Statistical analysis of magnetotail fast flows and related magnetic disturbances

Frühauff, Dennis; Glaßmeier, Karl‐Heinz

doi:10.5194/angeo-34-399-2016

Cited by 11 publications

(23 citation statements)

References 50 publications

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“…(1) is therefore reasonable. The TLS fit gives γ ≈ 1.493 ± 0.014, which is very close to the results of Baumjohann and Paschmann (1989), Zhu (1990), Goertz and Baumjohann (1991), and Borovsky et al (1998).…”

Section: Resultssupporting

confidence: 83%

“…Earlier studies have already emphasized the necessity to group the data according to magnetospheric activity, usually using the AE index as a proxy (Baumjohann and Paschmann, 1989;Goertz and Baumjohann, 1991;Pang et al, 2015). Therefore, in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Borovsky et al (1998) compare plasma sheet data of ISEE2 in near-Earth, midtail, and downtail regions and emphasize the necessity to analyze the radial dependence of datasets. Following suggestions of Goertz and Baumjohann (1991) to use only neutral sheet/midnight data they find an average γ = 1.52. Pang et al (2015) use CLUS-TER data of the central plasma and find a wide variety of polytropic indices ranging from 0.1 to 1.8.…”

Section: Frühauff Et Al: Average Plasma Sheet Polytropic Index Asmentioning

confidence: 96%

“…A reanalysis of ISEE1/FPE data in the n − P domain for individual spacecraft orbits gives 1 < γ < 5/3 using a plasma sheet criterion of β = P /(B 2 /(2µ 0 )) > 0.2, first introduced by Baumjohann et al (1988). Goertz and Baumjohann (1991), using AMPTE/IRM data as well but including the plasma sheet boundary layer, find a quiet time γ = 4/3 and active time γ = 5/3. They interpret their results as the presence of a mixture of bubbles and blobs and lead the partial contradiction of previous studies back to the choice of data selection criteria.…”

Section: Frühauff Et Al: Average Plasma Sheet Polytropic Index Asmentioning

confidence: 99%

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Average plasma sheet polytropic index as observed by THEMIS

Frühauff¹,

Mieth²,

Glaßmeier³

2017

Ann. Geophys.

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Abstract. Multi-spacecraft data from the years 2008 to 2015 of the THEMIS mission particularly in the near-Earth plasma sheet are used in order to empirically determine the polytropic index in the quiet and active time magnetotail. The results of a number of previous studies in the 1990s can be confirmed. An analysis of the total database, although showing poor correlation, results in an average polytropic index of γ = 1.72. The active time plasma sheet is well correlated with an average γ = 1.49. However, the data scattering suggests that the analysis of the data in total is not adequate. In order to reduce the timescales, individual spacecraft orbits are analyzed, giving a broad distribution of polytropic indices throughout the plasma sheet. The major part of the distribution falls in a range between γ = 0.67 and γ = 2. Our results indicate a variety of thermodynamic processes in the magnetotail and an all-time presence of heat exchange of the plasma. A description of the plasma sheet using an equation of state with a single γ is probably inadequate. This necessitates the application of more sophisticated approaches, such as a parametrization of the heat flux vector in magnetohydrodynamic equations or a superposition of polytropic indices.

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Section: Resultssupporting

confidence: 83%

Section: Resultsmentioning

confidence: 99%

Section: Frühauff Et Al: Average Plasma Sheet Polytropic Index Asmentioning

confidence: 96%

Section: Frühauff Et Al: Average Plasma Sheet Polytropic Index Asmentioning

confidence: 99%

See 2 more Smart Citations

Average plasma sheet polytropic index as observed by THEMIS

Frühauff¹,

Mieth²,

Glaßmeier³

2017

Ann. Geophys.

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“…Using superposed epoch analysis, Frühauff and Glassmeier (2016) recently showed the characteristics of fast flows and related magnetic disturbances in the magnetotail. They revealed that during the entire flow burst timescale, the directions of minimum magnetic field variations are perpendicular to the main flow and the background magnetic field directions.…”

Section: Comparison With Plasma Flow Datamentioning

confidence: 99%

Statistical analysis of severe magnetic fluctuations in the near-Earth plasma sheet observed by THEMIS-E

Shiokawa

Frühauff

2017

Ann. Geophys.

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Abstract. We statistically analyzed severe magnetic fluctuations in the nightside near-Earth plasma sheet at 6-12 R E (Earth radii; 1 R E = 6371 km), because they are important for non-magnetohydrodynamics (non-MHD) effects in the magnetotail and are considered to be necessary for current disruption in the inside-out substorm model. We used magnetic field data from 2013 and 2014 obtained by the Time History of Events and Macroscale Interactions during Substorms E (THEMIS-E) satellite (sampling rate: 4 Hz). A total of 1283 severe magnetic fluctuation events were identified that satisfied the criteria σ B /B > 0.5, where σ B and B are the standard deviation and the average value of magnetic field intensity during the time interval of the local proton gyroperiod, respectively. We found that the occurrence rates of severe fluctuation events are 0.00118, 0.00899, and 0.0238 % at 6-8, 8-10, and 10-12 R E , respectively, and most events last for no more than 15 s. From these occurrence rates, we estimated the possible scale sizes of current disruption by severe magnetic fluctuations as 3.83 R E 3 by assuming that four substorms with 5 min intervals of current disruption occur every day. The fluctuation events occurred most frequently at the Z GSM (Z distance in the geocentric solar magnetospheric coordinate system) close to the model neutral sheet within 0.2 R E . Most events occur in association with sudden decreases in the auroral electrojet lower (AL) index and magnetic field dipolarization, indicating that they are related to substorms. Sixty-two percent of magnetic fluctuation events were accompanied by ion flow with velocity V > 100 km s −1 , indicating that the violation of ion gyromotion tends to occur during high-speed flow in the near-Earth plasma sheet. The superposed epoch analysis also indicated that the flow speed increases before the severe magnetic fluctuations. We discuss how both the inside-out and outside-in substorm models can explain this increase in flow speeds before magnetic fluctuation events.

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An analysis of magnetic reconnection events and their associated auroral enhancements

et al. 2017

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An analysis of simultaneous reconnection events in the near‐Earth magnetotail and enhancements in the aurora is undertaken. Exploiting magnetospheric data from the Geotail, Cluster, and Double Star missions, along with auroral images from the IMAGE and Polar missions, the relationship between a reconnection signature and its auroral counterpart is explored. In this study of 59 suitable reconnection events, we find that 43 demonstrate a clear coincidence of reconnection and auroral enhancement. The magnetic local time (MLT) locations of these 43 reconnection events are generally located within ±1 h MLT of the associated auroral enhancement. A positive correlation coefficient of 0.8 between the two MLT locations is found. The enhancements are localized and short‐lived (τ≤10 min) and are as likely to occur during the substorm process as in isolation of a substorm. No significant dependence of the reconnection or auroral enhancement location on the dusk‐dawn components of the solar wind velocity (Vy), IMF (By) or local By or Vy, as measured by the reconnection‐detecting spacecraft, is found.

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Statistical analysis of magnetotail fast flows and related magnetic disturbances

Cited by 11 publications

References 50 publications

Average plasma sheet polytropic index as observed by THEMIS

Average plasma sheet polytropic index as observed by THEMIS

Statistical analysis of severe magnetic fluctuations in the near-Earth plasma sheet observed by THEMIS-E

An analysis of magnetic reconnection events and their associated auroral enhancements

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