An ionospheric conductance model based on ground magnetic disturbance data

Ahn, B.‐H.; Richmond, A. D.; Kamide, Y.; Kroehl, H. W.; Emery, B. A.; Beaujardière, O. de La; Akasofu, S.‐I.

doi:10.1029/97ja03088

Cited by 77 publications

(78 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The background electric potential utilized by AMIE is the Weimer (1996) model which is driven directly by upstream IMF and solar wind conditions. In the inversion process, Hall and Pederson conductance elements are obtained from the measured ground magnetic disturbance using the formulation by Ahn et al (1993Ahn et al ( , 1998. We use AMIE to invert ground magnetic measurements with supplementary IMF and solar wind data, hemispheric power index (HPI) computed by NOAA to adjust the background potential and conductivity patterns.…”

Section: Statistical Analysis Metholodogymentioning

confidence: 99%

Statistical analysis of ionospheric potential patterns for isolated substorms and sawtooth events

2006

View full text Add to dashboard Cite

Abstract. We present here results which contrast isolated substorms with individual sawtooth events. Sawtooth events are defined as quasi-periodic, large-amplitude oscillations in the energetic particle flux with a periodicity of 2-4 h observed at the geosynchronous orbit. Sawtooth events have several similarities to isolated substorms leading therefore, to different opinions about whether sawtooth events are just an intense periodic form of substorms or if they deserve a category of their own. To help resolve this, we examine the ionospheric potential patterns in the northern polar region for isolated substorms and sawtooth events using the assimilative mapping of ionospheric electrodynamics (AMIE) technique. First we show a statistical analysis of isolated substorm potential patterns. In order to examine the seasonal variation, isolated substorms are identified by mid-latitude positive bay in the north-south geomagnetic perturbation in each season, respectively. Superposed epoch analysis (SEA) is applied to obtain the typical polar potential patterns for each season. By examining the time evolution of the potential patterns and cross polar cap potential (CPCP) for isolated substorms during each season, we find only subtle seasonal variations in the results obtained using the AMIE analysis. This provides a basis for comparison with sawtooth events in the next step. From the averaged potential patterns of 213 isolated substorms and those of 184 individual sawtooth events, we find the sawtooth events show signatures similar to subtorms: the DP 1 potential pattern develops and dominates the polar region after the onset. However, the DP 1 potential cell of sawtooth events encompasses a larger area than that of isolated substorms. Moreover, the CPCP of sawtooth is stronger than that of isolated substorms. It is also shown that the sawtooth events displays greater variability between individual events than isolated substorms. We conclude that in terms of ionospheric electrodynamics, the sawtoothe events have features that are similar to those of isolates substorms, though larger in spatial extent and in magnitude.

show abstract

Section: Statistical Analysis Metholodogymentioning

confidence: 99%

Statistical analysis of ionospheric potential patterns for isolated substorms and sawtooth events

2006

View full text Add to dashboard Cite

show abstract

“…Galand et al (2001) derive conductances from ion precipitation. The formulations given by Ahn et al (1983) and Ahn et al (1998) relate the Hall and Pedersen conductances to ground-based magnetometer measurements.…”

Section: Introductionmentioning

confidence: 99%

Ionospheric control of the magnetosphere: conductance

2004

View full text Add to dashboard Cite

Abstract.It is well known that the ionosphere plays a role in determining the global state of the magnetosphere. The ionosphere allows magnetospheric currents to close, thereby allowing magnetospheric convection to occur. The amount of current which can be carried through the ionosphere is mainly determined by the ionospheric conductivity. This paper starts to quantify the nonlinear relationship between the ionospheric conductivity and the global state of the magnetosphere. It is found that the steady-state magnetosphere acts neither as a current nor as a voltage generator; a uniform Hall conductance can influence the potential pattern at low latitudes, but not at high latitude; the EUV generated conductance forces the currents to close in the sunlight, while the potential is large on the nightside; the solar generated Hall conductances cause a large asymmetry between the dawn and dusk potential, which effects the pressure distribution in the magnetosphere; a uniform polar cap potential removes some of this asymmetry; the potential difference between solar minimum and maximum is ∼11%; and the auroral precipitation can be related to the local field-aligned current through an exponential function.

show abstract

“…UV and ion contributions are neglected for this study in the nighttime sector. These methods are similar to these subsequently proposed by Robinson and Vondrak (1984), Robinson et al (1987), and Hardy et al (1987), (see (Ahn et al, 1998 for a review) but oversimpli®ed compared to more recent models (Gjerloev and Homan, 2000). Nevertheless, all methods predict that the conductivity increases at the same rate as the square root of the precipitating electron energy¯ux, and calculated height-integrated conductivities dier by less than 10±15%, which is much less than the variation of the conductivity across the auroral oval.…”

Section: Instrumentation and Methodsologymentioning

confidence: 54%

Experimental study of the formation of inverted-V structures and their stratification using AUREOL-3 observations

et al. 2000

View full text Add to dashboard Cite

Abstract. Multiple inverted-V structures are commonly observed on the same auroral zone crossing by a lowaltitude orbiting satellite. Such structures appear grouped and apparently result from an ionospheric and/or magnetospheric mechanism of strati®cation. More than two years of AUREOL-3 satellite observations were analyzed to study their properties and their formation in the framework of the ionosphere-magnetosphere coupling model proposed by Tverskoy. This model predicts some natural periodicity in the electrostatic potential pro®le (and subsequently in the ®eld-aligned current pro®les) that could account for oscillations experimentally observed in the auroral zone, such as successive inverted-Vs. Experimental results obtained during quiet or moderately active periods demonstrate that the number of structures observed within a given event is well described by a`scaling' parameter provided by the hot plasma strati®cation theory and expressed in terms of the ®eld-aligned current density, the total width of the current band, the plasma sheet ion temperature, and the heightintegrated Pedersen conductivity of the ionosphere. The latitudinal width, in the order of 100±200 km at ionospheric altitudes, is relatively independent of the current density, and is determined not only by the existence of a potential dierence above the inverted-Vs, but also by basic oscillations of the ionosphere-magnetosphere coupling system predicted by Tverskoy. The large number of cases studied by the AUREOL-3 satellite provides reliable statistical trends which permits the validation of the model and the inference that the multiple structures currently observed can be related directly to oscillations of the magnetospheric potential (or the pressure gradients) on a scale of $1000±2000 km in the near-Earth plasma sheet. These oscillations arise in the Tverskoy model and may naturally result when the initial pressure gradients needed to generate a largescale ®eld-aligned current have a suciently wide equatorial scale, of about 1 R E or more.

show abstract

An ionospheric conductance model based on ground magnetic disturbance data

Cited by 77 publications

References 21 publications

Statistical analysis of ionospheric potential patterns for isolated substorms and sawtooth events

Statistical analysis of ionospheric potential patterns for isolated substorms and sawtooth events

Ionospheric control of the magnetosphere: conductance

Experimental study of the formation of inverted-V structures and their stratification using AUREOL-3 observations

Contact Info

Product

Resources

About