J/A+A/578/A137 Solar acoustic modes in period 1996-2014 (Salabert+, 2015)
Seismic sensitivity to sub-surface solar activity from 18 years of GOLF/SoHO
observations.
Salabert D., Garcia R.A., Turck-Chieze S.
<Astron. Astrophys. 578, A137 (2015)>
=2015A&A...578A.137S 2015A&A...578A.137S
ADC_Keywords: Sun
Mission_Name: SOHO
Keywords: Methods: data analysis - Sun: helioseismology - Sun: activity
Abstract:
Solar activity has significantly changed over the last two Schwabe
cycles. After a long and deep minimum at the end of Cycle 23, the
weaker activity of Cycle 24 contrasts with the previous cycles. In
this work, the response of the solar acoustic oscillations to solar
activity is used in order to provide insights into the structural and
magnetic changes in the sub-surface layers of the Sun during this
on-going unusual period of low activity. We analyze 18 years of
continuous observations of the solar acoustic oscillations collected
by the Sun-as-a-star GOLF instrument on board the SoHO spacecraft.
From the fitted mode frequencies, the temporal variability of the
frequency shifts of the radial, dipolar, and quadrupolar modes are
studied for different frequency ranges that are sensitive to different
layers in the solar sub-surface interior. The low-frequency modes show
nearly unchanged frequency shifts between Cycles 23 and 24, with a
time evolving signature of the quasi-biennial oscillation, which is
particularly visible for the quadrupole component revealing the
presence of a complex magnetic structure. The modes at higher
frequencies show frequency shifts that are 30% smaller during Cycle
24, which is in agreement with the decrease observed in the surface
activity between Cycles 23 and 24. The analysis of 18 years of GOLF
oscillations indicates that the structural and magnetic changes
responsible for the frequency shifts remained comparable between
Cycle23 and Cycle 24 in the deeper sub-surface layers below 1400km as
revealed by the low-frequency modes. The frequency shifts of the
higher-frequency modes, sensitive to shallower regions, show that
Cycle 24 is magnetically weaker in the upper layers of Sun
Description:
The central frequencies of the l = 0, 1, 2, and 3 acoustic modes of
oscillations of the Sun between 1500{micro}Hz and 4000{micro}Hz and
their associated formal 1σ uncertainties extracted from 365-day
subseries of 18 years of the space-based, Sun-as-a-star GOLF/SoHO
observations between 1996 April 11, and 2014 March 5 are presented. As
a four-time overlap of 91.25 days was used, a total of 69 frequency
tables are provided. We note that one of every four frequency tables
contains frequencies extracted from independent subseries. Quality
criteria were defined based on the fitted mode parameters and their
associated uncertainties in order to remove outliers. An info file
containing the associated starting date and duty cycle of each 365-day
subseries is also provided. The corresponding mean 10.7cm radio flux
is also given in the info file.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
info.dat 40 69 Year/Month/Day, duty cycle, and 10.7cm radio flux
tables.dat 22 4485 Solar p-mode frequencies (11-Apr-1996/06-Apr-2014)
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See also:
J/A+A/309/655 : Solar chromospheric activity (HeI 10830A) (Shcherbakov+, 1996)
J/A+A/562/L10 : Solar activity reconstructed for 3 millennia (Usoskin+, 2014)
Byte-by-byte Description of file: info.dat
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Bytes Format Units Label Explanations
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1- 2 I02 --- Index [01/69] Index
4- 14 A11 "date" Obs.Start Starting date (YYYY-MMM-DD) of 365-day
observations
15 A1 --- --- [/]
16- 26 A11 "date" Obs.End Ending date (YYYY-MMM-DD) of observation
28- 33 F6.2 % dc [58/100] Duty cycle
35- 40 F6.2 10kJy Flux [68/193] 10.7cm radio flux in RF units (1)
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Note (1): 1 RF = 10-22J/s/m2/Hz = 104Jy = 10-22kg/s2.
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Byte-by-byte Description of file: tables.dat
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Bytes Format Units Label Explanations
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1- 2 I02 --- Index [01/69] Cycle index
4- 5 I2 --- n [9/27] Radial order
7 I1 --- l [0/3] Angular degree
9- 16 F8.3 uHz nu [1407/4045] Solar acoustic mode frequency
18- 22 F5.3 uHz e_nu [0/1] Uncertainty in nu
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Acknowledgements:
David Salabert, david.salabert(at)cea.fr
(End) David Salabert [AIM/CEA-DSM/CNRS], Patricia Vannier [CDS] 20-Mar-2015