At substorm onset, 40% of AL comes from underground

Tanskanen, Eija; Viljanen, A.; Pulkkinen, T. I.; Pirjola, Risto; Hakkinen, L.; Pulkkinen, A.; Amm, O.

doi:10.1029/2000ja900135

Cited by 79 publications

(80 citation statements)

References 28 publications

(30 reference statements)

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“…6 is that the ratio I L ext /I L tot also has the high-frequency component and that the relative contributions of external and internal parts can vary quite strongly around the average, a feature also seen clearly in Pulkkinen et al (2003b). We note that the peak internal contribution of 30% to the total I L is about 10% smaller than what was reported by Tanskanen et al (2001) for the average over a number of substorms, and, as mentioned above, 5% smaller than that reported by Pulkkinen et al (2003b). This may indicate that the conductivity model is slightly too resistive.…”

Section: Discussioncontrasting

confidence: 47%

“…as rapidly as that of the ionospheric currents (for a more detailed discussion on this see, e.g. Tanskanen et al, 2001). Varentsov et al (2002) found strong electromagnetic sounding parameter-related distortions caused by the same 3-D crust model.…”

Section: Discussionmentioning

confidence: 99%

“…Berdichevsky and Zhdanov, 1984, p. 191). Earlier investigations have shown that neglecting telluric effects may cause significant errors of up to 40% in the estimation of the ionospheric current intensity (Viljanen et al, 1995;Tanskanen et al, 2001), or even notable errors in the determination of some global magnetospheric indices like D st (Häkkinen et al, 2002). As finer spatial and temporal scales are investigated both in ionospheric and magnetospheric studies and more accurate estimates of the physical parameters are pursued, errors of 40% become significant and cannot be blindly neglected.…”

Section: Introductionmentioning

confidence: 99%

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The role of 3-D geomagnetic induction in the determination of the ionospheric currents from the ground geomagnetic data

Pulkkinen¹,

Engels

2005

Ann. Geophys.

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Abstract. The geomagnetic field variations measured at the surface of the Earth are composed of both internal and external parts. The external field arises from the sources in the magnetosphere and ionosphere, whereas the internal field is generated by the currents induced within the Earth. The internal part may in some situations comprise a notable part of the measured total field and thus a blind usage of geomagnetic field recordings potentially produces significant errors to estimated ionospheric currents. In this paper the role of geomagnetic induction in auroral ionospheric studies is investigated by modeling the induction using simultaneously the realistic ionospheric source and a realistic three-dimensional Earth conductivity structure.The modeling results imply that the effects of the lateral ground conductivity anomalies on ionospheric equivalent current patterns are, though clearly detected, less severe than anticipated for fields varying with periods from 5 to 120 min. However, the amplification of the determined currents caused by induction is significant, leading to an overestimation of up to 30% of the main current flow intensities, with the overestimation increasing sharply when moving away from the region of the main flow.In addition to the 3-D modeling, a simple method is introduced to help estimate the internal contribution to the measured variations of the I L index (local variant of the AL index). A test with the 26 June 1998 substorm event indicates that the method can help to extract the internal contribution from the I L index.

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Section: Discussioncontrasting

confidence: 47%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The role of 3-D geomagnetic induction in the determination of the ionospheric currents from the ground geomagnetic data

Pulkkinen¹,

Engels

2005

Ann. Geophys.

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“…Our E-field estimates can actually be even higher since the Hall conductance can, in reality, be smaller; our radar model is not sensitive to the low-altitude end of the N (h)-profile so that smaller densities are acceptable. We should mention that since the magnetic field variations were slow, less than 1 nTmin −1 , we could neglect the Earth induction effects considered by Tanskanen et al (2001).…”

Section: Modeling Of Slant-range Profiles Of Echo Parametersmentioning

confidence: 99%

CUTLASS HF radar observations of high-velocity E-region echoes

et al. 2001

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Abstract.A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ionacoustic speed of 400 ms −1 , while the other group had significantly larger velocities, of the order of 700 ms −1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ∼700 ms −1 echoes originated from larger heights and distances of 500-700 km, while all ∼400 ms −1 echoes came from lower heights and from farther distances; 700-1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong (∼70 mVm −1 ) and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.

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“…Based on the studies of the Earth's conductivity structure in Scandinavia (e.g. Viljanen, 1995;Tanskanen et al, 2001), we set a perfectly conducting layer at a depth of 100 km for the variations with T ∼ 1 min.…”

Section: Quantitative Characterization Of the Equivalent Current Systmentioning

confidence: 99%

Evaluation of the geometry of ionospheric current systems related to rapid geomagnetic variations

et al. 2004

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Abstract.To learn about the geometry and sources of the ionospheric current systems which generate strong geomagnetically induced currents, we categorize differential equivalent current systems (DEC) for events with strong dB/dt by decomposing them into the contributions of electrojet-type and vortex-type elementary systems. By solving the inverse problem we obtain amplitudes and locations of these elementary current systems. One-minute differences of the geomagnetic field values at the IMAGE magnetometer network in 1996-2000 are analysed to study the spatial distributions of large dB/dt events. The relative contributions of the two components are evaluated. In particular, we found that the majority of the strongest dB/dt events (100-1000 nT/min) appear to be produced by the vortex-type current structures and most of them occur in the morning LT hours, probably caused by the Ps6 pulsation events associated with auroral omega structures. For strong dB/dt events the solar wind parameters are shifted toward strong (tens nT) southward IMF, enhanced velocity and dynamic pressure, in order for the main phase of the magnetic storms to occur. Although these events appear mostly during magnetic storms when the auroral oval greatly expands, the area of large dB/dt stays in the middle part of the auroral zone; therefore, it is connected to the processes taking part in the middle of the magnetosphere rather than in its innermost region populated by the ring current.

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At substorm onset, 40% of AL comes from underground

Cited by 79 publications

References 28 publications

The role of 3-D geomagnetic induction in the determination of the ionospheric currents from the ground geomagnetic data

The role of 3-D geomagnetic induction in the determination of the ionospheric currents from the ground geomagnetic data

CUTLASS HF radar observations of high-velocity E-region echoes

Evaluation of the geometry of ionospheric current systems related to rapid geomagnetic variations

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