e -and He time profiled from Helios 1 (0.3 AU) and IMP-8 (1 AU) during 5 impulsive SEP event in 1980 [17]. Magnetic connections to the flare site are indicated at upper right. Helios 1 observed 5 injections that had merged into a single event by the time they reached IMP-8.

Contexts in source publication

Context 1

... many puzzles remained unsolved primarily due to the scarcity of in situ measurements well inside 1 AU [12]. Figure 1 shows a clear example of the need for SEP observations in the inner heliosphere. The Helios 1 s/c located at ~0.4 AU detected [17]. ...

Context 2

... concluded that the long apparent pathlength can be explained by a magnetic field line pathlength increase due to field line random walk, and EP transport about the guiding center with a nonzero effective pitch angle. SolO's inner heliospheric trajectory for the first year of measurements of EPD is shown in Figure 10, presented by [44] from 28 February 2020 to 28 February 2021 with intensities of 54-101 keV e -on the inner side and 124-218 keV ions on the outer side (EPD/EPT detector head). Apart from a low level of background activity (see [45] for an in-depth discussion) and small increases due to CIRs [46], a number of intensity increases can be seen. ...

Context 3

... diversity of time profiles and pitch-angle distributions (PADs) was observed. Figure 11 shows observations and analysis of the July 22, 2020 e -event [47]. EPT observed a very anisotropic e -event reaching energies slightly above 100 keV (Figure 11, left). ...

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... 11 shows observations and analysis of the July 22, 2020 e -event [47]. EPT observed a very anisotropic e -event reaching energies slightly above 100 keV (Figure 11, left). The spike-like time profile showed a sharp onset with clear velocity dispersion, starting at 23:40 UT ± 10 min at 58 keV. ...

Context 5

... period was clearly observed by STEP at lower energies, which revealed additional spike-like injections preceding and following the event observed by EPT. The EPD pitch-angle coverage was nearly optimal (Figure 11, top right). ...

Context 6

... bottom panel of Figure 11, right shows an inverse-speed vs time plot (typically used for velocity dispersion analysis) for the July 22 event, combining STEP and EPT e -data. The color scale represents the intensity, normalized to the maximum value for each energy channel. ...

Context 7

... black arrow at 23:34 UT marks the SRT shifted by the light propagation time to SolO in order to allow a direct comparison with electromagnetic observations from 0.69 AU. The top panel of Figure 11, bottom right, shows the radio dynamic spectrum observed by SolO/RPW during this period. A type III radio burst was observed by RPW, starting at 23:32 UT, thus the inferred e -release time and the type III radio burst differ only by 2 minutes. ...

Context 8

... concluded that the spike-like time profiles, prompts onsets and beamed PADs together with the in-situ detection of Langmuir waves by RPW (magenta line in Figure 11, bottom right) support a very good magnetic connection to the source. However, although STA observed a jet at the east solar limb, the nominal magnetic footpoint of SolO along the ideal Parker spiral was located more than 30º behind the east limb from the STA viewpoint. ...

Context 9

... Malandraki 12 injections coincide with EUV jets and brightenings near the east limb, not far from the nominal magnetic connection of SolO. Figure 12, right shows as an example the STA 195 Å EUV running difference images corresponding to injection #1 (top row), injection #2 (middle row) and injection #3 (bottom row). The arrow marks the solar source. ...

Context 10

... first widespread SEP event of solar cycle 25 observed on November 29, 2020 was analyzed and discussed by [54], enabling for the first time the comparison and combination of EP observations from four different locations ≤ 1 AU with a wide longitudinal separation. Figure 13 shows an overview of the EP observations from 2020 November 29 to 2020 December 3 collected by SolO, PSP, STA and by near-Earth s/c. Each panel shows intensity-time profiles of e -(upper portion of the panels) and protons (p + ) (lower portion of the panels) as observed by EPI-Lo (gray) and EPI-Hi (magenta) detectors oof ISIS on board PSP, the EPT (gray) and HET (blue) onboard SolO, the SEPT (gray) and HET (red) on board STA, EPAM (gray) onboard ACE and EPHIN (green) onboard SOHO. ...

Context 11

... PSP solar wind data are not available and the solar wind analyzer on SolO/SWA was not operational speed obtained from ENLIL simulations is used instead. The SEP event was associated with an M4.4 soft X-ray flare that occurred at NOAA AR 12790, located just behind the east limb as viewed from Earth ( Figure 13). STA/EUVI images at 13:00 UT show that the flare was located at E98S23 (in Stonyhurst Heliographic (HGS) coordinates). ...

Context 12

... in their first interpretation, inferred the particle release times at the Sun by means of Velocity Dispersion Analysis (VDA) and Time Shift Analysis (TSA) and compared them with the propagation of the EUV wave. Figure 14, left, shows the comparison of the inferred particle release times with the arrival time of the EUV wave at the s/c field line footpoints. The ⁕ markers ...

Context 13

... their second interpretation, [54] compared the observed e -and p + onset delays in the November 2020 event with observations of similar SEP events during solar cycle 24,and considered the implications of a simple interpretation of the observed EP delays. Figure 14, right shows the comparison of e -(top panels) and p + (middle panels) onset delays vs connection angle for the November 2020 SEP event (colored circles indicating the observing s/c as in Figure 13) with those for ~0.7-4 MeV e -and 14-24 MeV p + in the cycle 24 SEP events observed at both STEREO s/c and near the Earth discussed by Richardson et al. 2014 [57] (black circles). ...

Context 14

... their second interpretation, [54] compared the observed e -and p + onset delays in the November 2020 event with observations of similar SEP events during solar cycle 24,and considered the implications of a simple interpretation of the observed EP delays. Figure 14, right shows the comparison of e -(top panels) and p + (middle panels) onset delays vs connection angle for the November 2020 SEP event (colored circles indicating the observing s/c as in Figure 13) with those for ~0.7-4 MeV e -and 14-24 MeV p + in the cycle 24 SEP events observed at both STEREO s/c and near the Earth discussed by Richardson et al. 2014 [57] (black circles). ...

Context 15

... are slightly lower than the average for the cycle 24 events. The bottom panels in Figure 14 show the "source speeds" from the flare to the field line footpoint as a function of connection angle for e -(left) and p + inferred from the November 2020 event onset delays. The different source speeds suggest that the e -and p + onset delays cannot be accounted for by a connection to a single particle source moving away from the solar event near the Sun. ...

Context 16

... of these events occurred when PSP was inside of 0.65 AU (with two inside 0.5 AU), adding to the limited catalog of these events observed well inside Earth's orbit, having been previously only measured by Helios [21]. The top panel of Figure 15, left shows the energy and time variation of the seven events as observed by the sunward facing aperture LETA. The events are relatively small with p + increases evident up to only a few MeV but that last for several days. ...

Context 17

... magnetic footpoint of the s/c was determined by calculating the Parker spiral connecting the Sun and PSP, assuming a solar wind speed of 400 km s -1 . In the bottom panel of Figure 15, left the heliocentric distance of the s/c is plotted versus the calculated footpoint. The color intensity of the points corresponds to the ~1-2 MeV LETA p + counting rate. ...

Context 18

... this event is considered separate and unrelated to the previous two. Figure 15, right shows a comparison of the p + spectra of the seven events [58]. A power law corresponding to E -4.5 is also shown for reference. ...

Context 19

... of these events were also observed by EPI-Hi as reported by [58]. Figure 16 presents the first-ever measurements of suprathermal-through-energetic He ions with energy between ~0.03 and 2 MeV nuc -1 during one intensity enhancement between 2018, DOY 318-325 that was associated with a CIR or SIR when PSP was at ~0.35 AU following its first perihelion pass. Figure 16, left from top to bottom shows (a): 4 hr averages of the ~0.03-1.99 ...

Context 20

... of these events were also observed by EPI-Hi as reported by [58]. Figure 16 presents the first-ever measurements of suprathermal-through-energetic He ions with energy between ~0.03 and 2 MeV nuc -1 during one intensity enhancement between 2018, DOY 318-325 that was associated with a CIR or SIR when PSP was at ~0.35 AU following its first perihelion pass. Figure 16, left from top to bottom shows (a): 4 hr averages of the ~0.03-1.99 MeV MeV nuc -1 He intensities averaged over all 80 EPI-Lo apertures; (b): 4 hr averages of 0.031-0.062 ...

Context 21

... MeV nuc -1 He intensities averaged over all 80 EPI-Lo apertures; (b): 4 hr averages of 0.031-0.062 MeV nuc -1 He intensities averaged all apertures that measure particles flowing in the antisunward, transverse and sunward directions; (c): given by γ=log(j1/j2)/log(E1/E2), where j1 and E1 are the average intensity and center energy (arithmetic mean) of the lower energy range, and j2 and E2 are the average intensity and center energy, respectively, of the next higher energy range shown in Figure 16(a); (d): the 1/ion speed spectrogram versus time; (e)-(g): 1-minute averages of the magnetic field magnitude from FIELDS and the 1-minute averages of the solar wind density and speed from SWEAP. The latter panels show that the magnetic field magnitude and solar wind density become relatively steady as PSP exits an interaction region and encounters a moderately high speed (~~500 km s -1 ) solar wind stream on 2018, DOY 319 [59]. ...

Context 22

... nuc -1 He ions flowing toward the Sun during the peak of the enhancement are either slightly greater or comparable as those flowing in the antisunward and transverse directions. Furthermore, Figure 16(b) shows the late arrival of higher-energy ions as a substantial increase in the counts per bin for ions with the highest speeds between DOY 321 and DOY 322, thereby exhibiting inverse velocity dispersion. Figure 16, right compares the omnidirectional, event-averaged spectra in all six events [61]. ...

Context 23

... Figure 16(b) shows the late arrival of higher-energy ions as a substantial increase in the counts per bin for ions with the highest speeds between DOY 321 and DOY 322, thereby exhibiting inverse velocity dispersion. Figure 16, right compares the omnidirectional, event-averaged spectra in all six events [61]. Also included in Figure 16(a), right are data from EPI-Hi/LET as reported by [58], for events #1, # 5 and # 6 above ~1 MeV nuc -1 . ...

Context 24

... 16, right compares the omnidirectional, event-averaged spectra in all six events [61]. Also included in Figure 16(a), right are data from EPI-Hi/LET as reported by [58], for events #1, # 5 and # 6 above ~1 MeV nuc -1 . Figure 16(b), right shows the spectra for events #2, #3 and #4 From EPI-Lo only, as these events are not observed by EPI-Hi. ...

Context 25

... included in Figure 16(a), right are data from EPI-Hi/LET as reported by [58], for events #1, # 5 and # 6 above ~1 MeV nuc -1 . Figure 16(b), right shows the spectra for events #2, #3 and #4 From EPI-Lo only, as these events are not observed by EPI-Hi. Solid curves in panel (a) are fits to the spectra of the form j=jo E -γ exp(-Ε/Εo), where j is the differential intensity at energy E in MeV nuc -1 , jo is the normalization constant, γ is power-law spectral index, and Eo is the e-folding energy [62]. ...

Context 26

... further analyzed the p + enhancement that was observed by PSP on 2018, DOY 320 at 0.34 AU from the Sun. Figure 17, left provides an overview of the p + enhancement, which began on DOY 320, 2018 and persisted for almost four days. The event has been interpreted as being an SIR event ( [28], [58], [61]) related to the compression region that passed over the s/c one day prior to the event onset. ...

Context 27

... divided the event into 5 intervals containing equal counts measured by EPI-Lo and determined how the spectrum changes over time. Figure 17, right shows the p + spectrum measured by ISꙨIS for each interval shown in Figure 17, left as well as the total spectrum for the entire period. Except for interval 1, fit by a simple power law, each spectrum was fit with a power law with an exponential rollover function. ...

Context 28

... divided the event into 5 intervals containing equal counts measured by EPI-Lo and determined how the spectrum changes over time. Figure 17, right shows the p + spectrum measured by ISꙨIS for each interval shown in Figure 17, left as well as the total spectrum for the entire period. Except for interval 1, fit by a simple power law, each spectrum was fit with a power law with an exponential rollover function. ...

Context 29

... fits were obtained using the same fitting routine as [61]. Figure 17, right shows a significant difference between the observed energetic particle spectrum during the first interval and the rest of the event. The first interval yields a spectrum that is close to a simple power law across the full energy range. ...

Context 30

... configuration arises as a result of magnetic footpoints moving across the coronal hole boundary, causing the field line to be stretched across the compression region between the fast and slow solar wind streams. This results in a large-scale field orientation that is much less transverse than the nominal Parker spiral, as presented in Figure 18, left from the companion paper by [70] which provides a theoretical framework explaining the radial field configurations that are often observed in the rarefaction regions that follow SIRs. Figure 18, right shows results by [70] who carried out EP transport modeling for this event. A comparison between observed (blue data points) and modeled (curves) differential fluxes at higher and lower energies is shown [70]. ...

Context 31

... results in a large-scale field orientation that is much less transverse than the nominal Parker spiral, as presented in Figure 18, left from the companion paper by [70] which provides a theoretical framework explaining the radial field configurations that are often observed in the rarefaction regions that follow SIRs. Figure 18, right shows results by [70] who carried out EP transport modeling for this event. A comparison between observed (blue data points) and modeled (curves) differential fluxes at higher and lower energies is shown [70]. ...

Context 32

... applied a wellcomputed time-shift of the ULEIS observations to the SIS observations for a better comparison. As shown in Figure 19, CIR-events 1-5 are all observed by both SIS and ULEIS. CIR event 6 was not observed by ULEIS, possibly due to it being the weakest of the CIR events observed by SolO or due to differences in latitude. ...

Context 33

... turnover in the low energy part of the spectra as predicted by [18] was not observed. [46] also concluded that the radial gradients in the 4 He intensities between SIS and ULEIS are very similar to those found for more energetic H between Helios 1 and 2 and IMP-7 [21] (Figure 19, bottom). ...

Context 34

... show that the GCR decrease observed to begin at ~12:00 UT on 21 July (top panel, green line in Figure 20) is in very good agreement with the estimated recurrence time for the HSS. Recurrence of the same CIR in previous solar rotations is found to almost coincide with the time of corotating suprathermal ion events identified by [46] as CIR 1 and CIR 3 (see Figure 19). [73] present an interesting comparison of FDs at SolO and Earth using a multi-s/c approach. ...

Context 35

... Malandraki 20 [74] presented the first observations of ACRs in to 36 Rs (0.166 AU), focusing especially on helium as observed by PSP/ISꙨIS (Orbits 1-3). A strong radial gradient of ~25 ± 5%/AU over energies of ~4 to ~45 MeV/nuc is derived by applying three methods to the detrended, eventsubtracted helium fluxes for the LET1 and HETB telescopes (Figure 21, left). These values are higher than all prior He observations further out in the heliosphere and come at a unique time in the understanding and modeling of EP transport and acceleration, particularly as both Voyagers have crossed the heliopause and IBEX has accumulated a full solar cycle of observations. ...

Context 36

... values are higher than all prior He observations further out in the heliosphere and come at a unique time in the understanding and modeling of EP transport and acceleration, particularly as both Voyagers have crossed the heliopause and IBEX has accumulated a full solar cycle of observations. Figure 21, right presents simulated radial gradients of ACR helium in the equatorial plane as a function of kinetic energy for varying distances in the heliosphere using the model of [75] with some minor updates and modifications. Relatively good agreement with results at 1 AU is shown but as discussed by [74] their observations challenge considerably current transport models. ...