The 1–2 September 1859 magnetic storm was the most intense in recorded history on the basis of previously reported ground observations and on newly reduced ground‐based magnetic field data. Using empirical results on the interplanetary magnetic field strengths of magnetic clouds versus velocities, we show that the 1 September 1859 Carrington solar flare most likely had an associated intense magnetic cloud ejection which led to a storm on Earth of DST ∼ −1760 nT. This is consistent with the Colaba, India local noon magnetic response of ΔH = 1600 ± 10 nT. It is found that both the 1–2 September 1859 solar flare energy and the associated coronal mass ejection speed were extremely high but not unique. Other events with more intense properties have been detected; thus a storm of this or even greater intensity may occur again. Because the data for the high‐energy tails of solar flares and magnetic storms are extremely sparse, the tail distributions and therefore the probabilities of occurrence cannot be assigned with any reasonable accuracy. A further complication is a lack of knowledge of the saturation mechanisms of flares and magnetic storms. These topics are discussed in some detail.

We explore the ionospheric effects of prompt penetration electric fields (PPEFs) for a variety of interplanetary magnetic field directions. We use the great magnetic storm of 30–31 October as an example of PPEF effects. For intense southward interplanetary magnetic fields (IMFs), inward plasma sheet convection occurs with the result of magnetospheric ring current formation and an intense magnetic storm. Concurrent with the above, positive phase ionospheric storms occur in the dayside, and negative phase ionospheric storms occur on the nightside, the topics of this paper. The dayside ionospheric storms due to PPEFs are characterized by transport of near‐equatorial plasma to higher altitudes and latitudes, forming a giant plasma fountain. These features are part of what is called the dayside ionospheric superfountain (DIS). For these southward IMFs, dusk and dawn plasma are predicted to be transported toward the dayside. For northward IMFs, negative phase ionospheric storms are expected on the dayside if the PPEFs indeed reach that region of space. IMF By components are expected to have weak or neglible ionospheric effects. On the basis of PPEF arguments, intervals of IMF By should not be related to geomagnetic storms (they are not). IMF By intervals should, however, cause a shearing of the magnetotail, a feature that has been previously reported in the literature.

[1] The dayside outer zone (DOZ) portion of the magnetosphere is a region where chorus intensities are statistically found to be the most intense. In this study, DOZ chorus have been examined using OGO-5 plasma wave and GEOTAIL plasma wave, magnetic field and energetic particle data. Dayside chorus is noted to be composed of $0.1 to 0.5 s rising-tone emissions called ''elements.'' The duration of the elements and their frequency-time characteristics are repeatable throughout the chorus event (lasting from tens of minutes to hours), but may differ from event to event. Chorus is a right-hand, circularly polarized electromagnetic plane wave. Waves are detected propagating from along the ambient magnetic field, B o , to oblique angles near the Gendrin angle, q Gendrin . All waves, independent of wave direction of propagation relative to B o , are found to be circularly polarized, to first order. Chorus rising-tone elements are composed of coherent ''subelements'' or ''packets'' with durations of $5 to 10 ms. Consecutive subelements/ packets step in frequency with time to form the elements. The peak amplitudes within a packet can be $0.2 nT or greater. The subelement or packet amplitudes are at least an order of magnitude larger than previously estimated chorus amplitudes obtained by power spectral measurements. This discrepancy is due to the presence of interspacings between chorus elements, the interspacings between subelements/packets within an element, and the different frequencies of subelements/packets within a rising-tone. DOZ chorus studied here were found to be consistent with generation via the loss cone instability of substorm-injected temperature-anisotropic (T ? /T k > 1) E = 5 to 40 keV electrons drifting from the midnight sector to the DOZ region. Using a large amplitude subelement/packet wave magnetic field amplitude of $0.2 nT, it is shown that the instantaneous Kennel-Petschek pitch angle diffusion rate D aa is $5 Â 10 À2 s À1 . This latter quantity is based on incoherent waves. If energetic electrons stay in cyclotron resonance throughout their interaction with a coherent subelement of duration 10 ms, they may be ''pitch angle transported'' by $5°. Therefore electrons within 5°of the loss cone can be lost in a single wave-particle interaction. Several such interactions as the electrons traverse the wave region can lead to much larger pitch angle transport angles. The similar time-scales of chorus elements and bremsstrahlung X-ray microbursts ($0.5 s) can be explained by the ''pitch angle transport'' mechanism described above. Increasing and decreasing pitch angle transport via this mechanism will lead to much higher pitch angle diffusion or ''super diffusion'' rates. Isotropic unpolarized noise of $20 pT peak amplitude has also been detected. The noise is well above instrument noise levels and is speculated to be remnants of chorus or hiss.

[1] There has been considerable confusion in the literature about what mirror mode (MM), magnetic decrease (MD), and linear magnetic decrease (LMD) structures are and are not. We will reexamine past spacecraft observations to demonstrate the observational similarities and differences between these magnetic and plasma structures. MM structures in planetary magnetosheaths, cometary sheaths, and the heliosheath have the following characteristics: (1) the structures have little or no changes in the magnetic field direction across the magnetic dips; (2) the structures have quasiperiodic spacings, varying from ∼20 proton gyroradii (r p ) in the Earth's magnetosheath to ∼57 r p in the heliosheath; and (3) the magnetic dips have smooth edges. Magnetosheath MM structures are generated by the mirror instability where b ? /b k > 1 + 1/b ? (b is the plasma thermal pressure divided by the magnetic pressure). In general, the sources of free energy for the mirror instability are reasonably well understood: shock compression, field line draping, and, in the cases of comets and the heliosheath, also ion pickup. The observational properties of interplanetary MDs are as follows: (1) there is a broad range of magnetic field angular changes across them; (2) their thicknesses can range from as little as 2-3 r p to thousands of r p , with no "characteristic" size; and (3) they typically are bounded by discontinuities. The mechanism(s) for interplanetary MD generation is (are) currently unresolved, although at least five different mechanisms have been proposed in the literature.

Abstract. The physical concepts of wave-particle interactions in a collisionless plasma are developed from first principles. Using the Lorentz force, starting with the concepts of particle gyromotion, particle mirroring and the loss cone, normal and anomalous cyclotron resonant interactions, pitch angle scattering, and cross-field diffusion are developed. To aid the reader, graphic illustrations are provided. INTRODUCTIONWave-particle interactions play crucial roles in many phenomena occurring in the laboratory [Gill, 1981] and in space plasmas [Gary, 1992]. In laboratory plasmas, wave-particle interactions come into play in several important applications, including beat wave acceleration, plasma heating by radio waves at ion and electron cyclotron frequencies, and transport losses due to edge turbulence. In space plasmas, wave-particle interactions are thought to be important for the formation of the magnetopause boundary layer, generation of electromagnetic outer zone chorus and plasmaspheric hiss emissions, precipitation of particles causing auroras, etc. Further, low-frequency waves can interact with charged particles over long spatial scale lengths and within the magnetosphere can transport energy from one region to another. For example, the interaction of ion cyclotron and whistler mode waves with Van Allen belt particles can scatter energetic protons and electrons into the loss cone and thus lead to the ring current decay during a magnetic storm recovery phase. Similarly, pitch angle scattering resulting from cyclotron resonance between outer zone whistler mode chorus and 10-to 100-keV trapped substorm electrons can lead to the loss of electrons by precipitation. These precipitating electrons cause ionospheric phenomenon such as diffuse aurorae, enhanced ionization in the ionospheric D and E regions, and bremsstrahlung X rays.In space plasmas the collision time between charged particles is generally very long in comparison with the characteristic timescales of the system, namely, the inverse of the plasma frequency or cyclotron frequencies, and therefore the plasma can be treated as collisionless. This would imply that there is virtually no dissipation in space plasmas, as particle-particle collisions are infrequent. This statement is correct provided that there are no wave-particle interactions.The presence of waves can introduce finite dissipation in a collisionless plasma. Charged particles are scattered by the wave fields, and the particles' momenta and energies change through this process. The interaction between a wave and a charged particle becomes strong when the streaming velocity of the particle is such that the particle senses the Doppler-shifted wave at its cyclotron frequency or its harmonics. This is the so-called cyclotron resonance interaction between the waves and particles. The special case of the Doppler-shifted wave frequency being zero (i.e., zero harmonics of the cyclotron frequency) corresponds to the well-known Landau resonance. Landau [1946] showed that plasma waves in unmagnetiz...

In the region between L = 2 to 7 at all Magnetic Local Time (MLTs) plasmaspheric hiss was detected 32% of the time. In the limited region of L = 3 to 6 and 15 to 21 MLT (dusk sector), the wave percentage detection was the highest (51%). The latter plasmaspheric hiss is most likely due to energetic~10-100 keV electrons drifting into the dusk plasmaspheric bulge region. On average, plasmaspheric hiss intensities are an order of magnitude larger on the dayside than on the nightside. Plasmaspheric hiss intensities are considerably more intense and coherent during high-solar wind ram pressure intervals. A hypothesis for this is generation of dayside chorus by adiabatic compression of preexisting 10-100 keV outer magnetospheric electrons in minimum B pockets plus chorus propagation into the plasmasphere. In large solar wind pressure events, it is hypothesized that plasmaspheric hiss can also be generated inside the plasmasphere. These new generation mechanism possibilities are in addition to the well-established mechanism of plasmaspheric hiss generation during substorms and storms. Plasmaspheric hiss under ordinary conditions is of low coherency, with small pockets of several cycles of coherent waves. During high-solar wind ram pressure intervals (positive SYM-H intervals), plasmaspheric hiss and large L hiss can have higher intensities and be coherent. Plasmaspheric hiss in these cases is typically found to be propagating obliquely to the ambient magnetic field with θ kB0~3 0°to 40°. Hiss detected at large L has large amplitudes (~0.2 nT) and propagates obliquely to the ambient magnetic field (θ kB0~7 0°) with 2:1 ellipticity ratios. A series of schematics for plasmaspheric hiss generation is presented.

[1] The study of solar flare effects (SFEs) on the ionosphere is having a renaissance. The development of GPS ground and satellite data for scientific use has opened up new means for high time resolution research on SFEs. At present, without continuous flare photon spectra (X rays, EUV, UV, and visible) monitoring instrumentation, the best way to model flare spectral changes within a flare is through ionospheric GPS studies. Flare EUV photons can increase the total electron content of the subsolar ionosphere by up to 30% in $5 min. Energetic particles (ions) of 10 keV to GeV energies are accelerated at the flare site. Electrons with energies up to several MeV are also created. A coronal mass ejection (CME) is launched from the Sun at the time of the flare. Fast interplanetary CMEs (ICMEs) have upstream shocks which accelerate ions to $10 keV to $10 MeV. Both sources of particles, when magnetically connected to the Earth's magnetosphere, enter the magnetosphere and the high-latitude and midlatitude ionosphere. Those particles that precipitate into the ionosphere cause rapid increases in the polar atmospheric ionization, disruption of transpolar communication, and cause ozone destruction. Complicating the picture, when the ICME reaches the magnetosphere $1 to 4 days later, shock compression of the magnetosphere energizes preexisting 10-100 keV magnetospheric electrons and ions, causing precipitation into the dayside auroral zone ($60°-65°MLAT) ionospheres. Shock compression can also trigger supersubstorms in the magnetotail with concomitant energetic particle precipitation into the nightside auroral zones. If the interplanetary sheath or ICME magnetic fields are southwardly directed and last for several hours, a geomagnetic storm will result. A magnetic storm is characterized by the formation of an unstable ring current with energetic particles in the range $10 keV to $500 keV. The ring current decays away by precipitation into the middle latitude ionosphere over timescales of $10 h. A schematic of a time line for the above SFE ionospheric effects is provided. Descriptions of where in the ionosphere and in what time sequence is provided in the body of the text. Much of the terminology presently in use describing solar, interplanetary, magnetospheric, and ionospheric SFE-related phenomena are dated. We suggest physics-based terms be used in the future.

A Polar magnetosonic wave (MSW) study was conducted using 1 year of 1996-1997 data (during solar minimum). Waves at and inside the plasmasphere were detected at all local times with a slight preference for occurrence in the midnight-postmidnight sector. Wave occurrence (and intensities) peaked within~±5°of the magnetic equator, with half maxima at~±10°. However, MSWs were also detected as far from the equator as +20°and 60°MLAT but with lower intensities. An extreme MSW intensity event of amplitude B w =~± 1 nT and E w =~± 25 mV/m was detected. This event occurred near local midnight, at the plasmapause, at the magnetic equator, during an intense substorm event, e.g., a perfect occurrence. These results support the idea of generation by protons injected from the plasma sheet into the midnight sector magnetosphere by substorm electric fields. MSWs were also detected near noon (1259 MLT) during relative geomagnetic quiet (low AE). A possible generation mechanism is a recovering/expanding plasmasphere engulfing preexisting energetic ions, in turn leading to ion instability. The wave magnetic field components are aligned along the ambient magnetic field direction, with the wave electric components orthogonal, indicating linear wave polarization. The MSW amplitudes decreased at locations further from the magnetic equator, while transverse whistler mode wave amplitudes (hiss) increased. We argue that intense MSWs are always present somewhere in the magnetosphere during strong substorm/convection events. We thus suggest that modelers use dynamic particle tracing codes and the maximum (rather than average) wave amplitudes to simulate wave-particle interactions.