J/A+A/635/A79 Pitch-angle distributions of solar wind (Carcaboso+, 2020)
Characterisation of suprathermal electron pitch-angle distributions:
Bidirectional and isotropic periods in solar wind.
Carcaboso F., Gomez-Herrero R., Espinosa Lara F., Hidalgo M.A., Cernuda I.,
Rodriguez-Pacheco J.
<Astron. Astrophys. 635, A79 (2020)>
=2020A&A...635A..79C 2020A&A...635A..79C (SIMBAD/NED BibCode)
ADC_Keywords: Sun ; Solar system
Keywords: Sun: heliosphere - coronal mass ejections (CMEs) - solar wind -
methods: data analysis - methods: statistical - methods: analytical
Abstract:
Suprathermal electron pitch-angle distributions (PADs) contain
substantial information about the magnetic topology of the solar wind.
Their characterisation and quantification allow us to automatically
identify periods showing certain characteristics.
This work presents a robust automatic method for the identification
and statistical study of two different types of PADs: bidirectional
suprathermal electrons (BDE, often associated with closed magnetic
structures) and isotropic (likely corresponding to solar-detached
magnetic field lines or highly scattered electrons).
Spherical harmonics were fitted to the observed suprathermal PADs of
the 119-193eV energy channel of STEREO/SWEA from March 2007 to July
2014, and they were characterised using signal processing analysis in
order to identify periods of isotropic and bidirectional PADs. The
characterisation has been validated by comparing the results obtained
here with those of previous studies.
Interplanetary coronal mass ejections (ICMEs) present longer BDE
periods inside the magnetic obstacles. A significant amount of BDE
remain after the end of the ICME. Isotropic PADs are found in the
sheath of the ICMEs, and at the post-ICME region likely due to the
erosion of the magnetic field lines. Both isotropy and BDE are
solar-cycle dependent. The isotropy observed by STEREO shows a nearly
annual periodicity, which requires further investigation. There is
also a correspondence between the number of ICMEs observed and the
percentage of time showing BDE.
A method to characterise PADs has been presented and applied to the
automatic identification of two relevant distributions that are
commonly observed in the solar wind, such as BDE and isotropy. Four
catalogues (STEREO-A and STEREO-B for isotropic and BDE periods of at
least 10min) based on this identification are provided for future
applications.
Description:
Pitch-angle distributions observed by STEREO-A during 1st March 2007
and 31st July 2014.
A moving window of approximately 20 minutes calculates the time
percentage of fulfilling the condition A2>0, gamma>15% and
SNR24>5.76dB.
If the condition is fulfilled for at least 10 minutes of that moving
window, the period is a candidate for the list. When two or more
candidates have a separation of less than 2 hours, they are considered
as the same event.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
bidirsta.dat 150 1227 Bidirectional periods in solar wind observed by
STEREO-A (2007-03-03, 2014-07-16)
bidirstb.dat 150 1333 Bidirectional periods in solar wind observed by
STEREO-B (2007-03-01, 2014-07-29)
isosta.dat 150 2125 Isotropic periods in solar wind observed by
STEREO-A (2007-03-01, 2014-07-31)
isostb.dat 150 2367 Isotropic periods in solar wind observed by
STEREO-B (2007-03-01, 2014-07-29)
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Byte-by-byte Description of file: *.dat
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Bytes Format Units Label Explanations
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1- 19 A19 "datime" Obs.begin Beginning date (UTC)
21- 39 A19 "datime" Obs.end End date (UTC)
41- 47 F7.2 min Dur Time duration
49- 70 A22 --- Cat Catalogued (1)
72- 76 F5.2 nT B ? Magnetic field
78- 81 F4.2 nT e_B ? Magnetic field error
83- 87 F5.2 -- Beta ? Plasma beta
89- 93 F5.2 -- e_Beta ? Plasma beta error
95-100 F6.2 % Ripple ? Anisotropy index gamm
102-105 F4.2 % e_Ripple ? Anisotropy index gamma error
107-112 F6.2 --- SNR24 ? SNR24 index, in dB unit
114-117 F4.2 --- e_SNR24 ? SNR24 index error, in dB unit
119-127 E9.4 K Tp ? Proton temperature
129-137 E9.4 K e_Tp ? Proton temperature error
139-145 F7.2 km/s Vsw ? Solar wind speed
147-150 F4.2 km/s e_Vsw ? Solar wind speed error
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Note (1): Cataloged flags as follows:
FF = Fast-Forward shock
FR = Fast-Reverse shock
ICME = Interplanetary Coronal Mass Ejection
Post-ICME = Rear part of ICME (defined as 1.2 times its duration)
SIR = Stream Interaction Region
No = No catalogued
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Acknowledgements:
Fernando Carcaboso, fernando.carcaboso(at)edu.uah.es
History:
10-Mar-2020: on-lien version
03-Sep-2020: LABELS CORRECTED !!!! (from author)
(End) Patricia Vannier [CDS] 03-Feb-2020