Post on 26-Jan-2016
description
On the high frequency ingredients of the secular variation
C. Demetrescu, V. Dobrica, I. Vaduva
Institute of Geodynamics, Bucharest, Romaniae-mail: crisan@geodin.ro
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)
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
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
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
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)
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
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)
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
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.
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
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
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
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!
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
~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
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
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;