Low latitude geomagnetic field line resonance: Experiment and modeling

Abstract. Based on a detailed study of Pc3 events at an array between L = 1.5 and 3 in Central Europe, the authors found quick changes between upstream waves (UW, i.e. pulsation directly driven by UW) and field line resonance (FLR, i.e. azimuthal oscillations of geomagnetic field lines). The alternation of the two types is especially characteristic (and the UW part stronger) if the interplanetary magnetic field (IMF) is highly variable. Events due to field line resonance may have a structure consisting of multiple lines with frequencies differing by about 10%, corresponding to neighbouring shells of field lines separated by about 100 km at the surface. This coincides with previous findings (about 10% at a meridional distance of 80 km). The frequency of the UW type is well correlated with the frequency of waves in the interplanetary medium. Additionally, there are signals of unidentified origin which also seem to be influenced by IMF.>Key words. Magnetosphere Physics · MHD waves and instabilities · Plasmasphere · Solar wind/magnetosphere interactions

Download Full-text

The structure of low-latitude Pc3 pulsations observed by CHAMP and on the ground

Annales Geophysicae ◽

10.5194/angeo-27-1267-2009 ◽

2009 ◽

Vol 27 (3) ◽

pp. 1267-1277 ◽

Cited By ~ 21

Author(s):

D. C. Ndiitwani ◽

P. R. Sutcliffe

Keyword(s):

Magnetic Field ◽

Field Line ◽

Field Measurements ◽

Doppler Frequency ◽

Resonance Region ◽

Compressional Wave ◽

Mhd Waves ◽

Low Latitude ◽

Field Line Resonance ◽

Line Resonance

Abstract. The structure of low-latitude continuous pulsations termed Pc3, which are naturally occurring MHD waves in the Earth's magnetosphere, were studied by comparing ground and satellite magnetic field measurements. Data from two induction magnetometers, located at Hermanus and Sutherland in South Africa were used in conjunction with Challenging Minisatellite Payload (CHAMP) satellite observations to study a Pc3 event observed on 15 February 2003, at a time when CHAMP was passing over the ground stations. We observed a number of discrete frequency oscillations for the fast mode wave, one of which drives a field line resonance (FLR) at characteristic latitude as detected by both ground and satellite measurements. Consequently, our observations confirmed the compressional wave as being the driver of the field line resonance. The toroidal mode frequency observed on CHAMP experienced a Doppler frequency shift due to the rapid motion across the resonance region. Polarization hodograms in the resonance region clearly showed the expected 90° rotation of the field line resonant magnetic field components.

Download Full-text

On the Geomagnetic Field Line Resonance Eigenfrequency Variations during Seismic Event

Remote Sensing ◽

10.3390/rs13142839 ◽

2021 ◽

Vol 13 (14) ◽

pp. 2839

Author(s):

Mirko Piersanti ◽

William Jerome Burger ◽

Vincenzo Carbone ◽

Roberto Battiston ◽

Roberto Iuppa ◽

...

Keyword(s):

Field Line ◽

Density Variation ◽

Coupling Mechanism ◽

Geomagnetic Field Line ◽

Field Line Resonance ◽

Acoustic Gravity Waves ◽

Line Resonance ◽

Field Lines ◽

Remote Sensing Methods ◽

The Magnetic Field

In this paper, we report high statistical evidence for a seismo–ionosphere effects occurring in conjunction with an earthquake. This finding supports a lithosphere-magnetosphere coupling mechanism producing a plasma density variation along the magnetic field lines, mechanically produced by atmospheric acoustic gravity waves (AGWs) impinging the ionosphere. We have analysed a large sample of earthquakes (EQ) using ground magnetometers data: in 28 of 42 analysed case events, we detect a temporary stepwise decrease (Δf) of the magnetospheric field line resonance (FLR) eigenfrequency (f*). Δf decreases of ∼5–25 mHz during ∼20–35 min following the time of the EQ. We present an analytical model for f*, able to reproduce the behaviour observed during the EQ. Our work is in agreement with recent results confirming co-seismic direct coupling between lithosphere, ionosphere and magnetosphere opening the way to new remote sensing methods, from space/ground, of the earth seismic activity.

Download Full-text