208 research outputs found
Classification of solar wind with machine learning
No full textWe present a four-category classification algorithm for the solar wind, based on Gaussian Process. The four categories are the ones previously adopted in Xu and Borovsky (2015): ejecta, coronal hole origin plasma, streamer belt origin plasma, and sector reversal origin plasma. The algorithm is trained and tested on a labeled portion of the OMNI data set. It uses seven inputs: the solar wind speed Vsw, the temperature standard deviation σT, the sunspot number R, the F10.7 index, the Alfven speed vA, the proton specific entropy Sp, and the proton temperature Tp compared to a velocity-dependent expected temperature. The output of the Gaussian Process classifier is a four-element vector containing the probabilities that an event (one reading from the hourly averaged OMNI database) belongs to each category. The probabilistic nature of the prediction allows for a more informative and flexible interpretation of the results, for instance, being able to classify events as "undecided." The new method has a median accuracy larger than 90% for all categories, even using a small set of data for training. The Receiver Operating Characteristic curve and the reliability diagram also demonstrate the excellent quality of this new method. Finally, we use the algorithm to classify a large portion of the OMNI data set, and we present for the first time transition probabilities between different solar wind categories. Such probabilities represent the "climatological" statistics that determine the solar wind baseline
On the heating of the outer radiation belt to produce high fluxes of relativistic electrons: Measured heating rates at geosynchronous orbit for high-speed stream-driven storms
No full textMagnetic field at geosynchronous orbit during high-speed stream-driven storms: Connections to the solar wind, the plasma sheet, and the outer electron radiation belt
No full textSuperposed-epoch analysis is performed on magnetic field measurements from five GOES spacecraft in geosynchronous orbit during 63 high-speed stream-driven storms in 1995–2005. The field strength and the field stretching angle are examined as functions of time and local time, and these quantities are compared with the properties of the solar wind, the plasma sheet, and the outer electron radiation belt. Compression of the dayside magnetosphere coincides with an increased solar wind ram pressure commencing before the arrival of the corotating interaction region (CIR). Stretching of the nightside magnetosphere occurs in two phases: a strong-stretching phase early in the storm followed by a modest-stretching phase lasting for days. The strong-stretching phase coincides with the occurrence of the superdense plasma sheet, implying that ion pressure causes the strong stretching. This nightside strong-stretching perturbation corresponds to a ∼25% contribution to Dst*. The relativistic electron flux at geosynchronous orbit has a dropout recovery temporal profile that matches the strong-stretching temporal profile; however, the number density dropout and recovery of the electron radiation belt has a profile that leads the stretching profile. A comparison of geosynchronous field strengths and magnetopause field strengths indicates that magnetopause shadowing plays a role in the radiation belt dropout. Temporal fluctuations of the geosynchronous magnetic field are examined via 1 min changes of the GOES magnetic field vectors. Fluctuation amplitudes increase at all local times at storm onset and then slowly decay during the storms. The amplitude is linearly related to the Kp, PCI, and MBI indices, except during the strong-stretching phase of the storms
Differences between CME-driven storms and CIR-driven storms
No full textTwenty one differences between CME-driven geomagnetic storms and CIR-driven geomagnetic storms are tabulated. (CME-driven includes driving by CME sheaths, by magnetic clouds, and by ejecta; CIR-driven includes driving by the associated recurring high-speed streams.) These differences involve the bow shock, the magnetosheath, the radiation belts, the ring current, the aurora, the Earth's plasma sheet, magnetospheric convection, ULF pulsations, spacecraft charging in the magnetosphere, and the saturation of the polar cap potential. CME-driven storms are brief, have denser plasma sheets, have strong ring currents and Dst, have solar energetic particle events, and can produce great auroras and dangerous geomagnetically induced currents; CIR-driven storms are of longer duration, have hotter plasmas and stronger spacecraft charging, and produce high fluxes of relativistic electrons. Further, the magnetosphere is more likely to be preconditioned with dense plasmas prior to CIR-driven storms than it is prior to CME-driven storms. CME-driven storms pose more of a problem for Earth-based electrical systems; CIR-driven storms pose more of a problem for space-based assets
Solar wind turbulence and shear: A superposed epoch analysis of corotating interaction regions at 1 AU
No full textSuperposed epoch analysis of high-speed-stream effects at geosynchronous orbit: Hot plasma, cold plasma, and the solar wind
No full textSuperposed epoch analyses of magnetospheric plasma analyzer (MPA) data from Los Alamos National Laboratory (LANL) satellites are performed to reveal the density, temperature and flow velocity behavior of the hot ion plasma (0.1–45 keV), the hot electron plasma (0.03–45 keV) and the cold ion plasma (1–100 eV) at geosynchronous orbit following the arrival of high speed solar wind streams at the dayside magnetopause. The analyses reveal three striking features. (1) The arrival of a high density solar wind plasma at the leading edge of a high speed solar wind stream induces a sharp enhancement in magnetospheric convection which leads to the delivery of a hot, dense “plug” of fresh plasma sheet ions and electrons to the inner magnetosphere. On average, this superdense plasma is observed at geosynchronous orbit for ∼20 h following convection onset. There follows an extended period when exceptionally hot plasma sheet ions and electrons of more usual density are continually convected to the inner magnetosphere - a environment that persists at geosynchronous orbit while the high speed stream prevails. (2) Flow velocities and convection speeds of eroded cold plasma moving toward the dayside magnetopause are calculated from MPA statistical analyses. Average convection speeds of 8–12 km s−1 are typical in plume material moving sunwards following the arrival of high speed solar wind streams at the magnetopause. (3) The density of plume material convecting to the dayside magnetopause during high speed streams which follow very calm periods (Kp ∼ 0) is around double that during high speed streams following periods when higher levels of convection persist (Kp ∼ 2)
Correction to “Secondary‐electron yields of solar SYSTEM ices” by David M. Suszcynsky, Joseph E. Borovsky, and Christoph K. Goertz
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Electron loss rates from the outer radiation belt caused by the filling of the outer plasmasphere: The calm before the storm
No full textMeasurements from seven spacecraft in geosynchronous orbit are analyzed to determine the decay rate of the number density of the outer electron radiation belt prior to the onset of high-speed-stream-driven geomagnetic storms. Superposed-data analysis is used with a collection of 124 storms. When there is a calm before the storm, the electron number density decays exponentially before the storm with a 3.4-day e-folding time: beginning about 4 days before storm onset, the density decreases from ∼4 × 10−4 cm−3 to ∼1 × 10−4 cm−3. When there is not a calm before the storm, the number density decay is very small. The decay in the number density of radiation belt electrons is believed to be caused by pitch angle scattering of electrons into the atmospheric loss cone as the outer plasmasphere fills during the calms. This is confirmed by separately measuring the density decay rate for times when the outer plasmasphere is present or absent. While the radiation belt electron density decreases, the temperature of the electron radiation belt holds approximately constant, indicating that the electron precipitation occurs equally at all energies. Along with the number density decay, the pressure of the outer electron radiation belt decays, and the specific entropy increases. From the measured decay rates, the electron flux to the atmosphere is calculated, and that flux is 3 orders of magnitude less than thermal fluxes in the magnetosphere, indicating that the radiation belt pitch angle scattering is 3 orders weaker than strong diffusion. Energy fluxes into the atmosphere are calculated and found to be insufficient to produce visible airglow
A density-temperature description of the outer electron radiation belt during geomagnetic storms
No full textBi-Maxwellian fits are made to energetic-electron flux measurements from seven satellites in geosynchronous orbit, yielding a number density (n) and temperature (T) description of the outer electron radiation belt. For 54.5 spacecraft years of measurements the median value of n is 3.7 × 10−4 cm−3, and the median value of T is 148 keV. General statistical properties of n, T, and the 1.1–1.5 MeV flux F are investigated, including local-time and solar-cycle dependencies. Using superposed-epoch analysis where the zero epoch is convection onset, the evolution of the outer electron radiation belt through high-speed-stream-driven storms is investigated. The number-density decay during the calm before the storm, relativistic-electron dropouts and recoveries, and the heating of the outer electron radiation belt during storms are analyzed. Using four different “triggers” (sudden storm commencement (SSC), southward interplanetary magnetic field (IMF) portions of coronal mass ejection (CME) sheaths, southward-IMF portions of magnetic clouds, and minimum Dst) a selection of CME-driven storms are analyzed with superposed-epoch techniques. For CME-driven storms, only a very modest density decay prior to storm onset is found. In addition, the compression of the outer electron radiation belt at the time of SSC is analyzed, the number-density increase and temperature decrease during storm main phase are characterized, and the increase in density and temperature during storm recovery phase is determined. During the different phases of storms, changes in the flux are sometimes in response to changes in the temperature, sometimes to changes in the number density, and sometimes to changes in both. Differences are found between the density-temperature and flux descriptions, and it is concluded that more information is available using the density-temperature description
Active Experiments in Space: Past, Present, and Future
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
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