After a brief review of magnetospheric and interplanetary phenomena for intervals with enhanced solar wind-magnetosphere interaction, an attempt is made to define a geomagnetic storm as an interval of time when a sufficiently intense and long-lasting interplanetary convection electric field leads, through a substantial energization in the magnetosphere-ionosphere system, to an intensified ring current sufficiently strong to exceed some key threshold of the quantifying storm time Dst index. The associated storm/substorm relationship problem is also reviewed. Although the physics of this relationship does not seem to be fully understood at this time, basic and fairly well established mechanisms of this relationship are presented and discussed. Finally, toward the advancement of geomagnetic storm research, some recommendations are given concerning future improvements in monitoring existing geomagnetic indices as well as the solar wind near Earth.

/pdf/what-is-a-geomagnetic-storm-28nleury90.pdf

What is a geomagnetic storm

The Fast Plasma Investigation (FPI) was developed for flight on the Magnetospheric Multiscale (MMS) mission to measure the differential directional flux of magnetospheric electrons and ions with unprecedented time resolution to resolve kinetic-scale plasma dynamics. This increased resolution has been accomplished by placing four dual 180-degree top hat spectrometers for electrons and four dual 180-degree top hat spectrometers for ions around the periphery of each of four MMS spacecraft. Using electrostatic field-of-view deflection, the eight spectrometers for each species together provide 4pi-sr field-of-view with, at worst, 11.25-degree sample spacing. Energy/charge sampling is provided by swept electrostatic energy/charge selection over the range from 10 eV/q to 30000 eV/q. The eight dual spectrometers on each spacecraft are controlled and interrogated by a single block redundant Instrument Data Processing Unit, which in turn interfaces to the observatory’s Instrument Suite Central Instrument Data Processor. This paper describes the design of FPI, its ground and in-flight calibration, its operational concept, and its data products.

/pdf/fast-plasma-investigation-for-magnetospheric-multiscale-2nlygklc1c.pdf

Fast Plasma Investigation for Magnetospheric Multiscale

The NASA Radiation Belt Storm Probes (RBSP) mission addresses how populations of high energy charged particles are created, vary, and evolve in space environments, and specifically within Earth’s magnetically trapped radiation belts. RBSP, with a nominal launch date of August 2012, comprises two spacecraft making in situ measurements for at least 2 years in nearly the same highly elliptical, low inclination orbits (1.1×5.8 RE, 10∘). The orbits are slightly different so that 1 spacecraft laps the other spacecraft about every 2.5 months, allowing separation of spatial from temporal effects over spatial scales ranging from ∼0.1 to 5 RE. The uniquely comprehensive suite of instruments, identical on the two spacecraft, measures all of the particle (electrons, ions, ion composition), fields (E and B), and wave distributions (d E and d B) that are needed to resolve the most critical science questions. Here we summarize the high level science objectives for the RBSP mission, provide historical background on studies of Earth and planetary radiation belts, present examples of the most compelling scientific mysteries of the radiation belts, present the mission design of the RBSP mission that targets these mysteries and objectives, present the observation and measurement requirements for the mission, and introduce the instrumentation that will deliver these measurements. This paper references and is followed by a number of companion papers that describe the details of the RBSP mission, spacecraft, and instruments.

/pdf/science-objectives-and-rationale-for-the-radiation-belt-xiee4njaig.pdf

Science Objectives and Rationale for the Radiation Belt Storm Probes Mission

The subject of surface potentials on natural and artificial bodies in space is reviewed with particular emphasis on recent developments. Following a brief survey of work done up to the early 1970s on the charging of astrophysical objects in interstellar and interplanetary space and spacecraft charging, the various charging mechanisms in space are examined, including the collection of plasma particles, photoemission, and secondary electron emission by electron impact and ion impact, and the effects on charging of nonisotropic plasmas, wakes, and environmental magnetic and electric fields are considered. The concept of equilibrium potential is discussed, along with differential charging, potential barriers and discharge processes. The measurement of spacecraft potentials is then considered, and recent work on spacecraft potential modification and control by active and passive means is presented. Finally, astrophysical applications where charging effects may be important are discussed, and areas for further work are indicated.

http://iopscience.iop.org/article/10.1088/0034-4885/44/11/002/pdf

Potentials of surfaces in space

Dipole representations of the earth's magnetic field have been found to have insufficient accuracy for the study of magnetically trapped particles. A coordinate system consisting of the magnitude of the magnetic field B, and the integral invariant I has been found to adequately organize, measurements made at different geographic locations. It is shown in the present paper, that a parameter L = f(B,I) can be defined which retains most of the desirable properties of I and which has the additional property of organizing measurements along lines of force. Since the parameter L is the analog of a physical distance in a dipole field (the equatorial radius of a magnetic shell), it is usually found to present fewer conceptual difficulties than the integral invariant I.

/pdf/coordinates-for-mapping-the-distribution-of-magnetically-2llokep7yc.pdf

Coordinates for Mapping the Distribution of Magnetically Trapped Particles

Magnetospheric plasma clouds equatorial observation by ATS 5 satellite, revealing plasma injection during substorms and dispersion by earth magnetic and electric fields

Plasma clouds in the magnetosphere.

An improved magnetospheric electric field model is used to compute the initial locations of particles injected by several substorms. Trajectories are traced from the time of their encounter with the ATS-5 satellite backwards to the onset time given by ground-based magnetometers. A spiral shaped inner boundary of injection is found which is quite similar to that found by a statistical analysis. This injection boundary is shown to move in an energy dependent fashion which can explain the soft energy spectra observed at the inner edge of the electrons plasma sheet.

Substorm injection boundaries

The nature of particles producing two visible auroras at Fort Churchill, Canada, was determined with the aid of rocket-borne detectors. Magnetic fields were used to separate the proton and electron components of the particle flux. It was found in each case that a major fraction of the auroral light was produced by electron with energies of less than 10 kev. IGY rocket II6.26F was fired into a quiescent auroral glow of about intensity I. The integral number energy spectrum of protons incident upon the atmosphere during this flight was measured to be approximately 2.5 x 10/sup 6/ exp (-E/30) protons/sec cm/sup 2/ ster at 80 to 250 kev, where E is the proton energy in kev. The observed altitude dependence of the electron energy flux could have been produced by an integral number energy spectrum equal to 2.5x 10/sup 9/ exp (-E/5) electrons/sec cm/sup 2/ ster at 3 to 30 kev. IGY rocket II6.27F was fired into a bright active auroral arc. At least 75% of the light in this aurora was produced by nearly monoenergetic electrons with about 6-kev energy. The electron flux varied rapidly with time; peak values were about 5 x 10/sup 10/ electrons/sec cm/sup 2/ ster.more » The presence of monoenergetic electrons strongly suggests an electrostatic acceleration mechanism. (auth)« less

Direct Measurement of Particles Producing Visible Auroras

A preliminary report of results obtained concerning radiation intensities measured with single Geiger tubes carried by Explorer I and III is presented. Resonable cosmic-ray counting rates were obtained for altitudes below about 1000 km. A plot of omnidirectional intensity vs. height in the vicinity of California for the first two weeks in February was obtained, This curve, extrapolated down to altitudes previously reached by rockets, agrees with earlier data, At altitudes greater than about 1100 km, very high counting rates were obtained. (W.D.M,)

Carl E. McIlwain

Papers

Coordinates for Mapping the Distribution of Magnetically Trapped Particles

Plasma clouds in the magnetosphere.

Substorm injection boundaries

Direct Measurement of Particles Producing Visible Auroras

Observation of High Intensity Radiation by Satellites 1958 Alpha and Gamma