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Electron densities inferred from plasma wave spectra obtained by the Waves instrument on Van Allen Probes.

Kurth WS, De Pascuale S, Faden JB, Kletzing CA, Hospodarsky GB, Thaller S, Wygant JR - J Geophys Res Space Phys (2015)

Bottom Line: Good progress has been made in developing algorithms to identify f uh and create a data set of electron densities.However, it is often difficult to interpret the plasma wave spectra during active times to identify f uh and accurately determine ne .We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, University of Iowa Iowa City, Iowa, USA.

ABSTRACT

The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Field Instrument Suite and Integrated Science suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher-frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency f uh. Considerable work has gone into developing a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify f uh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify f uh and accurately determine ne . In some cases, there is no clear signature of the upper hybrid band, and the low-frequency cutoff of the continuum radiation is used. We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum.

No MeSH data available.


Detail of the upper hybrid band and the apparent cutoff of a type III radio emission. This example shows that the more intense higher frequency of these two bands includes fpe and not the weaker shadow band at lower frequencies.
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fig05: Detail of the upper hybrid band and the apparent cutoff of a type III radio emission. This example shows that the more intense higher frequency of these two bands includes fpe and not the weaker shadow band at lower frequencies.

Mentions: The ISEE 1 data showed that the band between fpe and fuh was often more intense than the Z-mode emission between fpe and fL = 0. Figure5 is an expanded view of Van Allen Probe A Waves HFR data from 27 February 2014 showing the plasma wave spectrum at the 5% spectral resolution afforded by the instrument. The white trace is fuh. For context, we have shown the ninth and tenth harmonics of fce in red. Among other things, these two bands provide a guide for the magnitude of fce relative to fuh. At the time of the vertical white arrow, 13:01 UT, we have used the relations in the previous section to compute various characteristic frequencies of the plasma based on the assumption that our identification of fuh is correct and is 302 kHz at this time. Based on the magnetic field strength, fce = 27.6 kHz, hence, fpe = 301 kHz. The left-hand ordinary cutoff fL = 0 = 287 kHz at this time. Note that the 5% spectral resolution at 300 kHz is approximately 15 kHz, hence, fuh and fpe are certainly unresolved. We suggest that the lower bound of the bright band we have identified as fuh is actually defined by fL = 0. For completeness, we also note that the right-hand cutoff fR = 0, defined as4is 315 kHz. Notice that a type III radio burst occurs just above the upper hybrid band and, in fact, is cutoff at the band. Type III bursts are unpolarized, hence, can propagate down to the local electron plasma frequency. Hence, the fact that there is no evidence of the radio emission below what we have identified as the upper hybrid band assures that this is the correct identification. The lower frequency “shadow” band at about 228 kHz is clearly too low in frequency to be confused with the plasma frequency and the cutoff of the type III emission. This shadow band has been observed by other plasma wave instruments, and its origin is unknown (P. Canu, personal communications, 2014).


Electron densities inferred from plasma wave spectra obtained by the Waves instrument on Van Allen Probes.

Kurth WS, De Pascuale S, Faden JB, Kletzing CA, Hospodarsky GB, Thaller S, Wygant JR - J Geophys Res Space Phys (2015)

Detail of the upper hybrid band and the apparent cutoff of a type III radio emission. This example shows that the more intense higher frequency of these two bands includes fpe and not the weaker shadow band at lower frequencies.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4497465&req=5

fig05: Detail of the upper hybrid band and the apparent cutoff of a type III radio emission. This example shows that the more intense higher frequency of these two bands includes fpe and not the weaker shadow band at lower frequencies.
Mentions: The ISEE 1 data showed that the band between fpe and fuh was often more intense than the Z-mode emission between fpe and fL = 0. Figure5 is an expanded view of Van Allen Probe A Waves HFR data from 27 February 2014 showing the plasma wave spectrum at the 5% spectral resolution afforded by the instrument. The white trace is fuh. For context, we have shown the ninth and tenth harmonics of fce in red. Among other things, these two bands provide a guide for the magnitude of fce relative to fuh. At the time of the vertical white arrow, 13:01 UT, we have used the relations in the previous section to compute various characteristic frequencies of the plasma based on the assumption that our identification of fuh is correct and is 302 kHz at this time. Based on the magnetic field strength, fce = 27.6 kHz, hence, fpe = 301 kHz. The left-hand ordinary cutoff fL = 0 = 287 kHz at this time. Note that the 5% spectral resolution at 300 kHz is approximately 15 kHz, hence, fuh and fpe are certainly unresolved. We suggest that the lower bound of the bright band we have identified as fuh is actually defined by fL = 0. For completeness, we also note that the right-hand cutoff fR = 0, defined as4is 315 kHz. Notice that a type III radio burst occurs just above the upper hybrid band and, in fact, is cutoff at the band. Type III bursts are unpolarized, hence, can propagate down to the local electron plasma frequency. Hence, the fact that there is no evidence of the radio emission below what we have identified as the upper hybrid band assures that this is the correct identification. The lower frequency “shadow” band at about 228 kHz is clearly too low in frequency to be confused with the plasma frequency and the cutoff of the type III emission. This shadow band has been observed by other plasma wave instruments, and its origin is unknown (P. Canu, personal communications, 2014).

Bottom Line: Good progress has been made in developing algorithms to identify f uh and create a data set of electron densities.However, it is often difficult to interpret the plasma wave spectra during active times to identify f uh and accurately determine ne .We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, University of Iowa Iowa City, Iowa, USA.

ABSTRACT

The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Field Instrument Suite and Integrated Science suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher-frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency f uh. Considerable work has gone into developing a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify f uh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify f uh and accurately determine ne . In some cases, there is no clear signature of the upper hybrid band, and the low-frequency cutoff of the continuum radiation is used. We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum.

No MeSH data available.