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 (dE and dB) 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.

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 (dE and dB) 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.

Magnetospheric substorms explosively release solar wind energy previously stored in Earth's magnetotail, encompassing the entire magnetosphere and producing spectacular auroral displays. It has been unclear whether a substorm is triggered by a disruption of the electrical current flowing across the near-Earth magnetotail, at approximately 10 R(E) (R(E): Earth radius, or 6374 kilometers), or by the process of magnetic reconnection typically seen farther out in the magnetotail, at approximately 20 to 30 R(E). We report on simultaneous measurements in the magnetotail at multiple distances, at the time of substorm onset. Reconnection was observed at 20 R(E), at least 1.5 minutes before auroral intensification, at least 2 minutes before substorm expansion, and about 3 minutes before near-Earth current disruption. These results demonstrate that substorms are likely initiated by tail reconnection.

We have assembled a data set of 1821 magnetopause crossings. Separate fits to subsets of this data set determine the magnetopause location as a function of solar wind dynamic pressure and interplanetary magnetic field orientation. Solar wind dynamic pressure variations produce self‐similar magnetopause motion on time scales of one hour or longer. We verify the pressure balance relationship between the solar wind dynamic pressure and the location of the subsolar magnetopause. We quantify the relationship between the IMF Bz, region l Birkeland current strength, the position of the subsolar magnetopause, and the shape of the dayside magnetosphere. Cross sections of the dayside magnetopause in planes perpendicular to the Earth‐Sun line are oblate.

Brief, impulsive, large-amplitude (•ip/p -1) solar wind dynamic pressure pulses, recurring on time scales of 5 to 15 min, are common just upstream of the Earth's bow shock. When each pulse strikes the magnetopause, it launches a fast-mode compressional wave in the magnetosphere that can propagate antisunward faster than the magnetosheath flow. Consequently, the magnetopause bulges outward ahead of each contraction associated with a pressure pulse. These ridges generally propagate antisunward, although sunward motion is common on the early post-noon magnetopause. The greatest amplitude (-1 to 2 RE) magnetopause motion occurs on the prenoon magnetopause, at high-latitudes, and during periods of southward interplanetary magnetic field. The signatures of the pressure-pulse-driven magnetopause motion include a bipolar magnetic field signature normal to the nominal magnetopause, a rotation of the magnetic fidd away from both magnetosheath and magnetospheric orientations, a mixture of magnetosheath and magnetospheric plasmas, and high-speed magnetosheath plasma flows. The magnetopause boundary motion, in turn, drives transient compressions and shears in the dayside magnetospheric magnetic field. These compressions and shears map to the dayside auroral ionosphere, where the ground signatures produced by a single, brief, solar wind dynamic pressure pulse are an antisunward moving (sunward at early post-noon local times) double-convection vortex, associated with northsouth magnetic field perturbations, increased ELF/VLF wave activity, precipitating particles, and cosmic noise absorption. The ionospheric and magnetospheric signatures driven by solar wind pressure pulses greatly resemble those previously associated with flux transfer events. SOLAR WIND AND MAGNETOSHEATH DYNAMIC PRESSURE VARIATIONSIn this section, we consider the characteristics of previously reported solar wind and magnetosheath dynamic pressure variations, emphasizing the variations associated with solar wind shocks, holes, and tangential discontinuities. We discuss recent evidence that the bow shock itself may modulate the solar wind dynamic pressure applied to the magnetosphere. Solar WindAt least three solar wind features are associated with significant dynamic pressure variations: shocks, holes, and tangential discontinuities. The properties of corotating and traveling solar wind shocks are relatively well known. They bring increases (and occasionally decreases) in the solar wind density, velocity, and dynamic pressure to the Earth every several hours to days [Burlaga, 1969]. Although the dynamic pressure can increase by a factor of as much as 20 across solar wind shocks, factors of 3 are more common [Siscoe et al., 1968b]. Corotating shocks are aligned with the spiral IMF [Siscoe, 1972].By contrast, the dynamic pressure changes associated with tangential discontinuities [Burlaga, 1968[Burlaga, , 1969 and holes [Turner et al., 1977] are poorly known, partly because high time resolution plasma parameters were not previously available. Such small-scale fe...

Global hybrid (electron fluid, kinetic ions) and fully kinetic simulations of the magnetosphere have been used to show surprising interconnection between shocks, turbulence, and magnetic reconnection. In particular, collisionless shocks with their reflected ions that can get upstream before retransmission can generate previously unforeseen phenomena in the post shocked flows: (i) formation of reconnecting current sheets and magnetic islands with sizes up to tens of ion inertial length. (ii) Generation of large scale low frequency electromagnetic waves that are compressed and amplified as they cross the shock. These "wavefronts" maintain their integrity for tens of ion cyclotron times but eventually disrupt and dissipate their energy. (iii) Rippling of the shock front, which can in turn lead to formation of fast collimated jets extending to hundreds of ion inertial lengths downstream of the shock. The jets, which have high dynamical pressure, "stir" the downstream region, creating large scale disturbances such as vortices, sunward flows, and can trigger flux ropes along the magnetopause. This phenomenology closes the loop between shocks, turbulence, and magnetic reconnection in ways previously unrealized. These interconnections appear generic for the collisionless plasmas typical of space and are expected even at planar shocks, although they will also occur at curved shocks as occur at planets or around ejecta. V C 2014 AIP Publishing LLC. [http://dx.

Although it has become well established that the low‐altitude polar cusp moves equatorward during intervals of southward interplanetary magnetic field (IMF Bz<0), many other important aspects of the cusp's response to IMF components are not as well investigated. An algorithm for identifying the cusp proper was applied to 12,569 high‐latitude dayside passes of the DMSP F7 satellite (which is in a nearly circular polar orbit at ∼838 km altitude), and the resulting cusp positioning data were correlated with the IMF (IMF data were available for about 25% of the cases). It was found that the peak probability of observing the cusp shifts prenoon for By negative (positive) in the northern (southern) hemisphere and postnoon for By positive (negative) in the northern (southern) hemisphere. The By induced shift is much more pronounced for southward than for northward Bz, a result that appears to be consistent with elementary considerations from, for example, the antiparallel merging model. No interhemispherical latitudinal differences in cusp positions were found that could be attributed to the IMF Bx component. As expected, the cusp latitudinal position correlated reasonably well (0.70) with Bz when the IMF had a southward component; the previously much less investigated correlation for Bz northward proved to be only 0.18, suggestive of a half‐wave rectifier effect. The ratio of cusp ion number flux precipitation for Bz southward to that for Bz northward was 1.75±0.12. The statistical local time (full) width of the cusp proper was found to be 2.1 hours for Bz northward and 2.8 hours for Bz southward.

We present a new method for determining the shape of the magnetopause as a bivariate function of the hourly averaged solar wind dynamic pressure (p) and the north‐south component of the interplanetary magnetic field (IMF) Bz. We represent the magnetopause (for XGSE>−40RE) as an ellipsoid of revolution in solar‐wind‐aberrated coordinates and express the (p, Bz) dependence of each of the three ellipsoid parameters as a second‐order (6‐term) bivariate expansion in lnp and Bz. We define 12 overlapping bins in a normalized dimensionless (p, Bz) “control space” and fit an ellipsoid to those magnetopause crossings having (p, Bz) values within each bin. We also calculate the bivariate (lnp, Bz) moments to second order over each bin in control space. We can then calculate the six control‐space expansion coefficients for each of the three ellipsoid parameters in configuration space. From these coefficients we can derive useful diagnostics of the magnetopause shape as joint functions of p and Bz: the aspect ratio of the ellipsoid's minor‐to‐major axes; the flank distance, radius of curvature, and flaring angle (at XGSE = 0); and the subsolar distance and radius of curvature. We confirm and quantify previous results that during periods of southward Bz the subsolar magnetopause moves inward, while at XGSE = 0 the flank magnetopause moves outward and the flaring angle increases. These changes are most pronounced during periods of low pressure, wherein all have a dependence on Bz that is stronger and functionally different for Bz southward as compared to Bz northward (i.e., the behavior of a “half‐wave rectifier”). In contrast, all these changes are much less sensitive to IMF Bz at the highest pressures. As an application of these new results, we use a pressure balance relationship to estimate the difference between the magnetic field strength just inside the subsolar magnetopause and that of the dipole field, and we find that this difference decreases rapidly as Bz becomes more negative (although it is relatively insensitive to northward changes in Bz). Quantitative comparison shows that Region 1 Birkeland currents could make the dominant contribution to this depression in the inferred magnetic field at the subsolar point.