<p>Around 17 December 2021, the Solar Orbiter spacecraft was predicted to have had ... more <p>Around 17 December 2021, the Solar Orbiter spacecraft was predicted to have had its closest approach to comet C/2021 A1 (Leonard) with a minimum streamline distance < 0.01 AU. This encounter provided an unprecedented opportunity to investigate in situ comet Leonard's interaction with the solar wind and the composition of pick-up ions produced by ionization and dissociation of outgassed neutrals from its coma. It was a long-period comet originating from the Oort Cloud with a nucleus about 1 km in diameter, with ground-based telescope observations after its perihelion pass (at ~0.62 AU on 3 January 2022) indicating that it had subsequently disintegrated. Prior to perihelion, outbursts had been reported as well as variations in brightness, which had resulted in speculation about an impending disintegration. However, the dimming in November 2021, before the Solar Orbiter encounter, was argued to be due to a transition from outgassing dominated by carbon dioxide to water. Comet Leonard was the brightest comet of the year and noted for its spectacular ion tail with complex structures, including knots and streamers. Preliminary analysis of in situ Solar Orbiter observations have revealed tell-tale signatures of a cometary encounter around the time of predicted closest approach, such as evidence for magnetic field line draping. However, the clearest evidence has come from Solar Wind Analyzer-Heavy Ion Sensor (SWA-HIS) observations of singly-charged oxygen ions, which are typically not of solar origin and are usually produced when the solar wind interacts with a comet or other Solar System body. In this presentation we use SWA-HIS and EDP-STEP data to investigate aspects of the solar wind interaction and composition of cometary pick-up ions from this active, long-period comet shortly before its disintegration.</p>
<p>Since the 1970s it has been empirically known that the area of solar coronal hol... more <p>Since the 1970s it has been empirically known that the area of solar coronal holes a ects the properties of high-speed solar wind<br />streams (HSSs) at Earth. We derive a simple analytical model for the propagation of HSSs from the Sun to Earth and thereby show<br />how the area of coronal holes and the size of their boundary regions a ect the HSS velocity, temperature, and density near Earth.<br />We assume that velocity, temperature, and density profiles form across the HSS cross section close to the Sun and that these spatial<br />profiles translate into corresponding temporal profiles in a given radial direction due to the solar rotation. These temporal distributions<br />drive the stream interface to the preceding slow solar wind plasma and disperse with distance from the Sun. The HSS properties at<br />1AU are then given by all HSS plasma parcels launched from the Sun that did not run into the stream interface at Earth distance.<br />We show that the velocity plateau region of HSSs as seen at 1AU, if apparent, originates from the center region of the HSS close<br />to the Sun, whereas the velocity tail at 1AU originates from the trailing boundary region. Small HSSs can be described to entirely<br />consist of boundary region plasma, which intrinsically results in smaller peak velocities. The peak velocity of HSSs at Earth further<br />depends on the longitudinal width of the HSS close to the Sun. The shorter the longitudinal width of an HSS close to the Sun, the<br />more of its “fastest” HSS plasma parcels from the HSS core and trailing boundary region have impinged upon the stream interface<br />with the preceding slow solar wind, and the smaller is the peak velocity of the HSS at Earth. As the longitudinal width is statistically<br />correlated to the area of coronal holes, this also explains the well-known empirical relationship between coronal hole areas and HSS<br />peak velocities. Further, the temperature and density of HSS plasma parcels at Earth depend on their radial expansion from the Sun<br />to Earth. The radial expansion is determined by the velocity gradient across the HSS boundary region close to the Sun and gives the<br />velocity-temperature and density-temperature relationships at Earth their specific shape. When considering a large number of HSSs,<br />the assumed correlation between the HSS velocities and temperatures close to the Sun degrades only slightly up to 1AU, but the<br />correlation between the velocities and densities is strongly disrupted up to 1AU due to the radial expansion. Finally, we show how<br />the number of particles of the piled-up slow solar wind in the stream interaction region depends on the velocities and densities of the<br />HSS and preceding slow solar wind plasma.</p>
<p>   Energy spectra of X-ray solar flares observed by th... more <p>   Energy spectra of X-ray solar flares observed by the Spectrometer-Telescope for Imaging X-rays (STIX) onboard the Solar Orbiter consist of both thermal and non-thermal parts. The thermal part is present in all solar events. When the non-thermal part of the energy spectrum begins to dominate, we can expect detection in interplanetary space of high-energy electron beams that have escaped the coronal loops. When hard X-ray flares are detected solar type III radio bursts are registered frequently with their numerous modifications like drift pairs, U-type, and structured bursts. The e-CALLISTO simple worldwide radio antenna stations allow us to identify the existence of non-thermal components in the energy spectra of strong X-ray flares. At the same time, some X-ray flares are accompanied by ejections of energetic ions including heavy ions. The specific features in X-ray bursts responsible for events with simultaneous light and heavy particle stream generation are still unclear compared with those with electron emission only.</p><p>    We present preliminary results of observations gathered in December 2022 and cross-analysis of data on energetic light and heavy particle fluxes and X-ray flare parameters. The end of 2022 was distinguished by moderate to high solar activity, the presence of three periods with enhanced proton and heavy-ion fluxes at the beginning of the month, in the middle, and on 25-26 December. We demonstrate also the presence of narrow directed electron beams detected by the Electron Proton Telescope (EPT) of EPD for selected events mentioned above, and heavy ions detected by the Suprathermal Ion Spectrograph (SIS) of EPD.</p>
Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sou... more Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low-temperature, circumneutral pH, rock-dominated aqueous conditions. Analyses of diagenetic features (including concretions, raised ridges, and fractures) at high spatial resolution indicate that they are composed of iron- and halogen-rich components, magnesium-iron-chlorine–rich components, and hydrated calcium sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. The geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagene...
Machine Learning Techniques for Space Weather, 2018
Abstract The solar wind represents the background into which other space weather phenomena are em... more Abstract The solar wind represents the background into which other space weather phenomena are embedded. Interplanetary coronal mass ejections (ICMEs) travel through and interact with the background solar wind. The nature of this interaction depends on plasma structures, the solar wind, and the typically faster ICME. It is well known that the solar wind that is continuously emitted from the Sun comes in at least two varieties. These are historically called slow solar wind and fast solar wind, although their most distinctive property is not the solar wind speed, but the elemental and charge state compositions. So far, solar wind categorization has been approached with different combinations of hand-crafted classifiers based on expert knowledge and heuristic methods. As a result, the actual number of different solar wind types differs between typical approaches and, in particular, the decision boundaries between solar wind regimes differ considerably. In this situation, a purely data-driven approach that aims at dividing solar wind plasma into categories based on their similarity to other observations can be insightful. Such an approach is in machine learning, realized by unsupervised clustering methods such as k-means clustering. Given a sufficiently large data set, k-means clustering can improve and validate the available solar wind categorization schemes. Here, we apply k-means clustering to solar wind data measured by instruments on the Advanced Composition Explorer, compare the resulting solar wind types to existing heuristic solar wind categorization schemes, determine the probable number of distinct solar wind types that are supported by the observations, discuss the physical interpretation of the resulting solar wind types, and finally utilize the k-means approach to investigate feature selection for solar wind categorization.
Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curios... more Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, calcium sulfates, iron oxide or hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The John Klein smectite has basal spacing of ~10 angstroms, indicating little interlayer hydration. The Cumberland smectite has basal spacing at both ~13.2 and ~10 angstroms. The larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating H 2 O retention. Basaltic minerals in the mudstone are similar to those in nearby eolian deposits. However, the mudstone has far less Fe-forsterite, possibly lost with formation of smectite plus magnetite. Late Noachian/Early Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time.
Inner source pickup ions originate most likely from the interaction of the solar wind with dust p... more Inner source pickup ions originate most likely from the interaction of the solar wind with dust particles in interplanetary space They are thought to be generated either through saturation of dust with solar wind subsequent desorption and pickup or through penetration of small dust grains by solar wind neutralization and subsequent re-ionization In both cases a velocity distribution emerges which is genuinely suprathermal but peaks below the solar wind speed Using Monte Carlo simulations we investigate the properties of inner-source pickup ions in more detail We apply experimental results for charge exchange of solar wind ions with carbon foils as a proxy for the interaction of ions with small interplanetary dust grains As the initial pickup ion distributions we adopt the velocity distribution functions VDFs of solar wind particles with which they exit from the grains Subsequent pitch angle scattering and cooling will spread the distributions through velocity space Since the emergin...
<p>Around 17 December 2021, the Solar Orbiter spacecraft was predicted to have had ... more <p>Around 17 December 2021, the Solar Orbiter spacecraft was predicted to have had its closest approach to comet C/2021 A1 (Leonard) with a minimum streamline distance < 0.01 AU. This encounter provided an unprecedented opportunity to investigate in situ comet Leonard's interaction with the solar wind and the composition of pick-up ions produced by ionization and dissociation of outgassed neutrals from its coma. It was a long-period comet originating from the Oort Cloud with a nucleus about 1 km in diameter, with ground-based telescope observations after its perihelion pass (at ~0.62 AU on 3 January 2022) indicating that it had subsequently disintegrated. Prior to perihelion, outbursts had been reported as well as variations in brightness, which had resulted in speculation about an impending disintegration. However, the dimming in November 2021, before the Solar Orbiter encounter, was argued to be due to a transition from outgassing dominated by carbon dioxide to water. Comet Leonard was the brightest comet of the year and noted for its spectacular ion tail with complex structures, including knots and streamers. Preliminary analysis of in situ Solar Orbiter observations have revealed tell-tale signatures of a cometary encounter around the time of predicted closest approach, such as evidence for magnetic field line draping. However, the clearest evidence has come from Solar Wind Analyzer-Heavy Ion Sensor (SWA-HIS) observations of singly-charged oxygen ions, which are typically not of solar origin and are usually produced when the solar wind interacts with a comet or other Solar System body. In this presentation we use SWA-HIS and EDP-STEP data to investigate aspects of the solar wind interaction and composition of cometary pick-up ions from this active, long-period comet shortly before its disintegration.</p>
<p>Since the 1970s it has been empirically known that the area of solar coronal hol... more <p>Since the 1970s it has been empirically known that the area of solar coronal holes a ects the properties of high-speed solar wind<br />streams (HSSs) at Earth. We derive a simple analytical model for the propagation of HSSs from the Sun to Earth and thereby show<br />how the area of coronal holes and the size of their boundary regions a ect the HSS velocity, temperature, and density near Earth.<br />We assume that velocity, temperature, and density profiles form across the HSS cross section close to the Sun and that these spatial<br />profiles translate into corresponding temporal profiles in a given radial direction due to the solar rotation. These temporal distributions<br />drive the stream interface to the preceding slow solar wind plasma and disperse with distance from the Sun. The HSS properties at<br />1AU are then given by all HSS plasma parcels launched from the Sun that did not run into the stream interface at Earth distance.<br />We show that the velocity plateau region of HSSs as seen at 1AU, if apparent, originates from the center region of the HSS close<br />to the Sun, whereas the velocity tail at 1AU originates from the trailing boundary region. Small HSSs can be described to entirely<br />consist of boundary region plasma, which intrinsically results in smaller peak velocities. The peak velocity of HSSs at Earth further<br />depends on the longitudinal width of the HSS close to the Sun. The shorter the longitudinal width of an HSS close to the Sun, the<br />more of its “fastest” HSS plasma parcels from the HSS core and trailing boundary region have impinged upon the stream interface<br />with the preceding slow solar wind, and the smaller is the peak velocity of the HSS at Earth. As the longitudinal width is statistically<br />correlated to the area of coronal holes, this also explains the well-known empirical relationship between coronal hole areas and HSS<br />peak velocities. Further, the temperature and density of HSS plasma parcels at Earth depend on their radial expansion from the Sun<br />to Earth. The radial expansion is determined by the velocity gradient across the HSS boundary region close to the Sun and gives the<br />velocity-temperature and density-temperature relationships at Earth their specific shape. When considering a large number of HSSs,<br />the assumed correlation between the HSS velocities and temperatures close to the Sun degrades only slightly up to 1AU, but the<br />correlation between the velocities and densities is strongly disrupted up to 1AU due to the radial expansion. Finally, we show how<br />the number of particles of the piled-up slow solar wind in the stream interaction region depends on the velocities and densities of the<br />HSS and preceding slow solar wind plasma.</p>
<p>   Energy spectra of X-ray solar flares observed by th... more <p>   Energy spectra of X-ray solar flares observed by the Spectrometer-Telescope for Imaging X-rays (STIX) onboard the Solar Orbiter consist of both thermal and non-thermal parts. The thermal part is present in all solar events. When the non-thermal part of the energy spectrum begins to dominate, we can expect detection in interplanetary space of high-energy electron beams that have escaped the coronal loops. When hard X-ray flares are detected solar type III radio bursts are registered frequently with their numerous modifications like drift pairs, U-type, and structured bursts. The e-CALLISTO simple worldwide radio antenna stations allow us to identify the existence of non-thermal components in the energy spectra of strong X-ray flares. At the same time, some X-ray flares are accompanied by ejections of energetic ions including heavy ions. The specific features in X-ray bursts responsible for events with simultaneous light and heavy particle stream generation are still unclear compared with those with electron emission only.</p><p>    We present preliminary results of observations gathered in December 2022 and cross-analysis of data on energetic light and heavy particle fluxes and X-ray flare parameters. The end of 2022 was distinguished by moderate to high solar activity, the presence of three periods with enhanced proton and heavy-ion fluxes at the beginning of the month, in the middle, and on 25-26 December. We demonstrate also the presence of narrow directed electron beams detected by the Electron Proton Telescope (EPT) of EPD for selected events mentioned above, and heavy ions detected by the Suprathermal Ion Spectrograph (SIS) of EPD.</p>
Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sou... more Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low-temperature, circumneutral pH, rock-dominated aqueous conditions. Analyses of diagenetic features (including concretions, raised ridges, and fractures) at high spatial resolution indicate that they are composed of iron- and halogen-rich components, magnesium-iron-chlorine–rich components, and hydrated calcium sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. The geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagene...
Machine Learning Techniques for Space Weather, 2018
Abstract The solar wind represents the background into which other space weather phenomena are em... more Abstract The solar wind represents the background into which other space weather phenomena are embedded. Interplanetary coronal mass ejections (ICMEs) travel through and interact with the background solar wind. The nature of this interaction depends on plasma structures, the solar wind, and the typically faster ICME. It is well known that the solar wind that is continuously emitted from the Sun comes in at least two varieties. These are historically called slow solar wind and fast solar wind, although their most distinctive property is not the solar wind speed, but the elemental and charge state compositions. So far, solar wind categorization has been approached with different combinations of hand-crafted classifiers based on expert knowledge and heuristic methods. As a result, the actual number of different solar wind types differs between typical approaches and, in particular, the decision boundaries between solar wind regimes differ considerably. In this situation, a purely data-driven approach that aims at dividing solar wind plasma into categories based on their similarity to other observations can be insightful. Such an approach is in machine learning, realized by unsupervised clustering methods such as k-means clustering. Given a sufficiently large data set, k-means clustering can improve and validate the available solar wind categorization schemes. Here, we apply k-means clustering to solar wind data measured by instruments on the Advanced Composition Explorer, compare the resulting solar wind types to existing heuristic solar wind categorization schemes, determine the probable number of distinct solar wind types that are supported by the observations, discuss the physical interpretation of the resulting solar wind types, and finally utilize the k-means approach to investigate feature selection for solar wind categorization.
Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curios... more Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, calcium sulfates, iron oxide or hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The John Klein smectite has basal spacing of ~10 angstroms, indicating little interlayer hydration. The Cumberland smectite has basal spacing at both ~13.2 and ~10 angstroms. The larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating H 2 O retention. Basaltic minerals in the mudstone are similar to those in nearby eolian deposits. However, the mudstone has far less Fe-forsterite, possibly lost with formation of smectite plus magnetite. Late Noachian/Early Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time.
Inner source pickup ions originate most likely from the interaction of the solar wind with dust p... more Inner source pickup ions originate most likely from the interaction of the solar wind with dust particles in interplanetary space They are thought to be generated either through saturation of dust with solar wind subsequent desorption and pickup or through penetration of small dust grains by solar wind neutralization and subsequent re-ionization In both cases a velocity distribution emerges which is genuinely suprathermal but peaks below the solar wind speed Using Monte Carlo simulations we investigate the properties of inner-source pickup ions in more detail We apply experimental results for charge exchange of solar wind ions with carbon foils as a proxy for the interaction of ions with small interplanetary dust grains As the initial pickup ion distributions we adopt the velocity distribution functions VDFs of solar wind particles with which they exit from the grains Subsequent pitch angle scattering and cooling will spread the distributions through velocity space Since the emergin...
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