Interplanetary Coronal Mass Ejection Events Research Articles

Discrete Aurora on the Nightside of Mars: Occurrence Location and Probability

AbstractThis paper represents the first attempt to predict the occurrence location and probability of discrete electron aurora on the nightside of Mars. We run a 3‐D time‐dependent magnetohydrodynamic model to characterize the spatial and temporal dynamics of magnetic field and plasma distributions over the course of one planetary rotation. We perform eight simulation cases under solar minimum quiet‐solar‐wind conditions (four equinox/solstice seasons, each with two interplanetary magnetic field polarities) and in an actual interplanetary coronal mass ejection (ICME) case to assess quiet and space weather situations, respectively. The occurrence of detectable discrete aurora is subject to the combination of the probabilities that (a) the ionosphere is magnetically connected with high altitudes through open field lines and (b) precipitating energy fluxes of >30 eV electrons exceed 0.1 erg/cm2/s. Our results show that during quiet solar activity, discrete aurora occurs likely on small‐scale patches embedded inside strong crustal magnetic field regions (with a magnitude greater than 50 nT at 150 km), and the overall chance across the globe is ∼0.77%. The higher probability over strong crustal field regions is attributed to the stronger magnetic field convergence. Modeling shows the occurrence probability dramatically increases during the ICME event, particularly by more than an order of magnitude in weak crustal field regions. Our model results reasonably agree with NASA Mars Atmosphere and Volatile EvolutioN and Mars Express observations. Our study suggests that nightside discrete electron aurora is not caused by the direct entry of magnetosheath plasma in a cusp‐like process but due to the recycling of nightside magnetospheric electrons.

Empirical modelling of auroral absorption during disturbed periods of interplanetary coronal mass ejection events

Energetic charged particle precipitation associated with solar wind perturbations causes enhanced high-frequency radiowave absorption in the high-latitude ionosphere. This study models 38.2 MHz cosmic noise absorption (CNA) by utilising measurements from the Imaging Riometer for Ionospheric Studies (IRIS) at Kilpisjärvi, Finland obtained during solar cycle 23 (1996–2009) associated with the passage of interplanetary coronal mass ejections (ICMEs) past Earth; ICMEs are a major driver of enhanced geomagnetic activity. Superposed epoch analysis suggests that the r6absorption vs. time profile depends on whether ICME arrival occurs in the day-time (10–14 MLT) or night-time (22-02 MLT) for IRIS, with peak absorption occurring ~2–3 h ahead of ICME arrival or ~4 h after ICME arrival, respectively. We determine which combinations of solar wind and IMF parameters show the best correlation with the absorption associated with day-time or night-time arriving ICMEs using superposed epoch analysis and the least squares estimation method. Various combinations of solar wind parameters (including bulk velocity v, density n, and the interplanetary magnetic field north and south components Bz and the SYMH geomagnetic index), have been ranked to obtain the best coupling function for the absorption associated with day- and night-time arriving ICMEs. The absorption for day-time events is found to correlate closely with the solar wind dynamic pressure, SYMH, and the northward direction of the Bz while the absorption for night-time events is most closely related to the direction of the Bz and SYMH. The coupling functions are found to model the observed absorption successfully, with correlation coefficients of ~0.7–0.8 between the observed and modelled absorption.

Effects of Energetic Electron and Proton Precipitations on Thermospheric Nitric Oxide Cooling During Shock‐Led Interplanetary Coronal Mass Ejections

AbstractSatellite measurements have revealed significant enhancement of 5.3‐μm nitric oxide (NO) emission during shock‐led interplanetary coronal mass ejections. Great discrepancies in modeled neutral density occur during these events and may be attributed to the abnormally high NO cooling. Meanwhile, the relative significance of protons, soft electrons, and keV‐electrons to NO emission is yet to be well determined. The goal of this study is to identify the contribution of electron and proton precipitations to the thermospheric NO cooling by using the Defense Meteorological Satellite Program (DMSP) data. The observed energetic electrons and protons (0.1–30.2 keV) during 36 shock‐led interplanetary coronal mass ejection events in 2002–2010 are binned into geomagnetic grids to provide statistical distributions of the particle precipitation for polar regions. The distributions are incorporated into the Global Ionosphere‐Thermosphere Model. The results show that electrons play a dominant role to NO cooling, but protons are also important and contribute to up to a quarter of NO cooling by electrons and ions combined. NO cooling enhancement during the events is proportional to the level of energy flux and is dominated by the electrons in the energy band of 1.4–3.1 keV. Both total electron content (TEC) and NO cooling enhance at the source regions, but they have different lifetime and correlation with the particle precipitations. Generally, NO cooling and TEC enhancements have a positive correlation with the precipitating energy. Cross correlation shows that particle precipitations have more instantaneous impact on TEC while it takes longer for the atmosphere to heat up for cooling to proceed.

Magnetic Topology Response to the 2003 Halloween ICME Event at Mars

AbstractUnderstanding how the Mars plasma environment responds to space weather events provides insights into the early Sun‐Mars interaction and helps constrain the extrapolation of atmospheric loss back in time. The 2003 Halloween interplanetary coronal mass ejection (ICME) event is one of the most extreme space weather events encountered by Mars during the last two decades. Mars Global Surveyor's circular orbit at ∼400 km allows us to observationally study the magnetic topology response to this extreme event globally for the first time. We analyze the suprathermal electron data and magnetic field measurements from Mars Global Surveyor to infer magnetic topology before, during, and after this ICME event and quantify the variation of the topology over both weak and strong crustal regions and correlate the variation with the upstream dynamic pressure. Over weak crustal regions, more draped field lines and fewer closed field lines are observed under high dynamic pressures, implying a deeper interplanetary magnetic field penetration during the ICME event. Over dayside strong crustal regions, the dominant magnetic topology switches from closed field lines during quiet periods to open field lines during disturbed periods, suggesting more reconnection occurring between the crustal magnetic fields and interplanetary magnetic field. This mixed magnetic topological response is consistent with predictions from magnetohydrodynamic simulations for ICME events in previous studies.

Magnetic Lasso: A New Kinematic Solar Wind Propagation Method

Solar wind propagation from the point of measurement to an arbitrary target in the heliosphere is an important input for heliospheric, planetary and cometary studies. In this paper a new kinematic propagation method, the magnetic lasso method is presented. Compared to the simple ballistic approach our method is based on reconstructing the ideal Parker spiral connecting the target with the Sun by testing a previously defined range of heliographic longitudes. The model takes into account the eventual evolution of stream–stream interactions and handles these with a simple model based on the dynamic pressure difference between the two streams. Special emphasis is given to input data cleaning by handling interplanetary coronal mass ejection events as data gaps due to their different propagation characteristics. The solar wind bulk velocity is considered radial and constant. Density and radial magnetic field are propagated by correcting with the inverse square of the radial distance. The model has the advantage that it can be coded easily and fitted to the problem; it is flexible in selecting and handling input data and requires little running time.

The Impact and Solar Wind Proxy of the 2017 September ICME Event at Mars

AbstractWe study a large interplanetary coronal mass ejection event impacting Mars in mid‐September 2017 numerically. During this time period, MAVEN remained inside the Martian bow shock and therefore could not measure the solar wind directly. We first simulate the event using three steady state cases with estimated solar wind conditions and find that these cases were able to reproduce the general features observed by MAVEN. However, these time‐stationary runs cannot capture the response of the system to large variations in the solar wind associated with the event. To address this problem, we derive a solar wind proxy based on MAVEN observations in the sheath region and their comparison with steady state magnetohydrodynamic model results. The derived solar wind proxy is then used to drive a time‐dependent magnetohydrodynamic model, and we find that the data‐model comparison is greatly improved, especially in the magnetosheath. We are able to reproduce some detailed structures observed by MAVEN during the period, despite the lack of a direct measurement of the solar wind, indicating that the derived solar wind conditions are reliable. Finally, we examine in detail the impact of the event on the Martian system: including variations of the three typical plasma boundaries and the ion loss rates. Our results show that these plasma boundary locations varied drastically during the event, and the total ion loss rate was enhanced by more than an order of magnitude.

MAVEN Observations of the Response of Martian Ionosphere to the Interplanetary Coronal Mass Ejections of March 2015

AbstractThe Mars Atmosphere and Volatile EvolutioN spacecraft provides an opportunity to observe the response of the Martian upper atmosphere to the passage of interplanetary coronal mass ejections. We study the response of Martian ionosphere to two successive solar disturbances during 3 and 4 March and 8 and 9 March 2015 using the observations from Neutral Gas and Ion Mass Spectrometer and Langmuir Probe and Waves aboard Mars Atmosphere and Volatile EvolutioN. During these events, the ionospheric boundary was significantly lowered. During 3 March the ionopause is seen to be at a lower altitude, compared to that during 8 March. The higher ionopause seen on 8 March could be due to the sustained effect of heating and inflation by the 3 March interplanetary coronal mass ejection event or due to the heating by the enhanced particle precipitation. The comparison of the O+/O ratio indicates that there is a preferential decrease of O and a relative enhancement in O+, probably due to increased dissociative recombination and charge exchange as a result of the higher solar wind densities during the 3 March event.

Correlation between auroral activity and rate of development of a storm in its main phase

We investigated the relationship between the rate of storm development in its main phase (|ΔDst|/ΔT) and the average value (ΣAE/ΔT) of AE index for the main phase where |ΔDst| is the Dst-index variation, ΣAE is the total value of AE index for the main phase of magnetic storm, ΔT is the main phase duration. We considered storms initiated by corotating interaction region (CIR) and interplanetary coronal mass ejection (ICME) (magnetic cloud and ejecta). For CIR events, the value of ΣAE/ΔT is shown to correlate with the rate of storm development in its main phase in contrast to the storms initiated by the ICME. As found, there is a weak correlation between ΣAE/ΔT and the minimum value of Dst index for CIR and ICME events.

Variations of the Martian plasma environment during the ICME passage on 8 March 2015: A time‐dependent MHD study

AbstractThe Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft observed a strong interplanetary coronal mass ejection (ICME) impacting Mars on 8 March 2015. We use a time‐dependent global MHD model to investigate the response of the Martian ionosphere and induced magnetosphere to the large solar wind disturbance associated with the ICME. Taking observed upstream solar wind conditions from MAVEN as inputs to the MHD model, the variations of the Martian plasma environments are simulated realistically in a time period from 2.5 h prior to the arrival of the ICME shock to about 12 h after the impact. Detailed comparisons between the model results and the relevant MAVEN plasma measurements are presented, which clearly show that the time‐dependent multispecies single‐fluid MHD model is able to reproduce the main features observed by the spacecraft during the ICME passage. Model results suggest that the induced magnetosphere responds to solar wind variation on a very short time scale (approximately minutes). The variations of the plasma boundaries' distances from the planet along the subsolar line are examined in detail, which show a clear anticorrelation with the magnetosonic Mach number. Plasma properties in the ionosphere (especially the induced magnetic field) varied rapidly with solar wind changes. Model results also show that ion escape rates could be enhanced by an order of magnitude in response to the high solar wind dynamic pressure during the ICME event.

MAVEN observations of a giant ionospheric flux rope near Mars resulting from interaction between the crustal and interplanetary draped magnetic fields

AbstractWe present Mars Atmosphere and Volatile EvolutioN (MAVEN) observations of a giant magnetic flux rope in the Martian dayside ionosphere. The flux rope was observed at an altitude of <300 km, downstream from strong subsolar crustal magnetic fields. The peak field amplitude was ∼200 nT, resulting in the largest difference between the observed magnetic field strength and a model for crustal magnetic fields of the entire MAVEN primary science phase. MAVEN detected planetary ions, including H+, O+, and , across the structure. The axial orientation estimated for the flux rope indicates that it likely formed as a result of interactions between the local crustal and overlaid draped interplanetary magnetic fields. Pitch angle distributions of ionospheric photoelectrons imply that this structure is connected to the Martian upper atmosphere. However, the flux rope is not present in observations at the next commensurable orbit crossing (approximately two Martian days later), implying that it eventually detaches from the atmosphere and is carried downstream. The flux rope observations occurred during an interplanetary coronal mass ejection event at Mars, suggesting that the disturbed upstream state played a role in allowing the interplanetary magnetic field to penetrate deeper into the Martian ionosphere than is typical, allowing the formation of the flux rope.

Корреляция скорости развития магнитной бури на главной фазе и авроральной активности

We investigated the relationship between the rate of storm development in its main phase (|ΔDst|/ΔT) and the average value (ΣAE/ΔT) of AE index for the main phase where |ΔDst| is a Dst-index variation, ΣAE is the total value of AE index for the main phase of magnetic storm, ΔT is the main phase duration. We considered storms initiated by corotating interaction region (CIR) and interplanetary coronal mass ejection (ICME) (magnetic cloud and ejecta). For CIR events, the value of ΣAE/ΔT is shown to correlate with the rate of storm development in its main phase, in contrast to the storms initiated by the ICME. As found, there is a weak correlation between ΣAE/ΔT and the minimum value of Dst index for CIR and ICME events.

Comparison of algorithms for determination of solar wind regimes

AbstractThis study compares the designation of different solar wind flow regimes (transient, coronal hole, and streamer belt) according to two algorithms derived from observations by the Solar Wind Ion Composition Spectrometer, the Solar Wind Electron Proton Alpha Monitor, and the Magnetometer on the ACE spacecraft, with a similar regime determination performed on board the Genesis spacecraft. The comparison is made for the interval from late 2001 to early 2004 when Genesis was collecting solar wind ions for return to Earth. The agreement between hourly regime assignments from any pair of algorithms was less than two thirds, while the simultaneous agreement between all three algorithms was only 49%. When the results of the algorithms were compared to a catalog of interplanetary coronal mass ejection events, it was found that almost all the events in the catalog were confirmed by the spacecraft algorithms. On the other hand, many short transient events, lasting 1 to 13 h, that were unanimously selected as transient like by the algorithms, were not included in the catalog.

Effect of Electron Pressure on the Grad–Shafranov Reconstruction of Interplanetary Coronal Mass Ejections

We investigate the effect of electron pressure on the Grad–Shafranov (GS) reconstruction of Interplanetary Coronal Mass Ejection (ICME) structures. The GS method uses in situ magnetic field and plasma measurements to solve for a magnetohydrostatic quasi-equilibrium state of space plasmas. For some events, a magnetic flux-rope structure embedded within the ICME can be reconstructed. The electron temperature contributes directly to the calculation of the total plasma pressure, and in ICMEs its contribution often substantially exceeds that of proton temperature. We selected ICME events observed with the Wind spacecraft at 1 AU and applied the GS reconstruction method to each event for cases with and without electron temperature measurements. We sorted them according to the proton plasma β (the ratio of proton plasma pressure to magnetic pressure) and the electron-to-proton temperature ratio. We present case studies of three representative events, show the cross sections of GS reconstructed flux-rope structure, and discuss the electron pressure contribution to key quantities in the numerical reconstruction procedure. We summarize and compare the geometrical and physical parameters derived from the GS reconstruction results for cases with and without electron temperature contribution. We conclude that overall the electron pressure effect on the GS reconstruction results contributes to a 10 – 20 % discrepancy in some key physical quantities, such as the magnetic flux content of the ICME flux rope observed at 1 AU.

Magnetohydrodynamic waves in interplanetary coronal mass ejections near 1AU observed by WIND spacecraft

Previous observations of interplanetary coronal mass ejections (ICMEs) show that only from 0.3 to 0.68AU did Alfven wave exist in the ICMEs, and rarely discovered at 1AU in ICMEs. Here we present a preliminary statistical result on the existence of magnetohydrodynamic (MHD) waves in ICMEs near 1AU. Based on all of 27 single ICME events which led to major magnetic storms during 1996-2005, several types of MHD waves in ICMEs are identified with the dispersion relations by SVD method: (1) in about 1/3 ICMEs near 1AU, 8 out of 27 events, some Alfven waves exist continuously ; (2) in 13 cases there are fast waves exist in the sheath of the ICMEs; (3) slow waves exist in all events. These observations may show some new clues to the basic wave property and dynamics of ICME.

Multipoint observations of coronal mass ejection and solar energetic particle events on Mars and Earth during November 2001

Multipoint spacecraft observations provide unique opportunities to constrain the propagation and evolution of interplanetary coronal mass ejections (ICMEs) throughout the heliosphere. Using Mars Global Surveyor (MGS) data to study both ICME and solar energetic particle (SEP) events at Mars and OMNI and Geostationary Operational Environmental Satellite (GOES) data to study ICMEs and SEPs at Earth, we present a detailed study of three CMEs and flares in late November 2001. In this period, Mars trailed Earth by 56deg solar longitude so that the two planets occupied interplanetary magnetic field lines separated by only approx.25deg. We model the interplanetary propagation of CME events using the ENLIL version 2.6 3-D MHD code coupled with the Wang-Sheeley-Arge version 1.6 potential source surface model, using Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph (LASCO) images to determine CME input parameters. We find that multipoint observations are essential to constrain the simulations of ICME propagation, as two very different ICMEs may look very similar in only one observational location. The direction and width of the CME as parameters essential to a correct estimation of arrival time and amplitude of the ICME signal. We find that these are problematic to extract from the analysis of SOHO/LASCO images commonly used for input to ICME propagation models. We further confirm that MGS magnetometer and electron reflectometer data can be used to study not only ICME events but also SEP events at Mars, with good results providing a consistent picture of the events when combined with near-Earth data.

Interplanetary coronal mass ejection influence on high energy pick-up ions at Venus

We have used the ion mass analyzer (IMA) and magnetometer (MAG) on Venus Express (VEX) to study escaping O + during interplanetary coronal mass ejections (ICMEs). Data from 389 VEX orbits during 2006 and 2007 revealed 265 samples of high energy pick-up ion features in 197 separate orbits. Magnetometer data during the same time period showed 17 ICMEs. The interplanetary conditions associated with the ICMEs clearly accelerate the pick-up ions to higher energies at lower altitudes compared to undisturbed solar wind. However, there is no clear dependence of the pick-up ion flux on ICMEs which may be attributed to the fact that this study used data from a period of low solar activity, when ICMEs are slow and weak relative to solar maximum. Alternatively, atmospheric escape rates may not be significantly changed during ICME events.

Venus Express observations of an atypically distant bow shock during the passage of an interplanetary coronal mass ejection

On 10–11 September 2006 the Venus Express magnetometer detected a very strong Interplanetary Coronal Mass Ejection (ICME) event with an average field about 2 times higher than that of a typical ICME at 0.72 AU. While the effective obstacle to the solar wind is compressed to a smaller dimension during this ICME event, the bow shock is located far upstream of its nominal location. The observed shocks are weak and appear very dynamic. The location of the shock crossing can be found all along the Venus Express trajectory, which has an apocenter of 12 RV. We attribute the atypical distant bow shock location as an effect of the extremely low Mach number during the ICME.

Venus Express observations of atmospheric oxygen escape during the passage of several coronal mass ejections

The solar wind interaction contributes to the loss of Venus atmospheric constituents, especially oxygen, by direct antisunward acceleration of planetary ions and possibly by related sputtering of neutrals. Both comet‐like “ion pickup” and related sputtering processes may have played a key role in Venus' atmosphere evolution, but the significance of their effects, as well as other proposed escape mechanisms, is still uncertain. In particular, recent reports of only modest ion escape rates measured on Venus Express (VEX) during the current low‐activity phase of the solar cycle make it important to reconsider the evidence seen in both Pioneer Venus Orbiter and VEX observations suggesting significantly enhanced escaping O+ ion fluxes during periods of disturbed interplanetary conditions. At present, the most extreme interplanetary conditions result from the effects of coronal mass ejections (CME), which may have been more prevalent in the first 1–2 billion years of the Sun's history. The Analyser of Space Plasmas and Energetic Atoms 4 (ASPERA‐4) Ion Mass Analyzer and Magnetometer on Venus Express have now made detailed measurements during several periods when CME disturbances encountered Venus. The observations and models described in this report provide further insights into the possible response of oxygen ion escape to solar activity. In particular, they illustrate nuances of in situ sampling of large‐gyroradius pickup ions, related to the atmospheric source properties, spacecraft orbit geometry, and the prevailing interplanetary conditions, that make the estimation of the variable global escape fluxes due to that process particularly challenging. In three of the four cases examined in some detail, ionospheric oxygen ions were either unobservable or below the limit of detectability for passes well within interplanetary coronal mass ejection (ICME) intervals. In the fourth example, where ionospheric ions were observed as expected from the model, O+ pickup ions were observed in greater abundance than is typical in undisturbed solar wind. Other escape processes are not considered here, although it is assumed the source population for the modeled pickup ions is a preaccelerated upper atmosphere component. Analysis of many more ICME events, expected to be obtained as the Sun becomes more active in future years, are necessary to resolve the question of the importance of ICME to Venus oxygen escape.

High‐Speed Solar Wind Streams: A Call for Key Research

The arrival of high‐speed solar wind streams (HSSs) at the Earth's magnetopause drives particle and wave phenomena that are distinct from the phenomena caused by other solar wind structures. Although HSS events do not generally produce a particularly strong ring current (the current caused by ions and electrons drifting around the Earth), they do produce storm levels of other magnetospheric phenomena (enhanced convection, heating, precipitation, relativistic electron energization, and so forth) that can persist for an extended time period (e.g., many days). These events contrast with interplanetary coronal mass ejection (ICME) events, where more transient driving (e.g., 1 day) is the norm. As such, the energy input to the magnetosphere during HSS events is comparable to, or may exceed, the energy input to the magnetosphere during ICME events.

October/November 2003 interplanetary coronal mass ejections: ACE/EPAM solar energetic particle observations

In late October and early November 2003 the ACE spacecraft at 1 AU detected two shock‐associated interplanetary coronal mass ejections (ICMEs). In the sheath region formed in front of both ICMEs, some of the highest speeds ever directly measured in the solar wind were observed. We analyze in detail the energetic particle signatures measured at 1 AU by the EPAM experiment on board ACE during the passage and in the vicinity of these ICMEs. Solar energetic particles (SEPs) are utilized as diagnostic tracers of the large‐scale structure and topology of the interplanetary magnetic field (IMF) embedded within both ICME events. In order to explain the bidirectional particle flows observed within both ICMEs, we have examined two candidate scenarios for these ICMEs in terms of open and closed magnetic field configurations. In the context of an open field configuration, the enhanced magnetic field regions associated with the CME‐driven shocks mirror the energetic particles and hence the observed bidirectional flows. In the context of a closed field configuration, bidirectional flows result from particle circulation and reflection in a looped field configuration. Furthermore, we use the ACE/EPAM observations to reassess the leading and trailing boundaries of the ICMEs with respect to those previously proposed based upon ACE/SWEPAM solar wind plasma, suprathermal electron measurements, and ACE/MAG magnetic field data.