Magnetic pulsations as probes of the magnetosphere
Duldig, M.L., R.M. Jacklyn, and M.A. Pomerantz. 1985. Isotropic intensity waves and features of their occurrence. Proceedings of the 19th International Cosmic Ray Conference, La Jolla, 5, 5-8. Jacklyn, R.M., and M.L.Duldig. 1983. A new underground telescope at the Mawson cosmic ray observatory, Proceedings of the Astronomical Society of Australia, 5, 262. Jacklyn, R.M., and M.A. Pomerantz. 1983. Anisotropic intensity waves observed underground at Mawson with proportional counter telescope. Proceedings of the 18th International Cosmic Ray Conference, Bangalore, 3, 206-209.
Jacklyn, R.M., M.A. Pomerantz, and M.L. Duldig. 1984. Cosmic ray
Magnetic pulsations as probes of the magnetosphere L.J. CAHILL, JR.
School of Physics and Astronomy University of Minnesota Minneapolis, Minnesota 55455
R.L. ARNOLDY
Space Science Center University of New Hampshire Durham, New Hampshire 03824
M.J. ENGEBRETSON
intensity waves and the north-south anisotrophy. Proceedings of the Astronomical Society of Australia, 5, 581.
Jacklyn, R.M., M.L.Duldig, and M.A. Pomerantz. 1984. Anisotropic and isotropic intensity waves. Proceedings of the International Symposium on Cosmic Ray Modulation in the Heliosphere, Morioka, Japan.
Nagashima, K., S.P. Duggal, and M.A. Pomerantz. 1968. Cosmic ray anisotrophy in three-dimensional space. Planetary Space Science, 16, 29-46. Pomerantz, M.A. 1984. Cosmic-ray intensity variations, Antarctic Journal of the U.S., 19(5), 215-216.
study of the origin of Pc 3 waves observed near the southern cusp. Pc 1 observations. When our receivers at Siple Station were first put in operation in the early 1970's, Pc I pulsations were frequently observed. In recent years, very few events have been observed. The occurrence rate of these pulsations is controlled by the 11-year solar cycle, so now in the early 1980's, there are again large numbers of Pc 1 events. These pulsations near 1 hertz in frequency are believed due to Doppler-shifted ion cyclotron resonance with energetic magnetospheric ions. The waves propagate at the Alfven speed in packets along the magnetic field line and gain energy as they pass through the resonant ions. The packets reflect at the ionosphere and bounce to the opposite hemisphere gaining energy in each bounce. The small amount of energy transmitted at each bounce can be seen on the ground with our pulsation antennas. Figure 1 is an example of a fairly simple Pc 1 event observed at Siple Station, L = 4.2. The event starts near 2230 universal time at a frequency of 1.5 hertz, grows in intensity until 2245 universal time, maintains constant intensity until 2255 universal time, and fades out
Physics Department Augsburg College Minneapolis, Minnesota 55455
We have been operating magnetic pulsation receivers at several stations in the Antarctic during the past decade. During this last year, receivers were operating at Siple, South Pole, and McMurdo Station. In previous reports, we have described work on the generation of Pc 1 pulsations near 1 hertz; on the associa tion of Pi 1 pulsations, near 0.1 hertz, with auroras; and on the conjugacy of pulsations, observed at the ends of the field line in each hemisphere and at the equatorial plane in the magnetosphere. The pulsation receivers consist of a remote antenna and a digital recording system. The antenna is a permalloy rod, 500,000 turns of fine copper wire wound around the rod, and a low-noise preamplifier. The recording system is a digital signal processing and programming units and a digital tape recorder. The digital system allows repeated signal analysis and enhancement using frequency and polarization techniques. We continue to work on a variety of pulsation studies including several collaborative projects. This report will be limited to two new studies that have commenced this year: a renewed effort in the study of the generation and propagation of Pc 1 waves and a 1986 REVIEW
P
L
2
00
cx
NJ
cc
Ji
2230 2300 30 00 ur
June J, 982 Figure 1. Dynamic power spectral density of the pulsation receiver signal, 2230 universal time) (UT), 5 June to 0030 universal time, 6 June 1982. The top, middle, and bottom panels are for plane, lefthand, and right-hand polarized waves. The vertical frequency scale is from 0 to 2.5 hertz (Hz) for each panel. The power density is represented by the gray scale shading; white is the most intense.
253
by 2320 universal time. Meanwhile, a separate pulsation starts at a slightly higher frequency than the first near 2340 universal time and fades out by 2330 universal time when other pulsation trains at higher frequencies start to grow. The dots within each pulsation train represent the wave packets arriving over Siple while the time interval between dots shows the travel time of the wave packet from Siple to the northern ionosphere and return. The increase in frequency seen within some individual dots is due to velocity dispersion in the propagation of the wave packets along the magnetic field lines. Most of the Pc 1 pulsations observed near Siple are generated near the plasmapause. We have earlier observed a diurnal variation in the center frequency of Pc 1 pulsations as the plasmapause reaches its closest approach to the Earth in the morning hours [with higher Pc 1 (cyclotron) frequencies reflecting the higher magnetic field magnitude at closer distances] and as the plasmapause reaches its greatest distance in the evening hours [with correspondingly lower Pc 1 frequencies (Lewis, Arnoldy, and Cahill 1977)]. The Siple antennas are able to observe pulsations from a range of L shells through horizontal ducting of the waves below the reflecting altitude in the ionosphere. The overall rise in frequency between 2230 and 0030 universal time (1800 and 2000 magnetic local time at Siple)
in figure 1 suggests an inward movement of the plasmapause although at this local time, on the average, the plasmapause is at its greatest distance from the Earth. It is tempting to speculate that the falling frequencies within some of the individual pulsation trains of figure 1 indicate outward movement of flux shells where the resonant ions are drifting. Overlapping pulsation trains within figure 1 indicate simultaneous wave generation on two or more magnetic shells at different radial distances from the Earth. There is, however, a complex relationship between the frequency, the resonant ion energy, and the distance of the generation region. Pc 1 pulsations are also observed at our other receiver locations in the Antarctic (Arnoldy et al. 1986). We are commencing an interpretation program including simultaneous pulsation and energetic ion observations from spacecraft in the magnetosphere. Pc 3 observations. The Pc 3 pulsations shown in figure 2(1320 to 1340 universal time; 1410 to 1440 universal time) are examples of the quasi-sinusoidal waves near 25 seconds in period that are frequntly observed at South Pole Station when it is near the noontime southern cusp, the dividing region between Earth's magnetic field lines that close in a dipole configuration and those that extend into the Earth's magnetic tail (Engebretson et al. 1986). Such sinusoidal pulsations inside the magnetosphere
SOUTH POLE JANUARY 1983 DAY 30 Kp = 4Y J 3nT/s
X o
13:00
J 04Mrv%i1
13:30
DAY 30 Kp = 4-
O\V%kJ% 14:00
14:30
Figure 2. Wave form of the pulsation signal from the South Pole Station, 1300 to 1500 universal time 30 January 1983.
254
ANTARCTIC JOURNAL
are usually considered as harmonics in a resonant standingwave structure of long-period waves on the closed Earth's magnetic field lines (Cahill et al. 1984). Their presence near the cusp, and therefore near the outer boundary of closed field lines, is surprising. The occurrence of these pulsations is strongly correlated with the x component of the interplanetary magnetic field. The Pc 3 pulsations are seen when the interplanetary field is within 45° of alignment with the Earth-Sun line. In addition, the pulsation period varies inversely with the magnitude of the interplanetary field, from 12 seconds when the field is 15 nanoTeslas to 40 seconds when it is 4 nanoTeslas. This research was supported by National Science Foundation grant DPP 83-18632.
Keogram camera and zenithal photometer measurements from South Pole and McMurdo Stations R.H. EATHER Department of Physics Boston College Chestnut Hill, Massachusetts 02167
I operated three optical instruments in Antarctica during the 1985 austral winter. Keogram camera (South Pole Station. This is a dual-channel, intensified monochromatic slit camera, which records the position ind intensity of two auroral emissions along the geomagnetic north-south meridian through South Pole Station. The data are color coded auto 35-millimeter color film (see Eather 1981). Data are distributed to other researchers in the form of color prints, and the last two seasons' operations resulted in 62 days of good data (free of cloud cover and strong moonlight contamination) for the 1983 winter and 58 for 1984. Analysis of these keograms led to two published papers (Eather 1984, 1985) describing various aspects of dayside auroral behavior and the effects interplanetary conditions. In addition, the keograms have been used in numerous correlative studies (Hones et al. 1985; Arnody et al. 1986; Wu et al. 1986). Zenithal photometer (South Pole Station.) This is a dual-channel instrument (4278N2 and 630001) with a field of view (55°) matched to that of the riometers. Data are digitally recorded on the University of Maryland data logging system and distributed to all investigators on request. These data have been and con-
1986 REVIEW
References
Arnoldy, R.L., L.J. Cahill, Jr., R.H. Eather, M.J. Engebretson. 1986. Greater than 0.1 Hz ULF magnetic pulsations measured at South Pole, Antarctica. Journal of Geophysical Research, 91,5700.
Cahill, L.J., Jr., M. Sugiura, N.G. Lin, R.L. Arnoldy, S.D. Shawhan, M.J. Engebretson, and B.G. Ledley. 1984. Observation of an oscillating magnetic field shell at three locations. Journal of Geophysical Research, 89, 2735.
Engebretson, M.J., C-I. Meng, R.L. Arnoldy, and L.J. Cahill, Jr. 1986. Pc 3 pulsations observed near the South Polar Cusp. Journal of Geophysical Research, 91, 8909.
Lewis, PB., R.L. Arnoldy, and L.J. Cahill, Jr. 1977. The relation of Pc I micropulsations measured at Siple, Antarctica, to the plasmapause. Journal of Geophysical Research, 82, 3261.
tinue to be used in various riometer studies, ultra-low-frequency magnetic pulsation studies (Arnody et al. 1986), morphological studies in conjunction with satellite data (Hones et al. 1985), and coordinated studies with Dynamics Explorer satellite auroral images (work in progress) and satellite X-ray images (Misera et al. in preparation). Zenithal photometer (McMurdo Station). This instrument is identical to the one at the South Pole Station and was installed in the new Arrival Heights laboratory in January 1985, operating through the 1985 austral winter. Data are logged on the University of Maryland data logger and will be used in correlative riometer and very-low-frequency and ultra-low-frequency studies. This research was supported by National Science Foundation grant DPP 82-15312. References
Arno!dy, R.L., L.J. Cahill, R.H. Eather, and M.J. Engebretson. 1986. Greater than 0.1Hz ULF magnetic pulsations measured at South Pole, Antarctica. Journal of Geophysical Research, 91, 5700. Eather, R.H. 1981. Dayside auroral studies with a color keogram camera. Antarctic Journal of the U.S., 16(5), 218.
Eather, R.H. 1984. Dayside aurora! dynamics. Journal of Geophysical Research, 89, 1695.
Eather, R.H. 1985. Polar cusp dynamics. Journal of Geophysical Research, 90, 1569.
Hones, E.W., T.J. Rosenberg, L.J. Lanzerotti, FT. Berkey, and R.H. Eather. 1985. Po!eward surges of the auroral e!ectroject over South Pole Station. EOS, 66, 336. Misera, P.F., D.J. Gorney, T.J. Rosenberg. In preparation. Simultaneous observations of soft X-rays, the visible aurora and ionospheric currents during a radio absorption event at South Pole Station. Journal of Geophysical Research.
Wu, Q . , T.J. Rosenberg, F.T. Berkey, R.H. Eather, and L.J. Lanzerotti. 1986. Auroral fading in the nightside polar cap. Transactions of the American Geophysical Union, 67, 337.
255
Jacklyn, R.M., M.A. Pomerantz, and M.L. Duldig. 1984. Cosmic ray
Magnetic pulsations as probes of the magnetosphere L.J. CAHILL, JR.
School of Physics and Astronomy University of Minnesota Minneapolis, Minnesota 55455
R.L. ARNOLDY
Space Science Center University of New Hampshire Durham, New Hampshire 03824
M.J. ENGEBRETSON
intensity waves and the north-south anisotrophy. Proceedings of the Astronomical Society of Australia, 5, 581.
Jacklyn, R.M., M.L.Duldig, and M.A. Pomerantz. 1984. Anisotropic and isotropic intensity waves. Proceedings of the International Symposium on Cosmic Ray Modulation in the Heliosphere, Morioka, Japan.
Nagashima, K., S.P. Duggal, and M.A. Pomerantz. 1968. Cosmic ray anisotrophy in three-dimensional space. Planetary Space Science, 16, 29-46. Pomerantz, M.A. 1984. Cosmic-ray intensity variations, Antarctic Journal of the U.S., 19(5), 215-216.
study of the origin of Pc 3 waves observed near the southern cusp. Pc 1 observations. When our receivers at Siple Station were first put in operation in the early 1970's, Pc I pulsations were frequently observed. In recent years, very few events have been observed. The occurrence rate of these pulsations is controlled by the 11-year solar cycle, so now in the early 1980's, there are again large numbers of Pc 1 events. These pulsations near 1 hertz in frequency are believed due to Doppler-shifted ion cyclotron resonance with energetic magnetospheric ions. The waves propagate at the Alfven speed in packets along the magnetic field line and gain energy as they pass through the resonant ions. The packets reflect at the ionosphere and bounce to the opposite hemisphere gaining energy in each bounce. The small amount of energy transmitted at each bounce can be seen on the ground with our pulsation antennas. Figure 1 is an example of a fairly simple Pc 1 event observed at Siple Station, L = 4.2. The event starts near 2230 universal time at a frequency of 1.5 hertz, grows in intensity until 2245 universal time, maintains constant intensity until 2255 universal time, and fades out
Physics Department Augsburg College Minneapolis, Minnesota 55455
We have been operating magnetic pulsation receivers at several stations in the Antarctic during the past decade. During this last year, receivers were operating at Siple, South Pole, and McMurdo Station. In previous reports, we have described work on the generation of Pc 1 pulsations near 1 hertz; on the associa tion of Pi 1 pulsations, near 0.1 hertz, with auroras; and on the conjugacy of pulsations, observed at the ends of the field line in each hemisphere and at the equatorial plane in the magnetosphere. The pulsation receivers consist of a remote antenna and a digital recording system. The antenna is a permalloy rod, 500,000 turns of fine copper wire wound around the rod, and a low-noise preamplifier. The recording system is a digital signal processing and programming units and a digital tape recorder. The digital system allows repeated signal analysis and enhancement using frequency and polarization techniques. We continue to work on a variety of pulsation studies including several collaborative projects. This report will be limited to two new studies that have commenced this year: a renewed effort in the study of the generation and propagation of Pc 1 waves and a 1986 REVIEW
P
L
2
00
cx
NJ
cc
Ji
2230 2300 30 00 ur
June J, 982 Figure 1. Dynamic power spectral density of the pulsation receiver signal, 2230 universal time) (UT), 5 June to 0030 universal time, 6 June 1982. The top, middle, and bottom panels are for plane, lefthand, and right-hand polarized waves. The vertical frequency scale is from 0 to 2.5 hertz (Hz) for each panel. The power density is represented by the gray scale shading; white is the most intense.
253
by 2320 universal time. Meanwhile, a separate pulsation starts at a slightly higher frequency than the first near 2340 universal time and fades out by 2330 universal time when other pulsation trains at higher frequencies start to grow. The dots within each pulsation train represent the wave packets arriving over Siple while the time interval between dots shows the travel time of the wave packet from Siple to the northern ionosphere and return. The increase in frequency seen within some individual dots is due to velocity dispersion in the propagation of the wave packets along the magnetic field lines. Most of the Pc 1 pulsations observed near Siple are generated near the plasmapause. We have earlier observed a diurnal variation in the center frequency of Pc 1 pulsations as the plasmapause reaches its closest approach to the Earth in the morning hours [with higher Pc 1 (cyclotron) frequencies reflecting the higher magnetic field magnitude at closer distances] and as the plasmapause reaches its greatest distance in the evening hours [with correspondingly lower Pc 1 frequencies (Lewis, Arnoldy, and Cahill 1977)]. The Siple antennas are able to observe pulsations from a range of L shells through horizontal ducting of the waves below the reflecting altitude in the ionosphere. The overall rise in frequency between 2230 and 0030 universal time (1800 and 2000 magnetic local time at Siple)
in figure 1 suggests an inward movement of the plasmapause although at this local time, on the average, the plasmapause is at its greatest distance from the Earth. It is tempting to speculate that the falling frequencies within some of the individual pulsation trains of figure 1 indicate outward movement of flux shells where the resonant ions are drifting. Overlapping pulsation trains within figure 1 indicate simultaneous wave generation on two or more magnetic shells at different radial distances from the Earth. There is, however, a complex relationship between the frequency, the resonant ion energy, and the distance of the generation region. Pc 1 pulsations are also observed at our other receiver locations in the Antarctic (Arnoldy et al. 1986). We are commencing an interpretation program including simultaneous pulsation and energetic ion observations from spacecraft in the magnetosphere. Pc 3 observations. The Pc 3 pulsations shown in figure 2(1320 to 1340 universal time; 1410 to 1440 universal time) are examples of the quasi-sinusoidal waves near 25 seconds in period that are frequntly observed at South Pole Station when it is near the noontime southern cusp, the dividing region between Earth's magnetic field lines that close in a dipole configuration and those that extend into the Earth's magnetic tail (Engebretson et al. 1986). Such sinusoidal pulsations inside the magnetosphere
SOUTH POLE JANUARY 1983 DAY 30 Kp = 4Y J 3nT/s
X o
13:00
J 04Mrv%i1
13:30
DAY 30 Kp = 4-
O\V%kJ% 14:00
14:30
Figure 2. Wave form of the pulsation signal from the South Pole Station, 1300 to 1500 universal time 30 January 1983.
254
ANTARCTIC JOURNAL
are usually considered as harmonics in a resonant standingwave structure of long-period waves on the closed Earth's magnetic field lines (Cahill et al. 1984). Their presence near the cusp, and therefore near the outer boundary of closed field lines, is surprising. The occurrence of these pulsations is strongly correlated with the x component of the interplanetary magnetic field. The Pc 3 pulsations are seen when the interplanetary field is within 45° of alignment with the Earth-Sun line. In addition, the pulsation period varies inversely with the magnitude of the interplanetary field, from 12 seconds when the field is 15 nanoTeslas to 40 seconds when it is 4 nanoTeslas. This research was supported by National Science Foundation grant DPP 83-18632.
Keogram camera and zenithal photometer measurements from South Pole and McMurdo Stations R.H. EATHER Department of Physics Boston College Chestnut Hill, Massachusetts 02167
I operated three optical instruments in Antarctica during the 1985 austral winter. Keogram camera (South Pole Station. This is a dual-channel, intensified monochromatic slit camera, which records the position ind intensity of two auroral emissions along the geomagnetic north-south meridian through South Pole Station. The data are color coded auto 35-millimeter color film (see Eather 1981). Data are distributed to other researchers in the form of color prints, and the last two seasons' operations resulted in 62 days of good data (free of cloud cover and strong moonlight contamination) for the 1983 winter and 58 for 1984. Analysis of these keograms led to two published papers (Eather 1984, 1985) describing various aspects of dayside auroral behavior and the effects interplanetary conditions. In addition, the keograms have been used in numerous correlative studies (Hones et al. 1985; Arnody et al. 1986; Wu et al. 1986). Zenithal photometer (South Pole Station.) This is a dual-channel instrument (4278N2 and 630001) with a field of view (55°) matched to that of the riometers. Data are digitally recorded on the University of Maryland data logging system and distributed to all investigators on request. These data have been and con-
1986 REVIEW
References
Arnoldy, R.L., L.J. Cahill, Jr., R.H. Eather, M.J. Engebretson. 1986. Greater than 0.1 Hz ULF magnetic pulsations measured at South Pole, Antarctica. Journal of Geophysical Research, 91,5700.
Cahill, L.J., Jr., M. Sugiura, N.G. Lin, R.L. Arnoldy, S.D. Shawhan, M.J. Engebretson, and B.G. Ledley. 1984. Observation of an oscillating magnetic field shell at three locations. Journal of Geophysical Research, 89, 2735.
Engebretson, M.J., C-I. Meng, R.L. Arnoldy, and L.J. Cahill, Jr. 1986. Pc 3 pulsations observed near the South Polar Cusp. Journal of Geophysical Research, 91, 8909.
Lewis, PB., R.L. Arnoldy, and L.J. Cahill, Jr. 1977. The relation of Pc I micropulsations measured at Siple, Antarctica, to the plasmapause. Journal of Geophysical Research, 82, 3261.
tinue to be used in various riometer studies, ultra-low-frequency magnetic pulsation studies (Arnody et al. 1986), morphological studies in conjunction with satellite data (Hones et al. 1985), and coordinated studies with Dynamics Explorer satellite auroral images (work in progress) and satellite X-ray images (Misera et al. in preparation). Zenithal photometer (McMurdo Station). This instrument is identical to the one at the South Pole Station and was installed in the new Arrival Heights laboratory in January 1985, operating through the 1985 austral winter. Data are logged on the University of Maryland data logger and will be used in correlative riometer and very-low-frequency and ultra-low-frequency studies. This research was supported by National Science Foundation grant DPP 82-15312. References
Arno!dy, R.L., L.J. Cahill, R.H. Eather, and M.J. Engebretson. 1986. Greater than 0.1Hz ULF magnetic pulsations measured at South Pole, Antarctica. Journal of Geophysical Research, 91, 5700. Eather, R.H. 1981. Dayside auroral studies with a color keogram camera. Antarctic Journal of the U.S., 16(5), 218.
Eather, R.H. 1984. Dayside aurora! dynamics. Journal of Geophysical Research, 89, 1695.
Eather, R.H. 1985. Polar cusp dynamics. Journal of Geophysical Research, 90, 1569.
Hones, E.W., T.J. Rosenberg, L.J. Lanzerotti, FT. Berkey, and R.H. Eather. 1985. Po!eward surges of the auroral e!ectroject over South Pole Station. EOS, 66, 336. Misera, P.F., D.J. Gorney, T.J. Rosenberg. In preparation. Simultaneous observations of soft X-rays, the visible aurora and ionospheric currents during a radio absorption event at South Pole Station. Journal of Geophysical Research.
Wu, Q . , T.J. Rosenberg, F.T. Berkey, R.H. Eather, and L.J. Lanzerotti. 1986. Auroral fading in the nightside polar cap. Transactions of the American Geophysical Union, 67, 337.
255
