Interplanetary Monitoring Platform Research Articles

Spectral Properties of the N Component of the Heliospheric Magnetic Field from IMP and ACE Observations for 1973–2020

Abstract We analyze the normal (N) component of the heliospheric magnetic field observed by the Interplanetary Monitoring Platform and the Advanced Composition Explorer spacecraft for the period 1973–2020. Parameters characterizing the frequency spectrum are calculated with a novel technique, which is based on calculating variances at incremental lags to yield the integral of a turbulence spectrum. We compare this technique with the standard second-order structure function to show their similarity in the inertial range, and use the latter to calculate correlation functions. We find that the yearly average for magnetic field magnitude and the variance attained their lowest values since spacecraft observations began for the period that includes the 2020 solar minimum, 4.2 nT and 3.3 nT2, respectively. The ratio of the magnitude of fluctuations of the N component to the field magnitude shows little variation, with an average value of 0.43 ± 0.04. The average value of the spectral index of the energy range for the whole data set is −1.0 ± 0.1, and shows some solar-cycle dependence. The average value for the inertial range is an almost constant −1.69 ± 0.04. While the break between the energy and the inertial range is difficult to determine accurately to search for a solar-cycle dependence, an indirect indication of such a dependence follows when the ratio of spectral levels in the energy and in the inertial range is calculated. The e-folding correlation length has an average value of 1.1 ± 0.3 Mkm, with a clear solar-cycle dependence.

A Study of Variations of Galactic Cosmic-Ray Intensity Based on a Hybrid Data-processing Method

Abstract The low-energy cosmic-ray (CR) fluxes measured by space-borne instruments are generally considered to consist of gradually changing galactic CRs (GCRs) and short-lived solar energetic particles (SEPs). The SEP events cause sharp and ephemeral increases in the time profile of CR observations, with a higher occurrence rate in solar maximum. It is necessary to eliminate such spikes and obtain the pure GCR component while studying the modulation of GCRs in both short and long timescales. A hybrid data-processing method based on spike detection and time series analysis techniques is developed to remove the spikes and decompose the GCR data observed by the Interplanetary Monitoring Platform 8 into the long-term variation trend and the 27 day variation components. With the hybrid data-processing method, the 11 yr and 27 day variations in the intensity of low-energy GCRs can be studied systematically. Using the fitted trend component, the time lag in the solar modulation of low-energy GCRs is studied, and the results show that the time lag is both epoch and energy dependent. The obtained 27 day variation component is anticorrelated with the changes in solar wind velocity even during solar maximum. Implementing the running Fourier series fit procedure, the 27 day variation amplitude of the proton flux is computed. It is found that the yearly averaged values clearly show 11 and 22 yr variation cycles. In addition, the energy spectrum of the 27 day variation amplitude is softer in the A < 0 solar minimum than that in the A > 0 solar minimum.

Energy spectra of carbon and oxygen with HELIOS E6

Context. Anomalous cosmic rays (ACRs) are well-suited to probe the transport conditions of cosmic rays in the inner heliosphere. We revisit the HELIOS data not only in view of the upcoming Solar Orbiter experiment but also to put constraints on particle transport models in order to provide new insight into the boundary conditions close to the Sun. Aims. We present here the energy spectra of galactic cosmic ray (GCR) carbon and oxygen, as well as of ACR oxygen during solar quiet time periods between 1975 to 1977, utilizing both HELIOS spacecraft at distances between ~0.3 and 1 AU. The radial gradient (Gr ≈ 50%/AU) of 9–28.5 MeV ACR oxygen in the inner heliosphere is about three times larger than the one determined between 1 and 10 AU by utilizing the Pioneer 10 measurements. Methods. The chemical composition as well as the energy spectra have been derived by applying the dE∕dx − E-method. In order to derive these values, special characteristics of the instrument have been taken into account. Results. A good agreement of the GCR energy spectra of carbon and oxygen measured by the HELIOS E6 instrument between 0.3 and 1 AU and the Interplanetary Monitoring Platform (IMP) 8 at 1 AU was found. For ACR oxygen, we determined a radial gradient of about 50%/AU that is three times larger than the one between 7 and 14 AU, indicating a strong change in the inner heliosphere.

Validation of the effect of cross‐calibrated GOES solar proton effective energies on derived integral fluxes by comparison with STEREO observations

AbstractThe derivation of integral fluxes from instrument coincidence rates requires accurate knowledge of their effective energies. Recent cross calibrations of GOES with the high‐energy‐resolution Interplanetary Monitoring Platform (IMP) 8 Goddard Medium Energy Experiment (GME) (Sandberg et al., Geophys. Res. Lett, 41, 4435, 2014a) gave significantly lower effective energies than those currently used by the NOAA Space Weather Prediction Center to calculate solar proton integral fluxes from GOES rates. This implies systematically lower integral fluxes than currently produced. This paper quantifies the differences between the current and the cross‐calibrated GOES integral fluxes and validates the latter. Care is taken to rule out the spectral resolution of the measurements or different integration algorithms as major contributors to differences in the magnitudes of the derived integral fluxes. The lower effective energies are validated by comparison with the independent, high‐resolution observations by the STEREO Low‐Energy Telescope (LET) and High‐Energy Telescope (HET) during the December 2006 solar proton events. The current GOES product is similar to the >10 MeV integral fluxes recalculated by using the Sandberg et al. [] effective energies but is substantially greater at higher energies. (The median ratios of the current to the recalculated fluxes are 1.1 at >10 MeV, 1.7 at >30 MeV, 2.1 at >60 MeV, and 2.9 at >100 MeV.) By virtue of this validation, the cross‐calibrated GOES integral fluxes should be considered more accurate than the current NOAA product. The results of this study also demonstrate good consistency between the two long‐term IMP 8 GME and STEREO LET and HET solar proton data sets.

RELEASE HISTORY AND TRANSPORT PARAMETERS OF RELATIVISTIC SOLAR ELECTRONS INFERRED FROM NEAR-THE-SUN IN SITU OBSERVATIONS

ABSTRACT We study four consecutive 300–800 keV electron events observed on 1980 May 28 by Helios-1, when the spacecraft was located at 0.31 au from the Sun. We use two different techniques to extract the release time history of electrons at the Sun: (1) a data-driven method based on the assumption that particles conserve their magnetic moment as they propagate between the Sun and the spacecraft and (2) an inversion method that utilizes particle transport simulation results. Both methods make use of the particle angular distributions measured relative to the local direction of the magnetic field. The general characteristics of the release time profiles obtained by these two techniques are similar, especially during their rising phases. We find indications that the strength of the interplanetary scattering varies with the size of the solar parent event, suggesting that scattering processes are not necessarily an inherent property of the medium but are related to the amount of released particles at the Sun. We use the inferred release profiles to compute the expected intensities at 1 au. In contrast to simultaneous near-Earth observations by the Interplanetary Monitoring Platform (IMP-8), our simulations predict the observation of four separate events at 1 au. Processes that could contribute to the observation of one single time-extended event at 1 au include (1) distinct magnetic connections of the spacecraft to the particle sources, (2) the spatio-temporal evolution of the particle sources, and (3) different particle transport conditions, including a variation of with radial distance and/or heliolongitude, as well as the possibility that electrons reached IMP-8 by diffusion perpendicular to the interplanetary magnetic field.

Protecting Lunar Colonies From Space Radiation

Protecting Lunar Colonies From Space Radiation

Shock Geometry, Seed Populations, and the Origin of Variable Elemental Composition at High Energies in Large Gradual Solar Particle Events

Above a few tens of MeV per nucleon, large, gradual solar energetic particle (SEP) events are highly variable in their spectral characteristics and elemental composition. The origin of this variability has been a matter of intense and ongoing debate. In this paper, we propose that this variability arises from the interplay of two factors—shock geometry and a compound seed population, typically comprising both solar-wind and flare suprathermals. Whereas quasi-parallel shocks generally draw their seeds from solar-wind suprathermals, quasi-perpendicular shocks—by requiring a higher initial speed for effective injection—preferentially accelerate seed particles from flares. Solar-wind and flare seed particles have distinctive compositional characteristics, which are then reflected in the accelerated particles. We first examine our hypothesis in the context of particles locally accelerated near 1 AU by traveling interplanetary shocks. We illustrate the implications of our hypothesis for SEPs with two very large events, 2002 April 21 and 2002 August 24. These two events arise from very similar solar progenitors but nevertheless epitomize extremes in high-energy SEP variability. We then test our hypothesis with correlation studies based on observations of 43 large SEP events in 1997-2003 by the Advanced Composition Explorer, Wind, the Interplanetary Monitoring Platform 8, and GOES. We consider correlations among high-energy Fe/O, event size, spectral characteristics, the presence of GeV protons, and event duration at high energies. The observed correlations are all qualitatively consistent with our hypothesis. Although these correlation studies cannot be construed as proof of our hypothesis, they certainly confirm its viability. We also examine the alternative hypothesis in which a direct flare component—rather than flare particles subsequently processed through a shock—dominates at high energies. This alternative would produce compositional characteristics similar to those of our hypothesis. However, the observed longitude distribution of the enhanced Fe/O events, their spectral characteristics, and recent timing studies all pose serious challenges for a direct flare component. We also comment on measurements of the mean ionic charge state of Fe at high energies. We conclude that shock geometry and seed population potentially provide a framework for understanding the overall high-energy variability in large SEP events. We suggest additional studies for testing this hypothesis.

Projected disappearance of the 11‐year cyclic minimum of galactic cosmic ray intensity in the antapex direction within the outer heliosphere

This paper reports observed galactic cosmic ray (GCR) intensity (kinetic energy T > 80 MeV/nucleon) by the University of Iowa instrument on the interplanetary spacecraft Pioneer 10 (P10) for the thirty‐year period, 1972–2002, during which it moved outward from 1 to 80 AU heliocentric radial distance (r). The trajectory of P10 since 1976 was in the approximate direction of the solar antapex. Comparable data for nearly the same time period from the Applied Physics Laboratory/Johns Hopkins University instrument on the Earth‐orbiting satellite Interplanetary Monitoring Platform – 8 (IMP‐8), as corrected (Van Allen and Randall, 1997), have been adopted as the 1 AU reference. An important new finding is that the solar modulation of GCR intensity had dwindled markedly at P10 during the most recent (2001) cyclic intensity minimum at r ∼ 78 AU relative to that at the two previous 11‐year cyclic minima in 1981 and 1991. A plausible projection of the trend established by the 1991 and 2001 values of a modulation index predicts the disappearance of direct solar modulation at r = 106 (±10) AU in the antapex direction. A similar finding from Voyager 1 and Voyager 2 data (Webber and Lockwood, 2004a and b) in the approximate apex direction confirms the previously noted absence of a apex/antapex asymmetry (Van Allen and Webber, 2002). Several heuristic comments of a general nature are included.

Model for solar proton risk assessment

A statistical model for cumulative solar proton event fluences during space missions is presented that covers both the solar minimum and solar maximum phases of the solar cycle. It is based on data from the Interplanetary Monitoring Platform and Geostationary Operational Environmental Satellites series of satellites, which are integrated together to allow the best features of each data set to be used to the best advantage. This allows the fluence-energy spectra to be extended out to energies of 327 MeV.

Solar cycle variations in solar and interplanetary ions observed with Interplanetary Monitoring Platform 8

Energetic protons (0.39–440 MeV), alpha particles (0.59–52 MeV/nucleon), and medium nuclei (carbon, nitrogen, and oxygen; 0.7–8.8 MeV/nucleon) have been observed with the Charged Particle Measurement Experiment (CPME) aboard the Interplanetary Monitoring Platform 8 (IMP 8) spacecraft from 1973 to the present. We summarize the results obtained for the period October 1973 through November 2000, more than two complete solar cycles. We believe that these observations of solar and interplanetary particles are the longest set from a single instrument yet obtained. Artifacts have been carefully removed from this data set, including background changes due to the failure in 1989 of an electronic anticoincidence shield. We have computed averages over individual solar cycles as well as “grand” averages of everything seen over the 27‐year period. The “grand” average energy spectrum of protons, alphas, and medium nuclei is well described by a power law function in total energy with exponent −2, where E is in units of MeV total energy and flux is particles/(cm2 s sr MeV). Compositional abundance ratios for energetic nuclei at the same speeds are calculated for times of minimum (H/He = 30; He/medium = 95) and maximum (H/He = 61; He/medium = 45) solar activity. We also considered possible relationships between sunspot number and interplanetary particle flux using a variety of averaging intervals and time lags and leads but found no result that could be used to predict particle fluxes from sunspot numbers over short intervals (typically several solar rotations).

Hydrogen atom lifetimes in the three‐dimensional heliosphere over the solar cycle

The three‐dimensional (3‐D) structure of the heliosphere is investigated using in situ and remote sensing measurements. The 3‐D structure of both neutral interplanetary gas and solar wind ions are affected by the solar latitude variation of the solar radiation fields (solar wind and solar EUV). Neutral hydrogen atom lifetimes against charge‐exchange with solar wind protons in the 3‐D heliosphere are calculated from measurements of the solar wind proton velocity, density, and mass flux by Ulysses SWOOPS (Solar Wind Observations Over the Poles of the Sun) from 1990–2001. These are compared to in‐ecliptic H atom lifetimes derived from solar wind measurements by the spacecraft IMP (Interplanetary Monitoring Platform) 6, 7, and 8, WIND, and ACE (Advanced Composition Explorer) SWEPAM (Solar Wind Electron Proton Alpha Monitor). Recent observations during the Ulysses rapid solar pole‐to‐solar pole passage (fast‐latitude scan) at solar maximum find a more isotropic rotationally averaged solar wind mass flux (and H atom lifetime) than was found during the previous fast latitude scan at solar minimum. During the solar minimum fast‐latitude scan the 27‐day averaged SWOOPS lifetime passed through two distinct regimes: it doubled from 2 × 106 s at low latitudes to 4 × 106 s at high latitudes in both hemispheres. During the solar maximum pass the 27‐day averaged SWOOPS H atom lifetime (corrected to 1 AU) at all southern latitudes and at all northern latitudes below 60° was (2–2.5) × 106 s, while at the very end of the pass, above 60° N latitude, it rose to 4 × 106 s as polar coronal holes reformed. Remote sensing studies of interplanetary H Lyman‐α emission, white light solar coronal observations, and radio scintillation experiments have also indicated that the time‐averaged solar wind mass flux (and H atom lifetime) is more isotropic at solar maximum than at solar minimum. This enlarges the polar H cavity at solar maximum. Results from in situ measurements are compared to remote sensing data. Ulysses GAS Lyman‐ α maps are modeled, with updated results. Comparisons of the H atom charge exchange loss rate with a weaker H atom loss process, photoionization, are made using the SOLAR2000 model [Tobiska et al., 2000] for in‐ecliptic solar Extreme UltraViolet (EUV) fluxes. The relative latitude invariance of the H atom lifetime at solar maximum is related to the absence of high‐speed solar wind at solar maximum and to the large inclination of the heliospheric current sheet.

Flare- and Shock-accelerated Energetic Particles in the Solar Events of 2001 April 14 and 15

We report heavy-ion composition and spectra for the solar energetic particle (SEP) events of 2001 April 14 and 15, using the combined capabilities of the Advanced Composition Explorer (ACE), Wind, and the Interplanetary Monitoring Platform 8 (IMP-8) to cover the energy range from ∼30 keV nucleon^(-1) to ∼400 MeV nucleon^(-1). These two events are, respectively, the largest impulsive event and the largest ground-level event observed so far in solar cycle 23. These events arose from the same active region and launched into similar interplanetary conditions. Both were associated with large western flares and fast coronal mass ejections (CMEs). However, the two events are distinctly different, thereby providing useful reminders of the fundamental differences between flare- and shock-accelerated SEPs. The detailed observations present challenges for our theoretical understanding of SEP production. Of particular note is the fact that iron has a harder power-law energy spectrum than oxygen above ∼3 MeV nucleon^(-1) in the shock-dominated April 15 event. This spectral difference, which is seen in many other gradual events of various sizes and heliolongitudes, leads to enhanced Fe/O at high energies. Simple shock acceleration models predict the same power-law index for all species. Thus, understanding the origin of this spectral difference will significantly contribute to the resolution of the ongoing debate about the relative roles of CME-driven shocks and flares in producing high-energy solar heavy ions.

Solar wind density and velocity control of auroral brightness under normal interplanetary magnetic field conditions

In this study we determine relationships between auroral brightness and each of the solar wind density and velocity under normal interplanetary magnetic field (IMF) conditions using Polar Lyman‐Birge‐Hopfield long band (∼170.0 nm) images and Interplanetary Monitoring Platform 8 solar wind data. Since IMF and season are parameters that can affect the auroral brightness, the determination of the relationships is performed on the basis of the IMF Bz polarity and season to reduce some contamination from these two parameters. It is found that for southward IMF and the winter case the solar wind density and velocity increase the auroral brightness mainly on the nightside. For southward IMF and the summer case the density and velocity also increase the auroral brightness mainly on the nightside, but the increase is not as large as that for southward IMF and the winter case.

Statistical analysis of extreme values in space science

The extreme values of many parameters measured by the space science community are important because they have a significant impact on human activities. For example, estimates of extreme radiation belt fluxes, plasma temperatures, and solar particle events must be considered when designing spacecraft, and extreme auroral currents must be considered when designing ground‐based electric power systems. The mathematical tools that have been developed to address such problems are known as the statistics of extreme values. Here these tools have been applied to three data sets in order to determine if extreme value parametric models can accurately describe space weather parameters. The three examples chosen are (1) the annual maxima of the magnetic index Ap for the years from 1932 to 1997, (2) the annual maxima of the daily average flux of >60 MeV protons measured by the Interplanetary Monitoring Platform spacecraft from 1973 to 1998, and (3) the exceedances of the flux over a threshold of 104 el cm−2 s−1 sr−1 of >2 MeV electrons at geosynchronous orbit measured by the GOES spacecraft from 1986 to 1999. The parameters for each model were determined using the maximum likelihood estimate. The validity of each model was tested using a quantile‐quantile (Q‐Q) plot. In each case an excellent fit to the extremes of the sample distribution function is given by an appropriate extreme value distribution function. These extreme value distribution functions were also used to estimate the 50‐ and 100‐year values for each data set. The results show that the extreme values observed to date are not unusual in that they are well fit by extreme value models. They also show that larger values than observed to date can be expected for each of the parameters during any 100‐year period.

Spatial variations of 0.2 to 5 MeV protons in the 1–5 AU in‐ecliptic region from Ulysses, Voyager 1 and 2, and IMP 8 gradient studies

Protons with energies ranging from 0.3 to 2 MeV are nearly always present in the environment of Earth. Solar flare events and interplanetary shock waves can be identified as producing or enhancing these fluxes. However, interplanetary particles are observed even in the absence of solar flares. Explaining the presence of these proton fluxes in the interplanetary medium and accounting for their variations is a major problem in space physics. Observations of interplanetary proton fluxes have been made continuously at 1 AU with the Interplanetary Monitoring Platform (IMP) 8 from 1973 to the present and in the 1–5 AU range by Voyagers 1 and 2 (1977–1978) and Ulysses (1990–1991). Daily averaged proton fluxes of IMP 8, Voyagers 1 and 2, and Ulysses have been carefully interpolated to matching energy passbands so that fluxes in the same passbands at two radial distances could be compared. These daily averaged fluxes were then compared as ratios and were autocorrelated and cross‐correlated as functions of time delay. The radial gradient, the energy spectra, and the distribution of these proton fluxes were also examined. The results showed that protons in the 0.3 to 5 MeV energy range using the Voyager 1/IMP 8, Voyager 2/IMP 8, and Ulysses/IMP 8 paired observations in the 1 to 5 AU in‐ecliptic region tend to “decorrelate” with increasing radial separation and become uncorrelated by about 4 or 5 AU. Higher‐energy fluxes decorrelate less rapidly, and lower‐energy proton fluxes have more dominantly positive radial gradients than those of higher energy. The radial gradient of 0.3 to 0.5 MeV proton fluxes is dominantly positive for 1–2 AU, while that of 2 to 4 MeV proton fluxes is negative. In contrast, from 2 to 4 AU the radial gradient of 0.3 to 0.5 MeV proton fluxes is weakly negative, and that of 2 to 4 MeV protons is weakly positive. This finding suggests that 0.3 to 0.5 MeV protons are more subject to interplanetary acceleration than are 2 to 4 MeV protons in the 1–2 AU range. The results also showed that radial gradients are robust and persist, evert if all heliolongitude coherence is purposely removed by shuffling the time order within 120‐day time intervals.

Statistical studies of impulsive events at high latitudes

A statistical study has been made of the high‐latitude impulsive events that were observed during the 1985–1986 South Pole Balloon Campaign. The events were selected by searching for unipolar pulses ≥ 10 nT above background in the vertical component of the magnetic field on the ground and/or pedestal or “W” shaped horizontal electric field perturbations ≥ 10 mV/m in amplitude and accompanied by perturbations in the vertical electric field at balloon altitude. A main event list comprising 112 events was compiled from the 468 hours of data available. Three aspects of the events were examined: the solar wind conditions prior to the event, local time of observation, and intrinsic properties of the events. The local time distribution was obtained from the 112 entry main event list and was found to be nearly uniform across the dayside, with no midday gap. The event rate found using our low‐amplitude selection criteria was 0.7 event/hr, comparable to expectations based on in situ studies of the magnetopause. A total of 42 events were found for which data were available from Interplanetary Monitoring Platform (IMP) 8. Of these events, 12 occurred when the ZGSM component (BZ) of the interplanetary magnetic field (IMF) was northward and 30 occurred when BZ was southward or fluctuating. Only three of the BZ northward cases and only five of the BZ southward cases were preceded by pressure pulses greater than 0.4 nPa in amplitude. Ten of the events were studied in detail by means of a model‐fitting method discussed elsewhere. This method infers values of several parameters, including the total current flowing in a coaxial or monopole system and a two‐dimensional dipole system. The intrinsic properties of the events showed that only ∼ 10% of the total current contributed to momentum transfer to the high‐latitude ionosphere, that the direction of the motion depended more on local time of observation than IMF By, and that events were usually several hundred kilometers in size. The observed Bz control found in the 42 event list and the prevalence of coaxial current dominated events are inconsistent with the predictions of the pressure pulse model.

Comment on “Intercalibration of solar wind instruments during the International Magnetospheric Study” by S. M. Petrinec and C. T. Russell

In their paper Petrinec and Russell (PR) (1993) claim to have developed a 'more homogeneous and accurate set of solar wind data' by 'correcting' the reported ion densities from three plasma instruments: the Los Alamos National Laboratory (LANL) ion electrostatic analyzer on ISEE 3 and the LANL electrostatic analyzer and the Massachusetts Institute of Technology (MIT) Faraday cup plasma instrument on Interplanetary Monitoring Platform 8 (IMP 8). Their data manipulation techniques are examined. The foundations on which their data set are built, are discussed. Reanalysis by MIT on the MIT instrument (IMP 8) was done. Initial results have been issued. The Petrinec & Russell (1993) (PR) paper does not provide accurate density estimates and is an exercise that will only bring confusion to users of the data. The results of PR should be treated with skepticism.

Solar wind oscillations with a 1.3 year period

The IMP‐8 and Voyager 2 spacecraft have recently detected a very strong modulation in the solar wind speed with an approximately 1.3 year period. Combined with evidence from long‐term auroral and magnetometer studies, this suggests that fundamental changes in the Sun occur on a roughly 1.3 year time scale.

Solar activity and coronal mass ejections on the western hemisphere of the Sun in mid‐August 1989: Association with interplanetary observations at the ICE and IMP 8 spacecraft

During the 10‐day period from August 12 to 21, 1989, a sequence of coronal mass ejections (CMEs) was observed above the west limb of the Sun by the Solar Maximum Mission (SMM) coronagraph. Most of these CMEs apparently originated in the vicinity of one particularly active region during its passage from near central meridian to behind the west limb of the Sun. We present observations made at 1 AU during this period by the ICE (formerly ISEE 3) and IMP 8 spacecraft which were separated by ∼75° in heliolongitude. Following CMEs on August 12 associated with solar events at ∼W40°, IMP 8 (in Earth orbit) detected a strong shock followed by signatures in magnetic field, solar wind plasma, and energetic ion data which suggest that CME‐related material (“ejecta”) forming the shock driver engulfed the spacecraft. This spacecraft only observed weak shocks, and no ejecta, from later CMEs originating further west of the spacecraft. In contrast ICE, off the west limb at ∼W75°, observed the shock from the W40° event but failed to encounter the shock driver, whereas clear ejecta signatures were observed following events further west, closer to the spacecraft heliolongitude. The disappearance of these signatures (which include bidirectional energetic ion flows, bidirectional solar wind heat fluxes, quiet, enhanced magnetic fields and anomalously cool plasma) at IMP 8 and their emergence at ICE as the solar source region moved westward supports the association of such signatures with ejecta related to CMEs. The dual‐spacecraft observations are also consistent with the conclusion of Richardson and Cane (1993) that ejecta at 1 AU typically extend ∼50° in longitude from the solar source. Some plausible associations between particular intervals of ejecta signatures at ICE and individual CMEs are made. However, these associations are complicated by the large number of CMEs present, by intermittent ICE data coverage, and by uncertainties in the ejecta propagation speeds to the spacecraft.

Postmodernism as Secondary Grammar

I should like to begin as synoptically as possible, measuring the postmodern all at once and as if from some immense orbital apogee, launched, adrift, but actively scanning-via satellite. We shall thus adopt a position like that of Joseph McElroy's orbiting cyborg-human brain transmogrified into Interplanetary Monitoring Platform (IMP Plus)-processing a series of signals that have been transmitted to us in complex code.1 The signals, scripting our movements and orientation, direct our sensory apparatus toward a quite large, as yet ill-defined informational site. A synoptic per-