The statistical relationship between tens of kiloelectron volts plasma sheet electrons and the solar wind, as well as >2 MeV geosynchronous electrons, is investigated using plasma sheet measurements ...from Cluster (2001–2005) and Geotail (1998–2005) and concurrent solar wind measurements from ACE. Plasma sheet selection criteria from previous studies are compared, and this study selects a new combination of criteria that are valid for both polar‐orbiting and equatorial‐orbiting satellites. Plasma sheet measurements are mapped to the point of minimum ∣B∣, using the Tsyganenko T96 magnetic field model, to remove measurements taken on open field lines, which reduces the scatter in the results. Statistically, plasma sheet electron flux variations are compared to solar wind velocity, density, dynamic pressure, interplanetary magnetic field (IMF) Bz, and solar wind energetic electrons, as well as >2 MeV electrons at geosynchronous orbit. Several new results are revealed: (1) There is a strong positive correlation between energetic plasma sheet electrons and solar wind velocity, (2) this correlation is valid throughout the plasma sheet and extends to distances of XGSM = −30 RE,, (3) there is evidence of a weak negative correlation between energetic plasma sheet electrons and solar wind density, (4) energetic plasma sheet electrons are enhanced during times of southward interplanetary magnetic field (IMF), (5) there is no clear correlation between energetic plasma sheet electrons and solar wind electrons of comparable energies, and (6) there is a strong correlation between energetic electrons (>38 keV) in the plasma sheet and >2 MeV electrons at geosynchronous orbit measured 2 days later.
We present two event studies of significant enhancements of relativistic electron flux in the slot region of Earth's radiation belts during storms, using electron measurements from the Akebono ...spacecraft at high altitudes and NOAA 15, 16, 17, and 18 at low altitudes. These flux enhancements take place during the main phase of storms, and occur rapidly on timescales of less than 60 min. In association with storm time substorms, the magnetic field at geosynchronous altitude becomes highly stretched, intensifies, and then returns to a more dipolar configuration. The flux enhancements in the slot region are likely associated with these large changes in the nightside magnetic field configuration. The observations imply that rapid particle acceleration and/or transport processes operate in the inner (L < 3) magnetosphere in association with large substorms during the main phase of a storm.
Key Points
The NWS SWPC released two new forecast productsForecasts will be in more frequent and more easily understood mannerInformation is at an appropriate level to meet the sophistication of the ...users
In recent years there has been a growing interest from the aviation community for space weather radiation forecasts tailored to the needs of the aviation industry. In 2019 several space weather ...centers began issuing advisories for the International Civil Aviation Organization alerting users to enhancements in the radiation environment at aviation flight levels. Due to a lack of routine observations, radiation modeling is required to specify the dose rates experienced by flight crew and passengers. While mature models exist, support for key observational inputs and further modeling advancements are needed. Observational inputs required from the ground-based neutron monitor network must be financially supported for research studies and operations to ensure real-time data is available for forecast operations and actionable end user decision making. An improved understanding of the geomagnetic field is required to reduce dose rate uncertainties in regions close to the open/closed geomagnetic field boundary, important for flights such as those between the continental US and Europe which operate in this region. Airborne radiation measurements, which are crucial for model validation and improvement, are lacking, particularly during solar energetic particle events. New measurement campaigns must be carried out to ensure progress and
in situ
atmospheric radiation measurements made available for real-time situational awareness. Furthermore, solar energetic particle forecasting must be improved to move aviation radiation nowcasts to forecasts in order to meet customer requirements for longer lead times for planning and mitigation.
Electrons above 50 eV are a sensitive indicator of field line topology at the magnetopause, particularly when the solar wind dynamic pressure is high and the shear across the boundary is low. ...AMPTE/CCE electron observations under conditions when these criteria are fulfilled indicate a clear topological transition from the magnetosheath to open field lines threading the magnetopause in the magnetosheath boundary layer (MSBL). Once across the magnetopause and in the low latitude boundary layer (LLBL), the fast moving electrons are no longer a good indicator of magnetic field topology. In particular, the counterstreaming electron observations in this region are not an indicator of a closed magnetic topology. Rather, the field topology continues to be open, and the counterstreaming occurs because electrons from the magnetopause region move rapidly enough along the LLBL magnetic field to make it to the ionosphere, mirror, and return to the observation point Slower moving ions provide important additional information on magnetic field topology in the LLBL. CCE observations discussed here indicate that two types of solar wind ion distributions are observed in this layer. One type consists of a single, heated distribution which resembles somewhat the electron distribution in the layer. The field‐aligned velocity of this distribution is near zero. The other type consists of a unidirectional streaming distribution. The field‐aligned velocity of this distribution is higher than in the adjacent magnetosheath. Combining these observations with magnetospheric ion observations (e.g., O+) in the LLBL and with electron observations in the MSBL, two distinct magnetic field topologies emerge for the low‐shear magnetopause. The first, which gives rise to single, low‐parallel‐velocity and heated solar wind ion distributions in the LLBL, is magnetic reconnection poleward of the cusp. The second, which gives rise to unidirectional streaming solar wind ion distributions in the LLBL, is magnetic reconnection equatorward of the cusp. This type of component reconnection may not be sustained in a quasi‐steady fashion.
The characteristics of particles and magnetic fields associated with a step‐like enhancement in solar wind dynamic pressure are investigated by using observations from the Polar spacecraft. At the ...time, Polar was located near its apogee of ∼9 RE at high latitude in the afternoon sector. Impulsive, energy‐dispersed injections of ions were observed by Polar in both parallel and antiparallel pitch angle directions, with a much shorter duration in the parallel direction (toward the Earth) than in the antiparallel direction (away from the Earth). The energies of the injected ions ranged from ∼200 eV to a few keV, and they are considered of magnetosheath origin. The energy dispersion of the injected ions is consistent with the interpretation of the velocity filter or time‐of‐flight effect as the magnetosheath ions enter the magnetosphere and propagate downward and then are mirrored at low altitude where magnetic field lines converge. It is estimated that the entrance of the magnetosheath ions was located ∼3.9–7.5 RE away from Polar, and the distance from the spacecraft to the mirror point was ∼7.7–8.1 RE, corresponding to ∼830–3600 km in altitude. The Polar data clearly favor magnetic reconnection as the primary mechanism for the transport of magnetosheath plasmas into the magnetosphere. A good correspondence is found between the magnetic field oscillation and the intermittence of the ion injections, implying that the impulsive ion injections were a consequence of the intermittent magnetic reconnection at the high‐latitude magnetopause that had been modulated by compressional waves produced by the solar wind dynamic pressure enhancement.
On the source of Pc1-2 waves in the plasma mantle Engebretson, M. J.; Onsager, T. G.; Rowland, D. E. ...
Journal of Geophysical Research - Space Physics,
June 2005, Letnik:
110, Številka:
A6
Journal Article
Recenzirano
Odprti dostop
Several ground‐based observational studies have reported unstructured Pc1‐2 waves near and poleward of the dayside cusp. Dyrud et al. (1997) were the first to suggest that these waves originated in ...the high‐altitude plasma mantle. We report here on simultaneous field and particle observations from the Polar satellite and from ground magnetometer data that confirm the presence of these “mantle” waves and characterize the ion distributions associated with them. Unstructured Pc1‐2 waves were found to occur during 45% of the available passes of Polar across the mantle during the interval March–May 2000, during which time the orbit of Polar was near local noon as it crossed these latitudes. Poynting vector calculations using Polar electric and magnetic field data show a mixture of upward and downward energy flux in the cusp but consistently downward flux when mantle waves are observed. This is consistent with earlier observations that ground‐based magnetometers can detect such mantle waves but not the more intense wave activity observed by spacecraft in the middle‐ and low‐altitude cusp. In situ particle observations from the Hydra instrument appear to confirm the generation mechanism suggested by Dyrud et al. that cusp particles mirroring at low altitudes and then traveling outward in the plasma mantle poleward of the cusp are the source of the free energy for these waves. Quantitative estimates of ion cyclotron instability of the observed ion distributions suggest they are stable at the ≤9 RE altitudes traversed by Polar but may be reasonably inferred to be unstable in the exterior mantle, a location consistent with their observed frequency.
The first geomagnetic storm of 1997 began on January 10. It is of particular interest because it was exceptionally well observed by the full complement of International Solar Terrestrial Physics ...(ISTP) satellites and because of its possible association with the catastrophic failure of the Telstar 401 telecommunications satellite. Here we report on the energetic electron environment observed by five geosynchronous satellites. In part one of this paper we examine the magnetospheric response to the magnetic cloud. The interval of southward IMF drove strong substorm activity while the interval of northward IMF and high solar wind density strongly compressed the magnetosphere. At energies above a few hundred keV, two distinct electron enhancements were observed at geosynchronous orbit. The first enhancement began and ended suddenly, lasted for approximately 1 day, and is associated with the strong compression of the magnetosphere. The second enhancement showed a more characteristic time delay, peaking on January 15. Both enhancements may be due to transport of electrons from the same initial acceleration event at a location inside geosynchronous orbit but the first enhancement was due to a temporary, quasi‐adiabatic transport associated with the compression of the magnetosphere while the second enhancement was due to slower diffusive processes. In the second part of the paper we compare the relativistic electron fluxes measured simultaneously at different local times. We find that the >2‐MeV electron fluxes increased first at noon followed by dusk and then dawn and that there can be difference of two orders of magnitude in the fluxes observed at different local times. Finally, we discuss the development of data‐driven models of the relativistic electron belts for space weather applications. By interpolating fluxes between satellites we produced a model that gives the >2‐MeV electron fluxes at all local times as a function of universal time. In a first application of this model we show that, at least in this case, magnetopause shadowing does not contribute noticeably to relativistic electron dropouts.
New, coordinated measurements from the International Solar‐Terrestrial Physics (ISTP) constellation of spacecraft are presented to show the causes and effects of recurrent geomagnetic activity during ...recent solar minimum conditions. It is found using WIND and POLAR data that even for modest geomagnetic storms, relativistic electron fluxes are strongly and rapidly enhanced within the outer radiation zone of the Earth's magnetosphere. Solar wind data are utilized to identify the drivers of magnetospheric acceleration processes. Yohkoh solar soft X‐ray data are also used to identify the solar coronal holes that produce the high‐speed solar wind streams which, in turn, cause the recurrent geomagnetic activity. It is concluded that even during extremely quiet solar conditions (sunspot minimum) there are discernible coronal holes and resultant solar wind streams which can produce intense magnetospheric particle acceleration. As a practical consequence of this Sun‐Earth connection, it is noted that a long‐lasting E>1MeV electron event in late March 1996 appears to have contributed significantly to a major spacecraft (Anik E1) operational failure.
Ion precipitation data from two co‐orbiting Defense Meteorological Satellite Program satellites (F6 and F8) are used to investigate magnetopause reconnection models. We examine differential fluxes ...between 30 eV and 30 keV, from a Southern Hemisphere, prenoon pass during the morning of January 10, 1990. Data from the first satellite to pass through the region (F6) show two distinct ion energy dispersions ∼1° of latitude apart, between 76° and 79° magnetic latitude. The electron data exhibit similar features at around the same region but with no or little energy dispersion, consistent with their high velocities. We suggest that the two energy dispersions can be explained by two separate injections resulting from two bursts of magnetopause reconnection. Data from the second satellite (F8), which moved through the same region l min later, reveal the same energy‐dispersed structures, only further poleward and with less overall flux. This temporal evolution is consistent with two recently reconnected flux tubes releasing their plasma as they move antisunward away from dayside merging sites. However, an observed overlap between the two ion energy dispersions suggests a more complex reconnection geometry than usual models can accommodate. We propose a generalized reconnection scenario that unifies the Bursty Single X‐Line and the Multiple X‐Line Reconnection models. A simple time‐of‐flight particle precipitation model is constructed to reproduce the ion dispersions and their overlap. The modeling results suggest that for time‐dependent reconnection the dispersion overlap is observed clearly at low altitudes only for a short period compared with the evolution timescale of the ion precipitation.
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