IP Shock Research Articles

On Weibull's Spectrum of Nonrelativistic Energetic Particles at IP Shocks: Observations and Theoretical Interpretation

Abstract Some interplanetary shocks are associated with short-term and sharp particle flux enhancements near the shock front. Such intensity enhancements, known as shock-spike events (SSEs), represent a class of relatively energetic phenomena as they may extend to energies of some tens of MeV or even beyond. Here we present an SSE case study in order to shed light on the nature of the particle acceleration involved in this kind of event. Our observations refer to an SSE registered on 2011 October 3 at 22:23 UT, by STEREO B instrumentation when, at a heliocentric distance of 1.08 au, the spacecraft was swept by a perpendicular shock moving away from the Sun. The main finding from the data analysis is that a Weibull distribution represents a good fitting function to the measured particle spectrum over the energy range from 0.1 to 30 MeV. To interpret such an observational result, we provide a theoretical derivation of the Weibull spectrum in the framework of the acceleration by “killed” stochastic processes exhibiting power-law growth in time of the velocity expectation, such as the classical Fermi process. We find an overall coherence between the experimental values of the Weibull spectrum parameters and their physical meaning within the above scenario. Hence, our approach based on the Weibull distribution proves to be useful for understanding SSEs. With regard to the present event, we also provide an alternative explanation of the Weibull spectrum in terms of shock-surfing acceleration.

Low Frequency Radio Experiment (LORE)

In this paper, we present a case study of Low Frequency Radio Experiment (LORE) payload to probe the corona and the solar disturbances at solar offsets greater than 2 solar radii, i.e., at frequencies below 30 MHz. The LORE can be complimentary to the planned Indian solar mission, “Aditya-L1” and its other payloads as well as synergistic to ground-based interplanetary scintillation (IPS) observations, which are routinely carried out by the Ooty Radio Telescope. We discuss the baseline design and technical details of the proposed LORE and its particular suitability for providing measurements on the detailed time and frequency structure of fast drifting type-III and slow drifting type-II radio bursts with unprecedented time and frequency resolutions. We also brief the gonio-polarimetry, which is possible with better-designed antennas and state-of-the-art electronics, employing FPGAs and an intelligent data management system. These would enable us to make a wide range of studies, such as nonlinear plasma processes in the Sun-Earth distance, in-situ radio emission from coronal mass ejections (CMEs), interplanetary CME driven shocks, nature of ICMEs driving decelerating IP shocks and space weather effects of solar wind interaction regions.

DENSITY FLUCTUATIONS UPSTREAM AND DOWNSTREAM OF INTERPLANETARY SHOCKS

ABSTRACT Interplanetary (IP) shocks as typical large-scale disturbances arising from processes such as stream–stream interactions or Interplanetary Coronal Mass Ejection (ICME) launching play a significant role in the energy redistribution, dissipation, particle heating, acceleration, etc. They can change the properties of the turbulent cascade on shorter scales. We focus on changes of the level and spectral properties of ion flux fluctuations upstream and downstream of fast forward oblique shocks. Although the fluctuation level increases by an order of magnitude across the shock, the spectral slope in the magnetohydrodynamic range is conserved. The frequency spectra upstream of IP shocks are the same as those in the solar wind (if not spoiled by foreshock waves). The spectral slopes downstream are roughly proportional to the corresponding slopes upstream, suggesting that the properties of the turbulent cascade are conserved across the shock; thus, the shock does not destroy the shape of the spectrum as turbulence passes through it. Frequency spectra downstream of IP shocks often exhibit “an exponential decay” in the ion kinetic range that was earlier reported at electron scales in the solar wind or at ion scales in the interstellar medium. We suggest that the exponential shape of ion flux spectra in this range is caused by stronger damping of the fluctuations in the downstream region.

Global magnetohydrodynamic simulation of the 15 March 2013 coronal mass ejection event—Interpretation of the 30–80 MeV proton flux

AbstractThe coronal mass ejection (CME) event on 15 March 2013 is one of the few solar events in Cycle 24 that produced a large solar energetic particle (SEP) event and severe geomagnetic activity. Observations of SEP from the ACE spacecraft show a complex time‐intensity SEP profile that is not easily understood with current empirical SEP models. In this study, we employ a global three‐dimensional (3‐D) magnetohydrodynamic (MHD) simulation to help interpret the observations. The simulation is based on the H3DMHD code and incorporates extrapolations of photospheric magnetic field as the inner boundary condition at a solar radial distance (r) of 2.5 solar radii. A Gaussian‐shaped velocity pulse is imposed at the inner boundary as a proxy for the complex physical conditions that initiated the CME. It is found that the time‐intensity profile of the high‐energy (>10 MeV) SEPs can be explained by the evolution of the CME‐driven shock and its interaction with the heliospheric current sheet and the nonuniform solar wind. We also demonstrate in more detail that the simulated fast‐mode shock Mach number at the magnetically connected shock location is well correlated (rcc ≥ 0.7) with the concurrent 30–80 MeV proton flux. A better correlation occurs when the 30–80 MeV proton flux is scaled by r−1.4(rcc = 0.87). When scaled by r−2.8, the correlation for 10–30 MeV proton flux improves significantly from rcc = 0.12 to rcc = 0.73, with 1 h delay. The present study suggests that (1) sector boundary can act as an obstacle to the propagation of SEPs; (2) the background solar wind is an important factor in the variation of IP shock strength and thus plays an important role in manipulation of SEP flux; (3) at least 50% of the variance in SEP flux can be explained by the fast‐mode shock Mach number. This study demonstrates that global MHD simulation, despite the limitation implied by its physics‐based ideal fluid continuum assumption, can be a viable tool for SEP data analysis.

Energetic electron response to interplanetary shocks at geosynchronous orbit

AbstractInterplanetary (IP) shocks have great impacts on Earth's magnetosphere, especially in causing global dynamic changes of energetic particles. In order to study the response of energetic electrons (50keV–1.5MeV) at geosynchronous orbit to IP shocks, we have systematically analyzed 215 IP shock events based on ACE, GOES, and LANL observations during 1998–2007. Our study shows that after the shock arrival low‐energy electron fluxes increase at geosynchronous orbit. However, in higher energy channels fluxes show smaller increases and eventually become unchanged or even decrease. The oscillations of electron fluxes following the shock arrival have also been studied in this paper. Statistical analysis revealed a frequency preference for 2.2 mHz and 3.3 mHz oscillations of energetic electron fluxes. The amplitude of these oscillations is larger under southward interplanetary magnetic field (IMF) than under northward IMF. Furthermore, oscillations from high‐energy and low‐energy electron fluxes show different phase characteristics and power distributions. The phase angles of the oscillations are the same in the dawn, dusk, and noon sectors for low‐energy channels (50–500keV), while they have a difference between two adjacent local time sectors for high‐energy channels (0.5–1.5MeV). The wave power distribution of electron fluxes shows different dawn‐dusk asymmetries for low‐energy channels and high‐energy channels. The results presented in this paper provide an energetic particle point of view of the magnetospheric response to the interplanetary shock impact.

A statistical study on the stand-off distances of interplanetary coronal mass ejections

We have analyzed the stand-off distance values of 101 interplanetary CMEs (ICMEs) observed during the period 1997–2005. Main aim of the present work is to study the stand-off distance and its dependence on various parameters of CMEs, ICMEs and IP shocks, Alfvenic Mach numbers and transit time. From the distribution, the stand-off time and stand-off distance values of many of the events are found to be in the range between ~2–20h and ~1–40R⊙ (R⊙=Solar radius). From the correlation between speed of CMEs and stand-off distance, we noted smaller stand-off distance for energetic CMEs, which indicated that the driver CME (CME which is generating the shock) and its shock travel closely together. From the correlation plot between CME acceleration and stand-off distance, we found that the highly decelerated events and highly accelerated events have lower stand-off distance range (i.e., 10–40R⊙) than the other events. The events with longer travel time to reach 1AU (>70h) show stand-off times ≤20h and for those faster events (VCME>2200km/s) with smaller travel time (≤40h), stand-off time is extremely low (≤10h). A wide range of stand-off distance is seen for a particular value of CME and ICME parameters. The poor correlations of stand-off distance with all the above parameters confirm that the stand-off distance does not strongly depend on CME, ICME and IP shock parameters, but depends on a combination of all these parameters. On the other hand, the faster CMEs having lower stand-off distance and/or stand-off time imply that as long as the CMEs are energetic, the CMEs and shocks travel closely together. Also, it can be noted that the stand-off distance is not only dependent on gamma, but it is related to other parameters.

Whistler waves associated with weak interplanetary shocks

We analyze the properties of 98 weak interplanetary shocks measured by the dual STEREO spacecraft over approximately 3 years during the past solar minimum. We study the occurrence of whistler waves associated with these shocks, which on average are high beta shocks (0.2 < β< 10). We have compared the waves properties upstream and downstream of the shocks. In the upstream region the waves are mainly circularly polarized, and in most of the cases (∼75%) they propagate almost parallel to the ambient magnetic field (<30°). In contrast, the propagation angle with respect to the shock normal varies in a broad range of values (20° to 90°), suggesting that they are not phase standing. We find that the whistler waves can extend up to 100,000 km in the upstream region but in most cases (88%) are contained in a distance within 30,000 km from the shock. This corresponds to a larger region with upstream whistlers associated with IP shocks than previously reported in the literature. The maximum amplitudes of the waves are observed next to the shock interface, and they decrease as the distance to the shock increases. In most cases the wave propagation direction becomes more aligned with the magnetic field as the distance to the shock increases. These two facts suggest that most of the waves in the upstream region are Landau damping as they move away from the shock. From the analysis we also conclude that it is likely that the generation mechanism of the upstream whistler waves is taking place at the shock interface. In the downstream region, the waves are irregularly polarized, and the fluctuations are very compressive; that is, the compressive component of the wave clearly dominates over the transverse one. The majority of waves in the downstream region (95%) propagate at oblique angles with respect to the ambient magnetic field (>60°). The wave propagation with respect to the shock‐normal direction has no preferred direction and varies similarly to the upstream case. It is possible that downstream fluctuations are generated by ion relaxation as suggested in previous hybrid simulation shocks.

우주선 Intensity 조정자로서 자기구름과 그 주위의 행성간 충격파 sheath 영역의 역할

우주선 intensity가 갑작스럽게 감소하는 대표적인 현상인 Forbush Decrease(FD)는 행성간 충격파(Interplanetary shock), 자기 구름(Magnetic cloud)과 같은 태양풍 이벤트와 밀접한 관련성을 가지고 있다. FD 현상에 대해 태양풍 이벤트 중 자기구름이 어느 정도 효과적으로 작용하는 지에 대해 알아보기 위해 1998-1999년의 2년 동안 발생한 44개의 자기 구름을 분석하였다. 그 결과 44개 중 11개의 자기 구름이 FD 현상과 관련이 있었으며, 자기 구름 영역이나 자기구름과 관계된 행성간 충격파의 sheath 영역의 평균 자기장 세기, 자기장 교란도 그리고 태양풍 속도와 같은 행성간 자기장 및 태양풍의 물리적 특성이 FD 현상과의 관련성을 대표해준다는 것을 밝혀냈다. 특히, 행성간 충격파 sheath 영역의 자기장 및 태양풍의 물리량이 자기장 세기가 13nT, 자기장 교란도는 3nT, 및 태양풍 속도가 평균 550km/s 이상의 태양풍 이벤트에서 FD 발생에 효과적으로 작용하는 것으로 분석되었다. Forbush Decreases (FDs) are representative events of abrupt decrease in galactic cosmic ray intensity. They are known to be strongly associated with solar wind events such as interplanetary shock (IP shock) and magnetic cloud (MC). In order to examine effectiveness of the MC on FDs, I studied the 44 MCs that occurred during the 2 years from 1998 to 1999 and investigated the properties of interplanetary magnetic field (IMF) and solar wind. As a result, I found that 11 out of 44 MCs are associated with the FDs. In particularly, it is noted that the FDs are driven by the IP shock sheaths which are associated with over 13 nT of IMF magnitude, 3 nT of IMF turbulence, and 550km/s of solar wind speed. This result indicates that magnetic cloud and its interplanetary shock sheath work as a modulator of the cosmic ray intensity.

Geo-effectiveness of CMEs

Coronal Mass Ejections (CMEs) are important phenomena in coronal dynamics causing interplanetary signatures (ICMEs). They eject large amounts of mass and magnetic fields into the heliosphere, causing major geomagnetic storms and interplanetary shocks. Geomagnetic storms are often characterized by abrupt increases in the northward component of the earth’s field, called sudden commencements (SSC) followed by large decreases of the magnetic field and slow recovery to normal values. The SSCs are well correlated with IP shocks. Here a case study of 10–15 February 2000 and also the statistical study of CME events observed by IPS array, Rajkot, during the years 2000 to 2003 and Radio Astronomy Center, Ooty are described. The geomagnetic storm index Dst, which is a measure of geo-effectiveness, is shown to be well correlated with normalized scintillation index ‘g’, derived from Ooty Radio Telescope (ORT) observations.

Type II 전파폭발이 관측된 행성간 충격파의 1AU 내에서의 전파 과정

ACE 위성이 1997년부터 2000년까지 관측한 행성간 충격파들 중에서 WIND 위성에서 관측된 Type II 태양 전파 폭발에 의한 것으로 연관되어지는 행성간 충격파 31개를 선별하였다. 이들 행성간 충격파 발생과 관련된 Type II 전파 폭발이 관측된 후에 행성 간 충격파가 인공위성들에 의해 관측될 때까지의 시간을 측정하여 행성간 충격파가 태양에서 지구까지 전달되는 전달속도를 구하였다. 이 속도와 ACE위성에서 실제 관측된 행성간 충격파의 진행속도를 비교하여 행성간 충격파의 태양 지구간 전파과정은 평균 가속도가 <TEX>$-1.02m/sec^2$</TEX>로 감속되는 과정임을 규명하였다. 더 나아가, 이로부터 행성간 충격파의 특성에 따른 행성간 충격파 전달 과정의 감속을 결정하는 가속도 값이 행성간 충격파의 진행속도나 마하수 등과 상관관계가 없음을 밝혀내었다. Among the interplanetary shock (IP shock)s observed by ACE spacecraft at 1AU during 1997 to 2000, we have selected 31 IP shocks which had triggered the interplanetary type II radio bursts detected by the WIND spacecraft while those shocks were leaving the Sun. We compared the observed IP shock propagation speeds and the IP shock transit speeds estimated by time difference between the interplanetary type II radio burst detection and the IP shock observation. Then, we found that the mean acceleration of the IP shocks between the Sun and the Earth is about <TEX>$-1.02m/sec^2$</TEX>, which means the deceleration contrary to the positive acceleration predicted by Parker solar wind model. It is also verified that the acceleration of the IP shock does not show any linear correlation with the shock propagation speed and the Mach number of the IP shock.

Effect of Interplanetary Shocks on theALandDstIndices

[1] The question of how much interplanetary shock (IP) events contribute to the geoeffectiveness of solar wind drivers is assessed through numerical experiments using the WINDMI model, a physics-based model of the solar wind-driven magnetosphere-ionosphere system. Analytic fits to solar wind input parameters (B⊥IMF, usw, nsw) allowed shocks and associated shock-sheath plasma to be removed while leaving other features of the solar wind driver undisturbed. Percent changes in WINDMI-derived AL and Dst indices between runs with and without the observed shock and sheath signatures were taken as a measure of its relative contribution to the geoeffectiveness. The major magnetic storms during 15–24 April 2002 and 3–6 October 2000 were selected for this experiment. In both cases, the IP shock and sheath features contributed significantly to the geoeffectiveness of the solar wind driver. The magnetic field compressional jump is important to producing the changes in the AL during these two storm intervals.

Propagation of interplanetary shocks into the Earth’s magnetosphere

This paper is devoted to the study of propagation of disturbances caused by interplanetary shocks (IPS) through the Earth’s magnetosphere. Using simultaneous observations of various fast forward shocks by different satellites in the solar wind, magnetosheath and magnetosphere from 1995 till 2002, we traced the interplanetary shocks into the Earth’s magnetosphere, we calculated the velocity of their propagation into the Earth’s magnetosphere and analyzed fronts of the disturbances. From the onset of disturbances at different satellites in the magnetosphere we obtained speed values ranging from 500 to 1300 km/s in the direction along the IP shock normal, that is in a general agreement with results of previous numerical MHD simulations. The paper discusses in detail a sequence of two events on November 9th, 2002. For the two cases we estimated the propagation speed of the IP shock caused disturbance between the dayside and nightside magnetosphere to be ∼590 km/s and ∼714–741 km/s, respectively. We partially attributed this increase to higher Alfven speed in the outer magnetosphere due to the compression of the magnetosphere as a consequence of the first event, and partially to the faster and stronger driving interplanetary shock. High-time resolution GOES magnetic field data revealed a complex structure of the compressional wave fronts at the dayside geosynchronous orbit during these events, with initial very steep parts (∼10 s). We discuss a few possible mechanisms of such steep front formation in the paper.

Heavy‐Ion Elemental Abundances in Large Solar Energetic Particle Events and Their Implications for the Seed Population

We have surveyed the ~0.1–10 MeV nucleon to the -1 abundances of heavy ions from 3He through Fe in 64 large solar energetic particle (LSEP) events observed on board the Advanced Composition Explorer from 1997 November through 2005 January. Our main results are (1) the 0.5–2.0 MeV nucleon to the -1 3He/ 4He ratio is enhanced between factors of ~2–150 over the solar wind value in 29 (~46%) events. (2) The Fe/O ratio in most LSEP events decreases with increasing energy up to ~60 MeV nucleon to the -1. (3) The Fe/O ratio is independent of CME speed, flare longitude, event size, the 3He/4He ratio, the pre-event Fe/O ratio, and solar activity. (4) The LSEP abundances exhibit unsystematic behavior as a function of M/Q ratio when compared with average solar wind values. (5) The survey-averaged abundances are enhanced with increasing M/Q ratio when compared with quiet coronal values and with average gradual SEP abundances obtained at 5–12 MeV nucleon to the -1. (6) The event-to-event variations in LSEP events are remarkably similar to those seen in CME-driven IP shocks and in 3He-rich SEP events. The above results cannot be explained by simply invoking the current paradigm for large gradual SEP events, i.e., that CME-driven shocks accelerate a seed population dominated by ambient coronal or solar wind ions. Instead, we suggest that the systematic M/Q-dependent enhancements in LSEP events are an inherent property of a highly variable suprathermal seed population, most of which is accelerated by mechanisms that produce heavy-ion abundances similar to those observed in impulsive SEP events. This heavy-ion-enriched material is subsequently accelerated at CME-driven shocks near the Sun by processes in which ions with higher M/Q ratios are accelerated less efficiently, thus causing the Fe/O ratios to decrease with increasing energy.

Origin of heavy ions in upstream events near the Earth's bow shock

We have surveyed the ∼20–160 keV/nucleon heavy ion composition of 2102 upstream events observed by the Wind/STEP instrument near the Earth's bow shock over a complete solar cycle from day 325, 1994 through day 90, 2006. Our main results are: (1) During solar minimum conditions, both the C/O and Fe/O ratios are similar to the corresponding values measured in the solar wind and/or CIRs. (2) During solar maximum conditions, the C/O ratio is similar to that measured in SEP and CME‐driven IP shock events, while the Fe/O ratio lies between the values measured in IP shock and SEP events. We conclude that the source material for upstream events near the Earth's bow shock originates from a dynamic suprathermal ion population that is dominated by ions accelerated in SEP events during solar maximum conditions and by suprathermal solar wind ions and/or those accelerated in CIRs during solar minimum conditions.

An unusual nightside distortion of the auroral oval: TIMED/GUVI and IMAGE/FUV observations

[1] A new and unusual nightside auroral distortion was detected around 1400 UT on 11 December 2004 by TIMED/GUVI (northern hemisphere) and IMAGE/FUV (southern hemisphere). The distortion has a special tongue shape (possibly a special auroral streamer) and is called the Nightside Auroral Tongue (NAT) hereafter. We found that the NAT is a conjugate phenomenon. The NAT consists of both diffuse aurora and nearly north-south arcs. The NAT extended from ∼72° Mlat to 62° Mlat in the 0100 MLT sector, well beyond the proton isotropic boundary (b2i) around 66° Mlat. The width of the NAT varies from 2 hour in MLT at magnetic latitude around 70° to 0.5 hour in MLT at Mlat < 65°. The width of the arcs within the NAT is only about 30 km on average. The observed unusual feature of NAT is associated with a strong IP shock and a large solar wind electric field.

Determination of shock parameters for the very fast interplanetary shock on 29 October 2003

We study a very fast interplanetary shock (IP shock) event observed on 29 October 2003 based on the Geotail particle and field measurements in the solar wind. During this event the intensity of high‐energy solar energetic particles (greater than several to several tens of MeV) was quite high, causing a serious background problem for plasma particle measurements on Geotail as well as on the other spacecraft. The magnetic/electric field measurements and the plasma wave measurement aboard Geotail, on the other hand, were free from such a background problem and provided a reliable estimate for the local plasma parameters including the plasma density. From these measurements, our best estimation for the local shock velocity is ∼2000 km/s in the observer's rest frame or ∼1400 km/s in the upstream plasma rest frame. The corresponding Alfvén Mach number is ∼12. It is found that the timing analysis of the shock arrivals at ACE and Geotail gives a shock velocity significantly lower than the above value. We argue that this difference is due to the shock surface rippling by 15–20 deg. We also comment that this IP shock had a property of “cosmic‐ray‐mediated” shock, namely a shock having a spatial structure affected by pressures exerted by nonthermal particles accelerated by the shock itself.

Deformation of interplanetary shock fronts in the magnetosheath

We present in detail the propagation of an IP shock observed by multiple spacecraft in the solar wind and by INTERBALL (IB) in the magnetosheath (hereafter MSH). Our investigation brings an evidence that the observed IP shock slightly decelerates in the MSH contrary to gasdynamic prediction. This result motivates a statistical study of a small number of similar shocks observed in the solar wind and in the MSH that confirmed the case study result. Moreover, we model the interaction of IP shocks with the magnetosphere using an MHD model and show that the observation of shock deceleration agrees with the model prediction. The MHD model suggests that the speed of the shock front propagation in the MSH decreases from the bow shock toward the magnetopause and the front of the IP shock deforms. However, the experimental data are not sufficient to undoubtedly confirm this trend.

Comment on “Coronal mass ejections, interplanetary ejecta and geomagnetic storms” by H. V. Cane, I. G. Richardson, and O. C. St. Cyr

Comment on “Coronal mass ejections, interplanetary ejecta and geomagnetic storms” by H. V. Cane, I. G. Richardson, and O. C. St. Cyr

Geomagnetic disturbances and their relationship to Interplanetary shock parameters

We identify 107 fast, forward‐propagating interplanetary shocks observed by the Wind spacecraft from 1995–2000 to examine the influence of shock parameters on geomagnetic disturbances following the shock arrival at Earth. We find that the angle between the shock front normal and the interplanetary magnetic field (IMF) direction might play a useful role in forecasting the severity of geomagnetic storms occurring within 48 hours from the shock passage. Quasi‐perpendicular shocks, i.e. those nearly orthogonal to the IMF direction, constrain IMF components in the plane parallel to the shock front, making it more likely to produce southward IMF. We demonstrate that, regardless of the shock driver, about 40% of forward IP shocks result in intense magnetic storms when the shock normal is almost perpendicular to the IMF, compared to about 10–15% of shocks with normals not perpendicular to the IMF direction.

Radio‐rich solar eruptive events

We report on the analysis of a large number of solar eruptive events that produced radio emission in the dekameter‐hectometric (DH) radio window (1–14 MHz), newly opened by the Wind/WAVES experiment. The distinguishing characteristics of coronal mass ejections (CMEs) associated with the DH type II radio bursts are larger‐than‐average width and speed. Flares of all sizes (X‐ray importance B to X) occurring at all longitudes were associated with the DH type II bursts and CMEs. We found a global enhancement in EUV over an area much larger than the flaring active region in the beginning many events. A comparison between the ‘Shock Associated‧ events and microwave bursts shows that at least half of the events do not have temporal relation. A majority of the DH type II bursts were associated with IP shocks and kilometric type II bursts. In particular, we found a very close relationship between the kilometric type II bursts and the IP shocks.