The GGS/POLAR magnetic fields investigation

Russell, C. T.; Snare, R. C.; Means, J. D.; Pierce, David R.; Dearborn, D.; Larson, M. J.; Barr, G.; Le, G.

doi:10.1007/bf00751341

Cited by 247 publications

(163 citation statements)

References 16 publications

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“…The data used are the vector magnetic field measurements of a one-minute average combined from three spacecraft, including the first 5 years of the Polar mission (Russell et al, 1995), the entire 5 years of the AMPTE/CCE mission (Potemra et al, 1985), and the entire 10 years of the ISEE mission (Russell, 1978). Table 1 lists some information about the three missions.…”

Section: Data Setmentioning

confidence: 99%

Morphology of the ring current derived from magnetic field observations

2004

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Abstract. Our examination of the 20 years of magnetospheric magnetic field data from ISEE, AMPTE/CCE and Polar missions has allowed us to quantify how the ring current flows and closes in the magnetosphere at a variety of disturbance levels. Using intercalibrated magnetic field data from the three spacecraft, we are able to construct the statistical magnetic field maps and derive 3-dimensional current density by the simple device of taking the curl of the statistically determined magnetic field. The results show that there are two ring currents, an inner one that flows eastward at ∼3 R E and a main westward ring current at ∼4-7 R E for all levels of geomagnetic disturbances. In general, the insitu observations show that the ring current varies as the D st index decreases, as we would expect it to change. An unexpected result is how asymmetric it is in local time. Some current clearly circles the magnetosphere but much of the energetic plasma stays in the night hemisphere. These energetic particles appear not to be able to readily convect into the dayside magnetosphere. During quiet times, the symmetric and partial ring currents are similar in strength (∼0.5 MA) and the peak of the westward ring current is close to local midnight. It is the partial ring current that exhibits most drastic intensification as the level of disturbances increases. Under the condition of moderate magnetic storms, the total partial ring current reaches ∼3 MA, whereas the total symmetric ring current is ∼1 MA. Thus, the partial ring current contributes dominantly to the decrease in the D st index. As the ring current strengthens the peak of the partial ring current shifts duskward to the pre-midnight sector. The partial ring current is closed by a meridional current system through the ionosphere, mainly the field-aligned current, which maximizes at local times near the dawn and dusk. The closure currents flow in the sense of region-2 field-aligned currents, downward into the ionosphere near the dusk and upward out of the ionosphere near the dawn.

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Section: Data Setmentioning

confidence: 99%

Morphology of the ring current derived from magnetic field observations

2004

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“…For surveying purposes these are usually combined into 12-s and 28-energy distributions and displayed in the spectral forms of Figures 1 and 2. Final pitch angles are calculated during ground data processing with magnetic field information from the Polar MFE instrument [Russell et al, 1995]. The Polar satellite, with perigee and apogee at 1.8 and 9.0 R E (geocentric), respectively, carries the TIMAS instrument through the auroral regions four times each 17.63-hour revolution, and this occurs, for data to be discussed here, near perigee altitude in the Southern Hemisphere and, depending on geomagnetic conditions, at some 4 to 8 R E (geocentric) in the Northern Hemisphere.…”

Section: The Timas Instrumentmentioning

confidence: 99%

“…The electric field portion, sampled at a rate of 40 Hz, is from the EFI instrument [Harvey et al, 1995] and represents the instantaneous ''quasi-steady'' field. It has been combined with the magnetic field vector (sampled at about 9 Hz [Russell et al, 1995]) to form the E Â B B À2 vector, expressed in km s À1 and divided into its three GSE (geocentric solar ecliptic) components. The GSE x-component is relatively small, because the average magnetic field vector is nearly parallel to the x axis.…”

Section: Electric Field Observationsmentioning

confidence: 99%

In situ Polar observation of transverse cold‐ion acceleration: Evidence that electric field generation is a hot‐ion finite gyroradii effect

Lennartsson

2003

J. Geophys. Res.

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[1] Recent results with the Polar TIMAS instrument (ion mass spectrometer) have revealed that earthward magnetic field-aligned and velocity-dispersed flows of 1-to 33-keV protons (and other ions) from the outer magnetosphere are inherently ''blast-like'' and exhibit a complex filamentary structure where transverse scale sizes may often be a few proton gyroradii. These velocity-dispersed protons (and accompanying hot electrons) have been found to have a close association with enhanced large pitch angle outflow of accelerated (sometimes to more than 10 keV) ionospheric ions (H + , O + , and He + ) at Polar. Theoretical considerations suggest a mechanism by which the difference in gyroradii between hot ions and electrons in earthward plasma bursts generates charge imbalance and strong transverse electric fields at density gradients, as the bursts move into an increasingly strong magnetic field, which in turn accelerate the ambient cold ions. Model electric fields greater than 1 V m À1 at Polar are readily generated with density gradient scale lengths of a few earth radii in an equatorial source region of the bursts, assuming that the magnetic moments of the burst protons are preserved. The nonadiabatic acceleration of cold ions may act to reduce these fields to the ca 0.1-V m À1 amplitude and few-second period fluctuations actually observed. Sample TIMAS data are shown to be consistent with the transverse acceleration of cold O + ions to keV energy on a timescale of less than a single gyroperiod.

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“…For the surveying, these are combined into 12-s and 28-energy pairs and displayed in the spectral forms of differential number flux versus energy and time (averaged over all angles) and flux versus pitch angle and time (averaged over some energies). Pitch angles are calculated during ground data processing with magnetic field information from the Polar Magnetic Fields Investigation (MFI) instrument [Russell et al, 1995].…”

Section: Introductionmentioning

confidence: 99%