Examples of high-latitude electric and magnetic-field perturbations that ...
Examples of high-latitude electric and magnetic-field perturbations that were not accompanied by solar wind pressure fluctuations EDGAR A. BERING, III, and Z.-M. LIN
Physics Department University of Houston Houston, Texas 77004
The study of impulsive magnetic and electric-field perturbations has been a topic of extreme interest recently. Attention was first focused on these perturbations by the suggestion that they represent the ionospheric signature of flux-transfer events (Goertz et al. 1985; Sandholt et al. 1986; Lanzerotti et al. 1986, 1987; Southwood 1985, 1987; Todd et al. 1986; Bering et al. 1988; Lockwood, Sandholt, and Cowley 1989). Subsequently, it was determined that many of these events were propagating east or west along the auroral oval, rather than anti-sunward, and that their diameter was 3 to 5 times larger than expected on the basis of simple flux-transfer-event models (Friis-Christensen et al. 1988; GlaI3meier, Hönisch, and Untiedt 1989). Recently, there have been several suggestions made regarding the possibility that these events are all the result of pressure pulses in the solar wind passing the Earth (Sibeck et al. 1989a, 1989b; Southwood and Kivelson in press; Fairfield et al. in preparation). The generation of current vortices by means of impinging pressure pulses is a well-known model for the generation of mid-latitude Pc3 events (Yumoto, Saito, and Tanaka 1987). It is certainly possible for similar processes to be operating at higher latitude; however, the assertion that all highlatitude impulsive events result from such a process is a statement that seems overly broad. Proving such a sweeping assertion is, of course, very difficult. Disproving it, on the other hand, is easy. Strictly speaking, it requires only one counterexample to disprove such a statement. Ultimately, statistical study of a large set of events is required to determine the relative importance of pressure pulses vs. other sources in producing impulsive events in the high-latitude ionosphere. The purpose of this paper is to present examples of impusive events that are not accompanied by pressure pulses in the solar wind. Database. The electric field data were acquired during the 1985-1986 South Pole balloon campaign (Bering et al. 1987) in which eight balloon payloads carrying three-axis double-probe electric-field detectors and X-ray scintillation counters were launched sequentially from South Pole Station, Antarctica, at an invariant latitude of 74.5°. The noise level of the electricfield instrument was approximately 0.4 millivolts per meter, the digitization increment was 0.1 millivolts per meter, and the data were sampled at 8 hertz. Balloon payload attitude was determined from an on-board magnetometer. The high-resolution magnetic field data used for this study were measured at the Cusp Lab at South Pole Station, Antarctica (Lanzerotti, Medford, and Rosenberg 1982), and at Iqaluit, Northwest Territories, Canada (Wolfe et al. 1986), two stations nominally conjugate to a distance of order 200-300 kilometers (Lanzerotti et al. 1987). 266
Data. The first example is an event that took place at 1627 universal time on 3 January 1986 (Lin et al. in preparation). This event is shown in figure 1, which displays the electric field measured by the South Pole balloon (bottom three panels) and the magnetic-field perturbations measured at South Pole (solid line, top three panels) and Iqaluit (dashed line). Detailed model studies of these data and the Greenland chain magnetometer data (Lin et al. in preparation) have shown that this event was a combination of a twin current vortex of the type discussed by Friis-Christensen et al. (1988) ("towing system") and a coaxial current system of the type discussed by Lanzerotti et al. (1986) ("twisting system"). This event has been found to have a radius of approximately 284 kilometers and to have moved eastward at 3.9 kilometers per second. The current in the towing system was approximately 1.2 x 105 amps and the current in the twisting system was approximately 2.0 x iO amps (Lin et al. in preparation. Figure 2 shows the solar wind ram pressure and interpla netary magnetic field magnitude and orientation detected by the IMP 8 spacecraft between 1550 and 1650 universal time on 3 January 1986. In this figure, 0 is the cone angle of the magnetic field about the XGSM axis and ci) is the azimuth angle in Y GSM - ZGSM plane, measured counterclockwise from the positive Y axis. The data have been shifted by the calculated 616second propagation delay between the IMP 8 spacecraft and the ionosphere above South Pole. Figure 2 shows that the impulsive event in the ionosphere was not preceded by an appreciable change in solar wind dynamic pressure. Furthermore, the field cone angle indicates that field orientation was fluctuating somewhat between typical "garden-hose" orientation and a purely perpendicular orientation. Note particularly that the cone angle did not approach
SOUTH POLE BALLOON CAMPAIGN University of Houston Flight 6 -220 1W 360
I , j
-10
1600
1615 1630 1645 UNIVERSAL TIME, JANUARY 3. 1986
1700
Figure 1. The top three panels show 15-second averages of geomagnetic field variations observed at South Pole Station (solid lines) and Iqaluit (dashed lines). The bottom three panels show 15second averages of the electric field measured by payload on 19851986 South Pole balloon flight 6 from 1600 to 1700 on 3 January 1986. (nT denotes nanotessla. mV/m denotes millivolts per meter.) ANTARCTIC JOURNAL
IMP 8 Pressure, Field Angles 2
References
I I I 16 I)
0.4
I
I
I
I I
I
jo
a
I
180 108 -108 I I I I I ]-180 180
Bering, E.A., III, J.R. Benbrook, G.J. Byrne, B. Liao, J.R. Theall, L.J. Lanzerotti, C.G. Maclennan, A. Wolfe, and G.L. Siscoe. 1988. Impulsive electric and magnetic field perturbations observed over South Pole: Flux transfer events? Geophysical Research Letters, 15, 1,5451,548. Bering, E.A., III, J.R. Benbrook, J.M. Howard, D.M. Oró, E.G. Stansbery, J.R. Theall, D.L. Matthews, and T.J. Rosenberg. 1987. The 1985-86 South Pole balloon campaign. In Proceedings of the Nagata Symposium on Geomagnetically Conjugate Studies and Upper Atmospheric Physics. Japan: Memoirs of the National Institute of Polar Research.
(Special Issue No. 48, 313-317. Fairfield, D.H., W. Baumjohann, G. Paschmann, H. Lühr, and D.G. Sibeck. In preparation. Upstream pressure variations associated with the bow shock and their effects on the magnetosphere. Journal of Geophysical Research,
IIIIII
1550 1600 1610 1620 1630 1640 1650
UT, 03 January 1986
Figure 2. Solar wind pressure, interplanetary magnetic field strength and orientation, where 0 is the cone angle of the magnetic field about XGSM and CF is the azimuth angle in the Y - Z plane (0° + Y). Figure shows interval from 1550 to 1650 universal time on 3 January 1986. (nT denotes nanotessla. UT denotes universal time.)
00 or
180° during the event. The most dramatic change that was observed in the solar wind at this time was the brief and abrupt southward turning of the interplanetary magnetic force that took place at about 1615 universal time. It seems, therefore, that the only variation of solar wind properties that could be causally related to the impulsive event shown in figure 1 is this southward turning. A second example is shown in figure 3, which is a two-part figure, with part A corresponding to figure 1 and part B to figure 2. This figure shows an event that began at 1242 universal time on 4 January 1986. As shown in figure 3a, this event was a typical impulsive event. Figure 3b shows that the solar wind pressure was essentially constant throughout the event. Furthermore, the interplanetary magnetic field was not radially aligned. The interplanetary magnetic field did, however, turn slightly southward at 1237 universal time (delayed time). Conclusions. It is easy to find examples of high-latitude impulsive perturbation events that are not associated with solar wind pressure variations detectable by the IMP 8 spacecraft. Therefore, the assertion that all such impulsive events are responses to pressure pulses is contradicted by the available data. This work was supported by National Science Foundation grants DPP 84-15203 and DPP 86-14091. We thank L.J. Lanzerotti, C.G. Maclennan, and A. Wolfe for the South Pole and Iqaluit magnetometer data and many discussions. We than E. Friis-Christensen for providing the Greenland magnetometer chain data and for useful discussion. The IMP 8 interplanetary magnetic field data of N. Ness were provided by R. Lepping. The IMP 8 plasma data were provided by A. Lazarus who was supported by National Aeronautics and Space Administration grant NAG5-584. 1989 REVIEW
Friis-Christensen, E., M.A. McHenry, C.R. Clauer, and S. Vennerstrom. 1988. Ionospheric traveling convection vortices observed near the polar cleft: A triggered response to sudden changes in the solar wind. Geophysical Research Letters, 15, 253-256. Glal3meier, K.-H., M. HOnisch and J . Untiedt. 1989. Ground-based and satellite observations of traveling magnetospheric convection twin vortices. Journal of Geophysical Research, 94, 2,520-2,528. Goertz, C.K., E. Nielsen, A. Korth, K.H. Glal3meier, C. 1-laldoupis, P. Hoeg, and D. Hayward. 1985. Observations of a possible ground signature of flux transfer events. Journal of Geophysical Research, 90, 4,069-4,078. Lanzerotti, L.J., R.D. Hunsucker, D. Rice, L.C. Lee, A. Wolfe, C.G. Maclennan, and L.V. Medford. 1987. Ionosphere and ground-based response to field-aligned currents near the magnetospheric cusp region. Journal of Geophysical Research, 92, 7,739-7,743. Lanzerotti, L.J., L.C. Lee, C.G. Maclennan, A. Wolfe, and L.V. Medford. 1986. Possible evidence of flux transfer events in the polar ionosphere. Geophysical Research Letters, 13, 1,089-1,092. Lanzerotti, L.J., L.V. Medford, and T.J. Rosenberg. 1982. Magnetic field and particle precipitation observations at the South Pole. Antarctic Journal of the U.S., 17(5), 235-236. Lin, A.-M., J.R. Benbrook, E.A. Bering, G.J. Byrne, D. Liang, B. Liao, and J . Theall. In preparation. Observations of ionospheric flux ropes above South Pole. Physics of magnetic flux ropes. (Geophysical monograph.) Washington, D.C.: American Geophysical Union. Lockwood, M., P.E. Sandholt, and S.W.H. Cowley. 1989. Dayside auroral activity and magnetic flux transfer from the solar wind. Geophysical Research Letters, 16, 33-36. Sandholt, P.E., C.S. Deehr, A. Egeland, B. Lybekk, R. Viereck, and G.J. Romick. 1986. Signatures in the dayside aurora of plasma transfer from the magnetosheath. Journal of Geophysical Research, 91, 10,06310,079. Sibeck, D.G., W. Baumjohann, and R.E. Lopez. 1989a. Solar wind dynamic pressure variations and transient magnetospheric signatures. Geophysical Research Letters, 16, 13-16. Sibeck, D.G., W. Baumjohann, R.C. Elphic, D.H. Fairfield, J.F. Fennell, W.B. Gail, L.J. Lanzerotti, R.E. Lopez, H. Lühr, A.T.Y. Lui, C.G. Maclennan, R.W. McEntire, T.A. Potemra, T.J. Rosenberg, and K. Takahashi. 1989b. The magnetospheric response to 8-minute period strong-amplitude upstream pressure variations. Journal of Geophysical Research, 94, 2,505-2,519. Southwood, D.J., and M.G. Kivelson. In preparation. The magnetohydrodynamic response of the magnetospheric cavity to changes in solar wind pressure. Journal of Geophysical Research.
Southwood, D.J. 1985. Theoretical aspects of ionospheric-magnetospheric-solar wind coupling. Advanced Space Research, 5, 7. Southwood, D.J. 1987. The ionospheric signature of flux transfer events. Journal of Geophysical Research, 92, 3,207-3,213. Todd, H., B.J.I. Bromage, S.W.H. Cowley, M. Lockwood, A.P. van Eykers, and D.M. Willis. 1986. EISCAT observations of rapid flow in the high latitude dayside ionosphere. Geophysical Research Letters, 13, 909-912. 267
Wolfe, A., L.J. Lanzerotti, C . G. Maclennan, and L.V. Medford. 1986. Geomagnetic studies near the magnetospheric cusps. Antarctic Journal of the U.S., 21(5) 277-279.
Yumoto, K., I. Saito, and Y. Tanaka. 1987. Pc3 magnetic pulsations observed at low latitudes: A possible model. Menth'r National institute of Polar Research, Japan. (Special issue no. 47), 139-147.
SOUTH POLE BAlLOON CAPA1GN University of Houston Flight 6
IMP 8 Pressure, Field Angles
6 1.6
124
1.2 14
260 V
i I I I
0.8 IL 4
20 0
I
I I
I
I
U 0.4 i
120i-
120 0 -140
I
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- 2.4 1.2
180 108 36 —36 —108
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-180 180 144
108 72 36 to
1200 1210 1220 1230 1240 1250 1300
r4
UT, 04 January 1986
520 *11111^ 1200
1215 1230 1215 1300 UNIVERSAL 111w. JANUARY 4. 1986
Figure 3. A. Same as figure 1 for the period 1200-1300 on 4 January 1986. B. Same as figure 2 for the same period as panel A. (nT denotes nanotessla. UT denotes universal time.)
268
ANr,\1c lIC JOLRNAI.
Physics Department University of Houston Houston, Texas 77004
The study of impulsive magnetic and electric-field perturbations has been a topic of extreme interest recently. Attention was first focused on these perturbations by the suggestion that they represent the ionospheric signature of flux-transfer events (Goertz et al. 1985; Sandholt et al. 1986; Lanzerotti et al. 1986, 1987; Southwood 1985, 1987; Todd et al. 1986; Bering et al. 1988; Lockwood, Sandholt, and Cowley 1989). Subsequently, it was determined that many of these events were propagating east or west along the auroral oval, rather than anti-sunward, and that their diameter was 3 to 5 times larger than expected on the basis of simple flux-transfer-event models (Friis-Christensen et al. 1988; GlaI3meier, Hönisch, and Untiedt 1989). Recently, there have been several suggestions made regarding the possibility that these events are all the result of pressure pulses in the solar wind passing the Earth (Sibeck et al. 1989a, 1989b; Southwood and Kivelson in press; Fairfield et al. in preparation). The generation of current vortices by means of impinging pressure pulses is a well-known model for the generation of mid-latitude Pc3 events (Yumoto, Saito, and Tanaka 1987). It is certainly possible for similar processes to be operating at higher latitude; however, the assertion that all highlatitude impulsive events result from such a process is a statement that seems overly broad. Proving such a sweeping assertion is, of course, very difficult. Disproving it, on the other hand, is easy. Strictly speaking, it requires only one counterexample to disprove such a statement. Ultimately, statistical study of a large set of events is required to determine the relative importance of pressure pulses vs. other sources in producing impulsive events in the high-latitude ionosphere. The purpose of this paper is to present examples of impusive events that are not accompanied by pressure pulses in the solar wind. Database. The electric field data were acquired during the 1985-1986 South Pole balloon campaign (Bering et al. 1987) in which eight balloon payloads carrying three-axis double-probe electric-field detectors and X-ray scintillation counters were launched sequentially from South Pole Station, Antarctica, at an invariant latitude of 74.5°. The noise level of the electricfield instrument was approximately 0.4 millivolts per meter, the digitization increment was 0.1 millivolts per meter, and the data were sampled at 8 hertz. Balloon payload attitude was determined from an on-board magnetometer. The high-resolution magnetic field data used for this study were measured at the Cusp Lab at South Pole Station, Antarctica (Lanzerotti, Medford, and Rosenberg 1982), and at Iqaluit, Northwest Territories, Canada (Wolfe et al. 1986), two stations nominally conjugate to a distance of order 200-300 kilometers (Lanzerotti et al. 1987). 266
Data. The first example is an event that took place at 1627 universal time on 3 January 1986 (Lin et al. in preparation). This event is shown in figure 1, which displays the electric field measured by the South Pole balloon (bottom three panels) and the magnetic-field perturbations measured at South Pole (solid line, top three panels) and Iqaluit (dashed line). Detailed model studies of these data and the Greenland chain magnetometer data (Lin et al. in preparation) have shown that this event was a combination of a twin current vortex of the type discussed by Friis-Christensen et al. (1988) ("towing system") and a coaxial current system of the type discussed by Lanzerotti et al. (1986) ("twisting system"). This event has been found to have a radius of approximately 284 kilometers and to have moved eastward at 3.9 kilometers per second. The current in the towing system was approximately 1.2 x 105 amps and the current in the twisting system was approximately 2.0 x iO amps (Lin et al. in preparation. Figure 2 shows the solar wind ram pressure and interpla netary magnetic field magnitude and orientation detected by the IMP 8 spacecraft between 1550 and 1650 universal time on 3 January 1986. In this figure, 0 is the cone angle of the magnetic field about the XGSM axis and ci) is the azimuth angle in Y GSM - ZGSM plane, measured counterclockwise from the positive Y axis. The data have been shifted by the calculated 616second propagation delay between the IMP 8 spacecraft and the ionosphere above South Pole. Figure 2 shows that the impulsive event in the ionosphere was not preceded by an appreciable change in solar wind dynamic pressure. Furthermore, the field cone angle indicates that field orientation was fluctuating somewhat between typical "garden-hose" orientation and a purely perpendicular orientation. Note particularly that the cone angle did not approach
SOUTH POLE BALLOON CAMPAIGN University of Houston Flight 6 -220 1W 360
I , j
-10
1600
1615 1630 1645 UNIVERSAL TIME, JANUARY 3. 1986
1700
Figure 1. The top three panels show 15-second averages of geomagnetic field variations observed at South Pole Station (solid lines) and Iqaluit (dashed lines). The bottom three panels show 15second averages of the electric field measured by payload on 19851986 South Pole balloon flight 6 from 1600 to 1700 on 3 January 1986. (nT denotes nanotessla. mV/m denotes millivolts per meter.) ANTARCTIC JOURNAL
IMP 8 Pressure, Field Angles 2
References
I I I 16 I)
0.4
I
I
I
I I
I
jo
a
I
180 108 -108 I I I I I ]-180 180
Bering, E.A., III, J.R. Benbrook, G.J. Byrne, B. Liao, J.R. Theall, L.J. Lanzerotti, C.G. Maclennan, A. Wolfe, and G.L. Siscoe. 1988. Impulsive electric and magnetic field perturbations observed over South Pole: Flux transfer events? Geophysical Research Letters, 15, 1,5451,548. Bering, E.A., III, J.R. Benbrook, J.M. Howard, D.M. Oró, E.G. Stansbery, J.R. Theall, D.L. Matthews, and T.J. Rosenberg. 1987. The 1985-86 South Pole balloon campaign. In Proceedings of the Nagata Symposium on Geomagnetically Conjugate Studies and Upper Atmospheric Physics. Japan: Memoirs of the National Institute of Polar Research.
(Special Issue No. 48, 313-317. Fairfield, D.H., W. Baumjohann, G. Paschmann, H. Lühr, and D.G. Sibeck. In preparation. Upstream pressure variations associated with the bow shock and their effects on the magnetosphere. Journal of Geophysical Research,
IIIIII
1550 1600 1610 1620 1630 1640 1650
UT, 03 January 1986
Figure 2. Solar wind pressure, interplanetary magnetic field strength and orientation, where 0 is the cone angle of the magnetic field about XGSM and CF is the azimuth angle in the Y - Z plane (0° + Y). Figure shows interval from 1550 to 1650 universal time on 3 January 1986. (nT denotes nanotessla. UT denotes universal time.)
00 or
180° during the event. The most dramatic change that was observed in the solar wind at this time was the brief and abrupt southward turning of the interplanetary magnetic force that took place at about 1615 universal time. It seems, therefore, that the only variation of solar wind properties that could be causally related to the impulsive event shown in figure 1 is this southward turning. A second example is shown in figure 3, which is a two-part figure, with part A corresponding to figure 1 and part B to figure 2. This figure shows an event that began at 1242 universal time on 4 January 1986. As shown in figure 3a, this event was a typical impulsive event. Figure 3b shows that the solar wind pressure was essentially constant throughout the event. Furthermore, the interplanetary magnetic field was not radially aligned. The interplanetary magnetic field did, however, turn slightly southward at 1237 universal time (delayed time). Conclusions. It is easy to find examples of high-latitude impulsive perturbation events that are not associated with solar wind pressure variations detectable by the IMP 8 spacecraft. Therefore, the assertion that all such impulsive events are responses to pressure pulses is contradicted by the available data. This work was supported by National Science Foundation grants DPP 84-15203 and DPP 86-14091. We thank L.J. Lanzerotti, C.G. Maclennan, and A. Wolfe for the South Pole and Iqaluit magnetometer data and many discussions. We than E. Friis-Christensen for providing the Greenland magnetometer chain data and for useful discussion. The IMP 8 interplanetary magnetic field data of N. Ness were provided by R. Lepping. The IMP 8 plasma data were provided by A. Lazarus who was supported by National Aeronautics and Space Administration grant NAG5-584. 1989 REVIEW
Friis-Christensen, E., M.A. McHenry, C.R. Clauer, and S. Vennerstrom. 1988. Ionospheric traveling convection vortices observed near the polar cleft: A triggered response to sudden changes in the solar wind. Geophysical Research Letters, 15, 253-256. Glal3meier, K.-H., M. HOnisch and J . Untiedt. 1989. Ground-based and satellite observations of traveling magnetospheric convection twin vortices. Journal of Geophysical Research, 94, 2,520-2,528. Goertz, C.K., E. Nielsen, A. Korth, K.H. Glal3meier, C. 1-laldoupis, P. Hoeg, and D. Hayward. 1985. Observations of a possible ground signature of flux transfer events. Journal of Geophysical Research, 90, 4,069-4,078. Lanzerotti, L.J., R.D. Hunsucker, D. Rice, L.C. Lee, A. Wolfe, C.G. Maclennan, and L.V. Medford. 1987. Ionosphere and ground-based response to field-aligned currents near the magnetospheric cusp region. Journal of Geophysical Research, 92, 7,739-7,743. Lanzerotti, L.J., L.C. Lee, C.G. Maclennan, A. Wolfe, and L.V. Medford. 1986. Possible evidence of flux transfer events in the polar ionosphere. Geophysical Research Letters, 13, 1,089-1,092. Lanzerotti, L.J., L.V. Medford, and T.J. Rosenberg. 1982. Magnetic field and particle precipitation observations at the South Pole. Antarctic Journal of the U.S., 17(5), 235-236. Lin, A.-M., J.R. Benbrook, E.A. Bering, G.J. Byrne, D. Liang, B. Liao, and J . Theall. In preparation. Observations of ionospheric flux ropes above South Pole. Physics of magnetic flux ropes. (Geophysical monograph.) Washington, D.C.: American Geophysical Union. Lockwood, M., P.E. Sandholt, and S.W.H. Cowley. 1989. Dayside auroral activity and magnetic flux transfer from the solar wind. Geophysical Research Letters, 16, 33-36. Sandholt, P.E., C.S. Deehr, A. Egeland, B. Lybekk, R. Viereck, and G.J. Romick. 1986. Signatures in the dayside aurora of plasma transfer from the magnetosheath. Journal of Geophysical Research, 91, 10,06310,079. Sibeck, D.G., W. Baumjohann, and R.E. Lopez. 1989a. Solar wind dynamic pressure variations and transient magnetospheric signatures. Geophysical Research Letters, 16, 13-16. Sibeck, D.G., W. Baumjohann, R.C. Elphic, D.H. Fairfield, J.F. Fennell, W.B. Gail, L.J. Lanzerotti, R.E. Lopez, H. Lühr, A.T.Y. Lui, C.G. Maclennan, R.W. McEntire, T.A. Potemra, T.J. Rosenberg, and K. Takahashi. 1989b. The magnetospheric response to 8-minute period strong-amplitude upstream pressure variations. Journal of Geophysical Research, 94, 2,505-2,519. Southwood, D.J., and M.G. Kivelson. In preparation. The magnetohydrodynamic response of the magnetospheric cavity to changes in solar wind pressure. Journal of Geophysical Research.
Southwood, D.J. 1985. Theoretical aspects of ionospheric-magnetospheric-solar wind coupling. Advanced Space Research, 5, 7. Southwood, D.J. 1987. The ionospheric signature of flux transfer events. Journal of Geophysical Research, 92, 3,207-3,213. Todd, H., B.J.I. Bromage, S.W.H. Cowley, M. Lockwood, A.P. van Eykers, and D.M. Willis. 1986. EISCAT observations of rapid flow in the high latitude dayside ionosphere. Geophysical Research Letters, 13, 909-912. 267
Wolfe, A., L.J. Lanzerotti, C . G. Maclennan, and L.V. Medford. 1986. Geomagnetic studies near the magnetospheric cusps. Antarctic Journal of the U.S., 21(5) 277-279.
Yumoto, K., I. Saito, and Y. Tanaka. 1987. Pc3 magnetic pulsations observed at low latitudes: A possible model. Menth'r National institute of Polar Research, Japan. (Special issue no. 47), 139-147.
SOUTH POLE BAlLOON CAPA1GN University of Houston Flight 6
IMP 8 Pressure, Field Angles
6 1.6
124
1.2 14
260 V
i I I I
0.8 IL 4
20 0
I
I I
I
I
U 0.4 i
120i-
120 0 -140
I
4.8
- 2.4 1.2
180 108 36 —36 —108
IY\IIIIIIIIIV
-180 180 144
108 72 36 to
1200 1210 1220 1230 1240 1250 1300
r4
UT, 04 January 1986
520 *11111^ 1200
1215 1230 1215 1300 UNIVERSAL 111w. JANUARY 4. 1986
Figure 3. A. Same as figure 1 for the period 1200-1300 on 4 January 1986. B. Same as figure 2 for the same period as panel A. (nT denotes nanotessla. UT denotes universal time.)
268
ANr,\1c lIC JOLRNAI.
