Interplanetary Disturbances Research Articles

Correction to “Three‐dimensional propagation of interplanetary disturbances detected with radio scintillation measurements at 327 MHz” by Munetoshi Tokumaru et al.

Correction to “Three‐dimensional propagation of interplanetary disturbances detected with radio scintillation measurements at 327 MHz” by Munetoshi Tokumaru et al.

Three‐dimensional propagation of interplanetary disturbances detected with radio scintillation measurements at 327 MHz

Interplanetary scintillation (IPS) measurements at 327 MHz have been used to study the three‐dimensional propagation of interplanetary (IP) disturbances between 0.2 AU and near‐Earth distance (∼ 1 AU). IPS data of four events, September 23 and August 24, 1998, and November 4 and 6, 1997, events, in which marked IP disturbances were observed in association with energetic solar flares, have been analyzed in this study. From the analysis of these events it is found that the propagation speed of IP disturbances varies with longitude and latitude. We also found that the fast speed direction does not necessarily agree with the flare normal direction. Slow propagation speeds of IP disturbances appear to be closely associated with the slow speed region of ambient solar wind. This suggests that the large‐scale structure of the solar wind speed may play an important role in determining the propagation speed of IP disturbances, although further study is necessary.

Interplanetary disturbances through the minimum to the maximum solar activities

A comparative study of three-dimensional propagation properties of transient interplanetary disturbances is made for two different phases of 11-year solar activity; early ascending phase (November 1997) and the maximum phase (June 1991). These events were apparently associated with solar flares. Principal data source is solar wind speed measurements by multi-station IPS observations at 327 MHz. Broad interplanetary disturbances with the maximum speed of 800 km/sec were observed in early November 1997, in association with a series of broad flare-associated CMEs observed by SOHO/LASCO coronagraphs. These disturbances propagated both in the northern and the southern hemispheres approximately in a symmetrical manner with respect to the heliospheric current sheet (or the streamer belt). The eruption of the streamer belt is suggested to be the principal sources of the CMEs and their interplanetary consequences. The propagation speed of the disturbance in the region along the heliospheric current sheet were considerably smaller than those in the region apart from the sheet. On the other hand, in the period of the solar maximum, high-speed interplanetary disturbances (about 1000 km/sec at 1 AU), associated with a series of six X10–12 class solar flares in June 1991, showed highly anisotropic characteristics; the enhanced solar wind speeds (>600 km/sec) were predominantly observed in the northern hemisphere of interplanetary space (or to the north of the heliospheric current sheet), in the same hemisphere where the solar flares took place. Close connection between these energetic solar flares and the associated interplanetary disturbances is suggested.

The relative recovery of galactic and anomalous cosmic rays in the distant heliosphere: Evidence for modulation in the heliosheath

At Voyager 1 (46 AU, 33°N) the recovery of anomalous cosmic rays (ACR) is found to be very different from that of galactic cosmic rays (GCR) following the passage of the large interplanetary disturbances produced by the intensive solar activity of March/June 1991. If the modulation boundary for the GCR were at the termination shock, where anomalous cosmic rays are believed to originate, it would be expected that the intensity of the higher‐energy galactic cosmic rays would recover more rapidly than the relatively low energy anomalous component. On the contrary, we find that the time constant for the recovery of 265 MeV/nucleon GCR He is approximately twice as large as that of 43 MeV/nucleon ACR He+ and 13 MeV/nucleon O+. A regression plot of the ACR versus GCR intensity indicates a broad plateau in the ACR intensity over a period of several years while the GCR continues to increase. These differences in the relative recovery of the ACR and GCR strongly suggest that the combined interplanetary disturbances in the form of a global merged interaction region (GMIR) produced by the March/June 1991 solar activity remain an effective modulation agent for GCR after passing beyond the termination shock and into the region of the heliosheath. Some 0.37 years after the passage of the leading portion of the GMIR by Voyager 1, there is a large anisotropy in the ACR He+. One possible interpretation of this anisotropy is that it is produced by the initial flow of the ACR back into the heliosphere at the time that the leading portion of the interplanetary disturbance moves beyond the termination shock. If this interpretation is correct, then the inferred transit time between Voyager 1 and the termination shock of the GMIR along with an estimate of its velocity at 40 AU based on similar features in the Voyager 1 and Pioneer 11 energetic particle data give a value of the heliocentric distance to the termination shock of 88.5 ± 7 AU at ∼33°N in early 1992.

Integration of Neutron Monitor Data with Spacecraft Observations: a Historical Perspective

Beginning in the early 1950s, data from neutron monitors placed the taxonomy of cosmic ray temporal variations on a firm footing, extended the observations of the Sun as a transient source of high energy particles and laid the foundation of our early concepts of a heliosphere. The first major impact of the arrival of the Space Age in 1957 on our understanding of cosmic rays came from spacecraft operating beyond the confines of our magnetosphere. These new observations showed that Forbush decreases were caused by interplanetary disturbances and not by changes in the geomagnetic field; the existence of both the predicted solar wind and interplanetary magnetic field was confirmed; the Sun was revealed as a frequent source of energetic ions and electrons in the 10–100 MeV range; and a number of new, low-energy particle populations was discovered. Neutron monitor data were of great value in interpreting many of these new results.

Response of large-scale geoelectric fields to identified interplanetary disturbances and the equatorial ring current

The changes in the geoelectric field G (mV/km) between Hawaii and Guam are examined during four small geomagnetic disturbances in 1995 and 1996 when interplanetary magnetic field and plasma data are available to provide the interplanetary integrated Poynting flux ε input to the magnetosphere. In agreement with a previous study of the geoelectric field at the time of the encounter of an interplanetary magnetic cloud event with the magnetosphere, we conclude that the maximum geoelectric field across this near-equatorial route can be estimated to better than about 50% if the interplanetary conditions are known by using the expression G = 2.3 × 10 −11 ε(W).

The Causes and Effects of Adverse Space Weather

Space weather refers to highly disturbed conditions on the sun, in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life and health. Adverse changes in the near-Earth space environment can cause disruption of satellite operations, communications, navigation, and electric power distribution grids, leading to a variety of socioeconomic losses. This paper discusses some of the causes that lead to adverse space environment. The sources are believed to be on the sun. The propagation of these sources through the interplanetary space is reviewed. Finally, the interactions of the interplanetary disturbances with the earth’s magnetosphere that include bow shock, magnetopause, magnetosphere, and ionosphere are considered. The example of the June 24-28, 1999 event is given to demonstrate the solar/interplanetary/ magnetosphere inter-relationships. There is no doubt that the future COSMIC project will be important for the study of adverse space weather.

Correction to “The interplanetary events of January–May, 1997 as inferred from energetic particle data, and their relationship with solar events”

We use observations from the Goddard particle detectors on IMP 8 to investigate near-Earth interplanetary disturbances and the associated solar events in January–May 1997. We infer the presence of high-speed streams and ejecta (material in the solar wind associated with coronal mass ejections (CMEs) at the Sun) using depressions in the counting rate of >60 MeV/amu particles measured by the anti-coincidence guard. In addition to a sequence of high-speed streams, the guard detected four ejecta. A fifth ejecta (January 10–11), evident in solar wind observations, did not produce a particle decrease. During the study period there were five particle enhancements, indicating the occurrence of energetic CMEs at the Sun. All the particle enhancements were associated with halo CMEs observed by the SOHO LASCO coronagraphs. Five of the total of nine halo CMEs in this period impacted the Earth. None of the other ∼120 CMEs detected by LASCO did so. Only the four CMEs associated with traditional flare signatures were also associated with >10 MeV particle increases.

Relationships between coronal mass ejection speeds from coronagraph images and interplanetary characteristics of associated interplanetary coronal mass ejections

With an eye toward space weather forecasting and the planned Solar Terrestrial Relations Observatory mission, a combination of Solwind and SMM coronagraph data and Helios‐1 and Pioneer Venus Orbiter interplanetary field and plasma data are used to study statistical relationships between the speeds of coronal mass ejections (CMEs) observed near the Sun and key characteristics of the associated interplanetary disturbances (interplanetary coronal mass ejections (ICMEs)) detected near the ecliptic at ≤ 1 AU. When confident associations can be made between the coronagraph observations and interplanetary observations, a predictable relationship is found between observed coronagraph CME speeds and subsequently observed ICME bulk plasma speeds. Consistent with earlier work, the CMEs, regardless of their speed, produce ICMEs moving at least as fast as the minimum solar wind speed. As a rule, the CMEs observed at speeds below the average solar wind speed produce ICMEs that travel faster than the associated CME, implying acceleration, while CMEs with coronagraph speeds above the average solar wind speed produce ICMEs that travel slower than the associated CME, implying deceleration of initially fast low‐heliolatitude ejecta. A formula is provided for estimating ICME speed from CME speed. As also previously found, faster CMEs tend to produce ICMEs with larger internal magnetic field magnitudes. While the size and occurrence of southward Bz in an ICME are not generally related to the observed CME speed, Bz in the sheath region preceding the ICME shows some positive correlation. These observations confirm that while the occurrence of large interplanetary magnetic field magnitudes and high bulk plasma speeds associated with ICME passage may be predictable from coronagraph‐derived CME speeds, other important ICME features like large‐magnitude southward Bz require other diagnostics and tools for forecasts.

Recent advances, open questions and future directions in solar-terrestrial research

The International Symposium on Solar-Terrestrial Coupling Processes was held in Paros, Greece, on June 23–27, 1997. The Symposium was sponsored by NASA, the European Geophysical Society, the Greek Ministry of the Aegean, and the Greek Ministry of Development. It was attended by 85 scientists from 13 countries, and included six sessions on topics ranging from Interplanetary Disturbances to Particle Acceleration. In addition to the six sessions a panel discussion session was held. Eight scientists reported on recent advances, open questions and future directions in solar-terrestrial research. This review paper is based on the panelists' reports and includes individual sections on seven particular topics of special interest to solar-terrestrial research. The topics range from the significance of solar wind composition and interplanetary disturbances to promising new technologies and methods. Solar-terrestrial research deserves the special attention of the scientific community, both because of the attractive physics underlying the various phenomena associated with them, as well as because of the applied aspect of the sometimes destructive effects of solar-terrestrial coupling on a wide variety of technological systems.

Influence of interplanetary disturbances on the terrestrial ionospheric outflow

Following the discovery of the terrestrial ionospheric outflow in the early 1970s, and the confirmation of its significance in the late 1970s and the 1980s, a large number of studies investigated the processes leading to the escape of ionospheric ions to the magnetosphere. In general, ionospheric outflow was found to increase proportionally with geomagnetic activity. In the late 1980s and the 1990s several studies showed that whenever the abundance of ionospheric origin ions in the magnetosphere is extraordinarily high, their effects on geospace activity are substantial. It has been suggested that the large abundance of ionospheric origin ions regulates major dynamic processes like storms and substorms. This appears to be the case during great magnetic storms. A number of factors have been identified, which have a critical influence on the extent and the characteristics of ionospheric outflow. There are certainly several internal geospace factors, but a major influence on ionospheric outflow presumably originates in certain interplanetary structures. Such structures are for example high-speed streams, magnetic clouds, and coronal mass ejections. We will discuss the relationship between interplanetary structures and ionospheric outflow, on the basis of both theoretical expectations and observational facts.

Cosmic ray decreases and interplanetary disturbances during early November 1969

Using the cosmic-ray intensity data recorded with ground-based monitors at Mt. Washington, Deep River and Kula, and with the cosmic ray telescopes on Pioneer 8 and 9 spacecraft, the Forbush decrease events, 2–10 November 1969 were investigated, taking into account the associated interplanetary magnetic field and solar wind plasma data. A moving magnetic cloud, without any associated interplanetary shock wave, triggered the small Forbush decrease observed near Earth, with the onset time at 0700 UT on 2 November 1969 coinciding with the arrival time of the low density moving magnetic cloud. This result is consistent with shock unassociated moving magnetic cloud model (e.g., Zhang and Burlaga, 1988). We also found that an IMF shock wave caused the large Forbush decrease with onset time at 1837 UT on 8 November 1969 and with enhanced IMF intensity and SWP speed, a result which is consistent with Parkers blast wave model ( Parker, 1963). This IMF shock wave together with the accompanying moving magnetic cloud produced the large Forbush decrease with the onset time at 1800 UT on 9 November 1969, for which the arrival time of the moving magnetic cloud coincided with the onset time of the Forbush decrease, a result which is consistent with the shock associated moving magnetic cloud model (e.g., Zhang and Burlaga, 1988). The latter observations are also consistent with the model of Barnden, 1973which interprets the two-step Forbush decrease as caused by the post-shock turbulence followed by entry into the shock driver or ejecta. For the Forbush decrease event, 9–10 November 1969, there was no corotation delay in the Earth, Pioneer 8 and 9 data; nearly radial propagation of the IMF shock wave and the moving magnetic cloud, with expansion, is sufficient to explain the observations at Earth, Pioneer 8 and 9. The essential simultaneity of this large Forbush decrease at the Earth, at Pioneer 8, and at Pioneer 9, which established a heliocentric longitudinal spread of at least 109° from the flare/CME position on the Sun, is a notable result on the Forbush decrease process, considering the relatively small spread recently observed ( Cliver and Cane, 1996; Ifedili, 1997) for the angular extents of solar modulation of galactic cosmic rays during Forbush decreases.

A 2.5‐dimensional MHD parametric study of interplanetary shock interactions with the heliospheric current sheet/heliospheric plasma sheet

A study of the interaction of interplanetary shock waves with the heliospheric current sheet/heliospheric plasma sheet (HCS/HPS) and the disturbed flow behind them is made with a 2.5 dimensional MHD code that uses improved computational techniques. The aim is to determine if such interactions for typical shocks can produce sufficiently large changes in the interplanetary plasma and field to be geoeffective. The mutual interaction of the shock waves with the HCS/HPS is examined for several angles between the shock normal and the HCS/HPS. We separate the effects of the HCS from those due to angular distance of observer from the initial shock center. The shocks are initiated at 0.1 AU by a finite‐duration increase in initial radial velocity. We examine the transit times of the resultant shocks to 1‐AU and their strengths along their peripheries. We also examine the 1‐AU signatures of the polar component of the magnetic field, Bθ, in the interplanetary disturbance at and following the leading fast mode MHD shock. Note that Bθ = −Bz. We show the differences that result from the presence of the HCS, both qualitatively and quantitatively. The largest effects occur in Bθ, which reaches its largest excursions within 10° of the edge of the HPS. For the moderate shocks simulated in this study, deflections of the field lines produce values of Bθ between 4 and 5 nT in the presence of a HCS. These values are at the lower end of the range considered necessary for interplanetary events to initiate moderate geomagnetic storms. Further study is required to investigate the nature of input pulses and HCS that would give larger Bθ variations.

Solar Wind Eight: Proceedings of the Eighth International Solar Wind Conference

Most of us think of the Sun only for the pleasure and sustenance it provides on a diurnal and seasonal basis. Thankfully, this is not so for the authors of Solar Wind Eight! The public is aware of the Sun's waxing and waning during its approximately 11‐year sunspot cycle. Some solar physicists continue, since Galileo's 17th century observations, to count sunspots that provide a crude, cyclic proxy for this waxing and waning of solar activity. Fortunately, the general public has recently become aware of solar wind‐induced concerns such as “space weather” effects on electrical power grids, satellite system components, and communication disruptions. Since the 1960s, when the solar wind was discovered, we have known that space weather effects are caused by interplanetary disturbances transmitted to the Earth and the other planets through solar activity by this ever‐present solar plasma and magnetic field.

Cosmic-Ray Decreases and Interplanetary Disturbances During the Solar Magnetic Polarity Reversal in Solar Cycle 20

Using the cosmic-ray intensity data recorded with ground-based monitors at Mt. Washington and Deep River, and with cosmic-ray telescopes on Pioneer 8 and 9 spacecraft as well as the 2-hour averages of the IMF (magnitude and direction) and the solar wind bulk speed and density at 1 AU, the cosmic-ray decreases and interplanetary disturbances, that occurred during the period of solar magnetic polarity reversal in solar cycle 20, were investigated.

On the Solar Origins of Intense Geomagnetic Storms Observed During 6–11 March 1993

Intense geomagnetic storms with DST index ≤-100 nT were recorded on 9 March and 11 March 1993 associated with solar activity on 6 March and 9-10 March, respectively. In this paper, we discuss the characteristic features of the solar origins of the two events that gave rise to coronal and interplanetary disturbances and as a consequence produced strong geomagnetic activity at the Earth. The source of the activity in one case is attributed to a major 3M7.0 flare that occurred on 6 March 1993 and in the other case, to two large filament disruptions on the disk during 9-10 March, 1993. Both these sources were found to be located near changing or varying low-latitude coronal holes. They were also located close to the heliospheric currents sheets. Distinct X-ray activity was observed for both the events as observed by the Yohkoh SXT telescope. The detailed evolution and a comparison of these events on the basis of Yohkoh soft X-ray observations are presented here.

The solar cause of interplanetary disturbances observed in the distance range 0.24–1 AU

Interplanetary disturbances are an important aspect of the physics of the sun and heliosphere. They are identified as an increase in the density turbulence compared with the ambient solar wind. Here, we report the detection of a large number of interplanetary disturbances within the distance range 0.25–1 AU based on interplanetary scintillation measurements made between 1986 and 1991. For the first time, this yields the helio‐latitudinal distribution of interplanetary transients at different phases of the solar cycle, thereby providing insight into the physical processes influencing these phenomena. It is found that near solar minimum (1986–mid–1988), transients originate in the equatorial region of the Sun. As solar activity increases, they are observed at higher latitudes, and even in the polar regions at solar maximum (1989–1991). These disturbances also show a wide range of speeds, with a global average speed of ∼450 kms−1. More than 80% of the disturbances are associated with the active prominences on the Sun, which are suggested to be the source of coronal mass ejections.

Response of the termination shock to interplanetary disturbances: 2. MHD

The interaction of the solar wind termination shock with disturbances incident from the upstream solar wind is considered using a one‐dimensional MHD (both transverse and oblique) model. This paper extends the work of Story and Zank [1995] (Paper 1) to include the effects of the interplanetary magnetic field. A decay law is derived to describe the damping of compound rarefaction/shock structures. The inclusion of a parallel magnetic field component leads to the production of slow‐mode rarefactions and shocks. Therefore, depending on parameters, the interaction of the termination shock with interplanetary disturbances may serve to generate both slow‐ and fast‐mode magnetosonic waves that propagate through the heliosheath. Furthermore, it follows from the simulations presented here that slow‐mode waves and rotational discontinuities can be expected to occur, at least to some extent, at any region of the solar system where collisions between oblique MHD shocks occur. Some discussion regarding the relative local orientation of the heliospheric magnetic field, with respect to the interstellar magnetic field, is presented to address the possibility of a global rotational discontinuity(s) which may be necessary to connect the interplanetary magnetic field to the interstellar field. Some further results concerning the interaction of waves and shocks reflected from heliosheath structure with the termination shock are also presented.

Plasma flow in the cometosheath of comet Halley

Plasma parameters are investigated in the regions upstream and downstream of the bow shock of comet Halley based on the ion spectra measured by the Plasmag-1 instrument aboard the Vega-2 spacecraft. Proton velocities observed by the Solar Direction Analyser and by the Cometary Ram Analyser are compared with the simulated bulk velocity profile provided by a three-dimensional multiscale MHD model (Gombosi et al., 1996). Disregarding the effects of presumably interplanetary disturbances, the simulated and measured values are in good agreement at cometocentric distances larger than about 0.5 million km.

Solar Activity and Interplanetary Disturbances

The Sun is not only a source of energy but also a tremendous source of interplanetary disturbances. The continuous stream of plasma (solar wind) is propelled by a pressure gradient near the photosphere. The pressure gradient and the Sun's gravitational field drive the plasma to supersonic velocities at the Earth's orbit. Solar activity is discussed in terms of the characteristics of the origin, x-ray flare class, optical classification, radio emission, energy particle emission and geophysical effects. Solar activities during March–June 1991 and February 20–21, 1994 are but two activities in recent times which resulted in large scale Interplanetary Waves (IPW), medium-scale gravity waves and geomagnetic disturbances. The disturbances of these activities are also discussed.