Statistical Study and Live Catalogue of Multi -Spacecraft 3He-Rich Time Periods over Solar Cycles 23 24 and 25 Short Title Live Catalogue of 3He-Rich Time Periods

2025-05-03 0 0 666.69KB 23 页 10玖币

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Statistical Study and Live Catalogue of Multi-Spacecraft 3He-Rich Time Periods

over Solar Cycles 23, 24, and 25

Short Title: Live Catalogue of 3He-Rich Time Periods

S.T. Hart1,2*, M.A. Dayeh2,1, R. Bučík2, M.I. Desai2,1, R.W. Ebert2,1, G.C. Ho3,

G. Li4, G.M. Mason3

1The University of Texas at San Antonio, San Antonio, TX, USA, 78249

2Southwest Research Institute, San Antonio, TX, USA, 78238

3Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA, 20723

4University of Alabama in Huntsville, Huntsville, AL, USA, 35899

*Corresponding author: samuel.hart@contractor.swri.org

Abstract

Using ion measurements from Ultra-Low-Energy Isotope Spectrometer (ULEIS)

observations onboard Advanced Composition Explorer (ACE) and Solar Isotope

Spectrometer (SIS) observations onboard the Solar Terrestrial Observatory

(STEREO)-A and STEREO-B spacecraft, we have identified 854 3He-rich time periods

between 1997 September and 2021 March. We include all event types with observed

3He enhancements such as corotating interaction regions (CIRs), gradual solar

energetic particle (SEP) events, interplanetary shocks, and impulsive SEP events.

We employ two different mass separation techniques to obtain 3He, 4He, Fe, and

O fluences for each event, and we determine the 3He/4He and Fe/O abundance ratios

between 0.32 – 0.45 MeV/nucleon and 0.64 – 1.28 MeV/nucleon. We find a clear

correlation in the 3He/4He and Fe/O abundance ratios between both energy ranges.

We find two distinct trends in the 3He/4He vs. Fe/O relation. For low 3He/4He

values, there is a positive linear correlation between 3He/4He and Fe/O. However,

at 3He/4He ~ 0.3, Fe/O appears to reach a limit and the correlation weakens

significantly. We provide a live catalogue of

3He-rich time periods that includes

the robust determination of the onset and end times of the 3He enhancements in

SEP-associated periods for different types of events observed my multiple

spacecraft. This catalogue is available for public use. New releases will follow

after major additions such as adding new periods from new missions (e.g., Parker

Solar Probe and Solar Orbiter), identifying event types (impulsive SEP events,

etc.), or adding new parameters such as remote observations detailing

characteristics of the events’ active regions.

1. Introduction

The Sun is capable of accelerating particles to >MeV energies. Coronal

mass ejections (CMEs) and corotating interaction regions (CIRs) can drive

interplanetary (IP) shocks or large compression regions that accelerate

particles via diffusive shock acceleration (DSA, e.g. Decker 1981, Lee 1983,

Zank et al. 2015, Giacalone et al. 2002). Solar flares may also accelerate

particles via magnetic reconnection within solar active regions by converting

magnetic energy into kinetic energy that accelerates and heats particles within

the reconnection site (e.g. Wang et al. 2006; Bučík 2020). The resulting

energetic particle populations from these processes are referred to as solar

energetic particles (SEPs). The primary candidate for accelerating energetic

particles at IP shocks is the shock-drift mechanism at quasiperpendicular shocks

(Decker, 1981) and first-order Fermi acceleration mechanism at quasi-parallel

shocks (Lee, 1983). The strongest shockwaves originate at the front of fast

CMEs, producing gradual SEPs (GSEPs) that often increase in intensity over

several days until peaking at shock passage before decreasing quickly in

intensity. DSA is a highly efficient acceleration method and thus tends to

produce SEPs with energies greater than tens of MeV/nucleon. (Desai & Giacalone

et al. 2016). Additionally, IP shocks can propagate over a wide range of

heliospheric longitudes. As a result, GSEP events observed near Earth originate

from a broad range of source locations on the solar disc (e.g. Reames 1999).

Magnetic reconnection occurs as a result of compressing anti-parallel

components of magnetic field lines (Gonzalez & Parker 2016). Particles at

reconnection sites are stochastically accelerated by significant amounts of

magnetic turbulence (Petrosian et al. 2012). In some reconnection events, the

newly reconnected field lines are open (insofar as they close well beyond the

orbit of Earth) and the energetic particles along these field lines are injected

into IP space and observed as EUV jets (Bučík 2020). This process is often

referred to as interchange reconnection, and the escaping particles are called

impulsive SEPs (ISEPs) due to their short-lived nature. Unlike GSEPs, ISEPs are

rarely observed to have energies greater than 10 MeV/nucleon. In fact, GSEP

event identification criteria often include a significant abundance enhancement

in SEPs greater than 10 MeV/nucleon to exclude ISEP events (e.g., Cane et al.

2010, Desai et al. 2016, the NOAA proton event list).

The difference in elemental composition of GSEPs and ISEPs can be

attributed to some combination of their source region as well as their

acceleration mechanisms (Reames & Ng 2004). GSEPs, produced in the upper corona

and in interplanetary space, have similar compositions to the solar wind or

corona (e.g., Desai et al. 2006), whereas most observed ISEPs occur lower corona

and chromosphere and contain enhanced Fe/O abundance ratios as well as 3He/4He

abundance ratios of unity (e.g., Mason et al. 2007). For reference, the 3He/4He

abundance ratio is less than 1 in 10-4 in our solar system (Gloeckler & Geiss

1998) making the 3He enhancement in ISEPs one of the largest known fractionation

processes and bringing rise to their alternate name, 3He-rich SEPs.

3He-rich SEP events are of particular interest because of their peculiar

behavior. First, the nature behind enhanced 3He/4He abundance ratios is still

unresolved. Theoretical studies attribute the 3He enhancement to wave-particle

interactions in the flaring regions (Temerin & Roth 1992, Liu et al. 2004, Zhang

1995, see Klecker et al. 2006 and Miller 1998 for review). Second, although

3He-rich SEP events are produced in solar flares, the 3He/4He abundance ratio

and 3He fluences do not correlate with the soft X-ray peak flux of solar flares

(Nitta et al. 2006). They are more closely correlated with type III radio bursts

(emissions generated by escaping non-relativistic electrons at the reconnection

site), but a recent study by Köberle et al. (2021) shows that not all 3He-rich

SEP events have an associated electron enhancement. Third, 3He-rich SEP events

display considerable interevent variations in relative abundances and spectral

shape (e.g., Reames et al. 1994, Mason et al. 2007), suggesting that a single

acceleration mechanism is insufficient and instead supports a combination of

multiple independent acceleration mechanisms. Fourth, 3He at suprathermal

energies is commonly observed to have enhanced abundances in IP space during

quiet-times throughout the solar cycle (Dayeh et al. 2009, Wiedenbeck et al.

2005), suggesting that interchange reconnection may happen on small scales near

active regions, similar to the theory of nanoflares (Parker et al. 1988).

Finally, 3He-rich SEP events were originally believed to have access to only a

narrow range of pre-existing interplanetary magnetic field lines, and they were

observed to have source regions on a tight longitudinal band on the western

hemisphere of the Sun (e.g., Reames 1999). However, more recent studies (Nitta

et al. 2015 and references therein) show much broader longitudinal distributions.

Furthermore, observations of 3He-rich SEP events with longitudinally separated

spacecraft show that a single 3He-rich event can be distributed 180° in

heliospheric longitude (Wiedenbeck et al. 2010, 2013). Following these

observations, simulations have been developed seeking to explain this phenomena.

Magnetic field models near the solar surface show that magnetic field lines

near the open-closed boundary can be widely dispersed at the source surface,

resulting in the occasional broad longitudinal dispersion of 3He-rich SEP events

(Scott et al. 2018). Once in the heliosphere, magnetic field lines can wander,

deviating significantly from the ideal Parker spiral and altering the path of

flowing energetic particles (Howes & Bourouaine 2017, Moradi & Li 2019, Bian &

Li 2021, 2022). Still, the dominant process governing the longitudinal

distribution of 3He-rich SEP events is not fully understood, and remains an

active topic of debate within the community.

In this work, we identify and examine the properties of 3He-rich time

periods observed by the Advanced Composition Explorer (ACE; 1997 Sept. – 2021

Mar.) and the Solar Terrestrial Observatory’s Ahead (STEREO-A; 2007 – 2021 Mar.)

and Behind (STEREO-B; 2007 – 2014) spacecraft. In total, we have identified 854

events at the time of publication. We use a simple mass cutoff for measurements

on instruments with high mass resolution (ACE/ULEIS), and a triple-peaked

Gaussian on top of a linear background for instruments with lower mass

resolution (STEREO-A & B/SIT) to extract the fluences of 3He, 4He, Fe, and O.

We then determine the 3He/4He and Fe/O abundance ratio at 0.32 – 0.45 MeV/nucleon

and 0.64 – 1.28 MeV/nucleon, and we comment on their distributions and relations.

Ultimately, we introduce a new live catalogue of 3He-rich time periods.

These time periods include all possible event types such as CIRs, IP shock

passages, GSEP events, and ISEP events. The catalogue includes all of the time

periods identified in this paper, and we will continue to update it as current

missions observe more events during solar cycle 25 and beyond. The intent is to

also include events from Parker Solar Probe and Solar Orbiter. In addition to

event start/stop dates and abundance ratios, the future of this catalogue will

include all subsequent data relevant to the event such as the event type (e.g.,

GSEP, ISEP, etc.), parameters inferred from in-situ observations (e.g., fluences,

travel path length, etc.) and characteristics of the source region (e.g., X-

ray flare class, EUV flare shape, type III radio burst), flag for the multi-

spacecraft detection, and potentially relevant IP space parameters in the inner

heliosphere (e.g., ambient times, preceding CMEs, shocks, etc.). This catalogue

is live and publicly available and will continue to build into a unique and

comprehensive catalogue to be used in the process of answering fundamental

questions pertaining to the nature of 3He-rich SEP events noted above.

2. Data & Instrumentation

We use the Ultra-Low-Energy Ion Spectrometer (ULEIS; Mason et al. 1998)

onboard ACE (Stone et al. 1998) and the Suprathermal Ion Telescope (SIT; Mason

et al. 2008) onboard both STEREO A & B (Kaiser et al. 2008). Both ULEIS and SIT

are mass spectrometers equipped with time-of-flight sensors to allow for mass

resolution between 0 – 80 amu in the 0.04 MeV/nucleon to ~5 MeV/nucleon kinetic

energy range. ULEIS data has a 24-second time cadence and STEREO data has a

one-minute time cadence. In both cases, we study the 0.16 MeV/nucleon to ~5

MeV/nucleon energy range with masses between 0 – 80 amu.

3. Methodology

3.1 Selecting 3He-Rich Time Periods

3He-rich time periods are determined visually using the publicly available

(Level 3), 4-day mass spectrogram plots provided by the ACE Science Center

(izw1.caltech.edu/ACE) and the STEREO Science Center (izw1.caltech.edu/STEREO).

We take several factors into account when selecting the time range of each

event. For each event, we require an increase in the count rates near 3 amu

(3He) in the mass spectrograms. We exclude events whose 3He enhancement is solely

due to H and 4He spillover into the 3He mass range. An example of our selection

process is illustrated in Figure 1 (see Figure 2 for STEREO). Figure 1 is a

modified version of the publicly available 4-day browse plots, and it shows an

ISEP event observed by ACE beginning on 1999 Sept. 30 and lasting four days.

Figure 1b shows a 2 – 80 amu mass spectrogram between 0.32 – 3.6 MeV/nucleon.

The dashed vertical line indicates the start of the count rate increase near 3

amu, signifying a 3He enhancement. Figure 1a shows the flux time profiles of

4He, O, & Fe between 0.16 – 0.226 MeV/nucleon, noting that the Fe (orange) & O

(red) flux temporal profiles nearly overlap for the duration of the event,

whereas other heliospheric populations have O fluxes typically a factor of 10

greater than that of Fe (Desai et al. 2006). Figure 1c displays the one-over-

ion speed plot along with the red line being the approximate velocity dispersion

of this particular event. We repeat this process for ACE and both STEREO

spacecraft to obtain 854 3He-rich time periods since September 1997.

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StatisticalStudyandLiveCatalogueofMulti-Spacecraft3He-RichTimePeriodsoverSolarCycles23,24,and25ShortTitle:LiveCatalogueof3He-RichTimePeriodsS.T.Hart1,2*,M.A.Dayeh2,1,R.Bučík2,M.I.Desai2,1,R.W.Ebert2,1,G.C.Ho3,G.Li4,G.M.Mason31TheUniversityofTexasatSanAntonio,SanAntonio,TX,USA,782492SouthwestResearch...

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Statistical Study and Live Catalogue of Multi -Spacecraft 3He-Rich Time Periods over Solar Cycles 23 24 and 25 Short Title Live Catalogue of 3He-Rich Time Periods

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