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We present a statistical survey of large-amplitude, asymmetric plasma and magnetic field enhancements detected outside the diamagnetic cavity at comet 67P/Churyumov–Gerasimenko from December 2014 to June 2016. Based on the concurrent observations of plasma and magnetic field enhancements, we interpret them to be magnetosonic waves. The aim is to provide a general overview of these waves' properties over the mission duration. As the first mission of its kind, the ESA Rosetta mission was able to study the plasma properties of the inner coma for a prolonged time and during different stages of activity. This enables us to study the temporal evolution of these waves and their characteristics. In total, we identified ∼ 70 000 steepened waves in the magnetic field data by means of machine learning. We observe that the occurrence of these steepened waves is linked to the activity of the comet, where steepened waves are primarily observed at high outgassing rates. No clear indications of a relationship between the occurrence rate and solar wind conditions were found. The waves are found to propagate predominantly perpendicular to the background magnetic field, which indicates their compressional nature. Characteristics like amplitude, skewness, and width of the waves were extracted by fitting a skew normal distribution to the magnetic field magnitude of individual steepened waves. With increasing mass loading, the average amplitude of the waves decreases, while the skewness increases. Using a modified 1D magnetohydrodynamic (MHD) model, we investigated if the waves can be described by the combination of nonlinear and dissipative effects. By combining the model with observations of amplitude, width and skewness, we obtain an estimate of the effective plasma diffusivity in the comet–solar wind interaction region and compare it with suitable reference values as a consistency check. At 67P/Churyumov–Gerasimenko, these steepened waves are of particular importance as they dominate the innermost interaction region for intermediate to high activity.

In this erratum we rectify the parts of the paper that were not corrected before the publication of the paper. The conclusions of the paper are unchanged.

The occurrence of geomagnetically induced currents (GICs) poses serious threats to modern technological infrastructure. Large GICs result from sharp variations of the geomagnetic field (dB/dt) caused by changes of large-scale magnetospheric and ionospheric currents. Intense dB/dt perturbations are known to occur often in high-latitude regions as a result of storm time substorms. Magnetospheric compressions usually caused by interplanetary shocks increase the magnetopause current leading to dB/dt perturbations more evident in midlatitude to low-latitude regions, while they increase the equatorial electrojet current leading to dB/dt perturbations in dayside equatorial regions. We investigate the effects of shock impact angles and speeds on the subsequent dB/dt perturbations with a database of 547 shocks observed at the L1 point. By adopting the threshold of dB/dt = 100 nT/min, identified as a risk factor to power systems, we find that dB/dt generally surpasses this threshold when following impacts of high-speed and nearly frontal shocks in dayside high-latitude locations. The same trend occurs at lower latitudes and for all nightside events but with fewer high-risk events. Particularly, we found nine events in equatorial locations with dB/dt > 100 nT/min. All events were caused by high-speed and nearly frontal shock impacts and were observed by stations located around noon local time. These high-risk perturbations were caused by sudden strong and symmetric magnetospheric compressions, more effectively intensifying the equatorial electrojet current, leading to sharp dB/dt perturbations. We suggest that these results may provide insights for GIC forecasting aiming at preventing degradation of power systems due to GICs.

The European Space Agency's spacecraft ROSETTA has reached its final destination, comet 67P/Churyumov-Gerasimenko. Whilst orbiting in the close vicinity of the nucleus the ROSETTA magnetometers detected a new type of low-frequency wave possibly generated by a cross-field current instability due to freshly ionized cometary water group particles. During separation, descent and landing of the lander PHILAE on comet 67P/Churyumov-Gerasimenko, we used the unique opportunity to perform combined measurements with the magnetometers onboard ROSETTA (RPCMAG) and its lander PHILAE (ROMAP). New details about the spatial distribution of wave properties along the connection line of the ROSETTA orbiter and the lander PHILAE are revealed. An estimation of the observed amplitude, phase and wavelength distribution will be presented as well as the measured dispersion relation, characterizing the new type of low-frequency waves. The propagation direction and polarization features will be discussed using the results of a minimum variance analysis. Thoughts about the size of the wave source will complete our study.

We study solar wind–ionosphere coupling through the late declining phase/solar minimum and geomagnetic minimum phases during the last solar cycle (SC23) – 2008 and 2009. This interval was characterized by sequences of high-speed solar wind streams (HSSs). The concomitant geomagnetic response was moderate geomagnetic storms and high-intensity, long-duration continuous auroral activity (HILDCAA) events. The JPL Global Ionospheric Map (GIM) software and the GPS total electron content (TEC) database were used to calculate the vertical TEC (VTEC) and estimate daily averaged values in separate latitude and local time ranges. Our results show distinct low- and mid-latitude VTEC responses to HSSs during this interval, with the low-latitude daytime daily averaged values increasing by up to 33 TECU (annual average of ~20 TECU) near local noon (12:00 to 14:00 LT) in 2008. In 2009 during the minimum geomagnetic activity (MGA) interval, the response to HSSs was a maximum of ~30 TECU increases with a slightly lower average value than in 2008. There was a weak nighttime ionospheric response to the HSSs. A well-studied solar cycle declining phase interval, 10–22 October 2003, was analyzed for comparative purposes, with daytime low-latitude VTEC peak values of up to ~58 TECU (event average of ~55 TECU). The ionospheric VTEC changes during 2008–2009 were similar but ~60% less intense on average. There is an evidence of correlations of filtered daily averaged VTEC data with Ap index and solar wind speed. We use the infrared NO and CO2 emission data obtained with SABER on TIMED as a proxy for the radiation balance of the thermosphere. It is shown that infrared emissions increase during HSS events possibly due to increased energy input into the auroral region associated with HILDCAAs. The 2008–2009 HSS intervals were ~85% less intense than the 2003 early declining phase event, with annual averages of daily infrared NO emission power of ~ 3.3 × 1010 W and 2.7 × 1010 W in 2008 and 2009, respectively. The roles of disturbance dynamos caused by high-latitude winds (due to particle precipitation and Joule heating in the auroral zones) and of prompt penetrating electric fields (PPEFs) in the solar wind–ionosphere coupling during these intervals are discussed. A correlation between geoeffective interplanetary electric field components and HSS intervals is shown. Both PPEF and disturbance dynamo mechanisms could play important roles in solar wind–ionosphere coupling during prolonged (up to days) external driving within HILDCAA intervals.

We have explored the use of COSMIC data to provide valuable scientific information on the ionospheric impacts of energetic particle precipitation during geomagnetic storms. Ionospheric electron density in the E region, and hence ionospheric conductivity, is significantly altered by precipitating particles from the magnetosphere. This has global impacts on the thermosphere–ionosphere because of the important role of conductivity on high-latitude Joule heating. Two high-speed stream (HSS) and two coronal mass ejection (CME) storms are examined with the COSMIC data. We find clear correlation between geomagnetic activity and electron density retrievals from COSMIC. At nighttime local times, the number of profiles with maximum electron densities in the E layer (below 200 km altitude) is well correlated with geomagnetic activity. We interpret this to mean that electron density increases due to precipitation are captured by the COSMIC profiles. These "E-layer-dominant ionosphere" (ELDI) profiles have geomagnetic latitudes that are consistent with climatological models of the auroral location. For the two HSS storms that occurred in May of 2011 and 2012, a strong hemispheric asymmetry is observed, with nearly all the ELDI profiles found in the Southern, less sunlit, Hemisphere. Stronger aurora and precipitation have been observed before in winter hemispheres, but the degree of asymmetry deserves further study. For the two CME storms, occurring in July and November of 2012, large increases in the number of ELDI profiles are found starting in the storm's main phase but continuing for several days into the recovery phase. Analysis of the COSMIC profiles was extended to all local times for the July 2012 CME storm by relaxing the ELDI criterion and instead visually inspecting all profiles above 50° magnetic latitude for signatures of precipitation in the E region. For 9 days during the July 2012 period, we find a signature of precipitation occurs nearly uniformly in local time, although the magnitude of electron density increase may vary with local time. The latitudinal extent of the precipitation layers is generally consistent with auroral climatology. However, after the storm main phase on 14 July 2012 the precipitation tended to be somewhat more equatorward than the climatology (by about 5–10° latitude) and equatorward of the auroral boundary data acquired from the SSUSI sensor onboard the F18 DMSP satellite. We conclude that, if analyzed appropriately, high-latitude COSMIC profiles have the potential to contribute to our understanding of MI coupling processes and extend and improve existing models of the auroral region.

The development of quantitative models that describe physical processes from the solar corona to the Earth’s upper atmosphere creates the possibility of numerical space weather forecasting with a lead time of a few days [Merkin et al., 2007; Toth et al., 2007]. Developing such a capability for the thermosphere and ionosphere is the objective of an effort described here sponsored by the NASA/National Science Foundation (NSF) Partnership for Collaborative Space Weather Modeling [Schunk, 2014]. Despite significant scientific progress in Sun-to-Earth modeling over the last few years, there is currently no system in place that relies on the physics-based model development of the past 10 years, to forecast moderate to intense upper atmosphere storms caused by solar wind disturbances. Mannucci [2012] suggests that a physics-based approach to forecasting upper atmospheric space weather has scientific as well as practical benefits.

We study the solar cycle and seasonal dependences of high-intensity, long-duration, continuous AE activity (HILDCAA) events and associated solar wind/interplanetary external drivers for ~ 3 1 2 solar cycle period, from 1975 to 2011. 99 HILDCAAs which had simultaneous solar wind/interplanetary data are considered in the present analyses. The peak occurrence frequency of HILDCAAs was found to be in the descending phase of the solar cycle. These events had the strongest time-integrated AE intensities and were coincident with peak occurrences of high-speed solar wind streams. The event initiations were statistically coincident with high-to-slow speed stream interactions, compressions in the solar wind plasma and interplanetary magnetic field (IMF). The latter were corotating interaction regions (CIRs). The signatures of related CIRs were most prominent for the events occurring during the descending and solar minimum phases of the solar cycles. For these events, the solar wind speed increased by ~41% and ~57% across the CIRs, respectively. There was weak or no stream–stream interaction or CIR structure during the ascending and solar maximum phases. HILDCAAs occurring during spring and fall seasons were found to occur preferentially in negative and positive IMF sector regions (toward and away from the Sun), respectively.

A series of four geomagnetic storms (the minimum SYM-H~−148 nT) occurred during the March 6–17, 2012 in the ascending phase of the solar cycle 24. This interval was selected by CAWSES II for its campaign. The GPS total electron content (TEC) database and JPL's Global Ionospheric Maps (GIM) were used to study vertical TEC (VTEC) for different local times and latitude ranges. The largest response to geomagnetic activity is shown in increases of the low-latitude dayside VTEC. Several GPS sites feature post-afternoon VTEC “bite-outs”. During Sudden Impulse (SI+) event on March 8th a peak daytime VTEC restores to about quiet-time values. It is shown that the TIMED/SABER zonal flux of nitric oxide (NO) infrared cooling radiation correlates well with auroral heating. A factor of ~5 cooling increase is noted in some storms. The cooling radiation intensifies in the auroral zone and spreads towards the equator. Effects of the storm appear at lower latitudes ~18.6 h later. The column density ratio Σ[O/N2] is analyzed based on TIMED/GUVI measurements. Both increases (at low latitudes) and decreases (from auroral to middle latitudes) in the ratio occurs during the geomagnetic storms. We suggest that the column density ratio could be enhanced at low to middle latitudes on the dayside partially due to the superfountain effect (atomic oxygen uplift due to ion-neutral drag). It is suggested that decreases in the Σ[O/N2] ratio at high to middle-latitudes may be caused by high thermospheric temperatures. During SI+s, there is an increase in Σ[O/N2] ratio at auroral latitudes.

Large magnitude increases in ionospheric total electron content (TEC) that occur over 1–3 h on the dayside are a significant manifestation of the main phases of superstorms. For the largest superstorms of solar cycle 23 (based on the Dst index), ground networks of GPS receivers measured peak total electron content increases greater than a factor of 2 relative to quiet time TEC averaged over the broad latitude band ±40° for local times 1200–1600 LT. Near 30° latitude, the Halloween storms of October 29–30, 2003 appeared to produce storm-time TEC exceeding quiet time values by a factor of 5 within 2–3 h of storm onset, at 1300 LT. The physical cause of these large positive phase ionospheric storms is usually attributed to prompt penetration electric fields (PPEFs) initiated by Region 1 current closure through the ionosphere ( Nopper and Carovillano, 1978 mechanism). An unresolved question is what determines variation of the TEC response for different superstorms. It has been suggested that the cross polar cap potential and Region 1 currents are significant factors in determining PPEF in the equatorial ionosphere, which are related to the solar wind reconnection electric field estimated by Kan–Lee and others. In this paper, we show evidence that suggests B y may be a significant factor controlling the TEC response during the main phase of superstorms. We analyzed the interplanetary conditions during the period that TEC was increasing for eight superstorms. We find that increasing daytime TEC during superstorms only occurs for large reconnection electric fields when B y magnitude is less than B z . The data suggest that B z is a far more important factor in the TEC response than the reconnection electric field. We also find that TEC decreases following its peak storm-time value for two superstorms, even though B z remains large and B y magnitudes are less than B z . Such decreases during the geomagnetic disturbance may indicate the role of magnetospheric shielding currents, or of changes in the thermosphere that have developed over the prolonged period of large solar wind electric field. Further analysis is warranted covering a wider range of storm intensities on the role of B y in affecting the daytime TEC response for a range of storm intensities.

The observational rate of mirror mode waves in Venus's magnetosheath for solar maximum conditions is studied and compared with previous results for solar minimum conditions. It is found that the number of mirror mode events is approximately 14 % higher for solar maximum than for solar minimum. A possible cause is the increase in solar UV radiation, ionizing more neutrals from Venus's exosphere and the outward displacement of the bow shock during solar maximum. Also, the solar wind properties (speed, density) differ for solar minimum and maximum. The maximum observational rate, however, over Venus's magnetosheath remains almost the same, with only differences in the distribution along the flow line. This may be caused by the interplay of a decreasing solar wind density and a slightly higher solar wind velocity for this solar maximum. The distribution of strengths of the mirror mode waves is shown to be exponentially falling off, with (almost) the same coefficient for solar maximum and minimum. The plasma conditions in Venus's magnetosheath are different for solar minimum as compared to solar maximum. For solar minimum, mirror mode waves are created directly behind where the bow shock will decay, whereas for solar maximum all created mirror modes can grow.

In our estimation, Rishbeth et al. (2010) have made several fundamentally incorrect statements. We have great admiration for the past works of the now deceased first author, but we feel that corrections need to be made to set the scientific record straight. Rishbeth et al. have stated “Mannucci et al. (2005) have shown that, in response to these (meridional E×B) drifts, storm TEC enhancements occur across the dayside ionosphere at low and middle latitudes.” “The work of Mannucci et al. (2005) shows quiet-day TEC at the equator near 50 units with middle latitude values near 30 units of 1016 m−2. Even if the entire plasma content at the equator were transported without loss to middle latitudes, it is not possible to account for TEC enhancements to 200 and sometimes 300 units.” “Thus TEC enhancements at latitudes beyond 25 degrees cannot generally be attributed to transport from the equator”. Later they say “Whenever plasma transport is invoked to explain an ionospheric phenomenon, one must ask: Can the plasma travel far enough in its lifetime to produce the observed effect? Detailed modeling is needed to settle this question, but in some cases the time required is so long that changes in local time and in the imposed electric field pattern become the dominant consideration. With these considerations, a longitudinally confined, latitudinally extended, TEC enhancement at middle latitudes, such as is observed during superstorm events, would require a similar configuration in the electric field. Evidence for this feature, how it is formed and how it evolves during a storm epoch also represent some key challenges to our understanding.” It is the purpose of this short note to explain (1) how the “TEC enhancements to 200 and sometimes 300 units” occurs by meridional E×B drifts and photoionization alone, (2) how “TEC enhancements beyond 25 can be caused by this same process” and (3) why “the time required is so long that changes in local time and the imposed electric field pattern becomes the dominant consideration” is not a real concern.

Electron microburst energy spectra in the range of 170 keV to 360 keV have been measured using two solid-state detectors onboard the low-altitude (680 km), polar-orbiting Korean STSAT-1 (Science and Technology SATellite-1). Applying a unique capability of the spacecraft attitude control system, microburst energy spectra have been accurately resolved into two components: perpendicular to and parallel to the geomagnetic field direction. The former measures trapped electrons and the latter those electrons with pitch angles in the loss cone and precipitating into atmosphere. It is found that the perpendicular component energy spectra are harder than the parallel component and the loss cone is not completely filled by the electrons in the energy range of 170 keV to 360 keV. These results have been modeled assuming a wave-particle cyclotron resonance mechanism, where higher energy electrons travelling within a magnetic flux tube interact with whistler mode waves at higher latitudes (lower altitudes). Our results suggest that because higher energy (relativistic) microbursts do not fill the loss cone completely, only a small portion of electrons is able to reach low altitude (~100 km) atmosphere. Thus assuming that low energy microbursts and relativistic microbursts are created by cyclotron resonance with chorus elements (but at different locations), the low energy portion of the microburst spectrum will dominate at low altitudes. This explains why relativistic microbursts have not been observed by balloon experiments, which typically float at altitudes of ~30 km and measure only X-ray flux produced by collisions between neutral atmospheric particles and precipitating electrons.

International audience; We present a geomagnetic quiet time (Dst > À50 nT) empirical model of ionospheric total electron content (TEC) for the northern equatorial ionization anomaly (EIA) crest over Calcutta, India. The model is based on the 1980–1990 TEC measurements from the geostationary Engineering Test Satellite-2 (ETS-2) at the Haringhata (University of Calcutta, India: 22.58° N, 88.38° E geographic; 12.09° N, 160.46° E geomagnetic) ionospheric field station using the technique of Faraday rotation of plane polarized VHF (136.11 MHz) signals. The ground station is situated virtually underneath the northern EIA crest. The monthly mean TEC increases linearly with F 10.7 solar ionizing flux, with a significantly high correlation coefficient (r = 0.89–0.99) between the two. For the same solar flux level, the TEC values are found to be significantly different between the descending and ascending phases of the solar cycle. This ionospheric hysteresis effect depends on the local time as well as on the solar flux level. On an annual scale, TEC exhibits semiannual variations with maximum TEC values occurring during the two equinoxes and minimum at summer solstice. The semiannual variation is strongest during local noon with a summer-to-equinox variability of ~50–100 TEC units. The diurnal pattern of TEC is characterized by a pre-sunrise (0400–0500 LT) minimum and near-noon (1300–1400 LT) maximum. Equatorial electrodynamics is dominated by the equatorial electrojet which in turn controls the daytime TEC variation and its maximum. We combine these long-term analyses to develop an empirical model of monthly mean TEC. The model is validated using both ETS-2 measurements and recent GNSS measurements. It is found that the present model efficiently estimates the TEC values within a 1-r range from the observed mean values.

The statistical characterization of the relationship between thermosphere-ionosphere anomalies and space weather events, also referred to as space weather anomalies, such as solar coronal mass ejections (CMEs) and geomagnetic storms, is a crucial component in the development of a forecast capability for thermosphere-ionosphere disturbances. This manuscript presents a systematic statistical approach for analyzing historical ionosphere and space weather observations to derive a quantitative characterization of the relationships between the thermosphere-ionosphere anomalies and space weather anomalies. Based on 2 years of historical data, our analysis reveals the complex nature of the relationship between space weather disturbances and ionospheric responses.

The data from all Rosetta plasma consortium instruments and from the ROSINA COPS instrument are used to study the interaction of the solar wind with the outgassing cometary nucleus of 67P/Churyumov-Gerasimenko. During 6 and 7 June 2015, the interaction was first dominated by an increase in the solar wind dynamic pressure, caused by a higher solar wind ion density. This pressure compressed the draped magnetic field around the comet, and the increase in solar wind electrons enhanced the ionization of the outflow gas through collisional ionization. The new ions are picked up by the solar wind magnetic field, and create a ring/ring-beam distribution, which, in a high-β plasma, is unstable for mirror mode wave generation. Two different kinds of mirror modes are observed: one of small size generated by locally ionized water and one of large size generated by ionization and pick-up farther away from the comet.

Conditions in the ionosphere have become increasingly important to forecast, since more and more spaceborne and ground-based technological systems rely on ionospheric weather. Here we explore the feasibility of ionospheric forecasts with the current generation of physics-based models. In particular, we focus on total electron content (TEC) predictions using the Global Ionosphere-Thermosphere Model (GITM). Simulations are configured in a forecast mode and performed for four typical high-speed-stream events during 2007–2012. The simulated TECs are quantified through a metric, which divides the globe into a number of local regions and robustly differentiates between quiet and disturbed periods. Proposed forecast products are hourly global maps color-coded by the TEC disturbance level of each local region. To assess the forecasts, we compare the simulated TEC disturbances with global TEC maps derived from Global Positioning System (GPS) satellite observations. The forecast performance is found to be merely acceptable, with a large number of regions where the observed variations are not captured by the simulations. Examples of model-data agreements and disagreements are investigated in detail, aiming to understand the model behavior and improve future forecasts. For one event, we identify two adjacent regions with similar TEC observations but significant differences in how local chemistry versus plasma transport contribute to electron density changes in the simulation. Suggestions for further analysis are described.

A catalog of 1377 geomagnetic storms with peak Dst (Dstp)≤−50 nT for the period 1957–2008 has been compiled. The dependence of Dstp on the solar cycle and annual variation are studied in this paper. It is found that geomagnetic storm peak intensity distribution can be described by an exponential form, P ( D s t p ) ≈ 1.2 e − D s t p / 34 , where P is the probability of geomagnetic storm occurrence with a given value Dstp. The updated solar cycle and annual distribution of geomagnetic storms have confirmed the expected behavior. For the solar cycle variation, geomagnetic storms display a two-peak distribution, with one peak close to solar maximum and the other a few years later in the beginning of the declining phase. Geomagnetic storms follow the well-known seasonal variation of geomagnetic activity. More intense storms show a peak in probability occurrence in July, confirming previous observations. These results are of practical importance for space weather applications.

We present a new method of calculating cross-field diffusion of charged particles due to their interactions with interplanetary magnetic decreases (MDs) in high heliospheric latitudes. We use a geometric model that evaluates perpendicular diffusion to the ambient magnetic field as a function of particle's gyroradius, MD radius, ratio between fields outside and inside the MD, and a random impact parameter. We use Ulysses magnetic field data of 1994 to identify the MDs and get the empirical size and magnetic field decrease distribution functions. We let protons with energies ranging from 100 keV to 2 MeV interact with MDs. The MD characteristics are taken from the observational distribution functions using the Monte Carlo method. Calculations show that the increase in diffusion tends to saturate when particles' gyroradius becomes as large as MD radii, and that particles' gyroradius increases faster than diffusion distance as the energy of the particles is increased.

Extreme historical and space era geomagnetic storms ( Δ H or Dst ≤ − 400 nT ) are studied in terms of their sunspot and Gleissberg solar cycle distributions. Interplanetary and magnetospheric processes associated with the Carrington storm are summarized and the intense storm of August 4, 1972 is discussed in the context of the possibility of having occurred as an extreme storm instead, if the polarity of the related magnetic cloud would have been opposite. We also discuss about superintense geomagnetic storms ( Dst ≤ − 250 nT ) that occurred in the space era, showing their solar cycle and seasonal distributions and also providing averages for the peak values of their main associated interplanetary parameters. A discussion about the possible occurrence of more Carrington type storms is also addressed.

The seven CAWSES interplanetary fast forward shocks and their geomagnetic effects during 2004–2005 have been analyzed. It is found that the arrival time of the shocks at Earth can be estimated within an accuracy of ∼5 min. Furthermore, AL decreases are found to occur within 10 min of shock impingement on the magnetopause. It was also determined that there is a direct correlation between the interplanetary magnetic field southward directed (IMF B s ) prior to shock arrival and substorms triggered by the shocks. If the IMF is northward prior to shock arrival, the geomagnetic activity is present but is low. One interpretation of this result is that the preconditioning energy stored in the magnetotail leaks away rapidly. A correlation between substorm peak AL and shock strength (Mach number) has also been noted, which could imply that shock strength is important for the amount of energy released into the magnetosphere/ionosphere.

We experimentally identify mirror mode (MM) structures in the Voyager 1 heliosheath data for the first time. This is done using the magnetic field data alone. The heliosheath MM structures are found to have the following characteristics: (1) quasiperiodic spacings with a typical scale size of ∼57 ρ p , (2) little or no angular changes across the structures (∼3° longitude and ∼3° latitude), and (3) a lack of sharp boundaries at the magnetic dip edges. It is demonstrated that the pickup of interstellar neutrals in the upstream region of the termination shock (TS) and quasiperpendicular TS plasma compression are the causes of MM instability during intervals when the IMF is nearly orthogonal to the solar wind flow direction. Concomitant additional injection of pickup ions (PUIs) throughout the heliosheath will lead to further MM amplification. MM structures in planetary magnetosheaths and interplanetary sheaths are discussed for comparative purposes. Multiple sources of free energy are often involved.

Minima in geomagnetic activity (MGA) at Earth at the ends of SC23 and SC22 have been identified. The two MGAs (called MGA23 and MGA22, respectively) were present in 2009 and 1997, delayed from the sunspot number minima in 2008 and 1996 by ~1/2–1 years. Part of the solar and interplanetary causes of the MGAs were exceptionally low solar (and thus low interplanetary) magnetic fields. Another important factor in MGA23 was the disappearance of equatorial and low latitude coronal holes and the appearance of midlatitude coronal holes. The location of the holes relative to the ecliptic plane led to low solar wind speeds and low IMF (Bz) variances (σBz2) and normalized variances (σBz2/B02) at Earth, with concomitant reduced solar wind-magnetospheric energy coupling. One result was the lowest ap indices in the history of ap recording. The results presented here are used to comment on the possible solar and interplanetary causes of the low geomagnetic activity that occurred during the Maunder Minimum.

We present a statistical analysis of equatorial F-peak height vertical drifts during a 5-day HILDCAA event (3–7 July 2003). Prompt penetration-PP drifts have been identified in this study by means of a correlation analysis carried out between the magnitude of disturbed height variations over the equatorial station Sao Luis-SL (44.6W, 2.33S, dip angle 1.5S) and the magnitudes of the interplanetary electric field at the magnetopause. A comparison between the correlation coefficients for the HILDCAA and the post-HILDCAA days clearly shows that coupling on the post-HILDCAA period is suppressed. The daytime (nighttime) ionospheric responses to magnetopause electric field changes were found to occur within ∼55 min (∼45 min).

Two high speed stream (HSS) solar wind intervals (days 283–294 and 314–318, 2003, hereafter called Events 1 and 2) during the declining phase of solar cycle 23 have been examined in detail for their interplanetary characteristics and their resultant geomagnetic activity. Event 1 had an associated storm initial phase with peak Dst=+9 nT. This was caused by a high plasma density heliospheric plasma sheet (HPS) which impacted the magnetosphere. The southward component of IMF Bz fluctuations in the corotating interaction regions (CIRs) of both Events 1 and 2 led to peak storm main phases of Dst=−85 and −62 nT, respectively. The extended storm “recovery” phases were associated with ΔB/Bo ∼1–2 Alfvenic fluctuations in the HSS proper. High-intensity, long-duration, continuous AE (HILDCAA) intervals were present, presumably due to the southward component of the Alfven waves. The IMF Bx–Vx 4-h cross-correlation values were >0.8 in Event 2, and lower, >0.6, in Event 1. The difference in Alfvenicity between the two HSS events is not understood at present. The IMF Bz 10-min to 3-h variances ( σ z 2 ) and are highest during the CIRs. The normalized variances ( σ z 2 / B o 2 ) during the HSS proper are approximately the same as those for the CIRs. For Event 1, the 1-h IMF σ z 2 and σ z 2 / B o 2 are 5.0 nT2 and 1.1×10−1, respectively. The IMF Bz-AE cross-correlation (c.c.) coefficients during the storm main phase of Event 1 and for 24-h of the HSS of Event 2 give similar results. For the Event 1, a peak c.c. of −0.4 occurred with a lag of 103 min, and for Event 2 a peak c.c of −0.38 with a lag of 67 min was obtained. Both c.c. results were sharply peaked. The decay-portion of a HSS prior to Event 1 was characterized by low Np, low Bo and low Alfven wave amplitudes. The 1-h IMF σ z 2 and σ z 2 / B o 2 were 0.84 nT2 and 2.9×10−2, respectively. This quiet interplanetary interval led to a quiet geomagnetic activity period (AE The e parameter was calculated using both GSE and GSM coordinates. It was found that e is ∼30% larger for GSM coordinates. Thus, the major cause of geomagnetic activity during HSSs is the large amplitude Alfven waves but not coordinate transformations. Sector polarities (IMF By values) may be a secondary factor. However, other models, like the tilted solar dipole, should be considered as well.

Interplanetary discontinuities and their geomagnetic effects are reviewed for magnetospheric/space weather researchers. Discontinuities are particularly useful as diagnostics since they are clearly identifiable in interplanetary data and their geomagnetic effects are unambiguous most of the time. Directional discontinuities (DDs) are abrupt changes in the interplanetary magnetic field direction and plasma parameters. DDs may be rotational discontinuities (RDs), tangential discontinuities (TDs) contact discontinuities (CDs) or shocks (fast (FS), intermediate (IS) and slow (SS). Shocks can propagate in the direction of the driver (forward shocks or FSs) or opposite to the driver (reverse shocks of RSs). Discontinuities interacting with other discontinuities may create new discontinuities. Fast forward shocks (FFSs) are shown to energize trapped particles by compressive effects, cause dayside aurora, lead to the creation of new radiation belts and to trigger nightside sector magnetospheric substorms. Fast reverse shocks (FRSs) or reverse waves (RWs) lead to magnetospheric expansions and the cessation of geomagnetic activity. TD-bow shock interactions create hot flow anomalies (HFAs) which then lead to outward expansions of the local magnetopause and dayside auroral enhancements. Some DD crossings may cause sudden southward IMF turnings. These cause magnetic reconnection and energy input into the magnetosphere–ionosphere–magnetotail system. Substorms sometimes occur thereafter. DDs that entail northward IMF turnings may lead to the triggering of substorms.

In this article, we study fast shocks at CIR boundaries during an extended interval of 15 consecutive major high speed solar wind streams in 1992–1993. Ulysses was 4–5 AU from the sun. The Abraham-Schrauner shock normal method and the Rankine-Hugoniot relations were used to determine fast shock directions and speeds. Out of 33 potential CIR shocks, 14 were determined to be fast forward shocks (FSs) and 14 were fast reverse shocks (RSs). Of the remaining 5 events, 2 were forward waves and 3 were reverse waves. CIR edges at latitudes below ∼30 o were, for the most part, bounded by fast magnetosonic shocks. The forward shocks were generally quasi-perpendicular (average θ nBo = 67 o ). The reverse shocks were more oblique (average θ nBo = 52 o ), but they extended to all angles. Both FSs and RSs had magnetosonic Mach numbers ranging from 1 to 5 or 6. The average Mach numbers were 2.4 and 2.6 for FSs and RSs, respectively. The shock Mach numbers were noted to generally decrease with increasing latitude. The non-shock events or waves were noted to occur preferentially at high (∼−30° to −35°) heliolatitudes where stream-stream interactions were presumably weaker. These results are consistent with expectations, indicating the general accuracy of the Abraham-Schrauner technique.

The sun was very active in the declining phase of solar cycle 23. Large sunspot active regions gave origin to multiple flare and coronal mass ejection (CME) activity in the interval 2003–2005. On November 2004, the active region AR 10696 was the origin of dozens of flares and many CMEs. Some events of this solar activity region resulted in two large geomagnetic storms, or superstorms (Dst⩽−250 nT) on November 8, peak Dst=−373 nT, and on November 10, peak Dst=−289 nT. It is the purpose of this article to identify the interplanetary origins of these two superstorms. The southward-directed interplanetary magnetic fields (IMF Bs) that caused the two superstorms were related to a magnetic cloud (MC) field for the first superstorm, and a combination of sheath and MC fields for the second superstorm. However, this simple, classic picture is complicated by the presence of multiple shocks and waves. Six fast-forward shocks and, at least, two reverse waves were observed in the period of the two superstorms. A detailed analysis of these complex interplanetary features is performed in this work.

We show a case of an outer zone magnetospheric electromagnetic wave propagating at the Gendrin angle, within uncertainty of the measurements. The chorus event occurred in a "minimum B pocket". For the illustrated example, the measured angle of wave propagation relative to the ambient magnetic field θkB was 58°±4°. For this event the theoretical Gendrin angle was 62°. Cold plasma model is used to demonstrate that Gendrin mode waves are right-hand circularly polarized, in excellent agreement with the observations.

During the first half of November 2004, many solar flares and coronal mass ejections (CMEs) were associated with solar active region (AR) 10696. This paper attempts to identify the solar and interplanetary origins of two superstorms which occurred on 8 and 10 November with peak intensities of Dst = −373 nT and −289 nT, respectively. Southward interplanetary magnetic fields within a magnetic cloud (MC), and a sheath + MC were the causes of these two superstorms, respectively. Two different CME propagation models [Gopalswamy, N., Yashiro, S., Kaiser, M.L. et al. Predicting the 1-AU arrival times of coronal mass ejections. J. Geophys. Res. 106, 29207–29219, 2001; Gopalswamy, N.S., Lara, A., Manoharan, P.K. et al. An empirical model to predict the 1-AU arrival of interplanetary shocks. Adv. Space Res. 36, 2289–2294, 2005] were employed to attempt to identify the solar sources. It is found that the models identify several potential CMEs as possible sources for each of the superstorms. The two Gopalswamy et al. models give the possible sources for the first superstorm as CMEs on 2330 UT 4 November 2004 or on 1454 UT 5 November 2004. For the second superstorm, the possible solar source was a CME that on 0754 UT 5 November 2004 or one that occurred on 1206 UT 5 November 2004. We note that other propagation models sometimes agree and other times disagree with the above results. It is concluded that during high solar/interplanetary activity intervals such as this one, the exact solar source is difficult to identify. More refined propagation models are needed.

The prompt penetration of interplanetary electric fields (IEFs) to the dayside low-latitude ionosphere during the first ~2 h of a superstorm is estimated and applied to a modified NRL SAMI2 code for the 30 October 2003 event. In our simulations, the dayside ionospheric O+ is convected to higher altitudes (~600 km) and higher latitudes (~±25° to 30°), forming highly displaced equatorial ionospheric anomaly (EIA) peaks. This feature plus others are consistent with previously published CHAMP electron (TEC) measurements and with the dayside superfountain model. The rapid upward motion of the O+ ions causes neutral oxygen (O) uplift due to ion-neutral drag. It is estimated that above ~400 km altitude the O densities within the displaced EIAs can be increased substantially over quiet time values. The latter feature will cause increased drag for low-altitude satellites. This newly predicted phenomenon is expected to be typical for superstorm/IEF events.

We report on magnetic field measurements made in the innermost coma of 67P/Churyumov-Gerasimenko in its low activity state. Quasi-coherent, large-amplitude ($\delta B/B \sim 1$), compressional magnetic field oscillations at $\sim$ 40 mHz dominate the immediate plasma environment of the nucleus. This differs from previously studied comet-interaction regions where waves at the cometary ion gyro-frequencies are the main feature. Thus classical pick-up ion driven instabilities are unable to explain the observations. We propose a cross-field current instability associated with newborn cometary ion currents as a possible source mechanism., Comment: 6 pages, 3 Figures

Based on an estimated solar wind condition around 1–2 September 1859, we were able to reproduce the Carrington magnetic storm magnetometer record, with the H-component depression of −1600 nT, made at Colaba Observatory in Mumbai, India. We used an updated Dst prediction model from Temerin and Li (2002) , which provides a prediction efficiency of 0.91 for 1995–2002 interval using a fixed set of modeling parameters. The negative depression in the magnetometer record could be explained by assumptions as to the condition of the solar wind that, though far more geoeffective than any that have ever been observed, do not seem improbable given the known average speed of the interplanetary shock for this event. The extremely fast recovery of the magnetometer record, however, required that the dynamic pressure of the solar wind also be substantially larger than has ever been observed. We also showed how the strength of the magnetic storm would have depended on the season and the time of day. For the same solar wind conditions in GSM coordinates, the largest magnetic storms occur around the fall equinox and at the time of day when the dipole axis is most perpendicular to the solar wind velocity. Given the assumed very fast solar wind with a very large negative interplanetary magnetic field (IMF) B z directly impacting the Earth, our model together with the known magnetometer record indicates that a super magnetic storm with minimum Dst less than −1600 nT could have occurred and thus can occur again. For the magnetic storm of 1–2 September 1859, however, the extremely fast recovery of Dst requires an extremely large pressure enhancement. This suggests that this particular event was doubly unusual.

Extreme solar flares can cause extreme ionospheric effects. The Oct 28, 2003 flare caused a ∼25 TECU (a total electron content unit is 10 16 electron/m 2 column density), or a ∼30%, increase in the local noon equatorial ionospheric column density. This enhancement occurred within ∼5 min. This TEC increase was ∼5 times the TEC increases detected for the Oct 29, 2003, Nov 4, 2003, and the July 14, 2000 (Bastille Day) flares. In the 260–340 A EUV wavelength range, the Oct 28 flare peak count rate was more than twice as large as for the other three flares. Another strong ionospheric effect is the delayed influence (due to solar wind propagation) of interplanetary coronal mass ejection (ICME) electric fields on the ionosphere. For the Oct 28 and 29 flares, the associated ICMEs propagated from the sun to the Earth at particularly high speeds. The prompt penetration of the interplanetary electric field caused the dayside equatorial ionospheric to be strongly convected upward. This led to enhanced TEC to values >300% nominal values in ∼2 h. Proposed mechanisms for this TEC enhancement will be discussed.

High-intensity, long-duration, continuous AE activity (HILDCAA) are magnetospheric/ionospheric events that occur during high-speed solar wind streams. The AE increases are caused by intermittent magnetic reconnection between southward components of interplanetary Alfven waveuctuations and magnetopause magneticelds. During solar minimum, corotating interaction regions (CIRs) created by corotating stream interactions with slow-speed streams cause relatively short duration moderate to minor magnetic storms. These storms are followed by lengthy (days to weeks) of HILDCAA intervals characterized by low levels of enhanced ring current activity (DST). Shorter HILDCAA intervals are also noted following interplanetary coronal mass ejections (ICME)-related storm events. Two intervals were chosen to study in detail using POLAR UVI imaging data to identify substorms. Therst was an interval not associated with a storm. The second was a short interval following an ICME-related magnetic storm. Although substorms were detected during the HILDCAA intervals, there was little or no relationship between substorm occurrences and AE (−AL) increases. One possible explanation is that prompt penetration of interplanetary electricelds associated with magnetic reconnection lead to enhanced ionospheric westward electrojet current densities (−AL increases). These same dawn-to-dusk electricelds could lead to the convection of nightside outer magnetospheric/plasmasheet plasma, causing particle injection and DST decreases. Substorms must be caused by other processes, such as self-organized criticality. c � 2003 Published by Elsevier Ltd.

Using Polar UVI data, dawn and dusk auroras are studied. The auroras are shown to be controlled by gradual (T>30 min ) , intense (P ram ⩾10 nPa ) solar wind ram pressure events when the interplanetary magnetic field is northward. The UV auroral intensities vary linearly with the solar wind ram pressure ( ρV 2 ). As the pressure rises, the auroral intensity increases, and as the pressure returns to normal values, the auroral intensity decreases. Linear regression analyses have been performed, and resultant correlation coefficients for different events have been found to be significant. R values lie in a range of 0.79–0.97. The peak auroral intensities occur at peak solar wind pressures. The dawn and dusk auroras are speculated to be generated by some form of viscous interaction occurring on the magnetopause flanks, such as the Kelvin–Helmholtz instability, magnetic or by shearing, and Alfven wave heating.

Slow (V SW km s −1 ) magnetic clouds have been analyzed to determine their characteristics and geoeffectiveness. It is found that slow clouds have mean magnetic field strengths of ∼13 nT , peak B S ∼9 nT , and dawn–dusk electric fields of E SW ∼2.5 mV m −1 . The clouds are small in spatial size, typically ∼0.18 AU . The slowest events may have been accelerated to their speeds by interaction with the slow solar wind. Slow clouds are surprisingly geoeffective. Five out of 27 events caused major (D ST ⩽−100 nT ) magnetic storms. Likewise, these geoeffective clouds may have been decelerated to V SW km s −1 . The issue of interplanetary acceleration/deceleration will be examined with SOHO coronal mass ejection data in the near future.

From the analysis of different sets of magnetic clouds and focusing on the most probable value found for the peak amplitude of their negative B z fields, we present an estimate for the peak intensity of the associated geomagnetic storms (peak Dst ). Since the key parameter for this prediction scheme turns out to be the peak amplitude of the solar wind speed, we extend this prediction to halo CME events observed near the Sun and associated with the magnetic clouds. Thus, a prediction scheme for peak Dst , based on halo CME-expansion speed observation near the Sun and associated with magnetic clouds, is suggested for the first time. Furthermore, the relationship between the cloud's total magnetic field and its B s component, empirically found for the two sets of the studied clouds, is consistently supported by the results obtained from a numerical study of magnetic clouds.

Four different data sets pertaining to the neutral atom environment at 1 AU are presented and discussed. These data sets include neutral solar wind and interstellar neutral atom data from IMAGE/LENA, energetic hydrogen atom data from SOHO/HSTOF and plasma wave data from the magnetometer on ISEE-3. Surprisingly, these data sets are centered between 262° and 292° ecliptic longitude, ∼10–40° from the upstream interstellar neutral (ISN) flow direction at 254° resulting from the motion of the Sun relative to the local interstellar cloud (LIC). Some possible explanations for this offset, none of which is completely satisfactory, are discussed.

The properties of low frequency magnetotail waves observed during CASSINI’s Earth swing-by are examined. A maximum in the distribution of the waves about half the proton cyclotron frequency and a peak at linear polarisation are found and their implications are analysed in detail. Data on the fluid plasma velocity for the observation interval are not available and thus no unique conclusions about Doppler shift influence on the properties of the waves can be made. This determines the need to analyse different hypotheses in order to understand the origin of the waves. The plausibility of competing interpretations, such as off-resonance proton cyclotron waves and bi-ion cyclotron waves at the gyrofrequency of a heavy ion component of the magneto-tail plasma in the form of He ++ ions of solar wind origin is questioned.Key words. Space plasma physics (waves and instabilities) – Magnetospheric physics (plasma waves and instabilities; magnetotail)

The annual distribution of geomagnetic activity is studied through the geomagnetic indices Aa, Dst and AE, according to different levels of intensity for each of the indices. It is shown that the well known pattern of seasonal variation, with maxima around the equinoxes and minima near the solstices, is typical for thresholds that correspond to moderate to fairly intense storms, but may be not too realistic for levels associated to the occurrence of very intense storms. In fact, the monthly number of days with Aa ≥ 100 shows the possible existence of a peak in July. This occurrence seems to be evenly distributed along the 12 solar cycles covered by this index. The statistical analysis of the indices Dst and AE reinforce the hypothesis of the existence of this peak. These two indices seem also to indicate the presence of another peak in November in the annual distribution of very disturbed days.

Energetic particles and MHD waves are studied using simultaneous ISEE-3 data to investigate particle propagation and scattering between the source near the Sun and 1 AU. 3 He-rich events are of particular interest because they are typically low intensity "scatter-free" events. The largest solar proton events are of interest because they have been postulated to generate their own waves through beam instabilities. For 3 He-rich events, simultaneous interplanetary magnetic spectra are measured. The intensity of the interplanetary "fossil" turbulence through which the particles have traversed is found to be at the "quiet" to "intermediate" level of IMF activity. Pitch angle scattering rates and the corresponding particle mean free paths l W - P are calculated using the measured wave intensities, polarizations, and k directions. The values of l W - P are found to be ~ 5 times less than the value of l He , the latter derived from He intensity and anisotropy time profiles. It is demonstrated by computer simulation that scattering rates through a 90° pitch angle are lower than that of other pitch angles, and that this is a possible explanation for the discrepancy between the l W - P and l He values. At this time the scattering mechanism(s) is unknown. We suggest a means where a direct comparison between the two l values could be made. Computer simulations indicate that although scattering through 90° is lower, it still occurs. Possibilities are either large pitch angle scattering through resonant interactions, or particle mirroring off of field compression regions. The largest solar proton events are analyzed to investigate the possibilities of local wave generation at 1 AU. In accordance with the results of a previous calculation (Gary et al., 1985) of beam stability, proton beams at 1 AU are found to be marginally stable. No evidence for substantial wave amplitude was found. Locally generated waves, if present, were less than 10 -3 nT 2 Hz -1 at the leading proton event edge, where dispersion effects (beaming) are the greatest, and at the point of peak proton flux, where the particle energy flux is the greatest. Key words. Interplanetary physics (energetic particles; MHD waves and turbulence) – Space plasma physics (charged particle motion and acceleration; wave-particle interactions)

The dominant interplanetary phenomena that are frequently associated with intense magnetic storms are the interplanetary manifestations of fast coronal mass ejections (CMEs). Two such interplanetary structures, involving an intense and long duration Bs component of the IMF are: the sheath region behind a fast forward interplanetary shock, and the CME ejecta itself. Frequently, these structures lead to the development of intense storms with two-step growth in their main phases. These structures, when combined, lead sometimes to the development of very intense storms, especially when an additional interplanetary shock is found in the sheath plasma of the primary structure accompanying another stream. The second stream can also compress the primary cloud, intensifying the Bs field, and bringing with it an additional Bs structure. Thus, at times very intense storms are associated with three or more Bs structures. Another aspect that can contribute to the development of very intense storms refers to the recent finding that magnetic clouds with very intense core magnetic fields tend to have large velocities, thus implying large amplitude interplanetary electric fields that can drive very intense magnetospheric energization.

The Cassini spacecraft flew toward the Earth in a trajectory almost along the Sun-Earth line, giving a unique perspective of low-frequency plasma waves in the Earth's foreshock. At the time of the fly-through, the angle between the magnetic field and Sun-Earth direction was ∼70°. For this orientation, only the most energetic (>12 keV) ions could reach the upstream region, thus Cassini passed through an almost pure electron foreshock. We demonstrate the presence of nonlinear foreshock 1-Hz whistler-mode waves and their properties. Power spectra demonstrate that the waves span a frequency range from ∼0.3 to ∼10 Hz with a center frequency of ∼2 Hz. Close to the bow shock the waves had peak-to-peak transverse amplitudes as large as ∼14 nT in a 35-nT ambient field. The waves were compressive with a maximum value of Δ|B|/B 0 ≃ 0.25. The waves were propagating primarily along B 0 . Of the waves, 82% were right-hand-polarized, 9% were linearly polarized, and 9% were left-hand-polarized (in the spacecraft frame). The wave amplitudes were largest near the bow shock and decreased with increasing distance in the upstream direction. Further from the shock the waves are determined to be propagating obliquely to B 0 (θ kB ≥ 20°). There is an equal mix of right-hand, left-hand, and linearly polarized (in the spacecraft frame) waves. Left-hand-polarized waves propagating parallel to B 0 were not detected. Wave power changed dramatically as the interplanetary magnetic field rotated slightly. Arguments are presented for why low-energy (tens of eV) electrons are responsible for wave generation, rather than cyclotron resonant energetic (>13 keV) electrons.

Magnetometer data recorded by the Cassini spacecraft during the spacecraft's Earth swing-by maneuver in August 1999 are discussed. The primary purpose of this paper is to show the instrument's performance in detection of magnetic phenomena in a planetary environment. Companion papers put the data in a broader geophysical context. The low noise and high time resolution of the instrument coupled with the unusual orbit did produce new information about old phenomena (e.g., a whistler-like signal inside the near-subsolar magnetopause, lower hybrid noise in the current sheets around a magnetosheath field null, and sharp changes in the ion cyclotron wave spectrum between the boundary layer and magnetosphere proper). The detection of irregular isolated 1–2 s duration small-amplitude field strength dips in the vicinity of the nightside plasma trough appear to constitute a new discovery, tentatively identified as being evidence of plasmasphere interchange instability during a lull in background convection. The absolute scalar element of the instrument worked to plan, operating within 4 RE of Earth in parallel with the fluxgate sensors. In all respects, instrument performance bodes well for the Saturn orbital phase of the mission.

We use Wind solar wind data and Polar UV imaging data to study the nightside magnetospheric/magnetotail responses to interplanetary shocks/pressure pulses. Of 53 interplanetary shock/pressure pulse events that occurred in 1997 and 1998 at Wind, there are 18 cases where Polar near-midnight UV images are available. All of these 18 events are used in this study. The nightside auroral responses can be classified into three types: substorm expansion phase (SS) (or substorm further intensification) events, pseudobreakup (PB) events, and quiescent (QE) events. It is found that the solar wind preconditions determine the causes of the different auroral responses. A ∼1.5-hour interplanetary magnetic field (IMF) Bs “precondition” (upstream of the interplanetary shock) gives good empirical results. The upstream IMF is strongly southward prior to substorm expansion phase triggerings (44% of all events), the IMF Bz is ∼0 nT for PB triggerings (39% of all events), and the IMF is purely northward for quiescent events (17%). The evidence for IMF Bs preconditioning is interpreted in terms of a plasma sheet loading mechanism. The interplanetary shock compression effects on the near-Earth tail are discussed in light of existing substorm/PB triggering models.

Polar cap boundary layer waves are ELF/VLF electric and magnetic waves detected on field lines just adjacent to the polar cap. Intense waves are present at this location essentially all (96%) of the time. The wave latitude-local time distribution is shown to be the same as that of the Feldstein auroral oval, a distribution centered at ∼75° at local noon and ∼65° at local midnight. The most intense waves are detected coincident with the strongest magnetic field gradients (field-aligned currents). Statistically, the wave intensities are greatest near local noon (10−13 mV2 m−1 at 3 kHz) and midnight and are least near dawn and dusk (∼5 × 10−15 mV2 m−1 at 3 kHz). The noon and midnight wave intensities increase slightly when the interplanetary magnetic field is directed southward. The dawn and dusk waves appear to be controlled by the solar wind speed. Using high-resolution data, specific frequency bands of electromagnetic whistler-mode waves are identified: ∼200 Hz and 1-2 and ∼5 kHz. These may correspond to previously identified “magnetic noise bursts” and “auroral hiss”, respectively. Assuming cyclotron resonant interactions, the 1- to 5-kHz auroral hiss is shown to be resonant with ∼50-eV to ∼1.0-keV electrons. Several mechanisms, both resonant (nonlocal) and nonresonant (local), are suggested for the generation of the ∼200-Hz electromagnetic waves. Three types of intense electric signals are present: solitary bipolar pulses (electron holes), waves at ∼4 × 102 to 6 × 103 Hz (lower hybrid waves), and narrowband waves at ∼10 kHz (electrostatic waves near the upper hybrid resonance frequency). Solitary bipolar pulse onset events have been detected for the first time. The bipolar pulses reached 2 mV m−1 peak-to-peak amplitudes within 3 ms. An exponential growth rate of 0.72 ms, or 0.25 fce, was determined. The previously reported “broadband nature” of the polar cap boundary layer (and low-latitude boundary layer) waves is now postulated to be caused by a fast switching between the various electromagnetic and electrostatic modes described above. The polar cap boundary layer waves are most likely a consequence of instabilities associated with auroral zone field-aligned currents carried by 50-eV to 1.0-keV electrons and protons. The currents in turn have been ascribed to be driven by the solar wind-magnetosphere global interaction. One consequence of the presence of the waves at high altitudes is diffusion of magnetosheath plasma into the magnetosphere and magnetospheric plasma out into the magnetosheath (cross-field diffusion, due to parasitic wave-particle interactions). It is speculated that field-aligned currents and similar wave modes will be detected at all planetary magnetospheres.