R. L. Arnoldy’s research while affiliated with University of New Hampshire and other places

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Publications (172)


Statistical observations of spatial characteristics of Pi1B pulsations
  • Article

November 2007

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53 Reads

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24 Citations

Journal of Atmospheric and Solar-Terrestrial Physics

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P.V. Ponomarenko

We have examined the spatial and temporal correlation of high-latitude Pi1B and Pi2 pulsations, mid-latitude Pi2 pulsations, and auroral substorm onsets identified in the IMAGE far ultraviolet imager (FUV) data. Numerous search coil and fluxgate magnetometers at high latitudes (65–80° in Antarctica and Greenland) and mid-latitude fluxgate magnetometers are used. We find that Pi1B onset times agree well with onset times of intense isolated auroral substorms identified by the IMAGE FUV instrument: Pi1B onsets occurred within the 2 min cadence of the imager. For any given event, we find that Pi1B are localized to approximately 4 h of local time and 7° of magnetic latitude relative to the initial auroral brightening location as observed by IMAGE FUV. Not surprisingly, we also find that Pi1B pulsations occur typically between 2100 and 0200 MLT. Comparison to Pi2 records from these and other lower-latitude stations shows that in almost all cases Pi1B activity coincides within ±2 min with Pi2 activity. Power law fits showed that Pi1B amplitude fell off with distance−2.9 for two strong events (i.e., similar to the r−3 falloff of the signal from a dipolar source), and only slightly more rapidly than the falloff of Pi2 activity (d−2.8). Given the global nature of Pi2 pulsations versus the localized nature of Pi1B events in this study, we conclude that the mechanism that drives Pi1B pulsations is likely different from that responsible for Pi2 pulsations.


In situ measurement of thermal electrons on the SIERRA nightside auroral sounding rocket

December 2006

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22 Reads

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28 Citations

Journal of Geophysical Research Atmospheres

In January 2002 the SIERRA sounding rocket was launched from Alaska into active substorm expansion aurora. Direct measurements of the cold ionospheric population in darkness were made by the Thermal Electron Detector (TED), which was designed to measure thermal electrons that can carry auroral currents coupling the lower ionosphere and the magnetosphere. Measurement of thermal electrons must be accompanied by a careful study of electrostatic potentials forming near conducting bodies in a plasma. The TED instrument measurements show that a nonmonotonic potential barrier can form in the sheath around the attractively biased detector and prevent measurements of the core of the thermal electrons. The TED instrument design and response are discussed along with the current balance conditions which can lead to the formation of a potential barrier. A plasma distribution reconstruction technique enables key measurements of temperature, density, spacecraft potential, and an estimate of field-aligned current flow. Observed thermal electron core temperatures vary greatly, from ~0.1 eV in the polar cap to ~0.8 eV in auroral arcs. Outside active precipitation, the electron density agrees with an independent calculation based on measurements from the high-frequency (HF) wave receiver, verifying the method used for estimating the spacecraft potential. In the auroral regions the HF measurement of electron plasma density must be used to extract more accurate results for the spacecraft potential. The thermal electron data indicate that in the dark the nonnegligible auroral and secondary emission currents must be accounted for in order to understand the spacecraft potential and its impact on thermal electron measurements.


Nature of Pi1B pulsations as inferred from ground and satellite observations

July 2006

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40 Reads

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50 Citations

The occurrence of Pi1B pulsations is well-documented, including the fact that these pulsations can be observed both on the ground and at geosynchronous orbit at substorm onset, although information about their propagation characteristics has been lacking. In this paper, data are presented from FAST, GOES 9 and various ground stations that show the simultaneous observations of Pi1B pulsations in association with an onset. While the data at GOES 9 show that the pulsations are compressional in nature, data from FAST show the presence of shear mode waves, implying that Pi1B mode conversion of some type must take place in the region between geosynchronous orbit and FAST altitudes. An additional point is that Pi1B pulsations apparently propagate through auroral phenomena routinely, begging the question of what role they may play.


Pc 1-2 waves and associated ion distributions observed during three extended conjunctions between the Polar satellite and Antarctic ground stations

December 2005

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11 Reads

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3 Citations

We present ground and satellite observations of Pc 1 and 2 waves and associated ion distributions that occurred during three extended intervals in spring 2003 when the Polar satellite traveled northward across the magnetic equator near local noon along outer magnetospheric flux tubes (L = 9 - 11) that mapped to near the location of an array of search coil magnetometers in Antarctica. Observations of 5 keV protons were observed throughout each of the intervals shown. Their presence appears to be a "necessary but not sufficient" condition for ion cyclotron instability, suggesting that the outer dayside magnetosphere is near marginal stability but needs an additional trigger to cause rapid wave growth. During each of these three intervals, bursts of ~ 0.5 ± 0.2 Hz Pc 1 waves often coincided with short-lived increases in the flux of < 1 keV ions. Pc 2 waves, with frequency below the inferred equatorial He+ gyrofrequency, also occurred on February 11, 2003 in association with an inferred strong enhancement in trapped < 200 eV He+ ions. During the other two passes compressions and/or twists of the magnetic field were also associated with several wave bursts. Our observations thus suggest that either additional lower energy ions or compressions/twists of the magnetic field can often be sufficient to cause rapid wave growth in the outer dayside magnetosphere. Poynting vectors calculated along the satellite trajectory indicate mixed equatorward/poleward wave propagation below ± 20 ° magnetic latitude, but consistently poleward propagation at higher latitudes.


On the source of Pc1-2 waves in the plasma mantle

June 2005

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7 Reads

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19 Citations

Journal of Geophysical Research Atmospheres

Several ground-based observational studies have reported unstructured Pc1-2 waves near and poleward of the dayside cusp. Dyrud et al. (1997) were the first to suggest that these waves originated in the high-altitude plasma mantle. We report here on simultaneous field and particle observations from the Polar satellite and from ground magnetometer data that confirm the presence of these ``mantle'' waves and characterize the ion distributions associated with them. Unstructured Pc1-2 waves were found to occur during 45% of the available passes of Polar across the mantle during the interval March-May 2000, during which time the orbit of Polar was near local noon as it crossed these latitudes. Poynting vector calculations using Polar electric and magnetic field data show a mixture of upward and downward energy flux in the cusp but consistently downward flux when mantle waves are observed. This is consistent with earlier observations that ground-based magnetometers can detect such mantle waves but not the more intense wave activity observed by spacecraft in the middle- and low-altitude cusp. In situ particle observations from the Hydra instrument appear to confirm the generation mechanism suggested by Dyrud et al. that cusp particles mirroring at low altitudes and then traveling outward in the plasma mantle poleward of the cusp are the source of the free energy for these waves. Quantitative estimates of ion cyclotron instability of the observed ion distributions suggest they are stable at the


ULF waves in the solar wind, their coupling to the magnetosphere and associated higher-frequency pulsations

December 2004

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7 Reads

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1 Citation

Recent work has shown the existence at geosynchronous orbit of wave power at frequencies substantially below that of fundamental field-line resonances. The existence of spectral power below that of fundamental frequencies indicates that the driver must be external to the magnetosphere, i.e, that the source is contained in the solar wind. Other work has shown that frequencies matching field-line resonances can sometimes also be observed in the solar wind. The combined spectrum that includes power at fundamental frequencies and lower maps precisely to p-mode helioseismic spectra and the question has been raised whether these helioseismic modes may stimulate the magnetospheric fluctuations. Coherences have been calculated between the magnetometers on {ACE} and Ulysses (in the solar wind) and {GOES-10} (within the magnetosphere), and show several frequencies where nine coherences are significant. This presentation reviews previous work regarding possible coupling of helioseismic modes to the magnetosphere and provides new results to support the conjecture. In addition, we revisit the interesting higher frequency signatures (10-15 mHz), associated with at least one of these events, observed in space and on the ground. These higher-frequency waves are observed as bursts of pulsations, occurring simultaneously over an extended region in local time, but having different polarizations and frequencies at each station.


Figure 1. Interplanetary parameters measured by the Wind spacecraft. The magnetic field is in GSM coordinates.
Table 1 . Locations of the Ground Stations Used in This Study
Figure 2. Projection of the Polar spacecraft trajectory onto Antarctica using the Tsyganenko 1989 (Kp = 3.3) model.
Table 2 . Ion Density Models Used in Time Delay Calculations a
Figure 3. Differences between the Polar measured magnetic field and the IGRF model in GSM coordinates. 

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Pc 1 waves and associated unstable distributions of magnetospheric protons observed during a solar wind pressure pulse
  • Article
  • Full-text available

December 2004

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60 Reads

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70 Citations

Journal of Geophysical Research Atmospheres

1] We present observations of Pc 1 waves ($0.6 Hz) that occurred shortly after a strong (>20 nPa) compression of Earth's magnetosphere at 1321 UT, 18 March 2002. Intense Pc 1 waves were observed at several high-latitude ground stations in Antarctica and Greenland from 1321 UT to beyond 1445 UT. Two wave bursts were recorded at the Polar satellite at 1338 and 1343–1344 UT as it passed outbound in the Southern Hemisphere at 1154 local time (SM magnetic latitude of À22° and near L = 7.5) in good magnetic conjunction with the Antarctic. The pressure increase created a significant population of protons between a few hundred eV and several keV, whose fluxes were mostly perpendicular to B. These protons seem to have replaced the quiescent stream of protons (presumably convected from the plasma sheet) that existed before this increase. There was also a nearly two-order-of-magnitude increase in the population of thermal/suprathermal (0.32–410 eV) protons. The generation of ion cyclotron waves is expected to limit the proton temperature anisotropy A, defined as T ? /T k À 1. The ion cyclotron instability driven by the observed hot ion temperature anisotropy is studied using two models, with and without the presence of cold background plasma. Peaks in the calculated instability as a function of time show excellent agreement with the times of the Polar wave bursts, which were measured a few tens of seconds after maxima in the instability calculation. The time delay is consistent with the propagation time to the spacecraft from a source nearer to the equatorial plane. The hot proton population at Polar appears to be driven back to stability by a sudden increase in very field-aligned protons having energies less than the hot perpendicular population, suggesting a different source for the two populations. These observations confirm the importance of both the energization and/or increase in population of protons transverse to B in the several keV range (possibly betatron acceleration as a result of the pressure pulse), and the presence of greatly increased fluxes of lower energy protons (100s of eV to a few keV), predominantly aligned along B, in determining whether the particle population is unstable at a given time. Citation: Arnoldy, R. L., et al. (2005), Pc 1 waves and associated unstable distributions of magnetospheric protons observed during a solar wind pressure pulse, J. Geophys. Res., 110, A07229, doi:10.1029/2005JA011041.

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A comparison of Antarctic Pi1 signatures and substorm onsets recorded by the WIC imager on the IMAGE satellite

May 2004

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6 Reads

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1 Citation

The accurate timing and location of substorm onsets continues to be a controversial issue. In this study we will show that Pi1 pulsations (1 - 40 sec period) can at times provide more information than the more widely used Pi2 pulsations (40 - 150 sec period). We have examined a set of substorm onsets during the months of June 2000 through June 2001 identified at UC Berkeley by inspection of global auroral images from the IMAGE Far Ultraviolet Imager (FUV) - Wideband Imaging Camera (WIC) and have compared these onset times and locations to Pi1 activity seen in search coil magnetometer data from numerous high latitude stations in Antarctica from 65 ° - 80 ° MLAT, including South Pole Station, McMurdo, and the U. S. and British AGO arrays. Our study focused on the 41 substorm onsets identified using IMAGE data between 20 and 6 UT (corresponding to ~ 17 - 3 MLT on the ground). Our results indicate that Pi1 onset times most often agreed with those identified by IMAGE when the Antarctic ground stations were between 2200 and 2400 MLT. Unlike Pi2 pulsations, Pi1 weaken in amplitude as they propagate away from the footpoint of the source region and at times are not evident at distant stations. The observations presented here will be used to attempt to determine whether Pi1 observations from a large network of ground stations could successfully infer the time and location of onsets even in the absence of satellite imager data.


A Survey of Dayside Pc 3-4 Magnetic Pulsations Observed by the Polar Satellite and Antarctic Ground Stations

May 2004

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10 Reads

Pc 3-4 pulsations (with frequencies from ~15 to 50 mHz) are commonly observed in magnetic field data from satellites throughout much of the dayside magnetosphere, and in ground-based data at latitudes from the equator to the cusp. The precession of Polar's apogee from its initial location over the northern polar cap in 1996-1997 to equatorial latitudes in 2002-2003 allows it to survey the outer magnetosphere over a wide range of latitudes and L shells. In this study we compare simultaneous magnetic field data from the Polar satellite with data from a set of ground-based search coil magnetometers in Antarctica (at latitudes from 66° to 74° MLAT) in order to characterize the regions of Pc 3-4 pulsation activity in the noon sector in terms of L shell and magnetic latitude, and to characterize those waves which do or do not appear simultaneously in space and on the ground at high latitudes. We find that Pc 3-4 activity with observed compressional components consistently appeared over a range of L shells and latitudes between +20 and -30 degrees, typically crossing the equator; a small number of purely compressional wave events appeared to be localized very near the magnetic equator. Purely transverse pulsations occurred over a much broader latitudinal range than those with compressional components. The overall power of the compressional component of Pc 3-4 activity seems to increase with distance from the Earth.


Table 1. Locations of the Antarctic Stations Used in This Study 
Figure 3. Diurnal occurrence patterns (in 2-hour intervals) of ''all-station'' modulated ELF/VLF emissions in the QP 1, QP 2, PE 2, QPPE 1, and QPPE 2 categories during 1998. Local magnetic noon is at $1500 UT.  
Table 3 . Total Number of Occurrences in Any 2-Hour Interval for the Four Categories of QP Emissions During 1998 at Halley, AGO A80, AGO A81, and South Pole Station a
Figure 4. Diurnal occurrence patterns of PE events at South Pole (SP), BAS AGO A81, BAS AGO A80, and Halley during 1998.  
Latitudinal and seasonal variations of quasiperiodic and periodic VLF emissions in the outer magnetosphere

May 2004

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79 Reads

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51 Citations

Journal of Geophysical Research Atmospheres

1] We have analyzed ELF-VLF receiver and search coil magnetometer data from five Antarctic stations from 1998 and 1999 to study quasiperiodic emissions (QPs) and periodic emissions (PEs), which occur as ULF-range modulations of ELF-VLF signals between 0.5 kHz and 4kHz.QPsaremodulatedatfrequenciesof4 kHz. QPs are modulated at frequencies of 20–50 mHz, and PEs are modulated at frequencies of $200–500 mHz. The stations used covered a range of magnetic latitudes from À62° (Halley) to À74° (South Pole Station); three automated geophysical observatories (AGOs) were located at intermediate latitudes. Consistent with earlier studies, most QPs were observed with magnetic pulsations of identical period in the Pc3 range (type I QPs). Of those QPs not observed with simultaneous magnetic pulsations (type II QPs), nearly all were accompanied by PEs. Type I QPs, PEs, and events during which both appeared together (QPPEs) were found to have different latitudinal, seasonal, and diurnal occurrence patterns: QPs of both types were more likely to occur between À65° and À70° magnetic latitude, while PEs occurred more often around À60° magnetic latitude. QPs were more common during the months of October though March, while PEs were more common during the months of May through September. QPs, whether with or without simultaneous PEs or magnetic pulsations, were predominantly a dayside phenomenon, with a broad maximum near local noon. The occurrence of QPs unaccompanied by PEs was restricted to the dayside, however, while a small number of QPPEs appeared even during nighttime hours. PEs, on the other hand, could be seen at all local times, but with latitudinally dependent diurnal patterns. Most higher-latitude QPs were type I events (observed with magnetic pulsations), while type II QP events (without simultaneous magnetic pulsations) occurred relatively more often at lower latitudes. A case study from 1 August 1999 using wideband data from South Pole and Halley provides evidence of a transition from echoing whistler activity to PE activity and then to QP activity and suggests a causal relationship. (2004), Latitudinal and seasonal variations of quasiperiodic and periodic VLF emissions in the outer magnetosphere, J. Geophys. Res., 109, A05216, doi:10.1029/2003JA010335.


Citations (75)


... They were used to reveal variations of QP modulation periods related to substorms Manninen et al., 2013). While both ground-based (Engebretson et al., 2004;Morrison et al., 1994;A. J. Smith et al., 1998) and low-altitude spacecraft (Hayosh et al., 2014) surveys suggested that QP emissions are primarily daytime phenomenon, satellite surveys at larger radial distances revealed the emissions essentially at all local times (Němec et al., 2018;. ...

Reference:

Quasiperiodic Emissions and Related Particle Precipitation Bursts Observed by the DEMETER Spacecraft
A study of quasi-periodic ELF-VLF emissions at three Antarctic stations: Evidence for off-equatorial generation?
  • Citing Article
  • January 1994

... Wang et al. [29,30] recorded five types of triggered lightning bolts using a high-speed camera and fast antenna instruments and analyzed the phenomenon of lightning with multiple branches. In addition, transient luminous events over thunderstorms have been observed using a high-sensitivity camera (e.g., Winckler et al., 1989, Pasko et al., 2002, Van der Velde et al., 2009, Yang et al., 2017 [31][32][33][34]. Yang et al. [34] analyzed a single sprite produced using a mesoscale convective system (MCS). ...

ECHO 7: An electron beam experiment in the magnetosphere
  • Citing Article
  • June 1989

Eos Transactions American Geophysical Union

... There are several studies which have compared the electron temperature in the F region measured by Incoherent Scatter radar and instruments onboard rockets (cf. Svenes et al., 1992;Oyama and Schlegel, 1988), while there are few studies which have been conducted in the E-region. Thus, it is worthwhile to compare electron temperature measured by the EISCAT radar and the Fast Langmuir Probe (FLP) (Brace, 1998) onboard the DELTA rocket. ...

Combined rocket and ground observations of electron heating in the ionospheric F-layer
  • Citing Article
  • July 1992

Planetary and Space Science

... The Russian-US active geophysical Fluxus-1 and Fluxus-2 rocket experiments, carried out at 01:55:08 UT on January 31, 1997, and at 02:16:07 UT on February 5,1997, were aimed at investigation of the Earth's ionosphere and magnetosphere response to the pulse effect of a high-velocity plasma jet and at studying the behavior of artificial plasma formation under the conditions of its interaction with the atmosphere and the geomagnetic field [1][2][3]. Much attention was given to magnetic measurements with the purpose of studying the parameters of plasma, its dynamics, and the diamagnetic effect. ...

Heavy ion beam-ionosphere interactions: Electron acceleration
  • Citing Article
  • October 1985

Journal of Geophysical Research Atmospheres

... The most popular mechanism describing the ULF modulation of electron precipitation has originated from the theoretical work of Coroniti and Kennel (1970), who proposed that the compressional component of ULF waves preferentially affects the perpendicular energy of gyrating electrons via betatron acceleration, changing the pitch angle anisotropy and thus modifying the growth rate of chorus waves. This idea was indirectly supported by simultaneous ground-based observations of dayside Pc3-4 auroral and magnetic pulsations, and very low frequency modulation (Engebretson et al., 1990(Engebretson et al., , 1991. Contrary to such a conventional mechanism, Brito et al. (2012Brito et al. ( , 2015 and Rae et al. (2018) argued the possibility that the compressional component of ULF waves acts as a direct driver for precipitating keV electrons without any chorus wave mediation. ...

Ionospheric signatures of cusp latitude Pc 3 pulsations

Journal of Geophysical Research Atmospheres

... That is, Pc3 pulsations are shielded when the waves propagate from the magnetosphere to the ground through the ionosphere. Yoshikawa et al. (2002) and Engebretson et al. (2000) have come to the similar conclusion that Pc3 fluctuations are affected by ionospheric shielding. Furthermore, Obana et al. (2005), using magnetic field data from the magnetically conjugate stations at L ∼ 5.4, confirmed that the north-south difference of Pc3 fluctuation intensity is related to the season. ...

A conjugate study of Pc3-4 pulsations at cusp latitudes: Is there a clock angle effect?
  • Citing Article
  • July 2000

Journal of Geophysical Research Atmospheres

... When mapped to the equatorial plane, their source region is most likely in the dayside outer magnetosphere (>8 R E ). Early observations of dayside auroral pulsations (e.g., Brekke & Pettersen, 1971;Craven & Burns, 1990;Engebretson et al., 1994;Vorobjev et al., 1999;Wu & Rosenberg, 1992), which were mostly made with high temporal cadence zenith-viewing photometers, found the following key statistical features: (1) They have highly regular waveforms with periods in the Pc3 range (f = 22-100 mHz, T = 10-45 s); (2) their occurrence peaks in the prenoon sector; and (3) they are frequently (but not always) accompanied by coherent ground Pc3 magnetic pulsations. These ©2018. ...

Studies of the Occurrence and Properties of Pc 3-4 Magnetic and Auroral Pulsations at South Pole, Antarctica
  • Citing Article
  • January 1994

... Just equatorward of the cusp projection is the 'boundary-layer' that maps upwards along geomagnetic field lines out to the outer magnetosphere, near the boundary with the solar wind, and also a source of Pc1-2 waves Heacock, 1974). Just poleward of the cusp is the projection of the 'plasma mantle' that maps out to the magnetotail streaming away from the Sun, also a confirmed source of Pc1-2 waves (Dyrud et al., 1997;Engebretson et al., 2005Engebretson et al., , 2012. All of these plasma regions are possible sources of EMIC waves (Troitsakya et al., 1980;Hansen et al., 1992Hansen et al., , 1992Anderson et al., 1992a,b, Popecki et al., 1993. ...

On the source of Pc1-2 waves in the plasma mantle
  • Citing Article
  • June 2005

Journal of Geophysical Research Atmospheres

... Above 70 • the power in the Pc3 band is high. Engebretson et al. [1986] studied Pc3 pulsations in the southern polar region where they were found to have large amplitude. Between 40 • and 70 • , the diurnal variation shows increased power in the prenoon sector. ...

Pc 3 pulsations observed near the south polar cusp
  • Citing Article
  • August 1986

Journal of Geophysical Research Atmospheres

... Outside of ionospheric sounding rocket missions and the POLAR mission, there has yet to be a large magnetospheric spacecraft mission dedicated to measuring the source of both the low energy electron and ion particle populations robustly. While there are challenges to making measurements of the cold magnetospheric ions and electrons, a number of viable techniques exist for cold ions that have been conducted for sounding rocket (and low-earth orbiting) missions such as (1) mounting a low-resource (mass and volume) instrument on a boom (Brace 1998, Pollock, et al. 1996, Knudsen et al. 2015, and (2) biasing the electrostatic plasma spectrometer mounted to a boom or plate thus allowing for differential biasing of the instrument and/or spacecraft (Chappell, et al. 1981, Pollock, et al. 1996. Measuring cold ion bulk properties through the properties of the wake of the spacecraft (Engwall, Eriksson & Cully, et al. 2009) has also been performed successfully, but this technique does not yield the full energy distributions. ...

SCIFER-Cleft region thermal electron distribution functions
  • Citing Article
  • July 1996