Transcript Heliospheric Magnetic Field 1835-2009

Heliospheric Magnetic Field
1835-2010
Leif Svalgaard
Stanford University, CA
[email protected]
http://www.leif.org/research
http://arxiv.org/ftp/arxiv/papers/1002/1002.2934.pdf
Svalgaard & Cliver JGR 2009JA015069 (in press)
SORCE 2010, Keystone, CO, May 19, 2010
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24-hour running means of the Horizontal Component of the low- & midlatitude geomagnetic field remove most of local time effects and leaves a
Global imprint of the Ring Current [Van Allen Belts]:
A quantitative measure of the effect can be formed as a series of the unsigned
differences between consecutive days: The InterDiurnal Variability, IDV-index
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IDV is strongly correlated with HMF B,
but is blind to solar wind speed V
nT
10
9
8
7
6
5
4
3
2
1
0
IDV Independent of Solar Wind Speed
10
9
8
7
6
5
4
3
2
1
0
B obs
B calc from IDV
B obs median
B std.dev
100% =>
Coverage
1960 1965 1970
1975 1980 1985 1990
nT
600
V
20
500
400
15
IDV
300
?
10
200
5
100
B
0
1960
18
16
0
1970
1980
1990
2000
2010
IDV vs. Solar Wind Speed V (1963-2010)
IDV
1995 2000 2005 2010
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HMF B as a Function of IDV09
10
B nT
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1963-2010
10
8
8
6
6
4
2
4
y = 1.4771x0.6444
2
R = 0.8898
y = 0.4077x + 2.3957
2
R = 0.8637
4
10
0
0
2
6
8
12
14
2
R = 0.0918
2
V km/s
IDV
16
0
350
400
450
500
550
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IDV and Heliospheric Magnetic Field Strength B for years 1835-2009
IDV Index and Number of Contributing Stations
25
70
IDV nT
20
N
60
Individual stations
50
15
40
30
10
20
5
10
0
1830
0
1840 1850
B nT
1860
1870 1880
1890
1900 1910
1920 1930
1940
1950 1960
1970
1980 1990
2000
2010
Heliospheric Magnetic Field Strength B (at Earth) Inferred from IDV and Observed
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B (IDV)
8
6
13
23
4
B (obs)
2
0
1830
1840 1850
1860
1870 1880
1890
1900 1910
1920 1930
1940
1950 1960
1970
1980 1990
2000 2010
Year
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The previous Figures showed yearly average values. But we can also
do this on the shorter time scale of one solar rotation:
Heliospheric Magnetic Field Magnitude B from Geomagnetic Activity IDV (27-Day Bartels Rotations)
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B = 1.333 IDV
0.7
13-rotation running means
B obs.
12
10
8
6
4
Floor
2
0
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
The Figure shows how well the HMF magnitude B can be constructed from IDV.
Some disagreements in the 1980s are due to the HMF being only sparsely sampled
by spacecraft: in some rotations more than two thirds of the data is missing
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The negative part of the Dst-index is a measure of the strength of
the Ring Current. IDV has an excellent correlation with Dst
computed only from times when Dst was negative.
J. Love has reconstructed Dst back to 1905 using data from several
geomagnetic observatories. For yearly averages: IDV = -0.45 [-Dst]
Negative D st and IDV measure the same effect
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16
IDV nT
14
12
10
8
6
4
2
0
1900
<IDV>
-0.45 <-D st>
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
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The HMF [and the ‘open flux’
calculated from B] has been
controversial in the past, with
claims of a centennial doubling
of the Sun’s coronal magnetic
field. This is no longer the case.
Several groups have converged
to a firm consensus:
Convergence of HMF B of Lockwood & Rouillard et al. to Svalgaard & Cliver
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B nT
10
8
6
4
2
IDV05
0
1880
1890
1900
1910
IDV09
1920
1930
L1999
1940
1950
R2007
1960
L2009
1970
1980
HMF obs
1990
2000
2010
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Reconstruction of HMF B from cosmic ray modulation [measured (ionization
chambers and neutron monitors) and inferred from 10Be in polar ice cores]
first gave results [McCracken 2007] discordant from our geomagnetic method:
Heliospheric Magnetic Field Comparisons
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10
Be data spliced to Ionization Chamber data spliced to Neutron Monitor data
B nT
B S&C
8
6
4
2
0.2885
B OBS
B LR&F
B McC
Krakatoa?
0
1830
1850
1870
1890
1910
1930
1950
1970
1990
2010
The splicing of the ionization chamber data to the neutron monitor data around
1950 seems to indicate an upward jump in B of 1.7 nT which is not seen in the
geomagnetic data. The very low values in ~1892 are caused by excessive
10Be deposition [of unknown origin]
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A reconstruction by Steinhilber et al [2010] on basis of 10Be agrees
much better with ours based on IDV. The excessive deposition of 10Be
~1890 is still a problem for cosmogenically-based reconstructions [25-yr means]:
Webber & Higbie [2010] point out “those are most likely not solely related to
changes in solar heliospheric modulation, but other effects such as local and
regional climate near the measuring sites may play a significant role.
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Since we can also estimate solar wind speed from geomagnetic indices
[Svalgaard & Cliver, JGR 2007] we can calculate the radial magnetic flux
from the total B using the Parker Spiral formula:
Radial Component of Heliospheric Magnetic Field at Earth
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Br nT
5
Ceiling
4
R2 = 0.0019
3
2
Floor
1
Year
0
1830
1840
1850
1860
1870
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
There seems to be both a Floor and a Ceiling and most importantly no longterm trend since the 1830s.
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The absence of long-term trend probably means that there was no long-term
trend in TSI as well:
And that brings us within the subject of this meeting
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