scholarly journals Local time behaviour of low frequency geomagnetic field fluctuation power at low latitude

2001 ◽  
Vol 44 (1) ◽  
Author(s):  
S. Lepidi ◽  
P. Francia ◽  
M. De Lauretis
Keyword(s):  
Local Time ◽  
Geomagnetic Field ◽  
Field Component ◽  
Current System ◽  
Dynamic Pressure ◽  
Geomagnetic Latitude ◽  
Low Frequency ◽  
Time Behaviour ◽  
Field Fluctuation ◽  
Low Latitude

In this paper we present a statistical study of the local time behaviour of low frequency (0.7-4.0 mHz) geomagnetic field fluctuation power at a low latitude station (corrected geomagnetic latitude 36.2°N). The analysis was conducted for two contiguous years during the ascending phase of the solar cycle. We found that the power of the horizontal east-west geomagnetic field component shows a diurnal and seasonal variation which can be related to variations of the ionospheric current system (Sq) mainly produced by dynamo-action in the ionospheric E region. The power of the horizontal north-south geomagnetic field component is higher in the local afternoon with respect to the morning; this asymmetry is more evident during time intervals characterized by high solar wind dynamic pressure.

An analysis of geomagnetic field variations (3 min-2 h) at a low-latitude observatory (L=1.6)

1995 ◽  
Vol 13 (5) ◽  
pp. 522-531
Author(s):  
P. Francia ◽  
U. Villante ◽  
A. Meloni
Keyword(s):  
Geomagnetic Field ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Current System ◽  
Power Level ◽  
Low Frequency ◽  
Low Latitude ◽  
Wind Speeds ◽  
Low Frequency Power ◽  
Frequency Power

Abstract. An analysis of the geomagnetic field variations between 3 min and 2 h at L'Aquila (L=1.6) shows that the power level in the low-frequency range (i.e. for periods longer than approximately 10 min) at solar maximum (1989/90) is much higher than at solar minimum (1985/86). Conversely, at solar minimum, it emerges that there is a greater relative importance of fluctuations with periods smaller than 10 min which might be related to the greater percentage of solar wind speeds greater than approximately 540 km s–1. Diurnal, seasonal and solar cycle variations of both the high- and the low-frequency power are also discussed. We found that several aspects of these variations might be correlated with ionospheric features such as the ionisation of the F2 layer and the location and the intensity of the S current system.

Polarization pattern of low-frequency geomagnetic field fluctuations (0.8-3.6 mHz) at high and low latitude

1999 ◽  
Vol 104 (A1) ◽  
pp. 305-310 ◽  
Author(s):  
S. Lepidi ◽  
P. Francia ◽  
U. Villante ◽  
L. J. Lanzerotti ◽  
A. Meloni
Keyword(s):  
Geomagnetic Field ◽  
Low Frequency ◽  
Polarization Pattern ◽  
Low Latitude ◽  
Field Fluctuations

scholarly journals Influence of high-latitude geomagnetic pulsations on recordings of broadband force-balanced seismic sensors

2012 ◽  
Vol 1 (2) ◽  
pp. 85-101 ◽  
Author(s):  
E. Kozlovskaya ◽  
A. Kozlovsky
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Geomagnetic Latitude ◽  
Low Frequency ◽  
Auroral Oval ◽  
Polar Regions ◽  
Geomagnetic Pulsations ◽  
Seismic Sensors ◽  
Magnetic Poles ◽  
Magnetic Disturbances

Abstract. Seismic broadband sensors with electromagnetic feedback are sensitive to variations of surrounding magnetic field, including variations of geomagnetic field. Usually, the influence of the geomagnetic field on recordings of such seismometers is ignored. It might be justified for seismic observations at middle and low latitudes. The problem is of high importance, however, for observations in Polar Regions (above 60° geomagnetic latitude), where magnitudes of natural magnetic disturbances may be two or even three orders larger. In our study we investigate the effect of ultra-low frequency (ULF) magnetic disturbances, known as geomagnetic pulsations, on the STS-2 seismic broadband sensors. The pulsations have their sources and, respectively, maximal amplitudes in the region of the auroral ovals, which surround the magnetic poles in both hemispheres at geomagnetic latitude (GMLAT) between 60° and 80°. To investigate sensitivity of the STS-2 seismometer to geomagnetic pulsations, we compared the recordings of permanent seismic stations in northern Finland to the data of the magnetometers of the IMAGE network located in the same area. Our results show that temporary variations of magnetic field with periods of 40–150 s corresponding to regular Pc4 and irregular Pi2 pulsations are seen very well in recordings of the STS-2 seismometers. Therefore, these pulsations may create a serious problem for interpretation of seismic observations in the vicinity of the auroral oval. Moreover, the shape of Pi2 magnetic disturbances and their periods resemble the waveforms of glacial seismic events reported originally by Ekström (2003). The problem may be treated, however, if combined analysis of recordings of co-located seismic and magnetic instruments is used.

scholarly journals A study of geomagnetic field variations along the 80° S geomagnetic parallel

2017 ◽  
Vol 35 (1) ◽  
pp. 139-146 ◽  
Author(s):  
Stefania Lepidi ◽  
Lili Cafarella ◽  
Patrizia Francia ◽  
Andrea Piancatelli ◽  
Manuela Pietrolungo ◽  
...  
Keyword(s):  
Local Time ◽  
Geomagnetic Field ◽  
Daily Variation ◽  
Low Frequency ◽  
Magnetic Local Time ◽  
The Other ◽  
Ionospheric Currents ◽  
Wave Propagation Direction ◽  
Predominant Effect ◽  
Local Noon

Abstract. The availability of measurements of the geomagnetic field variations in Antarctica at three sites along the 80° S geomagnetic parallel, separated by approximately 1 h in magnetic local time, allows us to study the longitudinal dependence of the observed variations. In particular, using 1 min data from Mario Zucchelli Station, Scott Base and Talos Dome, a temporary installation during 2007–2008 Antarctic campaign, we investigated the diurnal variation and the low-frequency fluctuations (approximately in the Pc5 range, ∼ 1–7 mHz). We found that the daily variation is clearly ordered by local time, suggesting a predominant effect of the polar extension of midlatitude ionospheric currents. On the other hand, the pulsation power is dependent on magnetic local time maximizing around magnetic local noon, when the stations are closer to the polar cusp, while the highest coherence between pairs of stations is observed in the magnetic local nighttime sector. The wave propagation direction observed during selected events, one around local magnetic noon and the other around local magnetic midnight, is consistent with a solar-wind-driven source in the daytime and with substorm-associated processes in the nighttime.

scholarly journals Magnetic local time dependence of geomagnetic disturbances contributing to the AU and AL indices

2011 ◽  
Vol 29 (4) ◽  
pp. 673-678 ◽  
Author(s):  
S. Tomita ◽  
M. Nosé ◽  
T. Iyemori ◽  
H. Toh ◽  
M. Takeda ◽  
...  
Keyword(s):  
Local Time ◽  
Geomagnetic Field ◽  
Field Data ◽  
Geomagnetic Latitude ◽  
Magnetic Activity ◽  
Auroral Zone ◽  
Magnetic Local Time ◽  
Geomagnetic Disturbances ◽  
Current Systems ◽  
Local Time Dependence

Abstract. The Auroral Electrojet (AE) indices, which are composed of four indices (AU, AL, AE, and AO), are calculated from the geomagnetic field data obtained at 12 geomagnetic observatories that are located in geomagnetic latitude (GMLAT) of 61.7°–70°. The indices have been widely used to study magnetic activity in the auroral zone. In the present study, we examine magnetic local time (MLT) dependence of geomagnetic field variations contributing to the AU and AL indices. We use 1-min geomagnetic field data obtained in 2003. It is found that both AU and AL indices have two ranges of MLT (AU: 15:00–22:00 MLT, ~06:00 MLT; and AL: ~02:00 MLT, 09:00–12:00 MLT) contributing to the index during quiet periods and one MLT range (AU: 15:00–20:00 MLT, and AL: 00:00–06:00 MLT) during disturbed periods. These results are interpreted in terms of various ionospheric current systems, such as, Sqp, Sq, and DP2.

scholarly journals FEATURES OF EXCITATION AND AZIMUTHAL AND MERIDIONAL PROPAGATION OF LONG-PERIOD Pi3 OSCILLATIONS OF THE GEOMAGNETIC FIELD ON DECEMBER 8, 2017

2020 ◽  
Vol 6 (3) ◽  
pp. 56-72
Author(s):  
Aleksey Moiseev ◽  
Sergei Starodubtsev ◽  
Vladimir Mishin
Keyword(s):  
Geomagnetic Field ◽  
Large Scale ◽  
Current System ◽  
Dynamic Pressure ◽  
Small Scale ◽  
Frequency Range ◽  
Latitude Range ◽  
Magnetospheric Convection ◽  
Long Period ◽  
Geomagnetic Observations

We study the Pi3 pulsations (with a period T=15–30 min) that were recorded on December 8, 2017 at ground stations in the midnight sector of the magnetosphere at the latitude range of DP2 current system convective electrojets. We have found that Pi3 are especially pronounced in the pre-midnight sector with amplitude of up to 300 nT and duration of up to 2.5 hrs. The pulsation amplitude rapidly decreased with decreasing latitude from F′=72° to F′=63°. The event was recorded during the steady magnetospheric convection. In the southward Bz component of the interplanetary magnetic field, irregular oscillations were detected in the Pi3 frequency range. They correspond to slow magnetosonic waves occurring without noticeable variations in the dynamic pressure Pd. Ground-based geomagnetic observations have shown azimuthal propagation of pulsations with a 0.6–10.6 km/s velocity east and west of the midnight meridian. An analysis of the dynamics of pulsations along the meridian has revealed their propagation to the equator at a velocity 0.75–7.87 km/s. In the projection onto the magnetosphere, the velocities are close in magnitude to the observed propagation velocities of substorm injected electrons. In the dawn-side magnetosphere during ground-observed Pi3 pulsations, compression mode oscillations were recorded. We conclude that propagation of geomagnetic field oscillations in this event depends on the dynamics of particle injections under the action of a large-scale electric field of magnetospheric convection, which causes the plasma to move to Earth due to reconnection in the magnetotail. Small-scale oscillations in the magnetosphere were secondary, excited by the solar wind oscillations penetrating into the magnetosphere.

scholarly journals An intense SFE and SSC event in geomagnetic <i>H</i>, <i>Y</i> and <i>Z</i> fields at the Indian chain of observatories

1997 ◽  
Vol 15 (10) ◽  
pp. 1301-1308 ◽  
Author(s):  
R. G. Rastogi ◽  
D. R. K. Rao ◽  
S. Alex ◽  
B. M. Pathan ◽  
T. S. Sastry
Keyword(s):  
Solar Flare ◽  
Geomagnetic Storm ◽  
Geomagnetic Field ◽  
Current System ◽  
Equatorial Electrojet ◽  
Start Time ◽  
Low Latitude ◽  
Ionospheric Current ◽  
Ionospheric Current System ◽  
Solar Flare Effects

Abstract. Changes in the three components of geomagnetic field are reported at the chain of ten geomagnetic observatories in India during an intense solar crochet that occurred at 1311 h 75° EMT on 15 June 1991 and the subsequent sudden commencement (SSC) of geomagnetic storm at 1518 h on 17 June 1991. The solar flare effects (SFE) registered on the magnetograms appear to be an augmentation of the ionospheric current system existing at the start time of the flare. An equatorial enhancement in ΔH due to SFE is observed to be similar in nature to the latitudinal variation of SQ (H) at low latitude. ΔY registered the largest effect at 3.6° dip latitude at the fringe region of the electrojet. ΔZ had positive amplitudes at the equatorial stations and negative at stations north of Hyderabad. The SSC amplitude in the H component is fairly constant with latitude, whereas the Z component again showed larger positive excursions at stations within the electrojet belt. These results are discussed in terms of possible currents of internal and external origin. The changes in the Y field strongly support the idea that meridional current at an equatorial electrojet station flows in the ionospheric dynamo, E.

Determining the Polar Cusp Longitudinal Location from Pc5 Geomagnetic Field Measurements at a Pair of High Latitude Stations

2017 ◽  
Vol 13 (S335) ◽  
pp. 139-141
Author(s):  
Stefania Lepidi ◽  
Patrizia Francia ◽  
Lili Cafarella ◽  
Domenico Di Mauro ◽  
Martina Marzocchetti
Keyword(s):  
Magnetic Field ◽  
Satellite Data ◽  
High Latitude ◽  
Geomagnetic Field ◽  
Geomagnetic Latitude ◽  
Low Frequency ◽  
Field Measurements ◽  
Polar Cap ◽  
Polar Cusp ◽  
Local Noon

AbstractWe use low frequency geomagnetic field measurements at two Antarctic stations to statistically investigate the longitudinal location of the polar cusp. The two stations are both located in the polar cap at a geomagnetic latitude close to the cusp latitude; they are separated by one hour in magnetic local time. At each station the Pc5 power maximizes when the station approaches the cusp, i.e. around magnetic local noon. The comparison between the Pc5 power at the two stations allows to determine the longitudinal location of the cusp. Our analysis is conducted considering separately different orientation of the interplanetary magnetic field. The results, which indicate longitudinal shifts of the polar cusp depending on the selected conditions, are discussed in relation to previous studies of the polar cusp location based on polar magnetospheric satellite data.

scholarly journals Modeling of the Jovian Magnetosphere

2005 ◽  
Vol 23 (3) ◽  
pp. 809-826 ◽  
Author(s):  
I. I. Alexeev ◽  
E. S. Belenkaya
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Component ◽  
Current System ◽  
Dynamic Pressure ◽  
High Latitudes ◽  
Jovian Magnetosphere ◽  
Wind Influence ◽  
Magnetospheric Field ◽  
Normal Magnetic Field

Abstract. This paper presents a global model of the Jovian magnetosphere which is valid not only in the equatorial plane and near the planet, as most of the existing models are, but also at high latitudes and in the outer regions of the magnetosphere. The model includes the Jovian dipole, magnetodisc, and tail current system. The tail currents are combined with the magnetopause closure currents. All inner magnetospheric magnetic field sources are screened by the magnetopause currents. It guarantees a zero normal magnetic field component for the inner magnetospheric field at the whole magnetopause surface. By changing magnetospheric scale (subsolar distance), the model gives a possibility to study the solar wind influence on the magnetospheric structure and auroral activity. A dependence of the magnetospheric size on the solar wind dynamic pressure psw (proportional to psw-0.23) is obtained. It is a stronger dependence than in the case of the Earth's magnetosphere (psw-1/6). The model of Jupiter's magnetospheric which is presented is a unique one, as it allows one to study the solar wind and interplanetary magnetic field (IMF) effects.

scholarly journals Quiet Ionospheric Currents and Earth Conductivity Profile Computed from Quiet-time Geomagnetic Field Changes in the Region of Australia

1987 ◽  
Vol 40 (1) ◽  
pp. 73 ◽  
Author(s):  
Wallace H Campbell ◽  
Edward R Schiffmacher
Keyword(s):  
Geomagnetic Field ◽  
Current System ◽  
Geomagnetic Latitude ◽  
Internal Field ◽  
Quiet Time ◽  
Ionospheric Currents ◽  
Conductivity Profile ◽  
Earth Conductivity ◽  
Quiet Day ◽  
Vortex Source

Equivalent ionospheric source currents representing the quiet-day geomagnetic field variations were established for a half-sector. of the Earth that included Australia. The analysis used a spherical harmonic separation of the external and internal fields for the extremely quiet conditions existing in 1965. Month-by-month behaviour of the current system indicated a clockwise vortex source with a maximum of 12.8xl04 A in January and a minimum of 4.4xl04 A in June. The focus location shifted from about -32�5� geomagnetic latitude in summer to about - 30.0� in winter. The separated external and internal field coefficients were used to estimate the Earth's upper mantle electrical conductivity (J" at a depth d from about 250 to 350 km as (J" =0�00067 exp(O� 012 d) S m - I and from about 350 to 550 km as (J" = 0�0014exp(0�0088d) Sm- I .

Sign in / Sign up

Export Citation Format

Share Document