| 1. |
- Witasse, O., et al.
(författare)
-
Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov-Gerasimenko, Saturn, and New Horizons en route to Pluto : Comparison of its Forbush decreases at 1.4, 3.1, and 9.9 AU
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 122:8, s. 7865-7890
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Tidskriftsartikel (refereegranskat)abstract
- We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44h before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110-111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116 degrees, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.
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| 2. |
- Andrews, David J., et al.
(författare)
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MARSIS Observations of Field-Aligned Irregularities and Ducted Radio Propagation in the Martian Ionosphere
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 123:8, s. 6251-6263
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of Mars's ionosphere has been significantly advanced in recent years by observations from Mars Express and lately Mars Atmosphere and Volatile EvolutioN. A topic of particular interest are the interactions between the planet's ionospheric plasma and its highly structured crustal magnetic fields and how these lead to the redistribution of plasma and affect the propagation of radio waves in the system. In this paper, we elucidate a possible relationship between two anomalous radar signatures previously reported in observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument on Mars Express. Relatively uncommon observations of localized, extreme increases in the ionospheric peak density in regions of radial (cusp-like) magnetic fields and spread echo radar signatures are shown to be coincident with ducting of the same radar pulses at higher altitudes on the same field lines. We suggest that these two observations are both caused by a high electric field (perpendicular to B) having distinctly different effects in two altitude regimes. At lower altitudes, where ions are demagnetized and electrons magnetized, and recombination dominantes, a high electric field causes irregularities, plasma turbulence, electron heating, slower recombination, and ultimately enhanced plasma densities. However, at higher altitudes, where both ions and electrons are magnetized and atomic oxygen ions cannot recombine directly, the high electric field instead causes frictional heating, a faster production of molecular ions by charge exchange, and so a density decrease. The latter enables ducting of radar pulses on closed field lines, in an analogous fashion to interhemispheric ducting in the Earth's ionosphere.
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| 3. |
- Edberg, Niklas J. T., et al.
(författare)
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Effects of Saturn's magnetospheric dynamics on Titan's ionosphere
- 2015
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:10, s. 8884-8898
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Tidskriftsartikel (refereegranskat)abstract
- We use the Cassini Radio and Plasma Wave Science/Langmuir probe measurements of the electron density from the first 110 flybys of Titan to study how Saturn's magnetosphere influences Titan's ionosphere. The data is first corrected for biased sampling due to varying solar zenith angle and solar energy flux (solar cycle effects). We then present results showing that the electron density in Titan's ionosphere, in the altitude range 1600-2400km, is increased by about a factor of 2.5 when Titan is located on the nightside of Saturn (Saturn local time (SLT) 21-03h) compared to when on the dayside (SLT 09-15 h). For lower altitudes (1100-1600km) the main dividing factor for the ionospheric density is the ambient magnetospheric conditions. When Titan is located in the magnetospheric current sheet, the electron density in Titan's ionosphere is about a factor of 1.4 higher compared to when Titan is located in the magnetospheric lobes. The factor of 1.4 increase in between sheet and lobe flybys is interpreted as an effect of increased particle impact ionization from approximate to 200eV sheet electrons. The factor of 2.5 increase in electron density between flybys on Saturn's nightside and dayside is suggested to be an effect of the pressure balance between thermal plus magnetic pressure in Titan's ionosphere against the dynamic pressure and energetic particle pressure in Saturn's magnetosphere.
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| 4. |
- Hall, B. E. S., et al.
(författare)
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Annual variations in the Martian bow shock location as observed by the Mars Express mission
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:11, s. 11474-11494
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Tidskriftsartikel (refereegranskat)abstract
- The Martian bow shock distance has previously been shown to be anticorrelated with solar wind dynamic pressure but correlated with solar extreme ultraviolet (EUV) irradiance. Since both of these solar parameters reduce with the square of the distance from the Sun, and Mars' orbit about the Sun increases by similar to 0.3 AU from perihelion to aphelion, it is not clear how the bow shock location will respond to variations in these solar parameters, if at all, throughout its orbit. In order to characterize such a response, we use more than 5 Martian years of Mars Express Analyser of Space Plasma and EneRgetic Atoms (ASPERA-3) Electron Spectrometer measurements to automatically identify 11,861 bow shock crossings. We have discovered that the bow shock distance as a function of solar longitude has a minimum of 2.39 R-M around aphelion and proceeds to a maximum of 2.65 R-M around perihelion, presenting an overall variation of similar to 11% throughout the Martian orbit. We have verified previous findings that the bow shock in southern hemisphere is on average located farther away from Mars than in the northern hemisphere. However, this hemispherical asymmetry is small (total distance variation of similar to 2.4%), and the same annual variations occur irrespective of the hemisphere. We have identified that the bow shock location is more sensitive to variations in the solar EUV irradiance than to solar wind dynamic pressure variations. We have proposed possible interaction mechanisms between the solar EUV flux and Martian plasma environment that could explain this annual variation in bow shock location.
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| 5. |
- Stergiopoulou, Katerina, et al.
(författare)
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Mars Express Observations of Cold Plasma Structures in the Martian Magnetotail
- 2020
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:10
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Tidskriftsartikel (refereegranskat)abstract
- We present observations from five Mars Express (MEX) orbits in September 2016 while the spacecraft passed through the Martian induced magnetotail at altitudes up to 3,500 km. On these orbits, the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument was operated in Active Ionospheric Sounding (AIS) mode at much higher altitude than normal, acting as a local sounder and detecting cold plasma structures in this region. In this paper we combine MARSIS tail measurements with solar wind data from the Solar Wind Ion Analyzer (SWIA) instrument and the Magnetometer (MAG) from Mars Atmosphere and Volatile EvolutioN (MAVEN) in order to investigate possible factors affecting plasma transport from the dayside and through the terminator. MARSIS observed structured cold ionospheric plasma along its trajectory, at all altitudes and solar zenith angles (SZAs). Isolated regions of cold plasma were also observed on each orbit as the spacecraft crossed the terminator, even at high altitudes. We conclude that the variability of plasma seen in the tail results from a multifactorial transport process, the development of which cannot be attributed to a sole parameter influencing it, despite the availability of simultaneous high quality solar wind measurements.
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| 6. |
- Vaivads, Andris, et al.
(författare)
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Turbulence Heating ObserveR - satellite mission proposal
- 2016
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Ingår i: JOURNAL OF PLASMA PHYSICS. - 0022-3778. ; 82
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Tidskriftsartikel (refereegranskat)abstract
- The Universe is permeated by hot, turbulent, magnetized plasmas. Turbulent plasma is a major constituent of active galactic nuclei, supernova remnants, the intergalactic and interstellar medium, the solar corona, the solar wind and the Earth's magnetosphere, just to mention a few examples. Energy dissipation of turbulent fluctuations plays a key role in plasma heating and energization, yet we still do not understand the underlying physical mechanisms involved. THOR is a mission designed to answer the questions of how turbulent plasma is heated and particles accelerated, how the dissipated energy is partitioned and how dissipation operates in different regimes of turbulence. THOR is a single-spacecraft mission with an orbit tuned to maximize data return from regions in near-Earth space - magnetosheath, shock, foreshock and pristine solar wind - featuring different kinds of turbulence. Here we summarize the THOR proposal submitted on 15 January 2015 to the 'Call for a Medium-size mission opportunity in ESAs Science Programme for a launch in 2025 (M4)'. THOR has been selected by European Space Agency (ESA) for the study phase.
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| 7. |
- Welling, D. T., et al.
(författare)
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Recommendations for Next-Generation Ground Magnetic Perturbation Validation
- 2018
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Ingår i: Space Weather. - 1542-7390. ; 16:12, s. 1912-1920
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Tidskriftsartikel (refereegranskat)abstract
- Data-model validation of ground magnetic perturbation forecasts, specifically of the time rate of change of surface magnetic field, dB/dt, is a critical task for model development and for mitigation of geomagnetically induced current effects. While a current, community-accepted standard for dB/dt validation exists (Pulkkinen et al., 2013), it has several limitations that prevent more complete understanding of model capability. This work presents recommendations from the International Forum for Space Weather Capabilities Assessment Ground Magnetic Perturbation Working Team for creating a next-generation validation suite. Four recommendations are made to address the existing suite: greatly expand the number of ground observatories used, expand the number of events included in the suite from six to eight, generate metrics as a function of magnetic local time, and generate metrics as a function of activity type. For each of these, implementation details are explored. Limitations and future considerations are also discussed.
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| 8. |
- Andrews, David J., et al.
(författare)
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Determination of local plasma densities with the MARSIS radar : Asymmetries in the high-altitude Martian ionosphere
- 2013
-
Ingår i: Journal of Geophysical Research: Space Physics. - : American Geophysical Union (AGU). - 2169-9380. ; 118:10, s. 6228-6242
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel method for the automatic retrieval of local plasma density measurements from the Mars advanced radar for subsurface and ionospheric sounding (MARSIS) active ionospheric sounder (AIS) instrument. The resulting large data set is then used to study the configuration of the Martian ionosphere at altitudes above approximate to 300km. An empirical calibration routine is used, which relates the local plasma density to the measured intensity of multiple harmonics of the local plasma frequency oscillation, excited in the plasma surrounding the antenna in response to the transmission of ionospheric sounding pulses. Enhanced accuracy is achieved in higherdensity (n(e)>150cm(-3)) plasmas, when MARSIS AIS is able to directly measure the fundamental frequency of the local plasma oscillation. To demonstrate the usefulness of this data set, the derived plasma densities are binned by altitude and solar zenith angle in regions over weak (|B-c|<20nT) and strong (|B-c|>20nT) crustal magnetic fields, and we find clear and consistent evidence for a significant asymmetry between these two regions. We show that within the approximate to 300-1200km altitude range sampled, the median plasma density is substantially higher on the dayside in regions of relatively stronger crustal fields than under equivalent illuminations in regions of relatively weaker crustal fields. Conversely, on the nightside, median plasma densities are found to be higher in regions of relatively weaker crustal fields. We suggest that the observed asymmetry arises as a result of the modulation of the efficiency of plasma transport processes by the irregular crustal fields and the generally horizontal draped interplanetary magnetic field.
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| 9. |
- Andrews, David J., et al.
(författare)
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Oblique reflections in the Mars Express MARSIS data set : Stable density structures in the Martian ionosphere
- 2014
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Ingår i: Journal of Geophysical Research-Space Physics. - 2169-9380. ; 119:5, s. 3944-3960
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Tidskriftsartikel (refereegranskat)abstract
- The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) onboard the European Space Agency's Mars Express (MEX) spacecraft routinely detects evidence of localized plasma density structures in the Martian dayside ionosphere. Such structures, likely taking the form of spatially extended elevations in the plasma density at a given altitude, give rise to oblique reflections in the Active Ionospheric Sounder data. These structures are likely related to the highly varied Martian crustal magnetic field. In this study we use the polar orbit of MEX to investigate the repeatability of the ionospheric structures producing these anomalous reflections, examining data taken in sequences of multiple orbits which pass over the same regions of the Martian surface under similar solar illuminations, within intervals lasting tens of days. Presenting three such examples, or case studies, we show for the first time that these oblique reflections are often incredibly stable, indicating that the underlying ionospheric structures are reliably reformed in the same locations and with qualitatively similar parameters. The visibility, or lack thereof, of a given oblique reflection on a single orbit can generally be attributed to variations in the crustal field within the ionosphere along the spacecraft trajectory. We show that, within these examples, oblique reflections are generally detected whenever the spacecraft passes over regions of intense near-radial crustal magnetic fields (i.e., with a cusp-like configuration). The apparent stability of these structures is an important feature that must be accounted for in models of their origin.
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| 10. |
- Andrews, David J., et al.
(författare)
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Plasma observations during the Mars atmospheric "plume" event of March-April 2012
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:4, s. 3139-3154
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Tidskriftsartikel (refereegranskat)abstract
- We present initial analyses and conclusions from plasma observations made during the reported "Mars plume event" of March-April 2012. During this period, multiple independent amateur observers detected a localized, high-altitude "plume" over the Martian dawn terminator, the cause of which remains to be explained. The estimated brightness of the plume exceeds that expected for auroral emissions, and its projected altitude greatly exceeds that at which clouds are expected to form. We report on in situ measurements of ionospheric plasma density and solar wind parameters throughout this interval made by Mars Express, obtained over the same surface region but at the opposing terminator. Measurements in the ionosphere at the corresponding location frequently show a disturbed structure, though this is not atypical for such regions with intense crustal magnetic fields. We tentatively conclude that the formation and/or transport of this plume to the altitudes where it was observed could be due in part to the result of a large interplanetary coronal mass ejection (ICME) encountering the Martian system. Interestingly, we note that the only similar plume detection in May 1997 may also have been associated with a large ICME impact at Mars.
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| 11. |
- Edberg, Niklas J. T., et al.
(författare)
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Extreme densities in Titan's ionosphere during the T85 magnetosheath encounter
- 2013
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 40:12, s. 2879-2883
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Tidskriftsartikel (refereegranskat)abstract
- We present Cassini Langmuir probe measurements of the highest electron number densities ever reported from the ionosphere of Titan. The measured density reached 4310cm(-3) during the T85 Titan flyby. This is at least 500cm(-3) higher than ever observed before and at least 50% above the average density for similar solar zenith angles. The peak of the ionospheric density is not reached on this flyby, making the maximum measured density a lower limit. During this flyby, we also report that an impacting coronal mass ejection (CME) leaves Titan in the magnetosheath of Saturn, where it is exposed to shocked solar wind plasma for at least 2 h 45 min. We suggest that the solar wind plasma in the magnetosheath during the CME conditions significantly modifies Titan's ionosphere by an addition of particle impact ionization by precipitating protons.
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| 12. |
- Edberg, Niklas J. T., et al.
(författare)
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Solar cycle modulation of Titan's ionosphere
- 2013
-
Ingår i: Journal of Geophysical Research-Space Physics. - : American Geophysical Union (AGU). - 2169-9380. ; 118:8, s. 5255-5264
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Tidskriftsartikel (refereegranskat)abstract
- During the six Cassini Titan flybys T83-T88 (May 2012 to November 2012) the electron density in the ionospheric peak region, as measured by the radio and plasma wave science instrument/Langmuir probe, has increased significantly, by 15-30%, compared to previous average. These measurements suggest that a longterm change has occurred in the ionosphere of Titan, likely caused by the rise to the new solar maximum with increased EUV fluxes. We compare measurements from TA, TB, and T5, from the declining phase of solar cycle 23 to the recent T83-T88 measurements during cycle 24, since the solar irradiances from those two intervals are comparable. The peak electron densities normalized to a common solar zenith angle N-norm from those two groups of flybys are comparable but increased compared to the solar minimum flybys (T16-T71). The integrated solar irradiance over the wavelengths 1-80nm, i.e., the solar energy flux, F-e, correlates well with the observed ionospheric peak density values. Chapman layer theory predicts that NnormFek, with k=0.5. We find observationally that the exponent k=0.540.18. Hence, the observations are in good agreement with theory despite the fact that many assumptions in Chapman theory are violated. This is also in good agreement with a similar study by Girazian and Withers (2013) on the ionosphere of Mars. We use this power law to estimate the peak electron density at the subsolar point of Titan during solar maximum conditions and find it to be about 6500cm(-3), i.e., 85-160% more than has been measured during the entire Cassini mission.
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| 13. |
- Engebretson, Mark J., et al.
(författare)
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Interhemispheric Comparisons of Large Nighttime Magnetic Perturbation Events Relevant to GICs
- 2020
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:8
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Tidskriftsartikel (refereegranskat)abstract
- Nearly all studies of impulsive magnetic perturbation events (MPEs) with large magnetic field variability (dB/dt) that can produce dangerous geomagnetically induced currents (GICs) have used data from the Northern Hemisphere. Here we present details of four large‐amplitude MPE events (|ΔBx| > 900 nT and |dB/dt| > 10 nT/s in at least one component) observed between 2015 and 2018 in conjugate high‐latitude regions (65–80° corrected geomagnetic latitude), using magnetometer data from (1) Pangnirtung and Iqaluit in eastern Arctic Canada and the magnetically conjugate South Pole Station in Antarctica and (2) the Greenland West Coast Chain and two magnetically conjugate chains in Antarctica, AAL‐PIP and BAS LPM. From one to three different isolated MPEs localized in corrected geomagnetic latitude were observed during three premidnight events; many were simultaneous within 3 min in both hemispheres. Their conjugate latitudinal amplitude profiles, however, matched qualitatively at best. During an extended postmidnight interval, which we associate with an interval of omega bands, multiple highly localized MPEs occurred independently in time at each station in both hemispheres. These nighttime MPEs occurred under a wide range of geomagnetic conditions, but common to each was a negative interplanetary magnetic field Bz that exhibited at least a modest increase at or near the time of the event. A comparison of perturbation amplitudes to modeled ionospheric conductances in conjugate hemispheres clearly favored a current generator model over a voltage generator model for three of the four events; neither model provided a good fit for the premidnight event that occurred near vernal equinox.
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| 14. |
- Engebretson, Mark J., et al.
(författare)
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Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 3. Occurrence and Amplitude as Functions of Magnetic Latitude, Local Time, and Magnetic Disturbance Indices
- 2021
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Ingår i: Space Weather. - : American Geophysical Union (AGU). - 1542-7390. ; 19:3
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Tidskriftsartikel (refereegranskat)abstract
- Rapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5–10 min duration can induce geomagnetically induced currents (GICs) that can harm technological systems. This study compares the occurrence and amplitude of nighttime MPEs with |dB/dt| ≥ 6 nT/s observed during 2015 and 2017 at five stations in Arctic Canada ranging from 64.7° to 75.2° in corrected geomagnetic latitude (MLAT) as functions of magnetic local time (MLT), the SME (SuperMAG version of AE) and SYM/H magnetic indices, and time delay after substorm onsets. Although most MPEs occurred within 30 min after a substorm onset, ∼10% of those observed at the four lower latitude stations occurred over two hours after the most recent onset. A broad distribution in local time appeared at all five stations between 1700 and 0100 MLT, and a narrower distribution appeared at the lower latitude stations between 0200 and 0700 MLT. There was little or no correlation between MPE amplitude and the SYM/H index; most MPEs at all stations occurred for SYM/H values between −40 and 0 nT. SME index values for MPEs observed >1 h after the most recent substorm onset fell in the lower half of the range of SME values for events during substorms, and dipolarizations in synchronous orbit at GOES 13 during these events were weaker or more often nonexistent. These observations suggest that substorms are neither necessary nor sufficient to cause MPEs, and hence predictions of GICs cannot focus solely on substorms.
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| 15. |
- Hall, B. E. S., et al.
(författare)
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A survey of superthermal electron flux depressions, or "electron holes," within the illuminated Martian induced magnetosphere
- 2016
-
Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:5, s. 4835-4857
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Tidskriftsartikel (refereegranskat)abstract
- Since Mars lacks a global intrinsic magnetic field, the solar wind interacts directly with the Martian upper atmosphere and ionosphere. The presence of localized intense remnant crustal magnetic fields adds to this interaction, making the Martian plasma system a unique environment within the solar system. Rapid reductions in the electron flux, referred to as electron holes, occur within the Martian induced magnetosphere (IM). We present a statistical analysis of this phenomenon identified from proxy measurements of the electron flux derived from measurements by the Analyser of Space Plasmas and Energetic Neutral Atoms Electron Spectrometer experiment on board the Mars Express (MEX) spacecraft. The study is completed for the period of 9 February 2004 to 9 May 2014. Electron holes are observed within the IM in more than 56% of MEX orbits during this study period, occurring predominantly at altitudes less than 1300km, with the majority in the negative X Mars-Centric Solar Orbital direction. The spatial distribution above the surface of Mars is observed to bear close resemblance to that of the crustal magnetic fields as predicted by the Cain et al. [] magnetic field model, suggesting that they play an important role in the formation of these phenomena.
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| 16. |
- Opgenoorth, Hermann J., et al.
(författare)
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Mars ionospheric response to solar wind variability
- 2013
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Ingår i: Journal of Geophysical Research: Space Physics. - : American Geophysical Union (AGU). - 2169-9380. ; 118:10, s. 6558-6587
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Tidskriftsartikel (refereegranskat)abstract
- At planets with induced magnetospheres, the coupling between the ionosphere, the weak draped magnetosphere, and the solar wind is very direct in comparison to Earth. The weak induced magnetosphere itself is created by the prevailing Solar wind conditions and therefore in its shape and strength dynamically depending on it. In early 2010, Mars was located behind Earth in the Solar wind; thus, we can use coordinated data from multiple near-Earth spacecraft (Stereo, Wind) to evaluate what kind of Solar wind disturbances have passed by Earth and might consecutively hit Mars, and when. We employ plasma data from the ESA Mars-Express mission, the ASPERA-3 particle instrument, and the MARSIS Active Ionospheric Sounder (AIS) to investigate, for a number of isolated events in March and April 2010, how the ionosphere and the induced magnetosphere at Mars develop and decay in response to Solar wind variability in the magnetic field, density, and velocity. In a dedicated campaign mode, we use frequent long-duration MARSIS AIS operations for several consecutive orbits, to monitor for the first time the long-term development of the Martian plasma environment during solar wind disturbances. We find that the magnetosphere and ionosphere of Mars can become considerably compressed by solar wind dynamic pressure variations, which usually are also associated with changes in the magnetic draping of the interplanetary magnetic field around the planet. These are typically associated with corotating interaction regions and coronal mass ejections, and can last for several days. During such episodes of compression, we see signatures of increased plasma transport over the terminator and enhanced ion outflow from the upper atmosphere.
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| 17. |
- Sanchez-Cano, Beatriz, et al.
(författare)
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Mars' Ionospheric Interaction With Comet C/2013 A1 Siding Spring's Coma at Their Closest Approach as Seen by Mars Express
- 2020
-
Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:1
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 18. |
- Sanchez-Cano, B., et al.
(författare)
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Mars plasma system response to solar wind disturbances during solar minimum
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 122:6, s. 6611-6634
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Tidskriftsartikel (refereegranskat)abstract
- This paper is a phenomenological description of the ionospheric plasma and induced magnetospheric boundary (IMB) response to two different types of upstream solar wind events impacting Mars in March 2008, at the solar minimum. A total of 16 Mars Express orbits corresponding to five consecutive days is evaluated. Solar TErrestrial RElations Observatory-B (STEREO-B) at 1AU and Mars Express and Mars Odyssey at 1.644AU detected the arrival of a small transient interplanetary coronal mass ejection (ICME-like) on the 6 and 7 of March, respectively. This is the first time that this kind of small solar structure is reported at Mars's distance. In both cases, it was followed by a large increase in solar wind velocity that lasted for similar to 10days. This scenario is simulated with the Wang-Sheeley-Arge (WSA) - ENLIL + Cone solar solar wind model. At Mars, the ICME-like event caused a strong compression of the magnetosheath and ionosphere, and the recovery lasted for similar to 3 orbits (similar to 20h). After that, the fast stream affected the upper ionosphere and the IMB, which radial and tangential motions in regions close to the subsolar point are analyzed. Moreover, a compression in the Martian plasma system is also observed, although weaker than after the ICME-like impact, and several magnetosheath plasma blobs in the upper ionosphere are detected by Mars Express. We conclude that, during solar minimum and at aphelion, small solar wind structures can create larger perturbations than previously expected in the Martian system.
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| 19. |
- Andrews, David, et al.
(författare)
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Control of the topside Martian ionosphere by crustal magnetic fields
- 2015
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:4, s. 3042-3058
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Tidskriftsartikel (refereegranskat)abstract
- We present observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument onboard Mars Express of the thermal electron plasma density of the Martian ionosphere and investigate the extent to which it is influenced by the presence of Mars's remnant crustal magnetic fields. We use locally measured electron densities, derived when MARSIS is operating in active ionospheric sounding (AIS) mode, covering an altitude range from approximate to 300km to approximate to 1200km. We compare these measured densities to an empirical model of the dayside ionospheric plasma density in this diffusive transport-dominated regime. We show that small spatial-scale departures from the averaged values are strongly correlated with the pattern of the crustal fields. Persistently elevated densities are seen in regions of relatively stronger crustal fields across the whole altitude range. Comparing these results with measurements of the (scalar) magnetic field also obtained by MARSIS/AIS, we characterize the dayside strength of the draped magnetic fields in the same regions. Finally, we provide a revised empirical model of the plasma density in the Martian ionosphere, including parameterizations for both the crustal field-dominated and draping-dominated regimes.
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| 20. |
- Hamrin, Maria, 1972-, et al.
(författare)
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Space weather disturbances in non-stormy times : occurrence of dB/dt spikes during three solar cycles
- 2023
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 128:10
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Tidskriftsartikel (refereegranskat)abstract
- Spatio-temporal variations of ionospheric currents cause rapid magnetic field variations at ground level and Geomagnetically Induced Currents (GICs) that can be harmful for human infrastructure. The risk for large excursions in the magnetic field time derivative, “dB/dt spikes”, is known to be high during geomagnetic storms and substorms. However, less is known about the occurrence of spikes during non-stormy times. We use data from ground-based globally covering magnetometers (SuperMAG database) from the years 1985–2021. We investigate the spike occurrence (|dB/dt| > 100 nT/min) as a function of magnetic local time (MLT), magnetic latitude (Mlat), and the solar cycle phases during non-stormy times (−15 nT ≤ SYM-H < 0). We sort our data into substorm (AL < 200 nT) intervals (“SUB”) and less active intervals between consecutive substorms (“nonSUB”). We find that spikes commonly occur in both SUBs and nonSUBs during non-stormy times (3–23 spikes/day), covering 18–12 MLT and 65°–80° Mlat. This also implies a risk for infrastructure damage during non-stormy times, especially when several spikes occur nearby in space and time, possibly causing infrastructure weathering. We find that spikes are more common in the declining phase of the solar cycle, and that the occurrence of SUB spikes propagates from one midnight to one morning hotspot with ∼10 min in MLT for each minute in universal time (UTC). Finally, we discuss causes for the spikes in terms of spatio-temporal variations of ionospheric currents.
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| 21. |
- Kauristie, K., et al.
(författare)
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On the Usage of Geomagnetic Indices for Data Selection in Internal Field Modelling
- 2017
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Ingår i: Space Science Reviews. - : SPRINGER. - 0038-6308 .- 1572-9672. ; 206:1-4, s. 61-90
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Forskningsöversikt (refereegranskat)abstract
- We present a review on geomagnetic indices describing global geomagnetic storm activity (Kp, am, Dst and dDst/dt) and on indices designed to characterize high latitude currents and substorms (PC and AE-indices and their variants). The focus in our discussion is in main field modelling, where indices are primarily used in data selection criteria for weak magnetic activity. The publicly available extensive data bases of index values are used to derive joint conditional Probability Distribution Functions (PDFs) for different pairs of indices in order to investigate their mutual consistency in describing quiet conditions. This exercise reveals that Dst and its time derivative yield a similar picture as Kp on quiet conditions as determined with the conditions typically used in internal field modelling. Magnetic quiescence at high latitudes is typically searched with the help of Merging Electric Field (MEF) as derived from solar wind observations. We use in our PDF analysis the PC-index as a proxy for MEF and estimate the magnetic activity level at auroral latitudes with the AL-index. With these boundary conditions we conclude that the quiet time conditions that are typically used in main field modelling (, and ) correspond to weak auroral electrojet activity quite well: Standard size substorms are unlikely to happen, but other types of activations (e.g. pseudo breakups ) can take place, when these criteria prevail. Although AE-indices have been designed to probe electrojet activity only in average conditions and thus their performance is not optimal during weak activity, we note that careful data selection with advanced AE-variants may appear to be the most practical way to lower the elevated RMS-values which still exist in the residuals between modeled and observed values at high latitudes. Recent initiatives to upgrade the AE-indices, either with a better coverage of observing stations and improved baseline corrections (the SuperMAG concept) or with higher accuracy in pinpointing substorm activity (the Midlatitude Positive Bay-index) will most likely be helpful in these efforts.
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| 22. |
- Lillis, Robert J., et al.
(författare)
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MOSAIC: A satellite constellation to enable groundbreaking mars climate system science and prepare for human exploration
- 2021
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Ingår i: Planetary Science Journal. - : Institute of Physics (IOP). - 2632-3338. ; 2:5
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Tidskriftsartikel (refereegranskat)abstract
- The Martian climate system has been revealed to rival the complexity of Earth's. Over the last 20 yr, a fragmented and incomplete picture has emerged of its structure and variability; we remain largely ignorant of many of the physical processes driving matter and energy flow between and within Mars' diverse climate domains. Mars Orbiters for Surface, Atmosphere, and Ionosphere Connections (MOSAIC) is a constellation of ten platforms focused on understanding these climate connections, with orbits and instruments tailored to observe the Martian climate system from three complementary perspectives. First, low-circular near-polar Sun-synchronous orbits (a large mothership and three smallsats spaced in local time) enable vertical profiling of wind, aerosols, water, and temperature, as well as mapping of surface and subsurface ice. Second, elliptical orbits sampling all of Mars' plasma regions enable multipoint measurements necessary to understand mass/energy transport and ion-driven escape, also enabling, with the polar orbiters, dense radio occultation coverage. Last, longitudinally spaced areostationary orbits enable synoptic views of the lower atmosphere necessary to understand global and mesoscale dynamics, global views of the hydrogen and oxygen exospheres, and upstream measurements of space weather conditions. MOSAIC will characterize climate system variability diurnally and seasonally, on meso-, regional, and global scales, targeting the shallow subsurface all the way out to the solar wind, making many first-of-their-kind measurements. Importantly, these measurements will also prepare for human exploration and habitation of Mars by providing water resource prospecting, operational forecasting of dust and radiation hazards, and ionospheric communication/positioning disruptions.
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| 23. |
- Palin, Laurianne, et al.
(författare)
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Three-dimensional current systems and ionospheric effects associated with small dipolarization fronts
- 2015
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:5, s. 3739-3757
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Tidskriftsartikel (refereegranskat)abstract
- We present a case study of eight successive plasma sheet (PS) activations (usually referred to as bursty bulk flows or dipolarization fronts), associated with small individual B-ZGSM increases on 31 March 2009 (0200-0900 UT), observed by the Time History of Events and Macroscale Interactions During Substorms mission. This series of events happens during very quiet solar wind conditions, over a period of 7 h preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low-amplitude dipolarization fronts are associated with few (1 or 2) rapid flux transport events (RFT, E-h > 2 mV/m), whereas the large-amplitude ones encompass many more RFT events. All PS activations are associated with small and localized substorm current wedge (SCW)-like current system signatures, which seems to be the consequence of RFT arrival in the near tail. The associated ground magnetic perturbations affect a larger part of the contracted auroral oval when, in the magnetotail, more RFT are embedded in PS activations (> 5). Dipolarization fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found even those to be associated with clear small SCW-like current system and particle injections at geosynchronous orbit. This exceptional data set highlights the role of flow bursts in the magnetotail and leads to the conclusion that we may be observing the smallest form of a substorm or rather its smallest element. This study also highlights the gradual evolution of the ionospheric current disturbance as the plasma sheet is observed to heat up.
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| 24. |
- Sánchez-Cano, Beatriz, et al.
(författare)
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Mars’ plasma system. Scientific potential of coordinated multipoint missions : "The next generation"
- 2022
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Ingår i: Experimental astronomy. - : Springer. - 0922-6435 .- 1572-9508. ; 54, s. 641-676
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this White Paper, submitted to ESA’s Voyage 2050 call, is to get a more holistic knowledge of the dynamics of the Martian plasma system, from its surface up to the undisturbed solar wind outside of the induced magnetosphere. This can only be achieved with coordinated multi-point observations with high temporal resolution as they have the scientific potential to track the whole dynamics of the system (from small to large scales), and they constitute the next generation of the exploration of Mars analogous to what happened at Earth a few decades ago. This White Paper discusses the key science questions that are still open at Mars and how they could be addressed with coordinated multipoint missions. The main science questions are: (i) How does solar wind driving impact the dynamics of the magnetosphere and ionosphere? (ii) What is the structure and nature of the tail of Mars’ magnetosphere at all scales? (iii) How does the lower atmosphere couple to the upper atmosphere? (iv) Why should we have a permanent in-situ Space Weather monitor at Mars? Each science question is devoted to a specific plasma region, and includes several specific scientific objectives to study in the coming decades. In addition, two mission concepts are also proposed based on coordinated multi-point science from a constellation of orbiting and ground-based platforms, which focus on understanding and solving the current science gaps.
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| 25. |
- Schillings, Audrey, et al.
(författare)
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Distribution and Occurrence Frequency of dB/dt Spikes During Magnetic Storms 1980–2020
- 2022
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Ingår i: Space Weather. - : John Wiley & Sons. - 1542-7390. ; 20:5
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Tidskriftsartikel (refereegranskat)abstract
- The physical magnetospheric cause for geomagnetically induced currents (GICs) are rapid time-varying magnetic fields (dB/dt), which occur mainly during magnetic substorms and storms. When, where and why exactly such rapid dB/dt may occur is insufficiently understood. We investigated all storms since 1980 and analyzed the negative and positive dB/dt spikes (>|500| nT/min) in the north and east component using a worldwide coverage (SuperMAG). Our analysis confirmed the existence of two dB/dt spikes "hotspots" located in the pre-midnight and in the morning magnetic local time sector, independently of the geographic location of the stations. The associated physical phenomena are probably substorm current wedge onsets and westward traveling surges (WTS) in the evening sector, and wave- or vortex-like current flows in the morning sector known as Omega bands. We observed a spatiotemporal evolution of the negative northern dB/dt spikes. The spikes initially occur in the pre-midnight sector, and then develop in time toward the morning sector. This spatiotemporal sequence is correlated with bursts in the AE index, and can be repeated several times throughout a storm. Finally, we investigated the peak value of Dst and AE during the storm period in comparison with the dB/dt spike occurrence frequency, we did not find any correlation. This result implies that a moderate storm with many spikes can be as (or more) dangerous for ground-based infrastructures than a major storm with fewer dB/dt spikes. Our findings regarding the physical causes and characteristics of dB/dt spikes may help to improve the GIC forecast for the affected regions.
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