Search

Magnetospheric sawtooth events (STE) are periodic oscillations in Earth’s magnetic field and energetic particle fluxes, typically occurring during geomagnetic storms. While previous studies have helped to provide information about the characteristics of STEs and the conditions that lead to the onset of these events, very little research has been done in the past 10 years documenting STEs, and analyzing the inner magnetosphere magnetic configuration during sawtooth events. This information can help understand how storms and substorms affect ionosphere-thermosphere convection, and how low-latitude ionospheric disturbances are generated during substorms. This project uses observations from magnetospheric missions and ground-based magnetometer networks to study the sawtooth event processes. Using magnetic field measurements GOES and the auroral electrojet indices, we are able to identify and catalog sawtooth events. We present our methods for identifying sawtooth events and preliminary statistics of the event characteristics. Then using magnetic field measurements from the THEMIS, RBSP, and MMS missions, we will study the evolution of the ring current and its latitudinal and longitudinal variations during STEs. We will also assess the abilities of the empirical Tsyganenko field models to reproduce the magnetospheric conditions during sawtooth events.

In the solar wind, a bifurcated current sheet is often observed in a reconnection outflow region as predicted by the original Petchek reconnection model, with the detailed exhaust structure becoming more complex when asymmetries between reconnecting plasmas are present. Here we present the first multi-spacecraft mission in-situ observations of a solar wind reconnection exhaust populated with filamentary (Hall) currents at an interplanetary coronal mass ejection (ICME) sheath—ejecta boundary. At the ICME sheath—ejecta boundary, asymmetric inflow conditions control reconnection, a relatively hot and dense plasma of the sheath coupling with the sparse low-beta ejecta plasma. These novel high-resolution observations demonstrate a multi- layered exhaust, and speak for the opportunities that future missions, such as HelioSwarm, and Parker Solar Probe and Solar Orbiter open for investigating magnetic reconnection in the solar wind.

Solar wind-magnetosphere coupling drives magnetospheric dynamic phenomena by enabling energy exchange between magnetospheric and solar wind plasmas. In this study, we examine two-dimensional noon-midnight meridional plane simulation runs of the global hybrid-Vlasov code Vlasiator with southward interplanetary magnetic field driving. We compute the energy flux, which consists of the Poynting flux and hydrodynamic energy flux components, through the Earth's magnetopause during flux transfer events (FTEs). The results demonstrate the spatiotemporal variations of the energy flux along the magnetopause during an FTE, associating the FTE leading (trailing) edge with an energy injection into (escape from) the magnetosphere on the dayside. Furthermore, FTEs traveling along the magnetopause transport energy to the nightside magnetosphere. We identify the tail lobes as a primary entry region for solar wind energy into the magnetosphere, consistent with results from global magnetohydrodynamic simulations and observations.

Sheath regions of interplanetary coronal mass ejections (ICMEs) are formed when the upstream solar wind is deflected and compressed due to the propagation and expansion of the ICME. Small-scale flux ropes found in the solar wind can thus be swept into ICME-driven sheath regions. They may also be generated locally within the sheaths through a range of processes. This work applies wavelet analysis to obtain the normalized reduced magnetic helicity, normalized cross helicity, and normalized residual energy, and uses them to identify small-scale flux ropes and Alfv\'en waves in 55 ICME-driven sheath regions observed by the Wind spacecraft in the near-Earth solar wind. Their occurrence is investigated separately for three different frequency ranges between $10^{-2} - 10^{-4}$ Hz. We find that small scale flux ropes are more common in ICME sheaths than in the upstream wind, implying that they are at least to some extent actively generated in the sheath and not just compressed from the upstream wind. Alfv\'en waves occur more evenly in the upstream wind and in the sheath. This study also reveals that while the highest frequency (smallest scale) flux ropes occur relatively evenly across the sheath, the lower frequency (largest scale) flux ropes peak near the ICME leading edge. This suggests that they could have different physical origins, and that processes near the ICME leading edge are important for generating the larger scale population., Comment: 15 pages, 4 figures, accepted for publication in Frontiers in Astronomy and Space Sciences 2022 August 15

In this work, we investigate magnetic field fluctuations in three coronal mass ejection (CME)-driven sheath regions at 1 AU, with their speeds ranging from slow to fast. The data set we use consists primarily of high-resolution (0.092 s) magnetic field measurements from the Wind spacecraft. We analyse magnetic field fluctuation amplitudes, compressibility, and spectral properties of fluctuations. We also analyse intermittency using various approaches; we apply the partial variance of increments (PVIs) method, investigate probability distribution functions of fluctuations, including their skewness and kurtosis, and perform a structure function analysis. Our analysis is conducted separately for three different subregions within the sheath and one in the solar wind ahead of it, each 1 h in duration. We find that, for all cases, the transition from the solar wind ahead to the sheath generates new fluctuations, and the intermittency and compressibility increase, while the region closest to the ejecta leading edge resembled the solar wind ahead. The spectral indices exhibit large variability in different parts of the sheath but are typically steeper than Kolmogorov's in the inertial range. The structure function analysis produced generally the best fit with the extended p model, suggesting that turbulence is not fully developed in CME sheaths near Earth's orbit. Both Kraichnan–Iroshinikov and Kolmogorov's forms yielded high intermittency but different spectral slopes, thus questioning how well these models can describe turbulence in sheaths. At the smallest timescales investigated, the spectral indices indicate shallower than expected slopes in the dissipation range (between −2 and −2.5), suggesting that, in CME-driven sheaths at 1 AU, the energy cascade from larger to smaller scales could still be ongoing through the ion scale. Many turbulent properties of sheaths (e.g. spectral indices and compressibility) resemble those of the slow wind rather than the fast. They are also partly similar to properties reported in the terrestrial magnetosheath, in particular regarding their intermittency, compressibility, and absence of Kolmogorov's type turbulence. Our study also reveals that turbulent properties can vary considerably within the sheath. This was particularly the case for the fast sheath behind the strong and quasi-parallel shock, including a small, coherent structure embedded close to its midpoint. Our results support the view of the complex formation of the sheath and different physical mechanisms playing a role in generating fluctuations in them.

Like the solar wind in general, interplanetary coronal mass ejections (ICMEs) display magnetic field and velocity fluctuations across a wide range of scales. These fluctuations may be interpreted as Alfvénic wave packets propagating parallel or anti-parallel to the local magnetic field direction, with cross helicity, σc, quantifying the difference in power between the counter-propagating fluxes. We have determined σc at inertial range frequencies in a large sample of ICME flux ropes and sheaths observed by the Wind spacecraft at 1 au. The mean σc value was low for both the flux ropes and sheaths, with the balance tipped towards the positive, anti-sunward direction. The low values indicate that Alfvénic fluxes are more balanced in ICMEs than in the solar wind at 1 au, where σc tends to be larger and anti-sunward fluctuations show a greater predominance. Superposed epoch profiles show σc falling sharply in the upstream sheath and being typically close to balance inside the flux rope near the leading edge. More imbalanced, solar wind-like σc values are found towards the trailing edge and further from the rope axis. The presence or absence of an upstream shock also has a significant effect on σc. Coronal and interplanetary origins of low σc in ICMEs are discussed.

The sheath regions driven by coronal mass ejections (CMEs) are large-scale heliospheric structures where magnetic field fluctuations are observed over various temporal scales. Their internal structure and nature of embedded fluctuations are currently poorly understood. We report here the key characteristics of magnetic field fluctuations in CME-driven sheaths, including their spectral index, intermittency, amplitude and compressibility. The results highlight the gradual formation of sheaths over several days as they propagate through interplanetary and the presence of intermittent coherent structures such as strong current sheets. The Jensen-Shannon permutation entropy and complexity analysis suggest that sheath fluctuations are stochastic, but have lower entropy and higher complexity than the preceding wind. We also show the analysis results during the slow sheath at ~0.5 AU detected by Parker Solar Probe, highlighting that slow CMEs can have prominent sheaths with distinct fluctuation properties.

Magnetic clouds are large-scale transient structures in the solar wind with low plasma β, low-amplitude magnetic field fluctuations, and twisted field lines with both ends often connected to the Sun. We analyse the normalised cross helicity, σc, and residual energy, σr, in magnetic clouds observed by Parker Solar Probe (PSP). In the November 2018 cloud observed at 0.25 au, a low value of σc was present in the cloud core, indicating that wave power parallel and anti-parallel to the mean field was approximately balanced, while the cloud’s outer layers displayed larger amplitude Alfvénic fluctuations with high σc values and σr ~ 0. These properties are compared and contrasted to those found in clouds observed by PSP at larger heliocentric distances. We suggest that low σc is likely a common feature of magnetic clouds given their typically closed field structure, in contrast to the generally higher σc found on the open field lines of the solar wind.

A continuous flow of charged particles emanating from the Sun is ubiquitous in the solar system. This solar wind carries the magnetic field of the star and constitutes a fluid that has an electromagnetic interplay with flow obstacles, such as planetary magnetic fields. The regular conditions in the solar wind flow are drastically disturbed by transients that originate from huge eruptions of plasma and magnetic flux in the Sun. In interplanetary space, these eruptions are known as interplanetary coronal mass ejections (ICMEs). An ICME propagating faster than the ambient solar wind ploughs the solar wind deflecting it aside. Consequently, a solar wind plasma region having distinctive characteristics is formed in front of the driving ICME. These sheath regions driven by ICMEs consist of shocked turbulent plasma that in our imagination is comparable to the flow in the immediate downstream of a waterfall or to the flow around an obstacle in rapids. The magnetic configuration of an ICME sheath is exposed to continuous modification and thus has a complicated fine structure, which varies with distance from the Sun. In this thesis, the fine structure and radial evolution of ICME sheaths are investigated particularly in terms of their magnetic field by performing in-situ studies that utilise spacecraft measurements taken at 1 AU and closer to the Sun. The research conducted in this thesis shows that although ICME sheaths are highly turbulent plasma environments, a structure appearing on larger scales is embedded in sheath magnetic fields. Furthermore, magnetic fluctuations on smaller scales do result from different physical processes, more precisely, from plasma being regulated by plasma instabilities such as mirror and Alfveń ion cyclotron instabilities. These smaller-scale fluctuations can be interpreted to manifest the gradual energy dissipation process that ensures an irreversible shock crossing of the solar wind plasma. They may, however, be so localised and their origins so temporary that the consequent magnetic fluctuations display strong spatial inhomogeneity and no coherency is observed in sheath magnetic fields at those scales. This spatial inhomogeneity gradually decreases towards larger scales. This thesis contributes to the understanding of ICME-driven sheath regions not only by reporting the observations that result in the conclusions stated above but also by discussing the relevant physical processes occurring in the sheath that significantly contribute to the sheath magnetic fields. The shock preceding the sheath modifies the solar wind plasma and interplanetary magnetic field and is concluded to have a major role in the occurrence of the smaller-scale fluctuations that result from plasma instabilities. Together with field line draping, in which magnetic field drapes around the driving ICME ejecta, the shock also regulates the global magnetic field configuration of ICME sheaths. Moreover, these processes continuously modify and regulate the sheath fields when an ICME travels through interplanetary space. This results in steady accumulation of magnetic fields in the sheath. This thesis also discusses what avenues of research may be particularly scientifically beneficial. To include ICME sheaths in models that forecast space weather, the consequences of the spatial inhomogeneity should be comprehensively resolved. Thus, there is a need for additional multi-spacecraft studies on the non-radial extent of different magnetic fluctuations embedded in the magnetic fields of ICME sheaths. In addition, the latest missions providing high-resolution data offer great opportunities to investigate sheath magnetic fields with an improved accuracy. These missions can be utilised in multi-spacecraft studies on the radial evolution of ICME sheaths. Moreover, this thesis makes a contribution that is generally beneficial to the community by developing algorithms that are suitable for further applications, in which magnetic field waves are investigated in different space plasma environments, and also by applying novel techniques and thus adapting them in the context of space plasmas. Sähköisesti varattujen hiukkasten jatkuva virta Auringosta, aurinkotuuli, kuljettaa tähtemme magneettikenttää mukanaan planeettainvälisessä avaruudessa ja on läsnä kaikkialla Aurinkokunnassa. Aurinkotuulen tavanomaisiin olosuhteisiin poikkeuksen muodostavat Auringon koronasta peräisin olevat voimakkaat purkaukset. Näiden koronan massapurkausten aikana Auringosta sinkoutuu valtavia kaasupilviä, jotka ajavat shokkiaaltoja edessään. Shokkiaallon ja massapurkauksen välistä aluetta, jossa aurinkotuulen plasma ohjautuu massapurkauksen ohitse, kutsutaan välivyöhykkeeksi. Välivyöhyke on turbulenttinen plasmaympäristö, jossa magneettikentän suunta ja voimakkuus voivat vaihdella äkillisesti ja voimakkaasti. Tässä väitöskirjassa tutkitaan koronan massapurkausten välivyöhykkeiden magneettikenttien hienorakennetta ja siinä tapahtuvia muutoksia planeettainvälisessä avaruudessa tarkastelemalla Maan etäisyydellä ja lähempänä Auringosta sijaitsevien avaruusluotainten suorittamia mittauksia. Väitöskirjan tutkimus osoittaa, että magneettikentän fluktuaatioita muodostuu välivyöhykkeissä erilaisista plasman epävakaisuuksien sääntelymekanismeista, joiden esiintymisessä shokkiaallon ominaisuuksilla on keskeinen rooli. Nämä fluktuaatiot ovat kuitenkin niin paikallisia ja niiden muodostuminen mahdollisesti niin väliaikaista, että ne eivät ilmennä spatiaalista yhtenäisyyttä välivyöhykkeiden turbulentissa plasmassa. Magneettikentän fluktuaatiot välivyöhykkeissä ovatkin kokonaisuudessaan varsin paikallisia suhteutettuna massapurkausten kokoon. Välivyöhykkeiden globaali magneettikenttä, joka kertyy asteittain massapurkauksen edetessä planeettainvälisessä avaruudessa, ilmentää kuitenkin järjestäytyneisyyttä. Shokkiaalto ja magneettikentän verhoutuminen massapurkauksen ympärille suuntaavat magneettikenttää välivyöhykkeissä ja ovat keskeisimpiä tekijöitä tämän yhtenäisen rakenteen muodostumiselle. Paikalliset magneettikentän fluktuaatiot välivyöhykkeissä voivat vaikuttaa merkittävästi siihen, miten välivyöhykkeet vuorovaikuttavat Maan magneettikentän kanssa. Välivyöhykkeiden spatiaalisiin epähomogeenisuuksiin kohdistuvat täydentävät tutkimukset, jotka tarkastelevat useiden luotainten mittauksia, ovatkin erityisen hyödyllisiä tämän väitöskirjan tutkimuksen rinnalla välivyöhykkeiden syvällisen ymmärtämisen saavuttamiseksi.

Magnetic clouds are large-scale transient structures in the solar wind with low plasma-beta, low-amplitude magnetic field fluctuations, and twisted field lines with both ends often connected to the Sun. Their inertial-range turbulent properties have not been examined in detail. In this Letter, we analyze the normalized cross helicity, sigma(c), and residual energy, sigma(r), of plasma fluctuations in the 2018 November magnetic cloud observed at 0.25.au by the Parker Solar Probe. A low value of |sigma(c)| was present in the cloud core, indicating that wave power parallel and antiparallel to the mean field was approximately balanced, while the cloud's outer layers displayed larger amplitude Alfvenic fluctuations with high |sigma(c)| values and sigma(r) similar to 0. These properties are discussed in terms of the cloud's solar connectivity and local interaction with the solar wind. We suggest that low |sigma(c)| is likely a common feature of magnetic clouds given their typically closed field structure. Antisunward fluctuations propagating immediately upstream of the cloud had strongly negative sigma(r) values.

We report on the longitudinal coherence of sheath regions driven by interplanetary coronal mass ejections (ICMEs). ICME sheaths are significant drivers of geomagnetic activity at the Earth, with a considerable fraction of ICME-driven storms being either entirely or primarily induced by the sheath. Similarly to Lugaz et al. (2018; doi:10.3847/2041-8213/aad9f4), we have analyzed two-point magnetic field measurements made by the ACE and Wind spacecraft in 29 ICME sheaths to estimate the coherence scale lengths, defined as the spatial scale at which correlation between measurements falls to zero, of the field magnitude and components. Scale lengths for the sheath are found to be mostly smaller than the corresponding values in the ICME driver, an expected result given that ICME sheaths are characterized by highly fluctuating, variable magnetic fields, in contrast to the often more coherent ejecta. A relatively large scale length for the magnetic field component in the GSE y-direction was found. We discuss how magnetic field line draping around the ejecta and the alignment of pre-existing magnetic structures by the preceding shock may explain the observed results. In addition, we consider the existence of longitudinally extended and possibly geoeffective magnetic field fluctuations within ICME sheaths, the full understanding of which requires further multi-spacecraft analysis.

Interactions between coronal mass ejections (CMEs) in interplanetary space are a highly important aspect for understanding their physical dynamics and evolution as well as their space weather consequences. Here we present an analysis of three CMEs that erupted from the Sun on June 12-14, 2012 using almost radially aligned spacecraft at Venus and Earth, complemented by heliospheric imaging and modelling with EUHFORIA. These multi-spacecraft observations were critical for interpreting the event correctly, in particular regarding the last two CMEs in the series (June 13 and June 14). At the orbit of Venus these CMEs were mostly separate with the June 14 CME just about to reach the previous CME. A significant interaction occurred before the CMEs reached the Earth. The shock of the June 14 CME had propagated through the June 13 CME and the two CMEs had coalesced into a single large flux rope structure before they reached the Earth. This merged flux rope had one of the largest magnetic field magnitudes observed in the near-Earth solar wind during Solar Cycle 24. We discuss also the general importance of multi-spacecraft observations and modelling using them in analyzing solar eruptions.

The sheaths of compressed solar wind that precede interplanetary coronal mass ejections (ICMEs) commonly display large-amplitude magnetic field fluctuations. As ICMEs propagate radially from the Sun, the properties of these fluctuations may evolve significantly. We present a case study of an ICME sheath observed by a pair of radially aligned spacecraft at around 0.5 and 1 AU from the Sun. Radial changes in fluctuation amplitude, compressibility, inertial-range spectral slope, permutation entropy, Jensen-Shannon complexity, and planar structuring are characterised. We discuss the extent to which the observed evolution in the fluctuations is similar to that of solar wind emanating from steady sources at quiet times, how the evolution may be influenced by evolving local factors such as leading-edge shock orientation, and how the perturbed heliospheric environment associated with ICME propagation may impact the evolution more generally.

The longitudinal spatial coherence near 1 AU of the magnetic field in sheath regions driven by interplanetary coronal mass ejection (ICME) is studied by investigating ACE and Wind spacecraft measurements of 29 sheaths. During 2000-2002 Wind performed prograde orbits, and the non-radial spacecraft separation varied from 0.001 to 0.012 AU between the studied events. We compare the measurements by computing the Pearson correlation coefficients for the magnetic field magnitude and components and estimate the magnetic field coherence by evaluating the scale lengths that give the extrapolated distance of zero correlation between the measurements. The correlation is also separately examined for low- and high-pass filtered data. We discover magnetic fields in ICME sheaths have scale lengths that are larger than those reported in the solar wind but that, in general, are smaller than the ones of the ICME ejecta. Our results imply that magnetic fields in the sheath are more coherently structured and well correlated compared to the solar wind. The largest sheath coherence is reported in the GSE y-direction that has the scale length of 0.149 AU while the lengths for B-x, B-z, and vertical bar B vertical bar vary between 0.024 and 0.035 AU. The same sheath magnitude ordering of scale lengths also apply for the low-pass filtered magnetic field data. We discuss field line draping and the alignment of preexisting discontinuities by the shock passage giving reasoning for the observed results.

The sheaths of compressed solar wind that precede interplanetary coronal mass ejections (ICMEs) commonly display large-amplitude magnetic field fluctuations. As ICMEs propagate radially from the Sun, the properties of these fluctuations may evolve significantly. We have analyzed magnetic field fluctuations in an ICME sheath observed by MESSENGER at 0.47 au and subsequently by STEREO-B at 1.08 au while the spacecraft were close to radial alignment. Radial changes in fluctuation amplitude, compressibility, inertial-range spectral slope, permutation entropy, Jensen-Shannon complexity, and planar structuring are characterized. These changes are discussed in relation to the evolving turbulent properties of the upstream solar wind, the shock bounding the front of the sheath changing from a quasi-parallel to quasi-perpendicular geometry, and the development of complex structures in the sheath plasma., Comment: 13 pages, 5 figures

We report a detailed analysis of interplanetary flux ropes observed at Venus and subsequently at Earth’s Lagrange L1 point between June 15 and 17, 2012. The observation points were separated by about 0.28 AU in radial distance and 5◦ in heliographic longitude at this time. The flux ropes were associated with three coronal mass ejections (CMEs) that erupted from the Sun on June 12–14, 2012 (SOL2012-06-12, SOL2012-06-13, and SOL2012-06-14). We examine the CME–CME interactions using in-situ observations from the almost radially aligned spacecraft at Venus and Earth, as well as using heliospheric modeling and imagery. The June 14 CME reached the June 13 CME near the orbit of Venus and significant interaction occurred before they both reached Earth. The shock driven by the June 14 CME propagated through the June 13 CME and the two CMEs coalesced, creating the signatures of one large, coherent flux rope at L1. We discuss the origin of the strong interplanetary magnetic fields related to this sequence of events, the complexity of interpreting solar wind observations in the case of multiple interacting CMEs, and the coherence of the Q14 flux ropes at different observation points. ispartof: Frontiers in Astronomy and Space Sciences vol:6 status: published

We report on a statistical analysis of the occurrence and properties of Alfven ion cyclotron (AIC) waves in sheath regions driven by interplanetary coronal mass ejections (ICMEs). We have developed an automated algorithm to identify AIC wave events from magnetic field data and apply it to investigate 91 ICME sheath regions recorded by the Wind spacecraft. Our analysis focuses on waves generated by the ion cyclotron instability. AIC waves are observed to be frequent structures in ICME-driven sheaths, and their occurrence is the highest in the vicinity of the shock. Together with previous studies, our results imply that the shock compression has a crucial role in generating wave activity in ICME sheaths. AIC waves tend to have their frequency below the ion cyclotron frequency, and, in general, occur in plasma that is stable with respect to the ion cyclotron instability and has lower ion beta(parallel to) than mirror modes. The results suggest that the ion beta anisotropy beta(perpendicular to)/beta(parallel to) > 1 appearing in ICME sheaths is regulated by both ion cyclotron and mirror instabilities.

International audience; We present a statistical study of interplanetary conditions and geospace response to 89 coronal mass ejection‐driven sheaths observed during Solar Cycles 23 and 24. We investigate in particular the dependencies on the driver properties and variations across the sheath. We find that the ejecta speed principally controls the sheath geoeffectiveness and shows the highest correlations with sheath parameters, in particular in the region closest to the shock. Sheaths of fast ejecta have on average high solar wind speeds, magnetic (B) field magnitudes, and fluctuations, and they generate efficiently strong out‐of‐ecliptic fields. Slow‐ejecta sheaths are considerably slower and have weaker fields and field fluctuations, and therefore they cause primarily moderate geospace activity. Sheaths of weak and strong B field ejecta have distinct properties, but differences in their geoeffectiveness are less drastic. Sheaths of fast and strong ejecta push the subsolar magnetopause significantly earthward, often even beyond geostationary orbit. Slow‐ejecta sheaths also compress the magnetopause significantly due to their large densities that are likely a result of their relatively long propagation times and source near the streamer belt. We find the regions near the shock and ejecta leading edge to be the most geoeffective parts of the sheath. These regions are also associated with the largest B field magnitudes, out‐of‐ecliptic fields, and field fluctuations as well as largest speeds and densities. The variations, however, depend on driver properties. Forecasting sheath properties is challenging due to their variable nature, but the dependence on ejecta properties determined in this work could help to estimate sheath geoeffectiveness through remote‐sensing coronal mass ejection observations

We study how the the Earth's magnetosphere responds to the fluctuating solar wind conditions caused by two different amplitude interplanetary coronal mass ejection (ICME) events by using the Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4). ICME events are known to drive strong geomagnetic disturbances and thus generate conditions that may lead to saturation of the cross-polar cap potential (CPCP). The two ICME events occurred on 15–16 July 2012 and 29–30 April 2014. During the 2012 event, the solar wind upstream values reached up to 35 particles/cm3, speed of 694 km/s, and interplanetary magnetic field of 22 nT. The event of 2014 was a moderate one, with the corresponding upstream values of 30 particles/cm3, 320 km/s and 10 nT. The mean upstream Alfvén Mach number was 2.3 for the 2012 event, while it was 5.8 for the 2014 event. We examine how the Earth's space environment dynamics evolves during both ICME events covering both global and local perspectives. To validate the accuracy of the GUMICS-4 simulation we use satellite data from several missions located in different parts of the magnetosphere. It is shown that the CPCP saturation is affected by the upstream conditions, with strong dependence on the Alfvén Mach number.

We present a comprehensive statistical analysis of mirror mode waves and the properties of their plasma surroundings in sheath regions driven by interplanetary coronal mass ejection (ICME). We have constructed a semi-automated method to identify mirror modes from the magnetic field data. We analyze 91 ICME sheath regions from January 1997 to April 2015 using data from the Wind spacecraft. The results imply that similarly to planetary magnetosheaths, mirror modes are also common structures in ICME sheaths. However, they occur almost exclusively as dip-like structures and in mirror stable plasma. We observe mirror modes throughout the sheath, from the bow shock to the ICME leading edge, but their amplitudes are largest closest to the shock. We also find that the shock strength (measured by Alfvén Mach number) is the most important parameter in controlling the occurrence of mirror modes. Our findings suggest that in ICME sheaths the dominant source of free energy for mirror mode generation is the shock compression. We also suggest that mirror modes that are found deeper in the sheath are remnants from earlier times of the sheath evolution, generated also in the vicinity of the shock. Keywords. Interplanetary physics (plasma waves and turbulence; solar wind plasma) – space plasma physics (waves and instabilities)