on the high frequency ingredients of the secular variation c. demetrescu, v. dobrica, i. vaduva...
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![Page 1: On the high frequency ingredients of the secular variation C. Demetrescu, V. Dobrica, I. Vaduva Institute of Geodynamics, Bucharest, Romania e-mail: crisan@geodin.ro](https://reader036.vdocuments.us/reader036/viewer/2022062803/56649cce5503460f94999858/html5/thumbnails/1.jpg)
On the high frequency ingredients of the secular variation
C. Demetrescu, V. Dobrica, I. Vaduva
Institute of Geodynamics, Bucharest, Romaniae-mail: [email protected]
Acknowledgements: The study has been supported by the Institute of Geodynamics (Projects 2/2003-2007) and by the National Authority for Scientific Research (Projects 151/2007, 81-021/2007)
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Background from http://www.geomag.bgs.ac.uk/mercator.html
Outline
- have a look at time series of annual means from 22 observatories (15 with 100-150 years of activity) - discuss the ingredients of the main field and of its secular variation
- discuss the time-space evolution of the various main field ingredients
- comparison with main field models (IGRF, CM4) - conclusions
1840
1860
1880
1900
1920
1940
1960
1980
2000
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1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
19200
19600
20000
20400
20800
21200
H (
nT
)
C L F
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
17600
18000
18400
18800
19200
19600
H (
nT
)
H A D
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
16800
17000
17200
17400
17600
H (
nT
)
B F E
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
16400
16600
16800
17000
17200
17400
H (
nT
)
E S K
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
18500
19000
19500
20000
20500
21000
H (
nT
)
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
21000
22000
23000
24000
25000
26000
H (
nT
)
C O I
F R D
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
17600
18000
18400
18800
19200
19600
H (
nT
)
V A L
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
36500
37000
37500
38000
38500
39000
H (
nT
)
A B G
~80-year variation visible in the time series of annual means of geomagnetic elements
- the solar cycle signature has long been recognized (Chapman & Bartels, 1940; Alldredge, JGR, 1976; Courtillot&LeMouel, JGR, 1976)
- if not accounted for, the external contributions map into the modelled internal field when using observatory data
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
17600
18000
18400
18800
19200
19600
H (
nT
)
H A D
- correction limited to the 11-year solar cycle effects (Sabaka et al., GJI, 2004; Olsen & Mandea, EPSL, 2007, Verbanac et al., EPS, 2007 ) by parameterization with Dst (Est+Ist) and Ap
1940 1960 1980 2000
Y ea r
-20
-10
0
10
20
30
Su
nsp
ot-c
ycle
-rel
ated
var
iati
on (
nT
)
H
+ External contributions
Observatory data
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Geomagnetic indices to quantify long-term external field variations
Geomagnetic activity- aa (Mayaud, 1972; 1980) BV2
- IHV (Svalgaard et al., 2004; Svalgaard&Cliver, 2007; Mursula et al., 2004) BV2
- IDV (Svalgaard&Cliver, 2004) B- Dst for storm-time variations
Good correlation with the solar activity (R) in terms of 11-year averages, but differences in each solar cycle
1 8 6 0 1 8 8 0 1 9 0 0 1 9 2 0 1 9 4 0 1 9 6 0 1 9 8 0 2 0 0 0
Y ea r
4
8
1 2
1 6
2 0
2 4
2 8
3 2
3 6
4 0
aa (
nT
)
a aa a 1 1
Solar quiet daily variation Sq- x, y, z, r (Le Mouel et al., EPSL, 2005) TSI
1 8 6 0 1 8 8 0 1 9 0 0 1 9 2 0 1 9 4 0 1 9 6 0 1 9 8 0 2 0 0 0
Y ea r
4
8
1 2
1 6
2 0
IDV
(n
T)
ID VID V 1 1
A common trend is present also at longer timescales:- 22-year magnetic cycle (MC)- “secular”, “80-90-year”, Gleissberg cycle (GC)
R 1 1
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1 8 5 0 1 9 0 0 1 9 5 0 2 0 0 0
Y ea r
- 8- 40481 2
aa (nT
)
08
1 62 43 24 0
aa (
nT
)
G C
M C
S C
Successive extraction of the 11-, 22- and ~80-year variations (running averages)
1 8 5 0 1 9 0 0 1 9 5 0 2 0 0 0
Y ea r
- 4
- 2
0
2
4
a aI D VI H VRT S I
1 9 1 0 1 9 2 0 1 9 3 0 1 9 4 0 1 9 5 0
Y ea r
- 4
- 2
0
2
4
M C
G C
Sta
nd
ard
dev
iati
on(Demetrescu&Dobrica, JGR, 2008)
Curves are reduced to their means over the common time interval and scaled with their standard deviations about the mean as a unit
(Demetrescu&Dobrica, JGR, 2008)
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1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
17600
18000
18400
18800
19200
19600
H (
nT
)
1 1 -y ea r sm o o th in g2 2 -y ea r sm o o th in g7 8 -y ea r sm o o th in gm easu red v a lu es
Ingredients of the observed fieldExample of data treatment
Steady variation
The 11- (red), 22- (blue) and ~80-year (green) variations extracted from data.
Successively filtering out the sunspot cycle signature, a 22-year variation, and a ~80-year variation present in the time series of observatory annual means, by running averages with 11-, 22- and 78-year windows respectively, results in a so called “steady variation”.
1860 1880 1900 1920 1940 1960 1980 2000
Y e ar
-250
-200
-150
-100
-50
0
50
100
150
200
250
300
350
400
H (
nT)
H A D
1 1
2 2
~ 8 0 -y ea r v a r ia tio n
(Demetrescu&Dobrica, RRG, 2005)
HAD
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11-year variation ~80-year variation
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
-100
-80
-60
-40
-20
0
20
40
60S
un
spot
-cyc
le-r
elat
ed v
aria
tion
(n
T)
0
40
80
120
160
200
Su
nsp
ot nu
mb
er
H
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
-100
-80
-60
-40
-20
0
20
40
60
80
22-y
ear
vari
atio
n (
nT)
H
F R D
A B G
H O N K A K
E u ro p e
A P I
H E R
T R W
V S S
L N N
IR K
S S HO T TT F S
22-year variation
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
-100
-80
-60
-40
-20
0
20
40
60
80
100
Sun
spot
-cyc
le-r
elat
ed v
aria
tion
(n
T)
Z
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
-120
-100
-80
-60
-40
-20
0
20
40
60
80
100
120
22-y
ear
vari
atio
n (
nT
)
Z
K A K
A B GF R D
H O N
E u ro p e
A P I
L N N
O T T
S S H
IR K
H E R
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
-0 .1
-0.05
0
0.05
0.1
0.15
Sun
spot
-cyc
le-r
elat
ed v
aria
tion
(de
gree
) D
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
-0 .15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
22-y
ear
vari
atio
n (
deg
ree)
H E R
F R D
A B G
E u ro p e
D
A P I
O T T
S S H
IR KL N N
1860 1880 1900 1920 1940 1960 1980
Y ea r
-800
-400
0
400
800
80-y
ear
vari
atio
n (
nT
)
A B G
F R D
E u ro p e
S S H
H O N
L N N
A P I
O T T
K A KIR K
H
1860 1880 1900 1920 1940 1960 1980
Y ea r
-800
-400
0
400
800
80-y
ear
vari
atio
n (
nT
)
A B G
F R D
E u ro p eS S H
H O N
L N N
A P I
O T T
K A K
IR K
Z
1860 1880 1900 1920 1940 1960 1980
Y ea r
-0 .8
-0.4
0
0.4
0.8
80-y
ear
vari
atio
n (
deg
ree) A B G
F R D
E u ro p e
S S H
H O N
L N N
A P I
O T T
K A K
IR K
D
1860 1880 1900 1920 1940 1960 1980 2000
Y ea r
-80
-60
-40
-20
0
20
40
60
80
Sun
spot
-cyc
le-r
elat
ed v
aria
tion
(n
T)
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1860 1880 1900 1920 1940 1960 1980
Y ea r
-800
-400
0
400
800
stea
dy
vari
atio
n (
nT
)
A B G
F R D
E u ro p e
S S H
H O N
L N N
A P IO T T
K A K
IR K
H
1860 1880 1900 1920 1940 1960 1980
Y ea r
-2000
-1000
0
1000
2000
stea
dy
vari
atio
n (
nT
)
A B G
F R D
E u ro p e
S S H
H O N
L N N
A P I
O T T
K A K
IR K
Z
Steady variation
- carries the largest part of the field
- in terms of variation relative to the mean for the time interval with data
- large lateral differences in the time variation
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Jerk ingredients
1850 1900 1950 2000
Y ea r
-0 .05
0
0.05
0.1
0.15
0.2
0.25
dD/d
t (d
egre
e/ye
ar)
C L F- the long-term variation of the geomagnetic field, dominated by the presence of geomagnetic jerks separating intervals of a relative smooth variation of the field,
- is produced by the ~80-year variation combined with the 22-year variation, both of internal origin, on which the SC-related variation is superimposed.
- the 11-year variation is decisive though in establishing the very short time scale characterizing jerks, and to some extent also the amplitude and timing of the jerk.
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1880 1900 1920 1940 1960 1980 2000
Y ea r
19200
19600
20000
20400
20800
21200
H (
nT
)
m easu red v a lu es
C M 4 m o d e l
IG R F m o d e l
C L F
Comparison of H geomagnetic component - annual means, IGRF and CM4 models -
1880 1900 1920 1940 1960 1980 2000
Y ea r
18200
18400
18600
18800
19000
H (
nT
)
m easu red v a lu es
IG R F m o d e l
C M 4 m o d e lN G K
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11-year variation 22-year variation ~80-year variation
1880 1900 1920 1940 1960 1980 2000
Y ea r
-30
-20
-10
0
10
20
30
H (
nT
)
m easu red v a lu es
C M 4 m o d e l
IG R F m o d e l
C L F
1880 1900 1920 1940 1960 1980 2000
Y ea r
-40
-20
0
20
40
H (
nT
)
m easu red v a lu es
C M 4 m o d e l
IG R F m o d e l
C L F
1880 1900 1920 1940 1960 1980 2000
Y ea r
-200
-160
-120
-80
-40
0
40
H (
nT
)
m easu red v a lu es
IG R F m o d e lC L F
1880 1900 1920 1940 1960 1980 2000
Y ea r
-30
-20
-10
0
10
20
30
H (
nT
)
m easu red v a lu es
C M 4 m o d e l
IG R F m o d e l
N G K
1880 1900 1920 1940 1960 1980 2000
Y ea r
-40
-20
0
20
40
60
H (
nT
)
m easu red v a lu es
C M 4 m o d e l
IG R F m o d e l
N G K
1880 1900 1920 1940 1960 1980 2000
Y ea r
-250
-200
-150
-100
-50
0
50
H (
nT
)
m easu red v a lu es
IG R F m o d e lN G K
Comparison of ingredients of H
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1950.5 1960.5 1970.5 1980.5 1990.5 2000.5
Y e ar
-15
-10
-5
0
5
10
15
Hs
(nT
)
N G K
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Y ea r
-80
-60
-40
-20
0
20
40
60
80
Su
nsp
ot-c
ycle
-rel
ated
var
iati
on (
nT
)
1880 1900 1920 1940 1960 1980 2000
Y ea r
-30
-20
-10
0
10
20
30
H (
nT
)
m easu red v a lu es
C M 4 m o d e l
IG R F m o d e l
C L F
1880 1900 1920 1940 1960 1980 2000
Y ea r
-30
-20
-10
0
10
20
30
H (
nT
)
m easu red v a lu es
C M 4 m o d e l
IG R F m o d e l
N G K
1960 1970 1980 1990 2000
Y ea r
-30
-20
-10
0
10
20
H (
nT
)
N G K
C L F
K A K
H E R
IGRF: - no provision for external variations; the SC-related variation maps in the modelled main field
CM4: - the external field is accounted for via the Dst index
11-year SC-related variation in main field models
Unaccounted for, this variation leaks into the main field models
IGRF: - sampling the field every 5 years results in a distorted SC variation
CM4: - partially successful: CLF, NGK – yes; KAK, HER - no
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1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Y ea r
7.6e+024
7.8e+024
8e+024
8.2e+024
8.4e+024
M (
nT
m3 )
ca lcu la ted v a lu es
1 1 -y ea r sm o o th in g
2 2 -y ea r sm o o th in g
7 8 -y ea r sm o o th in g
Dipole moment, IGRF
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Y ear
-6e+021
-4e+021
-2e+021
0
2e+021
4e+021
M (
nT
m3 ) 1 1
2 2
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Y ea r
-2e+022
-1e+022
0
1e+022
2e+022
3e+022
M (
nT
m3 )
1 1
2 2
~ 8 0 -y ea r v a r ia tio n
211
211
201
3 )h()g()g(rM
The SC-related variation is even seen in the dipole part of the modelled main field!
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Maps of the 22- and ~80-year variations
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg rees)
-60
-45
-30
-15
0
15
30
45
60
Lat
itude
(de
gree
s)
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg rees)
-60
-45
-30
-15
0
15
30
45
60
Lat
itude
(de
gree
s)
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
900
1000
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg ree s)
-60
-45
-30
-15
0
15
30
45
60
Lat
itud
e (d
egre
es)
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg rees)
-60
-45
-30
-15
0
15
30
45
60
Lat
itude
(de
gree
s)
-140-130-120-110-100-90-80-70-60-50-40-30-20-1001020304050607080
1940 1965
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~80-year variation maps, IGRF
1940
1945
1955
1950
1960
1965
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg rees)
-60
-45
-30
-15
0
15
30
45
60
Lat
itude
(de
gree
s)
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
900
1000
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg rees)
-60
-45
-30
-15
0
15
30
45
60
Lat
itude
(de
gree
s)
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
900
1000
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg rees)
-60
-45
-30
-15
0
15
30
45
60
Lat
itud
e (d
egre
es)
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
900
1000
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg rees)
-60
-45
-30
-15
0
15
30
45
60
Lat
itud
e (d
egre
es)
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
900
1000
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg rees)
-60
-45
-30
-15
0
15
30
45
60
Lat
itude
(de
gree
s)
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
900
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg ree s)
-60
-45
-30
-15
0
15
30
45
60
Lat
itude
(de
gree
s)
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
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Time derivative of the steady radial field at Earth’s surface
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg rees)
-60
-45
-30
-15
0
15
30
45
60
Lat
itud
e (d
egre
es)
-140-130-120-110-100-90-80-70-60-50-40-30-20-100102030405060708090100110120130
1940, IGRF
-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180
L o n g itu d e (d eg ree s)
-60
-45
-30
-15
0
15
30
45
60
Lat
itud
e (d
egre
es)
-160
-140
-120
-100
-80
-60
-40
-20
0
20
40
60
80
100
120
1965, IGRF
WMM 2005
westward displacement of main secular variation foci
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Conclusions
- data (annual means) from 22 observatories with long activity (15 with 100-150 years) have been processed to show the existence and some of the characteristics of a 22-year variation and of a ~80-year variation, superimposed on a so-called steady variation;
- in terms of the present analysis, the jerks seem to be merely a result of the superposition of the 11-year solar-cycle-related on the 22-year and the ~80-year variations. The way the three combine makes the difference in timing, magnitude, and length of jerks as observed;
- the steady variation, which carries the largest part of the field is characterized by a westward movement of its secular variation foci;
- the ~80-year variation shows several maxima and minima with variable amplitudes, concentrated in two longitudinal bands;
- the 22-year variation shows a high temporal and spatial variability; - the external variation still present in data (annual means uncorrected or incompletely corrected for the 11-year SC-related variation) leaks into the main field models;
- in terms of secular variation, all ingredients presented contribute significantly;