Space Instrumentation - Magnetism and applications 7.6.2020 Prof. Eija Tanskanen Aalto University School of Electrical Engineering Department of ...
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Space
Instrumentation
Magnetism and applications
7.6.2020
Prof. Eija Tanskanen
Aalto University
School of Electrical Engineering
Department of Radio Science and Engineering
Today Ground-based space weather measurements: Magnetometers & all-sky cameras Magnetic measurements Geomagnetic activity indices
Brief history of magnetic measurements
• First scientific magnetometer 1832 (Gauss)
• First scientific satellite 1958 (Explorer I)
• First magnetotail observations 1965
• Continuous ground-based observations since 1966 (Kyoto AL)
• Solar wind observations since 1966, continuous L1 observations
since 1997 (ACE)
Space Instrumentation, Aalto University, Eija Tanskanen
14.6.2021
3
Detecting (geo)magnetic activity (and currents)
Geomagnetic activity can be detected by all-sky cameras,
magnetometers, radars, riometers, ionosondes, satellites ...
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4… or by an astronaut from a space shuttle
5Geomagnetic activity detected by magnetometers
Analog magnetometer from 1960´s
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7Modern ground-based magnetometers
Flux gate magnetometer Helicopter magnetometer
for scientific measurements for magnetic surveys
8Spacecraft magnetometers
Eija Tanskanen, 2016 Ingo Richter, 2010
9All-sky cameras
10Mawson, Antarctica Nurmijärvi, Suomi
Observatories
Addis Ababa, Ethiopia Canberra, Australia
Apia, Western Samoa
Dalat, Vietnam
L´Aquila, Italy Greenland
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11Magnetometer chains
• IMAGE network
• CARISMA (earlier
CANOPUS)
• 210 CHAIN
• Greenland chain
• MAGDAS
• Scandinavian SME (only
historical data).
12Magnetometer networks
12 Kyoto AL observatories 29 IMAGE observatories
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Courtesy of Häkkinen
13Conjugate magnetic measurements
14Geomagnetic storm signature & detection
180° 180°
220° 140°
80°
260° 100°
300° 340° 20° 60°
60°
40°
HONOLULU SAN JUAN KAKIOKA
20°
0°
-20°
HERMANUS
-40°
-60°
-80°
Dst NETWORK
Geomagnetic storms detected by magnetometers close to magnetic
equator, not exactly at the equator due to the equatorial electrojets.
15Equatorial electrojet
180° 180°
220° 140°
80°
260° 100°
300° 340° 20° 60°
60°
40°
HONOLULU SAN JUAN KAKIOKA
20°
0°
-20°
HERMANUS
-40°
-60°
-80°
Dst NETWORK
16Geomagnetic storm index: Dst index
Formed as an envelope curve from the 12 equatorial magnetometers.
Geomagnetic storm starting on 15th July 2000
- with a peak amplitude 300 nT
- duration 5 days
17Geomagnetic activity at high-latitudes
during storms
Pulsations
Storm-time
substorms
18Extreme and moderate activity Storm-time Non-storm substorm substorm 19
Magnetospheric substorm
• Magnetospheric substorms i.e. Birkeland’s polar
elementary storms, auroral substorms, etc.
20One substorm definition
“Magnetic substorm is a transient process, in which a significant
amount of energy is carried from the solar wind into the auroral
ionosphere and magnetosphere”.
McPherron et al. 1979
21“Typical” auroral substorm
- All substorms are different, there is not “a normal” substorm. Statistical properties can
be computed, but they need to be understood as average properties and not a single
such substorm does not need to exist.
- A typical substorm signature: a negative bay in north-south (X) component of the
terrestrial magnetic field.
22Westward electrojet index AL/IL/SML/CL
IMAGE chain 16-03 UT
(about 18:30 - 05:30 MLT)
• Following AL description IL index is formed based on IMAGE 12 MLT
ground-based magnetic measurements in UT-sector 16-03
UT.
18 MLT 06 MLT
00 MLT
IL
[ nT ] IL minimum
substorm
onset 23Latitudinal variation of substorms
• Substorms were categorized in Number Intensity
0°
the latitude bins according to the
NAL 20° 40°
LYR
Intensity
station where the maximum # 89 HOR
HOP 75°
340nT
deviation of the X component 341nT
was recorded
BJN
# 104 280nT
282nT
• Latitudinal zones from north to SOR 70°
# 143 430nT
south (geogr. coord.)
TRO KEV
AND MAS
LEK
KIL 428nT
MUO
– north of 76°
ABK LOZ
KIR SOD
PEL
# 12 65°
760nT
– 73° - 76° RVK
LYC
758nT
OUJ
– 69° - 73°
ND
IA
EN
AY
LA
SS
ED
HAN
RW
#5 792nT 790nT
RU
– 65° - 69°
FIN
SW
NO
NUR 60°
UPS
800
– south of 65° 800 600 400 200nT
50 100 150 # 800 600 400 200nT
24Auroral oval during a storm and a substorm
Storms Substorms
25Storm-time substorms and non-storm
substorms
Site of maximum dH/dt i.e. substorm onset location is dramatically more north
for non-storm than storm-time substorms.
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26Substorm morphology
Typical storm-time substorm is about twice as intense and
carries about 2.5 times more energy into the ionosphere
than a typical non-storm substorm.
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27You can also read
