3He-rich solar energetic particle events observed on the first perihelion pass of Solar Orbiter

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Volume 656 (December 2021)

A&A, 656 (2021) L1

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Solar Orbiter First Results (Cruise Phase)

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Table 1.

³He-rich solar energetic particle event properties.

Event	1	2	3	4	5
Estimated injection	18 Jun. (170)	11 Jul. (193)	20 Jul. (202)	5 Aug. (218)	17 Sep. (261)
Time ⁽¹⁾	13:15	02:25	20:15 ⁽²⁾	17:00	09:40
Angle (deg) ⁽³⁾	W 68.7	W 107	W 117	W 126	W 130
Footpoint (deg) ⁽⁴⁾	102	209	95.1	262	75.9
Dist. (au) ⁽⁵⁾	0.52	0.61	0.67	0.78	0.96
Lat. (deg) ⁽⁶⁾	−1.51	2.88	0.74	−2.08	−5.97
Active region ⁽⁷⁾	12765	12767	12768	12271	12773
AR-footpoint angle (deg) ⁽⁸⁾	11	12	18	35	7
⁴He fluence ⁽⁹⁾ × 10³	0.52 ± 0.11	1.67 ± 0.19	174 ± 2	4.8 ± 0.3	1.8 ± 0.2
³He/⁴He ⁽¹⁰⁾	0.1 ± 0.1	0.15 ± 0.06	0.61 ± 0.01	0.05 ± 0.01	0.04 ± 0.04
H spectral index ⁽¹¹⁾	−4.3	−3.7	−2.2	−1.0	−3.0
⁴He spectral index ⁽¹¹⁾	−4.5	−3.2	−2.2	−1.3	−3.4
Fe spectral index ⁽¹¹⁾	...	...	−2.7	...	...
35 keV electrons inj.? ⁽²⁾	Yes	...	Yes	Yes	Yes

Notes.

⁽¹⁾

Year: 2020; Event 1: based on weak type III (STEREO-A); Event 2: type III STEREO-A; Event 3: multiple type IIIs, the largest was chosen; Event 4: no type III was seen based on the rise at SO; Event 5: a possible feature in STEREO-A SWAVES.

⁽²⁾

See Gómez-Herrero et al. (2021); for Event 3 there appears to be a second injection corresponding to a type III burst at day 203 02:55.

⁽³⁾

The separation angle from Earth (deg).

⁽⁴⁾

In Carrington longitude, assuming a 300 km s⁻¹ solar wind speed typical of slow solar wind streams in 2020 observed on ACE.

⁽⁵⁾

Solar Orbiter heliocentric distance (au).

⁽⁶⁾

Solar Orbiter heliographic latitude (deg).

⁽⁷⁾

NOAA Active Regions observed from Earth.

⁽⁸⁾

Approximate angular separation of AR from nominal footpoint (deg).

⁽⁹⁾

Particles cm⁻² sr MeV/nucleon at 385 keV/nucleon.

⁽¹⁰⁾

Energy range 0.5−2.0 MeV/nucleon.

⁽¹¹⁾

In the range 0.1−1.0 MeV/nucleon.

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