Abstract
Both solar wind and ionospheric sources contribute to the magnetotail plasma sheet, but how their contribution changes during a geomagnetic storm is an open question. The source is critical ...because the plasma sheet properties control the enhancement and decay rate of the ring current, the main cause of the geomagnetic field perturbations that define a geomagnetic storm. Here we use the solar wind composition to track the source and show that the plasma sheet source changes from predominantly solar wind to predominantly ionospheric as a storm develops. Additionally, we find that the ionospheric plasma during the storm main phase is initially dominated by singly ionized hydrogen (H
+
), likely from the polar wind, a low energy outflow from the polar cap, and then transitions to the accelerated outflow from the dayside and nightside auroral regions, identified by singly ionized oxygen (O
+
). These results reveal how the access to the magnetotail of the different sources can change quickly, impacting the storm development.
The storm‐time ring current is formed by the inward convection of the near‐earth plasma sheet, so understanding the changing source of the plasma sheet is key for understanding ring current ...development. The ionospheric and solar wind sources can be distinguished by the charge state of the heavy ions; solar wind ions are highly iononized, while ionospheric ions are predominantly singly ionized. AMPTE/CHEM measurements are used to track the changing composition in the 6–9 Re plasma sheet as a storm develops in order to determine the fraction of the population that comes from each source. We find that prior to the storm, the solar wind source dominates. During the storm main phase, the solar wind contribution decreases, while the ionospheric contribution increases, making the source predominantly ionospheric. The source returns to predominantly solar wind plasma during the recovery phase.
Plain Language Summary
The ions trapped in the earth's magnetic field have two possible sources: the sun or the earth's ionosphere. A stream of ionized particles from the sun called the solar wind is constantly moving outward, flowing by the earth. These particles can enter the earth's magnetosphere and become trapped. Ions can also be accelerated out of the ionosphere into the magnetosphere. The interplay between these two sources is not well understood. In this paper, we test how the source changes as a large geomagnetic storm develops. We find that the source switches from being dominantly solar wind, to dominantly ionospheric during the peak of the storm.
Key Points
Ionospheric and solar wind sources to the near‐earth plasma sheet are tracked during one storm using the AMPTE/CHEM instrument
There is a sharp change from a predominantly solar wind to ionospheric source during both intensifications in the storm's main phase
The source changes back to predominantly solar wind during the recovery phase
Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on ...particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L‐shell (MLT‐L) frame within a limited magnetic latitude (MLAT) range. In this study, we present a statistical analysis of EMIC wave properties using 10 years (2001–2010) of data from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.
Key Points
A statistical study of EMIC waves is conducted over all MLATs and MLTs
Off‐equator peaks in wave occurrence are observed in the outer magnetosphere
Wave ellipticity, normal angle, propagation angle, and wave power are also investigated
Using the Cluster/Composition and Distribution Function (CODIF) analyzer data set from 2001 to 2013, a full solar cycle, we determine the ion distributions for H+, He+, and O+ in the inner ...magnetosphere (L < 12) over the energy range 40 eV to 40 keV as a function magnetic local time, solar EUV (F10.7), and geomagnetic activity (Kp). Concentrating on L = 6–7 for comparison with previous studies at geosynchronous orbit, we determine both the average flux at 90° pitch angle and the pitch angle anisotropy as a function of energy and magnetic local time. We clearly see the minimum in the H+ spectrum that results from the competition between eastward and westward drifts. The feature is weaker in O+ and He+, leading to higher O+/H+ and He+/H+ ratios in the affected region, and also to a higher pitch angle anisotropy, both features expected from the long‐term effects of charge exchange. We also determine how the nightside L = 6–7 densities and temperatures vary with geomagnetic activity (Kp) and solar EUV (F10.7). Consistent with other studies, we find that the O+ density and relative abundance increase significantly with both Kp and F10.7. He+ density increases with F10.7, but not significantly with Kp. The temperatures of all species decrease with increasing F10.7. The O+ and He+ densities increase from L = 12 to L ~ 3–4, both absolutely and relative to H+, and then drop off sharply. The results give a comprehensive view of the inner magnetosphere using a contiguous long‐term data set that supports much of the earlier work from GEOS, ISEE, Active Magnetospheric Particle Tracer Explorers, and Polar from previous solar cycles.
Key Points
We determine inner magnetosphere ion composition as a function of energy and MLT over a solar cycle
Changes in the MLT dependence of the spectra with F10.7 indicate changes in the convection pattern
Regions of high O+/H+ and He+/H+ on the dayside indicate effects of charge exchange loss
We study the spatial distribution of plasma sheet O+ and H+ ions using data from the COmposition and DIstribution Function (CODIF) instrument on board the Cluster spacecraft from 2001 to 2005. The ...densities are mapped along magnetic field lines to produce bidimensional density maps at the magnetospheric equatorial plane for various geomagnetic and solar activity levels (represented by the Kp and F10.7 indexes). We analyze the correlation of the O+ and H+ density with Kp and F10.7 in the midtail region at geocentric distances between 15 and 20 RE and in the near‐Earth regions at radial distances between 7 and 8 RE. Near Earth the H+ density slightly increases with Kp and F10.7 while in the midtail region it is not correlated with Kp and F10.7. On the contrary, the amount of O+ ions significantly increases with Kp and F10.7 independently of the region. In the near‐Earth region, the effects of solar EUV and geomagnetic activity on the O+ density are comparable. In the midtail region, the O+ density increases at a lower rate with solar EUV flux but strongly increases with geomagnetic activity although the effect is modulated by the solar EUV flux level. We also evidence a strong increase of the proportion of O+ ions with decreasing geocentric distance below ~10 RE. These results confirm the direct entry of O+ ions into the near‐Earth plasma sheet and suggest that both energetic outflows from the auroral zone and cold outflow from the high‐latitude ionosphere may contribute to feed the near‐Earth plasma sheet with ionospheric ions.
Key Points
O+ and H+ densitiy maps at the magnetospheric equatorial plane are produced
O+ and H+ density variation with geomagnetic and solar activity are analyzed
The direct entry of O+ ions at low geocentric distances is confirmed
Factors related to two sources of energy input to the ionosphere, the Poynting flux associated with both quasistatic fields (Sdc) and Alfvénic fluctuations (Sac), and the soft electron precipitation, ...are investigated to evaluate their correlations with the O+ and the H+ outflows in the dayside cusp region by using recalibrated FAST/Time‐of‐Flight Energy, Angle, and Mass Spectrograph (TEAMS) data during the 24–25 September 1998 geomagnetic storm studied by Strangeway et al. (2005, https://doi.org/10.1029/2004JA010829). The Poynting flux and the soft electron precipitation are well correlated with ion outflow flux in the dayside cusp region. Sdc shows the highest correlation with the O+ outflows, while it is the electron number flux that correlates best with the H+ outflows. The Alfvénic waves play an essential role in accelerating outflows. The averaged O+/H+ flux ratio is 3.0 and is positively correlated to the Poynting flux, suggesting that the O+ flux increases more strongly with the energy input.
Plain Language Summary
Ionospheric outflows are a major plasma source for the Earth's magnetosphere, especially during geomagnetic storms. Various parameters related to the electromagnetic energy input, the electron precipitation, and the extremely low frequency plasma waves are used to investigate their correlations with ion outflows in the dayside cusp region during the 24–25 September 1998 geomagnetic storm. We first recalibrated the data from the FAST/Time‐of‐Flight Energy, Angle, and Mass Spectrograph (TEAMS) instrument before using it. The electromagnetic energy has the highest correlations with the oxygen ion outflows, while it is the electron precipitation for proton outflows. The energy input associated with Alfvén waves also shows strong correlations. Maxima of the energy input show better correlations than the averages. The oxygen ion is the dominant outflow species in this storm with an average flux ratio of 3.0 to proton outflows. A higher ratio is observed with more energy input to the Earth's ionosphere.
Key Points
The best controlling factor for driving O+ and H+ outflows is quasistatic Poynting flux and soft electron precipitation, respectively
The averaged O+/H+ flux ratio is 3.0 over the cusp region. The ratio is positively correlated to energy input to the ionosphere
The Poynting flux associated with Alfvén waves also shows strong correlation with outflows in the dayside cusp region
We perform a statistical study of electromagnetic ion cyclotron (EMIC) waves detected by the Van Allen Probes mission to investigate the spatial distribution of their occurrence, wave power, ...ellipticity, and normal angle. The Van Allen Probes have been used which allow us to explore the inner magnetosphere (1.1 to 5.8 RE). Magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science on board the Van Allen Probes are used to identify EMIC wave events for the first 22 months of the mission operation (8 September 2012 to 30 June 2014). EMIC waves are examined in H+, He+, and O+ bands. Over 700 EMIC wave events have been identified over the three different wave bands (265 H+‐band events, 438 He+‐band events, and 68 O+‐band events). EMIC wave events are observed between L = 2–8, with over 140 EMIC wave events observed below L = 4. Results show that H+‐band EMIC waves have two peak magnetic local time (MLT) occurrence regions: prenoon (09:00 < MLT ≤ 12:00) and afternoon (15:00 < MLT ≤ 17:00) sectors. He+‐band EMIC waves feature an overall stronger dayside occurrence. O+‐band EMIC waves have one peak region located in the morning sector at lower L shells (L < 4). He+‐band EMIC waves average the highest wave power overall (>0.1 nT2/Hz), especially in the afternoon sector. Ellipticity observations reveal that linearly polarized EMIC waves dominate in lower L shells.
Key Points
A statistical study of EMIC waves observed by the Van Allen Probes is performed
The occurrence and wave properties of the EMIC waves are examined
Linearly polarized EMIC waves dominate lower L shells (L < 4)
The source of O+ in the storm time ring current Kistler, L. M.; Mouikis, C. G.; Spence, H. E. ...
Journal of geophysical research. Space physics,
June 2016, 2016-06-00, 20160601, Letnik:
121, Številka:
6
Journal Article
Recenzirano
Odprti dostop
A stretched and compressed geomagnetic field occurred during the main phase of a geomagnetic storm on 1 June 2013. During the storm the Van Allen Probes spacecraft made measurements of the plasma ...sheet boundary layer and observed large fluxes of O+ ions streaming up the field line from the nightside auroral region. Prior to the storm main phase there was an increase in the hot (>1 keV) and more isotropic O+ ions in the plasma sheet. In the spacecraft inbound pass through the ring current region during the storm main phase, the H+ and O+ ions were significantly enhanced. We show that this enhanced inner magnetosphere ring current population is due to the inward adiabatic convection of the plasma sheet ion population. The energy range of the O+ ion plasma sheet that impacts the ring current most is found to be from ~5 to 60 keV. This is in the energy range of the hot population that increased prior to the start of the storm main phase, and the ion fluxes in this energy range only increase slightly during the extended outflow time interval. Thus, the auroral outflow does not have a significant impact on the ring current during the main phase. The auroral outflow is transported to the inner magnetosphere but does not reach high enough energies to affect the energy density. We conclude that the more energetic O+ that entered the plasma sheet prior to the main phase and that dominates the ring current is likely from the cusp.
Key Points
Auroral outflow during the storm main phase mainly impacts <1 keV plasma sheet population
The >1 keV (hot) more isotropic plasma sheet O+ population increases prior to the main phase
Inward transport of the hot O+ dominates the ring current; this O+ is likely from the cusp
The warm plasma cloak is a source of magnetospheric plasma that contain significant O+. When the O+ density in the magnetosphere near the magnetopause is >0.2 cm‐3 and the H+ density is <1.5 cm‐3, ...then O+ dominates the magnetospheric ion mass density by more than a factor of 2. A survey is conducted of such O+‐rich warm plasma cloak intervals and their effect on reconnection at the Earth's magnetopause. The survey uses data from the Magnetospheric Multiscale mission (MMS) and the results are compared and combined with a previous survey of the warm plasma cloak. Overall, the warm plasma cloak and the O+‐rich warm plasma cloak reduce the magnetopause reconnection rate by >20% due to mass‐loading only about 2% to 4% of the time. However, during geomagnetic storms, O+ dominates the mass density of the warm plasma cloak and these mass densities are very high. Therefore, a separate study is conducted to determine the effect of the warm plasma cloak on magnetopause reconnection during geomagnetically disturbed times. This study shows that the warm plasma cloak reduces the reconnection rate significantly about 25% of the time during disturbed conditions.
Key Points
The magnetospheric warm plasma cloak is O+‐rich during geomagnetically active times
The warm plasma cloak reduces the magnetic reconnection rate at the magnetopause ~2‐4% of the time
During geomagnetic storms, the O+‐rich warm plasma cloak reduces the reconnection rate by >20% sometime during 25% of the storms
The Interstellar Mapping and Acceleration Probe (IMAP) is a revolutionary mission that simultaneously investigates two of the most important overarching issues in Heliophysics today: the acceleration ...of energetic particles and interaction of the solar wind with the local interstellar medium. While seemingly disparate, these are intimately coupled because particles accelerated in the inner heliosphere play critical roles in the outer heliospheric interaction. Selected by NASA in 2018, IMAP is planned to launch in 2024. The IMAP spacecraft is a simple sun-pointed spinner in orbit about the Sun-Earth L1 point. IMAP's ten instruments provide a complete and synergistic set of observations to simultaneously dissect the particle injection and acceleration processes at 1 AU while remotely probing the global heliospheric interaction and its response to particle populations generated by these processes. In situ at 1 AU, IMAP provides detailed observations of solar wind electrons and ions; suprathermal, pickup, and energetic ions; and the interplanetary magnetic field. For the outer heliosphere interaction, IMAP provides advanced global observations of the remote plasma and energetic ions over a broad energy range via energetic neutral atom imaging, and precise observations of interstellar neutral atoms penetrating the heliosphere. Complementary observations of interstellar dust and the ultraviolet glow of interstellar neutrals further deepen the physical understanding from IMAP. IMAP also continuously broadcasts vital real-time space weather observations. Finally, IMAP engages the broader Heliophysics community through a variety of innovative opportunities. This papersummarizes the IMAP mission at the start of Phase A development.
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