scholarly journals Pc5 geomagnetic field fluctuations at discrete frequencies at a low latitude station

2001 ◽  
Vol 19 (3) ◽  
pp. 321-325 ◽  
Author(s):  
U. Villante ◽  
P. Francia ◽  
S. Lepidi
Keyword(s):  
Solar Wind ◽  
Geomagnetic Field ◽  
Wind Pressure ◽  
Mhd Waves ◽  
Low Latitude ◽  
Time Intervals ◽  
Latitude Station ◽  
Field Fluctuations ◽  
Mhd Waves And Instabilities ◽  
Solar Wind Pressure

Abstract. A statistical analysis of the geomagnetic field fluctuations in the Pc5 frequency range (1–5 mHz) at a low latitude station (L = 1.6) provides further evidence for daytime power peaks at discrete frequencies. The power enhancements, which become more pronounced during high solar wind pressure conditions, may be interpreted in terms of ground signatures of magnetospheric cavity/waveguide compressional modes driven by solar wind pressure pulses. In this sense, the much clearer statistical evidence for afternoon events can be related to corotating structures mainly impinging the postnoon magnetopause. A comparison with results obtained for the same time intervals from previous investigations at higher latitudes and in the Earth’s magnetosphere confirms the global character of the observed modes.Key words. Magnetospheric physics (MHD waves and instabilities; solar wind-magnetospheric interactions)

scholarly journals Pc3 pulsations during variable IMF conditions

1999 ◽  
Vol 17 (4) ◽  
pp. 490-496 ◽  
Author(s):  
U. Villante ◽  
S. Lepidi ◽  
P. Francia ◽  
M. Vellante ◽  
A. Meloni ◽  
...  
Keyword(s):  
Solar Wind ◽  
Geomagnetic Field ◽  
Mhd Waves ◽  
Variable Frequency ◽  
Low Latitude ◽  
Terra Nova Bay ◽  
Field Fluctuations ◽  
Polarization Characteristics ◽  
Mhd Waves And Instabilities ◽  
Very High

Abstract. Pc3 geomagnetic field fluctuations detected at low latitude (L'Aquila, Italy) during the passage of a high velocity solar wind stream, characterized by variable interplanetary magnetic field conditions, are analyzed. Higher frequency resonant fluctuations and lower frequency phenomena are simultaneously observed; the intermittent appearance and the variable frequency of the longer period modes can be well interpreted in terms of the variable IMF elements; moreover their polarization characteristics are consistent with an origin related to external waves propagating in antisunward direction. A comparison with simultaneous observations performed at Terra Nova Bay (Antarctica) provides additional evidence for a clear relationship between the IMF and Pc3 pulsations also at very high latitudes.Key words. Magnetospheric physics (MHD waves and instabilities; solar wind · magnetosphere interactions)

scholarly journals Geomagnetic field fluctuations during the passage at the Earth’s orbit of the tail of the 15–16 July 2000 ejecta

2002 ◽  
Vol 20 (8) ◽  
pp. 1143-1152 ◽  
Author(s):  
P. Francia ◽  
S. Lepidi ◽  
K. Yumoto
Keyword(s):  
Solar Wind ◽  
Local Time ◽  
Geomagnetic Field ◽  
Dynamic Pressure ◽  
Recovery Phase ◽  
Wind Pressure ◽  
Mhd Waves ◽  
Time Interval ◽  
Field Fluctuations ◽  
Solar Wind Pressure

Abstract. In this work we present the analysis of the geomagnetic field fluctuations observed at different ground stations (approximately along two latitudinal arrays, separated by several hours in local time) during the passage at the Earth’s orbit of the tail of the 15–16 July 2000 coronal ejecta. The time interval of interest is characterized by northward interplanetary magnetic field conditions and several changes in the solar wind dynamic pressure. We found at all stations, both in the local morning and in the local evening, simultaneous and highly coherent waves at the same discrete frequencies (~ 1.8 and ~ 3.6 mHz) and suggest a possible interpretation in terms of global compressional modes driven by an impulsive variation of the solar wind pressure. Along the array situated in the morning sector, at the highest latitudes, the higher frequency mode seems to couple with the local field line resonance; on the other hand, along the array situated in the evening sector, the characteristics of the observed fluctuations suggest that the highest latitude station could be located at the footprint of open field lines. Our results also show that solar wind pressure variations observed during the recovery phase of the storm do not find correspondence in the geomagnetic field variations, regardless of local time and latitude; conversely, some hours later continuous solar wind pressure variations find a close correspondence in the geomagnetic field variations at all stations.Key words. Magnetospheric physics (solar wind-magnetosphere interaction; MHD waves and instabilities)

scholarly journals The Earth's passage of the April 11, 1997 coronal ejecta: geomagnetic field fluctuations at high and low latitude during northward interplanetary magnetic field conditions

1999 ◽  
Vol 17 (10) ◽  
pp. 1245-1250 ◽  
Author(s):  
S. Lepidi ◽  
P. Francia ◽  
U. Villante ◽  
A. Meloni ◽  
A. J. Lazarus ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Geomagnetic Field ◽  
Field Conditions ◽  
Mhd Waves ◽  
Low Latitude ◽  
Terra Nova Bay ◽  
Field Fluctuations ◽  
Terra Nova

Abstract. An analysis of the low frequency geomagnetic field fluctuations at an Antarctic (Terra Nova Bay) and a low latitude (L'Aquila, Italy) station during the Earth's passage of a coronal ejecta on April 11, 1997 shows that major solar wind pressure variations were followed at both stations by a high fluctuation level. During northward interplanetary magnetic field conditions and when Terra Nova Bay is close to the local geomagnetic noon, coherent fluctuations, at the same frequency (3.6 mHz) and with polarization characteristics indicating an antisunward propagation, were observed simultaneously at the two stations. An analysis of simultaneous measurements from geosynchronous satellites shows evidence for pulsations at approximately the same frequencies also in the magnetospheric field. The observed waves might then be interpreted as oscillation modes, triggered by an external stimulation, extending to a major portion of the Earth's magnetosphere. Key words. Magnetospheric physics (MHD waves and instabilities; solar wind-magnetosphere interactions)

scholarly journals Low frequency geomagnetic field fluctuations at low latitude during the passage of a higher pressure solar wind region

1997 ◽  
Vol 15 (6) ◽  
pp. 656-661
Author(s):  
U. Villante ◽  
P. Francia
Keyword(s):  
Solar Wind ◽  
Geomagnetic Field ◽  
Low Frequency ◽  
Frequency Range ◽  
Low Latitude ◽  
Wind Region ◽  
Spectral Peaks ◽  
Field Fluctuations ◽  
Term Analysis

Abstract. The passage of a higher pressure solar wind region at the Earth's orbit marked the onset of low latitude (L=1.6) fluctuations in the frequency range (0.8–5.5 mHz) for both the horizontal geomagnetic field components. Spectral peaks mostly occur at the same frequencies as the spectral enhancements which appeared in the long term analysis of experimental measurements from the same station and were tentatively interpreted in terms of ground signatures of global magnetospheric modes. A comparison with simultaneous observations discussed by previous investigations allows us to conclude that the same set of frequencies is enhanced in a wide portion of the Earth's magnetosphere.

scholarly journals A case study testing the cavity mode model of the magnetosphere

2005 ◽  
Vol 23 (5) ◽  
pp. 1867-1880 ◽  
Author(s):  
D. V. Sarafopoulos
Keyword(s):  
Solar Wind ◽  
Cavity Mode ◽  
Broad Band ◽  
Compressional Wave ◽  
Wind Pressure ◽  
Mhd Waves ◽  
Arrival Times ◽  
Power Spectral ◽  
Mhd Waves And Instabilities

Abstract. Based on a case study we test the cavity mode model of the magnetosphere, looking for eigenfrequencies via multi-satellite and multi-instrument measurements. Geotail and ACE provide information on the interplanetary medium that dictates the input parameters of the system; the four Cluster satellites monitor the magnetopause surface waves; the POLAR (L=9.4) and LANL 97A (L=6.6) satellites reveal two in-situ monochromatic field line resonances (FLRs) with T=6 and 2.5 min, respectively; and the IMAGE ground magnetometers demonstrate latitude dependent delays in signature arrival times, as inferred by Sarafopoulos (2004b). Similar dispersive structures showing systematic delays are also extensively scrutinized by Sarafopoulos (2005) and interpreted as tightly associated with the so-called pseudo-FLRs, which show almost the same observational characteristics with an authentic FLR. In particular for this episode, successive solar wind pressure pulses produce recurring ionosphere twin vortex Hall currents which are identified on the ground as pseudo-FLRs. The BJN ground magnetometer records the pseudo-FLR (alike with the other IMAGE station responses) associated with an intense power spectral density ranging from 8 to 12 min and, in addition, two discrete resonant lines with T=3.5 and 7 min. In this case study, even though the magnetosphere is evidently affected by a broad-band compressional wave originated upstream of the bow shock, nevertheless, we do not identify any cavity mode oscillation within the magnetosphere. We fail, also, to identify any of the cavity mode frequencies proposed by Samson (1992). Keywords. Magnetospheric physics (Magnetosphereionosphere interactions; Solar wind-magnetosphere interactions; MHD waves and instabilities)

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