Variations of Heavy Ions in Interplanetary Shock Driven by Interplanetary Coronal Mass Ejections and Stream Interaction Regions

In the solar wind, the fluctuation of heavy ion abundance serves as a crucial physical metric. This not only mirrors the attributes of the solar wind’s originating solar region but also signifies its influence on Earth’s magnetosphere. Utilizing data from the Advanced Composition Explorer satellite, this investigation scrutinizes heavy ion variations in stream interaction region (SIR)- and interplanetary coronal mass ejection (ICME)-driven shocks. We further delineate the disparities in heavy ion fluctuations between these two types of interplanetary shocks across diverse solar activity cycles. Our findings reveal that ICME-driven shocks typically manifest elevated shock velocities and magnetic field strengths relative to their SIR-driven counterparts. Additionally, heavy ion abundance ratios, such as C6+/O4+, O7+/O6+, He/O, Si/O, and Fe/O, are consistently higher in ICME-driven shocks than in SIR-driven shocks. During varying solar activity cycles, these ratios surge postarrival of ICME-driven shocks. At solar maximum, these elevated ratios persist, whereas they revert to baseline levels swiftly during solar minimum. For SIR-driven shocks, the alteration in heavy ion abundance ratios is comparatively subdued, yet a noteworthy correlation with the solar activity cycle is evident.


Introduction
The upstream and downstream of interplanetary (IP) shock have obvious rapid changes in speed, IP magnetic field strength, and solar wind density (Jurac et al. 2002), which is formed by the mutual extrusion of the IP matter ejected by the Sun when it propagates outward (Oh et al. 2007).There are two primary mechanisms that drive IP shocks: one is the stream interaction regions (SIR) formed by the interaction of solar winds with different velocities, and the other results from sudden solar eruptive activities, such as coronal mass ejections (CMEs; Jurac et al. 2002;Echer et al. 2003;Blanco-Cano et al. 2016;Zong et al. 2021).
Given that the two shock-driving mechanisms correspond to distinct solar activities, the solar wind composition within these shocks also varies.Ion abundance, a key parameter characterizing solar wind, displays distinct features in shocks compared to the background solar wind.In both SIR and CME-driven shocks, the abundance of He + and 3 He is often observed to exceed typical solar wind values.Furthermore, the abundance of He in IP CMEs (ICMEs) can provide information about the material source of plasma in ICMEs on the Sun.In shocks driven by different sources, heavy ions with a lower charge-tomass ratio are more susceptible to acceleration (Möbius et al. 2002;Allegrini et al. 2008).Owens (2018) analyzed the ion abundance and charge states of the solar wind during different speeds and types of ICME events, highlighting that the abundance of He and the charge state of Fe correlate with ICME speed rather than structure.Furthermore, compared to surrounding solar wind, ICMEs generally exhibit enhanced heavy ion abundance, with magnetic cloud ICMEs showing higher values than nonmagnetic cloud ICMEs.Allen et al. (2019) analyzed heavy ion abundance in solar wind during SIRs in solar cycles 23 and 24, finding a strong correlation between the Fe/O ratio and sunspot numbers.In contrast, the relative abundance of other heavy ions remained consistent across both solar cycles.In a separate study, Zeldovich et al. (2021) investigated the relative abundance of heavy ions such as C, O, and Fe in high-speed streamers from equatorial coronal holes during the solar minimum of cycles 23 and 24.They observed a correlation between the Fe/O ratio and solar wind speed during the minimum period, but no such trend was found for C/O.
Variations in the abundance of heavy ions in the solar wind can provide insights into the source region and activity characteristics of the solar wind.Zhao et al. (2009) classified solar wind into coronal hole wind, noncoronal hole wind, and ICMEs based on the O 7+ /O 6+ ratio.Subsequent analyses of heavy ion characteristics in different solar wind sources revealed that the O 7+ /O 6+ ratio is crucial for distinguishing the solar wind's coronal source (Zhao et al. 2017).von Steiger & Zurbuchen (2015) categorized solar wind into polar coronal holes, coronal holes, and streamer-associated wind based on heavy ion abundance and charge states, deriving the Sun's metallicity in the process.The heavy ions in the solar wind not only reflect the characteristics of their solar surface source Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.region but also demonstrate the impact of shock waves on heavy ions.Various factors such as the magnetic field strength, Mach number, and shape of the shock wave (quasi-parallel or quasi-perpendicular) have a positive influence on ion heating (Korreck et al. 2007).Blanco-Cano et al. (2016) compared ICME-driven shock waves and SIR-driven shock waves in terms of ion acceleration, concluding that ICME-driven shock waves exhibit a larger proton foreshock.Dresing et al. (2016) conducted research on 475 shock waves and found that shock waves have minimal acceleration effect on electrons, but significantly affect low-energy particles.Furthermore, ICMEdriven shock events account for two-thirds of all acceleration events (Dresing et al. 2016).Lario et al. (2019) explored the ion acceleration process in shock waves.
IP shocks can influence Earth's geomagnetic activity, leading to global electromagnetic field variations (Yue & Zong 2011;Zong et al. 2021).Statistical analyses indicate that 57% of IP shocks result in geomagnetic storms (Echer & Gonzalez 2004).Moreover, shocks amplify the impact of southward IP magnetic fields on the Earth's magnetosphere, intensifying geomagnetic storms (Yue & Zong 2011).When disturbances occur in the Earth's magnetosphere, such as geomagnetic storms, heavy ions from the solar wind can penetrate the magnetosphere, affecting Earth's space environment (Kronberg et al. 2014;Allen et al. 2016).When the abundance of heavy ions in the magnetosphere changes, it will not only affect the propagation of Alfvén waves (Moya et al. 2022), but also as high-energy particles are injected from the plasma layer into the magnetosphere, heavy ions play a key role in the generation of ring currents and radiation belts (Wang et al. 2019).It has been suggested that when the abundance of oxygen ions is relatively high, it will lead to a significant thickening of the current sheet, and it has also been verified in other magnetospheres of Earthlike planets in the solar system (Domrin et al. 2020).
The variation in heavy ion abundance in the solar wind, especially within IP shocks, holds significant implications for studying solar surface activity and magnetospheric structures.Due to the ion charge, the state could be frozen-in beyond several solar radii, so the charge state of heavy ions in the solar wind, such as Fe + and O 7+ /O 6+ , could mirror the temperature of the coronal source region (Lepri et al. 2001;Fu et al. 2020).Moreover, the abundance of ions in the plasma plays a crucial role in the interaction between the plasma particles and Alfvén waves.For instance, the propagation of Alfvén waves depends to a large extent on the relative abundance of He + and O + (Moya et al. 2022).Besides, charge exchange collisions of solar wind heavy ions with geocoronal hydrogen atoms can generate extreme-ultraviolet and soft-X-ray emissions in the magnetosheath and cusp region, which can be effectively used to image the global structure of the bow shock and magnetopause (He et al. 2015;Sun et al. 2015).Knowledge of the abundance of solar wind heavy ions could greatly benefit magnetosphere imaging research.However, research on the changing characteristics of heavy ions during different types of IP shock processes remains limited, as we propose to address in the present study.In this paper, we focus on the variations in the abundance of ions such as He, C, O, Ne, Mg, Si, and Fe in both ICME-driven and SIR-driven shocks, further analyzing their changing patterns across different solar activity cycles.

Data Selection
We selected shock events observed by the Advanced Composition Explorer (ACE) satellite from the IP shock database,6 spanning the period from 1998 to 2011.Using the ICME list by Richardson & Cane (2010) and the SIR list by Chi et al. (2018) as references, we identified 97 CME-driven events and 95 SIR-driven events, resulting in a total of 192 shock events for our analysis.The heavy ion composition and abundance ratios in the solar wind were derived from observations made by the Solar Wind Ion Composition Spectrometer (SWICS) instrument on ACE (Gloeckler et al. 1998).We use the 2 hr "merged" data set,7 which is available from 1998 to 2011.SWICS employs the triple coincidence technique, differentiating various ions in the solar wind based on their mass (m), charge (q), and energy (E) parameters (Gloeckler et al. 1998;Shearer et al. 2014).The systematic errors in the measurement results of this instrument are extensively discussed in von Steiger & Zurbuchen (2011), with the recognition that detector efficiency errors constitute the primary source of error.It is important to note that most data products measured by SWICS do not require crosscalibration with other instruments, except for data products containing H and He.The He 2+ density and He/O density ratio products utilized in this paper have undergone cross-calibration with Wind/Solar Wind Experiment products. 8omparing the solar wind characteristics of the two distinct shock types (as shown in Figure 1), the size of the circles in the left panel represents the magnetosonic Mach number of the event.It is evident that the magnetosonic Mach number increases with both magnetic field strength and shock speed.Furthermore, ICME-driven events generally exhibit higher magnetosonic Mach numbers than SIR-driven shocks.Notably, the magnetic field strength and shock speeds of ICME-driven events also surpass those of SIR-driven shocks.One of the primary factors influencing geomagnetic storm intensity is the IP magnetic field strength (Wu & Lepping 2016).In the probability density function of magnetic field strengths for all shock events, events with strengths exceeding 16 nT are predominantly driven by ICMEs, suggesting that ICME-driven shocks are more likely to induce geomagnetic storms (Yue et al. 2010;Yue & Zong 2011).The magnetic field strength distribution for SIR-driven events resembles a Gaussian distribution, mostly concentrated between 5 and 15 nT.In contrast, ICME-driven events display a distinct bimodal structure.The middle-right panel of Figure 1 displays the probability density function of speeds for all shock events.While both ICME-driven and SIR-driven events exhibit similar Gaussian speed distributions, the mean speed for ICME-driven events is higher.The speeds of ICME-driven shocks are predominantly within the range of 300-1200 km s −1 (Manoharan et al. 2004).The lower right panel of Figure 1 depicts the magnetosonic Mach number distribution for all shock events.SIR-driven events are primarily concentrated below a Mach number of 2, consistent with the findings of Blanco-Cano et al. (2016).ICME-driven events, however, exhibit a broader distribution with generally higher Mach numbers.
From the three plots on the right side of Figure 1, it is evident that intense shock events with speeds exceeding 700 km s −1 , magnetic field strengths above 25 nT, and magnetosonic Mach numbers greater than 3 are predominantly caused by ICMEs.This underscores the role of CME eruptions as primary drivers of severe disturbances in Earth's space environment (Shugay et al. 2022).The higher average magnetic field strength, average velocity, and other parameters of the ICME-driven shock wave compared to the SIR-driven shock wave may be attributed to two factors.First, there is a greater proportion of ICME-driven shocks occurring during solar maximum, as compared to the proportion of SIR-driven shocks (Jian et al. 2006a(Jian et al. , 2006b)).This leads to an overall increase in the average level of ICME-driven shock parameters.Second, the internal structure of ICME results in a steeper magnetic pressure gradient, further contributing to the higher average level of ICME-driven shock parameters when compared to the SIR-driven shock wave (An et al. 2019).

Ions in the Solar Wind
In this section, we conducted a superposed epoch analysis (SEA) to comprehend the temporal variations of ion composition in shocks driven by various sources.To ensure the precision of the SEA, we specifically chose forward shocks for our analysis, encompassing 97 ICME-driven shocks and 57 SIR-driven shocks.The time window for analysis extended from the initiation of the shock to the ending of the corresponding event (either the end of ICME or SIR).The initiation time of the shocks was obtained from the IP shock database, while the ending time of the events was derived from the ICME and SIR lists (Richardson & Cane 2010;Chi et al. 2018).The first and most important step in SEA is to define the phases of the disturbances.Both the ICME and SIR events are divided into two phases according to the onset time (T = 0 hr).The first phase refers to the period prior to the onset and is set to be 24 hr for both ICME and SIR.The second phase refers to the period from the onset to the ending of the event and is set to be 30 hr for CME and 60 hr for SIR, respectively, based on the statistics of the ICME and SIR lists.The individual ICME or SIR phases are thus essentially stretched or compressed proportionally to the corresponding average values of each phase using linear interpolation.Since the temporal resolution of the ion abundance data is 2 hr, the binning interval in the SEA is also set to be 2 hr.After the SEA, the data in each bin are averaged to obtain the final SEA curves as shown in the following figures.The standard deviations in each bin are also calculated and displayed as the shaded regions around the averaged curves.
3.1.He 2+ , C 6+ /O 4+ , C 6+ /O 5+ , and O 7+ /O 6+ First, we considered the abundance variations of He 2+ and the abundance ratios of ions C and O (as depicted in Figure 2).Prior to the arrival of the ICME-driven shock, the He 2+ abundance exhibited a swift ascent, reaching its zenith, and subsequently commenced a decline, persisting in decrement after the arrival of the ICME-driven shock.In contrast, following the arrival of the SIR-driven shock, the abundance of He 2+ initiated an ascent, attaining a level approximately commensurate with the peak observed during the ICME event within approximately 16 hr, after which it commenced a decline.
Besides the evident variations in He 2+ abundance, significant changes are also observed in the abundance ratios of ions C 6+ , O 4+ , O 5+ , O 6+ , and O 7+ .Post the ICME-driven shock arrival, the C 6+ /O 4+ ratio exhibits an increase, doubling in about 10 hr.Although fluctuations are observed in the subsequent day, the ratio remains elevated before gradually returning to typical levels within less than 10 hr.The variations in the C 6+ /O 5+ ratio post the ICME-driven shock are consistent with those of C 6+ /O 4+ , albeit with a smaller magnitude, indicating a greater increase in the O 5+ abundance compared to O 4+ .The O 7+ /O 6+ ratio also rises post the ICMEdriven shock, suggesting a higher increase in the O 7+ abundance relative to O 6+ , while the abundance of O 7+ is still smaller than that of O 6+ .This observation indicates that, although some ICMEs exhibit peak distributions of oxygen ion charge states at O 7+ (Gruesbeck et al. 2011), statistically, the more prevalent scenario is the peak distribution of oxygen ion charge states occurring at O 6+ .The variations in O 6+ and O 7+ coupled with the fluctuations in O 5+ and O 4+ abundances suggest that CMEs, following solar magnetic field acceleration, transport a greater quantity of high-charge-state oxygen ions compared to the background solar wind.It is noteworthy that within the 30 hr following the conclusion of an ICME, although C 6+ /O 4+ ratios (as well as C 6+ /O 5+ and O 7+ /O 6+ ) exhibit a noticeable decreasing trend, relatively high ratios persist.This is attributed to the occurrence of another ICME within the 30 hr following the end of some ICMEs, leading to an elevation in the abundance ratios of ions with different charge states.
Post the arrival of the SIR-driven shock, alongside the elevation in He 2+ abundance, the ratios of C 6+ /O 4+ , C 6+ /O 5+ , O 7+ /O 6+ , and others, exhibit a gradual decline.The SIR-driven shock induces additional ionization of ions (Allegrini et al. 2008), although the ionization effect on higher charge state ions appears relatively subdued.Moreover, the alterations in the ratios of C 6+ /O 4+ , C 6+ /O 5+ , and so forth, before and after the arrival of the SIR-driven shock are considerably smaller compared to those associated with the ICME-driven shock, strongly suggesting that the effects of SIR and ICME on heavy ions are distinct.

He, C, Ne, Mg, Si, and Fe
In addition to analyzing the variations of ions in different charge states before and after the arrival of the two types of shocks, we also examined the changes in the abundance ratios of various ions relative to oxygen ions, as illustrated in Figure 3.
Following the arrival of ICME-driven shocks, the He/O ratio exhibits a rapid increase within less than a day, maintaining an elevated level for 10 hr before gradually declining.This trend can be attributed to the chromospheric material heated during CME eruptions, resulting in a higher abundance of helium in CMEs (Fu et al. 2020).The C/O ratio displays a unique behavior.It slightly decreases after the arrival of ICME-driven shocks but returns to normal levels within 1-2 days.This suggests that the variations in carbon and oxygen ions are relatively similar postshock, with ICMEs having a more pronounced effect on the abundance of oxygen ions than carbon ions.The abundance ratios of Ne/O, Mg/O, Si/O, and Fe/O show similar trends postshock, with their mean values influenced by CMEs being higher than the background solar wind (Richardson & Cane 2004;Zurbuchen et al. 2004Zurbuchen et al. , 2016;;Owens 2018).Their patterns involve a rapid increase within about 6 hr post the ICME-driven shock arrival, maintaining elevated levels for approximately 1 day before gradually returning to typical values.This phenomenon aligns with the simulation results of Manchester et al. (2017) and is attributed to the compression of plasma by the ICME-driven shock.As a result, plasma accumulates in the sheath region between the shock and the flux rope, leading to the observed plasma density increase.An et al. (2019) further suggest that when the ICME-driven shock has a stronger magnetic field, a steeper magnetic pressure gradient is generated at the ICME boundary, causing the plasma density increase to occur earlier.The plasma in an ICME consists of two components.The first part is a large amount of magnetized plasma that is ejected from the corona during the breakout of a CME.The second part is the plasma present in the solar wind, which collides with the CME and accumulates on it.These processes result in a further increase in the mass of the plasma, leading to a higher abundance compared to the background solar wind (Feng et al. 2015;Georgoulis et al. 2019).
In contrast, prior to and after the arrival of SIR-driven shocks, the He/O ratio remains relatively stable, indicating that the solar wind source regions corresponding to SIRs differ significantly from CMEs.The C/O ratio experiences a slight increase post the SIR-driven shock arrival, with its overall average closely resembling the relative abundance in the solar wind (Zeldovich et al. 2021).The abundance ratios of Ne, Mg, Si, and Fe relative to oxygen all exhibit a minor decline within approximately 2 days post the arrival of the SIR-driven shock.This pattern is attributed to the plasma rarefaction region behind the CIR and suggests that the transit time of the plasma rarefaction region formed by CIRs past Earth averages about 2 days.
We then analyzed the variations in the abundance variations of He 2+ and the abundance ratios of ions C and O during these periods, as depicted in Figure 4. Figure 4(a) presents the variations in He 2+ abundance in the solar wind before and after the arrival of ICME-driven and SIR-driven shocks during different solar cycles.We set the onset time of the shock as 0 hr.The average time window from the onset of the shock to the end of the corresponding event (ICME or SIR) is designated as 30 hr (for ICMEs) and 60 hr (for SIRs).This is closer to the average duration of ICME proposed by Jian et al. (2006b).Through statistical analysis of ICMEs from 1995 to 2004, Jian et al. (2006b) found that the duration of ICMEs falls within a time range of 5.5 to 94 hr, with an average value of approximately 35 hr.It is evident that the ICME-driven shock increase in He 2+ abundance is most pronounced during the solar maximum, followed by other years.During the solar maximum, the He 2+ abundance also exhibits a significant increase post the SIR-driven shock arrival, with the magnitude of increase closely mirroring that observed prior to the ICMEdriven shock in other years.Conversely, the increase in He 2+ abundance before the ICME-driven shock during the solar minimum is the least pronounced.These variations suggest that, akin to CMEs being modulated by the evolution of the global solar magnetic field (Bilenko 2014), the characteristics of ICME-driven shocks are influenced by the solar cycle, with more pronounced ion acceleration and heating effects during the solar maximum.Notably, this differs from the variations discussed in the previous section, where the compression and rarefaction regions before and after the SIR led to changes in He 2+ abundance.For SIR-driven shocks, a significant increase in He 2+ abundance is observed in all solar cycles after the shock arrival, and the extent of this increase varies with the changing intensity of solar activity.This can be attributed to the fact that the intensity of SIR-driven shocks is influenced by the solar activity cycle, consequently causing variations in the ionization effects of the shocks in tandem with the solar activity cycle.
Figures 4(b), (c), and (d) reveal consistent trends in the variations of C 6+ /O 4+ , C 6+ /O 5+ , and O 7+ /O 6+ ratios before and after shock arrivals.All ratios exhibit an increase post the ICME-driven shock arrival, with the most rapid and prolonged increase (around 30 hr) observed during the solar maximum.During the solar minimum, while the increase in ion ratios post the ICME-driven shock is relatively gradual, the peak values achieved are comparable to those during the solar maximum.
However, the duration of elevated levels is shorter (around 1 day), and the decline is faster.This suggests that CMEs erupting during the solar maximum and minimum differ in size and speed, but their internal characteristics, such as temperature and ion abundance, are largely consistent.For SIR-driven shocks, ion ratios during the solar maximum and other years remain relatively unchanged, but they are higher than the ion ratios measured in coronal hole solar wind by Zhao et al. (2009).

He, C, Ne, Mg, Si, and Fe
To further elucidate the periodic variations in elemental abundances, we stratified the data set by solar cycle phases and analyzed the abundance ratios of He, C, Ne, Mg, Si, and Fe with respect to oxygen (O) during solar maximum, minimum, and other years, as illustrated in Figure 5.
For the He/O ratio, prior to the arrival of ICME-driven shocks, the sequence of He/O ratios in the solar wind from highest to lowest is solar maximum, other years, and solar minimum.This suggests a cyclical variation in the abundance of helium in the solar wind.Post the ICME-driven shock arrival, the He/O ratios for solar maximum, other years, and solar minimum, respectively, increase, with the duration of elevated levels decreasing in the same order.This can be attributed to the distinct characteristics of CMEs erupting during the solar maximum and minimum.This shows that although the abundance of helium will increase in ICMEdriven shocks (Zurbuchen et al. 2016), its duration is controlled by the distinct characteristics of CMEs erupting during the solar maximum and minimum.As highlighted in previous studies, the helium abundance in SIR-driven shocks varies with the solar cycle (Allen et al. 2019), and its changing trend in solar maximum is consistent with the 1992-1993 statistics of Von Steiger et al. (1995), and there are fluctuations to a certain extent.As highlighted in previous studies, not only does the helium abundance increase in ICME-driven shocks (Zurbuchen et al. 2016), but the helium abundance in SIR-driven shocks also exhibits a notable increase, varying with the solar cycle (Allen et al. 2019).For the C/O ratio, apart from a slight increase during the solar minimum before the arrival of SIR-driven shocks and a decline post the ICME-driven shock during other years, the ratio remains relatively stable across different solar cycle phases.
Considering the Ne/O, Mg/O, Si/O, and Fe/O ratios, a decline is observed during the solar minimum after the arrival of SIR-driven shocks, while the ratios remain relatively stable during other years and solar maximum.The observed reduction may be attributed to the lower intensity of SIR-driven shocks during periods of low solar activity, coupled with their smaller interaction regions.Consequently, this results in a smaller plasma accumulation region.Post shock arrival, the sequence of these ion ratios from highest to lowest is solar maximum, other years, and solar minimum.For ICME-driven shocks, the behavior of Ne, Mg, Si, and Fe ions relative to helium is consistent across the solar cycle, with higher abundances during the solar maximum and lower during the solar minimum.However, post shock arrival, the growth rates of these heavy ion abundances are consistent across different solar cycle phases.Notably, during the solar minimum, after the Ne, Mg, Si, and Fe to oxygen abundance ratios peak, they do not remain elevated for a short duration as observed during the solar maximum and other years.Instead, they decline rapidly, returning to preshock levels.

Summary and Conclusion
In this investigation, we utilized data from ACE-SWICS to analyze the heavy ion abundance before and after ICME-driven and SIR-driven shocks.We observed a more pronounced variation in heavy ion abundance following ICME-driven shocks compared to the subtle changes post SIR-driven shocks.Further stratifying the data by different years, we compared the abundance ratios of various ions to oxygen within 48 hr post shock occurrence against the average ratio for all events (refer to Figure 6).The abundance ratios of ions to oxygen in SIRdriven shocks exhibit a strong correlation with the solar activity cycle (Zhao et al. 2017;Allen et al. 2019).These ratios are generally lower than the average values for all events.While ICME-driven shocks also correlate with the solar cycle, the ratios during solar maximum and other years exceed the average.From Figure 6, the C/O ratio is unique, with higher values during solar minimum and lower during solar maximum, consistent with the results from Figure 3. Interestingly, the Ne/O ratio decreases sequentially from solar maximum ICME-driven shocks to solar minimum SIR-driven shocks.In contrast, the He/O, Mg/O, Si/O, and Fe/O ratios during solar maximum SIR-driven shocks exceed those during solar minimum ICME-driven shocks.In light of the above, the main results are summarized as follows.
1. ICME-driven shocks generally exhibit higher magnetic field strength, shock speed, and magnetosonic Mach number compared to SIR-driven shocks.Severe shock events with speeds exceeding 700 km s −1 , magnetic field strengths greater than 25 nT, and magnetosonic Mach numbers above 3 are predominantly triggered by ICMEs.2. The abundance ratios of C 6+ /O 4+ , C 6+ /O 5+ , and O 7+ /O 6+ , and heavy ions like Ne, Mg, Si, and Fe to oxygen rise rapidly within approximately 2-4 hr post ICME-driven shock arrival, maintaining elevated levels for about a day before gradually returning to background solar wind levels.In contrast, SIR-driven shocks do not exhibit a significant increase in these ion abundance ratios; a slight decline is observed instead.3.For ICME-driven shocks, the rate and intensity of ion ratio increases are consistent across different solar activity periods.However, during solar maximum, these elevated levels persist longer, while during solar minimum, they decline rapidly to background solar wind levels.For SIR-driven shocks, ion abundance ratios remain relatively unchanged during solar maximum and other years.
This study provides insights into the variations in solar wind heavy ion characteristics during different types of IP shock processes.Such insights are instrumental in tracing the origins of solar wind on the solar surface and understanding the distribution and evolution of heavy ions in Earth's magnetosphere.Future observations or simulations related to heavy ions in Earth's magnetosphere will pave the way for more in-depth research on the spatial impact of heavy ion abundance during different events.

Figure 1 .
Figure1.Solar wind characteristics of shock events.The size of the circles in the left panel corresponds to the magnetosonic Mach number of the event.The red dots represent shock events driven by ICMEs, while the blue dots represent shock events driven by SIRs (stream interaction regions).In the right panel, the color red indicates ICME-driven shock events, and the color blue indicates SIR-driven shock events.

Figure 2 .
Figure 2. Schematic diagram of the change of ion abundance ratio before and after shocks.The time interval used in the SEA is 2 hr.The first vertical red line indicates the initiation of shocks.The second vertical red line indicates the end of the ICME.The red and blue shades denote the error term.The shaded region in the figure represents the error, which is calculated based on the uncertainties listed in the data set.It is noteworthy that the error associated with He 2+ abundance is on the order of 10 −4 , making it challenging to visualize effectively in the figure.

Figure 3 .
Figure 3. Variations in abundance ratios of different ions relative to oxygen.The time interval used in the SEA is 2 hr.The first vertical red line indicates the initiation of shocks.The second vertical red line indicates the end of the ICME.The red and blue shades denote the error term.

Figure 4 .
Figure 4. Schematic diagram of the change of ion abundance ratio before and after shocks in different solar activity cycles.The time interval used in the SEA is 2 hr.(a) The temporal variation of He 2+ abundance, (b) the temporal variation of C 6+ /O 4+ ratio, (c) the temporal variation of C 6+ /O 5+ ratio, and (d) the temporal variation of O 7+ /O 6+ ratio.The label "0h" denotes the initiation of shocks.

Figure 5 .
Figure 5. Variations in abundance ratios of different ions relative to oxygen in different solar activity cycles.The time interval used in the SEA is 2 hr.(a) The temporal variation of He/O ratio, (b) the temporal variation of C/O ratio, (c) the temporal variation of Ne/O ratio, (d) the temporal variation of Mg/O ratio, (e) the temporal variation of Si/O ratio, and (f) the temporal variation of Fe/O ratio.The label "0h" denotes the initiation of shocks.

Figure 6 .
Figure 6.Elemental composition of shocks in different years compared to the mean value of all events.Events at the solar maximum are indicated in red, events at the solar minimum are indicated in blue, and events in years other than minimums and maximums are indicated in yellow.〈X/O〉 denotes the ratio between elemental composition (He, C, Ne, Mg, Si, and Fe, respectively, from left to right) in different solar phases.〈X/O〉 mean denotes the average values during the whole period.