasonal variations in cloudiness conditions are present over long-term measurements of 18 yr. The detected variations are connected to changes in seasons with a minimum of averaged clear sky hours in January. The minima of long-term variations occurred in the years 2016 and 2023 which implies the potential usage of ASI data in climatological studies. In total, 40,250 clear sky hours were identified. On average per year, ∼75% of all observed hours were without clouds. These periods can be used for further ionospheric and space physics studies with data obtained via particular ASI narrowband filters. The presented data-driven approach will be used also for these planned studies as it demonstrated a high potential for automation of image processing from ASI instruments.

Introduction:Sodium and potassium atoms produce the brightest emissions in Mercury’s tenuous exosphere. The existing body of work on K is substantially smaller than that of Na, since potassium is a more challenging observation from the ground and K emissions at 7665Å and 7699Å fall redward of the MESSENGER UVVS spectral range. Conversely, surface concentration of K in Mercury’s topmost soil has been mapped over the northern surface, while the Na regolith concentration has comparatively poor constraints [1][2]. In comparing the K and Na exosphere we also improve our understanding of the complex budget of sources and sinks in the alkali exosphere. The mechanisms generating sodium enhancements at the cold-pole longitudes, and variable hot spots near the magnetic cusp footprints, are not yet fully understood [3][4]. Mapping the structure of the potassium exosphere is therefore a worthwhile exercise, and better constraints on the Na/K ratio would be useful, since past literature offers a very broad range [5][6][7].Observations:K observations were performed with the Rapid Imaging Planetary Spectrograph (RIPS) at the 3.67m Advanced Electro Optical System Telescope (AEOS) at Haleakala in 2018. The data we analyze here consist of 5 observations with integration times of 100 to 200 seconds, where the planet’s image is stabilized using adaptive optics. RIPS simultaneously records a narrowband image and a spectrum on a single CCD using mirrored slit jaws. The imaging channel provides both spatial registration of the slit aperture across the planet’s disk and a reference for the atmospheric blurring so that absolute brightness can be calibrated in each frame. Fig. 1 shows a 200s frame with the spectral channel brightness multiplied by 15 for visibility. Continuing with Mercury as its target, RIPS will provide dedicated ground support for the BepiColombo mission.Analysis:After standard dark and flat corrections, a photometric model is spatially convolved with a kernel and matched to RIPS’ imaging channel in order to determine the atmospheric and optical blurring unique to each observation. This reference for absolute flux and image quality is critical for observations at very high airmass. We apply a basic Hapke formulation [8] with parameters determined from MESSENGER’s Mercury Dual Imaging System [9]. The rotation and location of Mercury’s disk on RIPS’ detector, as well as an estimate for the seeing, are extracted by matching the imaging channel and photometric model. The result determines the absolute flux of Mercury’s continuum in units of MegaRayleighs per angstrom along the slit-length of the spectral channel.The recorded spectrum is rectified and normalized to the theoretical flux of the continuum. The spectrum is then spatially binned across Mercury’s disk. We found that five bins best optimized signal-to-noise ratio while preserving spatial information. The continuum is fit and subtraction is performed using a solar model [10]. This produces a residual signal of exospheric K seen in Fig. 2, which is integrated to obtain the binned brightness.Results:Fig. 3 shows the potassium emission in five discrete slit positions across Mercury’s disk imposed on a photometric model blurred to the average of the individual frames. The brightest calculated value for K is 250 kiloRayleighs, with the lowest being 3 kR. The mapped data suggest polar enhancement, particularly in the south. Enhancement over the southern cusp is characteristic of Mercury’s Na exosphere [4], but more data need to be analyzed to support this claim for K. Standard “g-value” calculations of the K excitation rate by solar photons allows this absolute brightness to be converted to column density. The peak column density corresponding to 250 kR is 4.1 × 109 cm-2. Local densities may be higher if the emitting region is unresolved. This column, together with previous RIPS results for Na D1+D2 abundance [4], results in an estimate of the Na to K ratio in the Hermean exosphere of about 25. This value is smaller than disk-averaged ratios in Potter et al. [5] (Na/K~ 34 to 142), or the range of spatial variations in the ratio that Doressoundiram et al. [7] reported (Na/K~ 80 to 400), but lies within the lower range reported by Killen et al. [6] (Na/K~ 22 to 49) across the planet’s dayside. The ratio calculated here should be interpreted cautiously since, while this estimate represents Na and K measurements from the same technique, these species were not observed concurrently, and alkali emissions are known to vary temporally.References:[1] Peplowski P. N. et al (2012) JGRE 117, E00L10.[2] Peplowski P. N et al (2014) Icarus 228, 86.[3] Cassidy, T. A. et al (2016) GeoRL 43, 121.[4] Schmidt, C. A. et al (2020) Planet. Sci. J. 1, 4.[5] Potter, A. E. et al. (2002) J. Geophys. Res. 107, E6.[6] Killen, R. M. et al. (2010) Icarus 209, 75.[7] Doressoundiram, A. et al. (2010) Icarus 207, 1.[8] Hapke, B. (2012) Theory of Reflectance and Emittance Spectroscopy 2nd ed. (Cambridge: Cambridge Univ. Press).[9] Domingue, D. L et al (2016) Icarus 268, 172.[10] Kurucz, R. L. (2005) http://kurucz.harvard.edu/sun.html.

Berendzen was a tireless advocate for public literacy in science, a historian of astronomy, a consummate classroom teacher, a university president, and prolific public lecturer/commentator in space science.

During the 17 March 2015 geomagnetic storm, citizen scientist observations from Dunedin (45.95°S, 170.32°E), New Zealand, revealed a bright wide red arc known as stable auroral red (SAR) arc evolving into a thin white‐mauve arc, known as Strong Thermal Emission Velocity Enhancement (STEVE). An all‐sky imager at the Mount John Observatory (43.99°S, 170.46°E), 200 km north of Dunedin, detected an extremely bright arc in 630.0 nm, with a peak of ∼6 kR, colocated with the arc measured at Dunedin at an assumed height of 425 km. Swarm satellite data measured plasma parameters that showed strong subauroral ion drift signatures when the SAR arc was observed. These conditions intensified to extremely high values in a thinner channel when STEVE was present. Our results highlight the fast evolution of plasma properties and their effects on optical emissions. Current theories and models are unable to reproduce or explain these observations.

Abstract. We describe a multichannel camera operating in the visible to near-infrared wavelengths (450 to 900 nm) with an etendue of 0.08  cm2 sr that can be used to image extended sources across multiple optical bands, capable of 3σ detection of 20 Rayleigh signal in 120 s. It has an angular resolution of 0.1 deg and a 35  deg  ×  25  deg field of view, employing a charge-coupled device detector in a compact 1U CubeSat compatible form factor (10  ×  10  ×  8  cm3). The design uses commercial off-the-shelf components while offering versatility using a mosaic of bandpass filters to select different spectral channels to address a wide range of remote sensing needs. The specific implementation described here covers the application of the instrument to explore the neutral sodium and potassium atom density distribution in the atmospheres of the Earth or the Moon.

Aside from the well-studied sodium doublet, the potassium D lines are the only optical emissions in Mercury's exosphere that are amply bright to contrast with the dayside disk. Measurements of the K exosphere are limited compared to Na, but the K regolith abundance is better constrained, so new insights may help to understand surface–exosphere coupling. We use imaging spectroscopy to map the K brightness over Mercury's evening hemisphere, which shows an enhancement at low to midlatitudes, well equatorward of the Na peak. Both Na and K are brighter in the south, but the ratio between northern and southern hemisphere K emission appears less symmetric than that of Na. The disk-averaged Na/K column density ratio is between 70 and 130. During the same night, the dayside emission was mapped, we used a high-resolution spectrograph to attempt to resolve the Na and K line widths on the nightside. Forward-modeling the alkaline line profiles with hyperfine structure gives Na D1 and D2 line widths of 1114 ± 50 K and 1211 ± 45 K, respectively. D2 may appear hotter solely because its higher opacity adds preferentially to the profile wings. The K line width is surprisingly cold and cannot be easily distinguished from the instrumental line width, even at R = 137,500. Line widths roughly constrain K gas between the surface temperature and 1000 K, making it the coldest metallic constituent of Mercury's exosphere. Although Na and K are chemical analogs and often assumed to have similar properties, the results herein illustrate quite different characteristics between these elements in Mercury's exosphere.

This paper reports the climatology of medium‐scale traveling ionospheric disturbances (MSTIDs) observed between September 2018 and August 2019 in the nighttime redline airglow intensity measurements from an all‐sky imager located in Sutherland, South Africa (32.4°S, 20.8°E; magnetic latitude: 40.7°S). The nighttime MSTIDs appeared as either single or multiple dark bands, commenced mostly before midnight, and predominantly occurred during the southern winter solstice. They primarily propagated westward with speeds of 31–127 m/s. The periods and wavelengths of the multi‐band MSTIDs were in the ranges of 26–155 min and 134–578 km, respectively, while the temporal and spatial scales of the single band MSTIDs were 11–30 min and 43–143 km, respectively. Analysis of neutral wind measurements from a co‐located Fabry‐Perot interferometer showed that the thermospheric wind was mostly northeastward in the evenings of MSTID occurrence and that the favored westward propagation of the MSTIDs was the least restricted propagation direction by the background wind. Based on data from nearby ionosondes, the MSTIDs were mostly accompanied by sporadic E and spread‐F structures. From the seasonal occurrences of MSTIDs and sporadic E as well as the MSTID propagation and prevalent wind directions, it is concluded that Perkins instability is the most likely source of the majority of the observed nighttime MSTIDs, while the remainder may be seeded by gravity waves.

The lunar surface is constantly bombarded by the solar wind, photons, and meteoroids, which can liberate Na atoms from the regolith. These atoms are subsequently accelerated by solar photon pressure to form a long comet‐like tail opposite the sun. Near new moon, these atoms encounter the Earth's gravity and are “focused” into a beam of enhanced density. This beam appears as the ∼3° diameter Sodium Moon Spot (SMS). Data from the all sky imager at the El Leoncito Observatory have been analyzed for changes in the SMS shape and brightness. New geometry‐based relationships have been found that affect the SMS brightness. The SMS is brighter when the Moon is north of the ecliptic at new moon; the SMS is brighter when new moon occurs near perigee; and the SMS peaks in brightness ∼5 h after new moon. After removing these effects, the data were analyzed for long term and seasonal patterns that could be attributed to changes in source mechanisms. No correlation was found between the SMS brightness and the 11‐year solar‐cycle, the proton or the He ++ flow pressure, the density, the speed or the plasma temperature of the solar wind, but an annual pattern was found. A ∼0.83 correlation (Pearson's “ r ”) was found between the SMS brightness and a 4‐year average of sporadic meteor rates at Earth, suggesting a cause‐and‐effect. The new insights gained from this long‐term study put new constraints on the variability of the potential sources of the Na atoms escaping from the Moon.

On September 28, 2017 citizen scientist observations at Alberta, Canada (51°N, 113° W) detected aurora and a thin east‐west purplish arc, known as strong thermal emission velocity enhancement (STEVE) that lasted less than 20 min. All‐sky imagers at subauroral latitudes measured stable auroral red (SAR) arcs during the entire night. The imager at Bridger, MT (45.3°N, 108.9°W) also measured a STEVE. The overlapping geometry allowed to determine that the height of STEVE was 225–275 km. STEVE is brighter in the 630.0 nm images in the West and almost merges with the SAR arc in the East. A DMSP satellite pass in the southern hemisphere was at the conjugate location of the Bridger imager during the STEVE observation. When mapped into the northern hemisphere intense subauroral ion drift and subauroral polarization streams were detected associated with the two optical signatures measured in 630.0 nm.

An extensive and bright mesospheric gravity wave event occurred over the El Leoncito Observatory, Argentina (31.8ºS, 69.3ºW) during the night of 17–18 March 2016. The wave structures were exhibited in the nightglow and were easily visible to naked eye observers, a phenomenon known as a Bright Night. Analysis of a combination of ground-based and space-based data sources indicated that the event was generated by a large thunderstorm complex located to the south-east of the observation site. The event was associated with very large values of wave momentum flux: 150–300 m2s-2, which is over an order of magnitude larger than typical. The routine seasonality of such thunderstorm systems suggests that they may contribute significantly to the role of upward coupling to the upper atmosphere and ionosphere.

The Rapid Imaging Planetary Spectrograph (RIPS) was designed as a long-slit high-resolution spectrograph for the specific application of studying atmospheres of spatially extended solar system bodies. With heritage in terrestrial airglow instruments, RIPS uses an echelle grating and order-sorting filters to obtain optical spectra at resolving powers up to R~127,000. An ultra-narrowband image from the reflective slit jaws is captured concurrently with each spectrum on the same EMCCD detector. The "rapid" portion of RIPS' moniker stems from its ability to capture high frame rate data streams, which enables the established technique known as "lucky imaging" to be extended to spatially resolved spectroscopy. Resonantly scattered emission lines of alkali metals, in particular, are sufficiently bright to be measured in short integration times. RIPS has mapped the distributions of Na and K emissions in Mercury's tenuous exosphere, which exhibit dynamic behavior coupled to the planet's plasma and meteoroid environment. An important application is daylight observations of Mercury at solar telescopes since synoptic context on the exosphere's distribution comprises valuable ground-based support for the upcoming BepiColombo orbital mission. As a conventional long slit spectrograph, RIPS has targeted the Moon's surface-bound exosphere where structure in linewidth and brightness as a function of tangent altitude are observed. At the Galilean moons, RIPS can study the plasma interaction with Io and place new constraints on the sputtered atmosphere of Europa, which in turn provides insight into the salinity of Europa's subsurface ocean. The instrumental design and construction are described herein, and these astronomical observations are presented to illustrate RIPS' performance as a visiting instrument at three different telescope facilities.

Ground based observations have indicated that at times the lunar Sodium atmosphere extends beyond the Earth. However, to date no experiment has been conducted to perform an extended duration, in-situ observation of the lunar atmosphere. We have designed a small (10 × 10 × 10 cm3 and a mass of 1.3 Kg), multi-band imager that operates in the CCD-band (approximately, 450 – 900 nm). The instrument is easily tailored to meet a specific application by selecting the appropriate combination of interference filters. If such an instrument is placed on a lunar orbiting platform, it will generate a long-term database to study the morphology of the lunar atmosphere or surface features observable in this band. The instrument has an angular resolution of 0.1◦and a field of view of 35◦× 25◦. This large field of view is shared by a mosaic of interference filters chosen for a specific application. The instrument uses a custom-designed computer program for automatic exposure control and communicates using standard serial and ethernet protocols. This design has been validated using commercial off-the-shelf components for sodium and potassium resonance emissions at 589 nm and 770 nm, respectively.

630.0 nm all-sky imaging data are used to detect airglow depletions associated with equatorial spread F. Pairs of imagers located at geomagnetically conjugate locations in the American sector at low and mid-latitudes provide information on the occurrence rate and zonal motion of airglow depletions. Airglow depletions are seen extending to magnetic latitudes as high as 25°. An asymmetric extension is observed with structures in the northern hemisphere reaching higher latitudes. By tracking the zonal motion of airglow depletions, zonal plasma drifts in the thermosphere can be inferred and their simultaneous behavior in both hemispheres investigated. Case studies using El Leoncito and Mercedes imagers in the southern hemisphere, and the respective magnetically conjugate imagers at Villa de Leyva and Arecibo, provide consistent evidence of the influence of the South Atlantic Magnetic Anomaly on the dynamics and characteristics of the thermosphere–ionosphere system at low and mid-latitudes.

We report on estimates of the vertical flux of horizontal momentum associated with an extensive and bright mesospheric gravity wave event that occurred over the El Leoncito Observatory, Argentina (31.8 degrees S, 69.3 degrees W), during the night of 17-18 March 2016. Using a combination of ground-based and space-based data sources, we propose that the event was generated by a large and distant thunderstorm complex located to the southeast of the observation site. The nightglow, including the wave structures, was easily visible to naked eye observers, a phenomenon known as a Bright Night. Such "extreme events" illuminate the important role of upward coupling in space weather research.