Update on McMAC & Falcon
Ground Magnetometers
Peter Chi, The McMAC Team, and The Falcon Team
UCLA Institute of Geophysics and Planetary Physics
Joint GEM-ULTIMA Forum on Ground Magnetometers
December 4, 2011, San Francisco, California
McMAC, Falcon w.r.t. other arrays in North America
Kodiak
Harris
Stanford
Pueblo
Laurel
Wallops
Updates on McMAC and Falcon
Stations

McMAC:
◦ Richardson station (UT Dallas) has stopped operation in
April 2011 due to the construction of a new football field.
The plan is to move the magnetometer to a nearby
location hosted by Polatomic.
◦ We have discontinued the monitoring at the Linares
station (in Mexico) due to the difficulty in operation and
the lack of field line resonance signatures picked up from
Linares.

Falcon:
◦ The Wallops Island (Virginia) magnetometer is set up in
June 2011. The Wallops station and the Laurel station can
form a pair for FLR observations.
◦ The Laurel station now has Internet but is experiencing
problems with GPS reception.
Mid-continent MAgnetoseismic
Chain (McMAC)
● The mean north-south separation
between two adjacent McMAC stations
is 275 Km.
● Joint operation with CANOPUS
Churchill Line (Canada), IGPP-LANL
(U.S.) and MAGDAS (Japan) provides
the magnetic field data from L = 1.2 to
11+ at one local time.
Field Line Resonance Sounding of the
Magnetosphere by Ground Observations
•
Obayashi
&Jacobs
[1958]
•
•
Obayashi and Jacobs [1958] made the first known study using
FLR to estimate plasma density in the exosphere.
Baransky et al. [1985] developed the gradient method.
FLR sounding studies by the Newcastle group in the early
1990s motivated other groups in the world to follow.
Background
• FLR sounding using the gradient technique (crossphase and cross-power) has become a popular and
important use of ground magnetometer data.
• It has been found that the gradient technique can
work for low-latitude data for 80-90% of daytime
[see, for example, Waters et al., 1994].
• An often asked question when planning coordinate
studies with spacecraft data is the success rate of the
gradient technique for different LT hours and
latitudes.
• More studies are needed to answer this question.
Automatic Detection of FLR Frequencies
1.
2.
3.
4.
5.
Peaks in cross phase
Coherence
t-statistic
Positive slope in
power ratio
Remove isolated
selections
X-Phase: - (CAM)+  (WRTH) L mid=3.06 2007-10-25
60
100
55
50
45
Freq [mHz]
• In North America there
are potentially more than
100 pairs of stations
useful for gradient
analysis (e.g. cross-phase);
Picking FLR frequencies by
visual inspection is too
time-consuming
• Selection criteria:
50
40
35
0
30
25
20
-50
15
10
-100
5
2
4
6
8
10 12 14 16 18 20 22
UT [hours]
Data Set
• 4-s data (down-sampled from the 0.5-s data)
from 10 McMAC stations (L = 1.3 – 3.4)
• July 2006 – June 2007
FLR frequency (n=1) vs. L
L = 3.3
L = 3.1
L = 2.7
L = 2.4
2000
5000
5000
5000
1500
4000
4000
4000
3000
3000
3000
2000
2000
2000
1000
1000
1000
1000
500
0
0
50
f [mHz]
100
0
0
L = 2.1
50
f [mHz]
100
0
0
L = 1.9
50
f [mHz]
100
0
0
L = 1.8
2500
1000
400
2000
800
300
1500
600
1000
400
50
f [mHz]
100
L = 1.6
60
40
200
500
0
200
0
50
f [mHz]
100
0
20
100
0
50
f [mHz]
100
0
0
50
f [mHz]
100
0
0
50
f [mHz]
100
Occurrence Rate vs. Local Time
0.7
0.6
0.5
0.4
0.3
0.2
noon
L=3.3
L=3.1
L=2.7
L=2.4
L=2.1
L=1.9
L=1.8
midnight
0.1
0
5
10
15
UT [hours]
20
Occurrence vs. Separation
0.7
0.6
0.5
0.4
-BENN+AMER(318km)
-BENN+PCEL(708km)
-BENN+RICH(932km)
-BENN+SATX(1326km)
-BENN+LYFD(1664km)
-BENN+LRES(1842km)
0.3
0.2
0.1
0
5
10
15
UT [hours]
20
Summary
With the automatic identification of FLR
frequencies we can systematically investigate the
properties of field line resonance observations.
 We find that the success rate of the gradient
technique can exceed 50% near local time for L =
2.4.
 With similar separation between two stations the
occurrence rate of FLR drops at both higher and
lower latitudes for different reasons.
 We have found FLR signatures picked up by the
gradient technique even when the separation
between two stations exceeds 1000 km.
