High-Altitude Observations of the Polar Wind

Moore, T. E.; Chappell, C. R.; Chandler, M. O.; Craven, P. D.; Giles, B. L.; Pollock, C. J.; Young, D. T.; Waite, J. H.; Nordholt, J. E.; Thomsen, M. F.; McComas, D. J.; Berthelier, Jean‐Jacques; Williamson, W. S.; Robson, Robert; Mozer, F. S.

doi:10.1126/science.277.5324.349

Cited by 95 publications

(77 citation statements)

References 15 publications

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“…As was mentioned in the introductory section, there have been a large number of studies on ion outflow from the polar caps at low altitudes using different spacecraft: DE-1 (Nagai et al, 1984;Chandler et al, 1991), Akebono (Abe et al, 1993(Abe et al, , 1996(Abe et al, , 2004Cully et al, 2003a), and Polar (Moore et al, 1997;Su et al, 1998;Chappell et al, 2000;Lennartsson et al, 2004;Liemohn et al, 2005;Huddleston et al, 2005;Peterson et al, 2006Peterson et al, , 2008. The study at highest altitude so far was conducted by Su et al (1998) using Polar data at apogee altitude at 8 R E above the polar caps.…”

Section: Comparison To Previously Published Resultsmentioning

confidence: 99%

“…The current understanding of the high-latitude ion outflows, including the polar wind, can mainly be attributed to a wealth of studies from Akebono (Abe et al, 1993(Abe et al, , 1996(Abe et al, , 2004Cully et al, 2003a) and Polar (e.g. Moore et al, 1997;Su et al, 1998;Chappell et al, 2000;Lennartsson et al, 2004;Liemohn et al, 2005;Huddleston et al, 2005;Peterson et al, 2006). More details on the previous measurements of the high-latitude ion outflows can be found in the recent review articles by Yau et al (2007) and Moore and Horwitz (2007).…”

Section: Introductionmentioning

confidence: 99%

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Survey of cold ionospheric outflows in the magnetotail

et al. 2009

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Abstract. Low-energy ions escape from the ionosphere and constitute a large part of the magnetospheric content, especially in the geomagnetic tail lobes. However, they are normally invisible to spacecraft measurements, since the potential of a sunlit spacecraft in a tenuous plasma in many cases exceeds the energy-per-charge of the ions, and little is therefore known about their outflow properties far from the Earth. Here we present an extensive statistical study of cold ion outflows (0-60 eV) in the geomagnetic tail at geocentric distances from 5 to 19 R E using the Cluster spacecraft during the period from 2001 to 2005. Our results were obtained by a new method, relying on the detection of a wake behind the spacecraft. We show that the cold ions dominate in both flux and density in large regions of the magnetosphere. Most of the cold ions are found to escape from the Earth, which improves previous estimates of the global outflow. The local outflow in the magnetotail corresponds to a global outflow of the order of 10 26 ions s −1 . The size of the outflow depends on different solar and magnetic activity levels.

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Section: Comparison To Previously Published Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Survey of cold ionospheric outflows in the magnetotail

et al. 2009

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“…When they are in situ detected at one location, the ions appear as narrow-energy, tailward streaming "beams." As presented in a number of studies, this type of distributions has been observed over the polar cap [e.g., Moore et al, 1997Moore et al, , 1999Cladis et al, 2000;Elliott et al, 2001;Nilsson et al, 2004Nilsson et al, , 2006Kistler et al, 2010] and in the lobe/mantle [e.g., Sharp et al, 1981;Orsini et al, 1990;Lennartsson, 1994;Kistler et al, 2010]. In addition, the presence of a population of tailward streaming beams has been found to be a persistent feature in the lobes [Liemohn et al, 2005;Engwall et al, 2009], even in the far tail up to 210 Earth radii (R E ) Mukai et al, 1994;Seki et al, 1996].…”

Section: Introductionmentioning

confidence: 89%

Shock-driven variation in ionospheric outflow during the 11 October 2001 moderate storm

et al. 2011

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[1] The Composition and Distribution Function (CODIF) Analyzer on board the Cluster spacecraft frequently observes narrow-energy, field-aligned O + ions over the polar caps and in the lobes, particularly during storm times. This population is due to ion outflow from the cusp. During the 11 October 2001 moderate storm, CODIF, located in the southern lobe at ∼12 Earth radii (R E ) down the tail and moving inbound, observed a change in the outflow. A sudden increase in solar wind dynamic pressure at 1702 UT led to a sudden increase in the energy of peak O + flux from ∼0.2 to 5 keV or an abrupt increase in parallel velocity from 54.0 ± 3.8 to 212.5 km/s. This high-energy population gradually decreased in energy over the next ∼2 h. The energy increase resulted from the effects of the solar wind shock on preexisting outflow. To model the effects of the shock, we first determined how the magnetic field configuration changed, by comparing the local magnetic field before and after the shock with the predictions of the T04s empirical model. The local field, reasonably well reproduced by T04s, experienced a 0.8-R E perpendicular displacement and a first 8.3°then 0.9°rotation in 3.8 min when the solar wind shock hit. We used local measurements of the H + drift velocity and magnetic field to calculate if the observed velocity increase was due to centrifugal acceleration. We found that at the beginning centrifugal acceleration contributed only 11.4%, i.e., 18.0 km/s, to the sudden O + parallel velocity increase; the net effect of the centrifugal acceleration is against the velocity increase. We conclude that the increase was actually due to the field displacement, which brought a higher velocity population to the Cluster location. A higher velocity is expected at higher latitudes due to the velocity filter effect that results from higher-energy ions moving further along the field line than lower-energy ions, as the field line convects over the polar cap and into the tail.

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“…In the polar cap region, the plasma component from the CIS data is readily identified as the polar wind, a cold plasma flow known to fill these regions in number densities comparable to those indicated by V ps . By using artificial potential control, the Polar spacecraft could be brought down to close to zero values of V ps , enabling the ions to reach the spacecraft and consequently allowing Moore et al (1997) and Su et al (1998) Figure 6, with EFW (red) and EDI (blue) data at full time resolution in the plasma sheet boundary layer.…”

Section: Polar Capmentioning

confidence: 99%

Electric field measurements on Cluster: comparing the double-probe and electron drift techniques

et al. 2006

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Abstract. The four Cluster satellites each carry two instruments designed for measuring the electric field: a doubleprobe instrument (EFW) and an electron drift instrument (EDI). We compare data from the two instruments in a representative sample of plasma regions. The complementary merits and weaknesses of the two techniques are illustrated. EDI operations are confined to regions of magnetic fields above 30 nT and where wave activity and keV electron fluxes are not too high, while EFW can provide data everywhere, and can go far higher in sampling frequency than EDI. On the other hand, the EDI technique is immune to variations in the low energy plasma, while EFW sometimes detects significant nongeophysical electric fields, particularly in regions with drifting plasma, with ion energy (in eV) below the spacecraft potential (in volts). We show that the polar cap is a particularly intricate region for the double-probe technique, where large nongeophysical fields regularly contaminate EFW measurments of the DC electric field. We present a model explaining this in terms of enhanced cold plasma wake effects appearing when the ion flow energy is higher than the thermal energy but below the spacecraft potential multiplied by the ion charge. We suggest that these conditions, which are typical of the polar wind and occur sporadically in other regions containing a significant low energy ion population, cause a large cold plasma wake behind the spacecraft, resulting in spurious electric fields in EFW data. This interpretation is supported by an analysis of the direction of the spurious electric field, and by showing that use of active potential control alleviates the situation.

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High-Altitude Observations of the Polar Wind

Cited by 95 publications

References 15 publications

Survey of cold ionospheric outflows in the magnetotail

Survey of cold ionospheric outflows in the magnetotail

Shock-driven variation in ionospheric outflow during the 11 October 2001 moderate storm

Electric field measurements on Cluster: comparing the double-probe and electron drift techniques

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