Intense energetic electron flux enhancements in Mercury's magnetosphere: An integrated view with high‐resolution observations from MESSENGER

Baker, D. N.; Dewey, R. M.; Lawrence, D. J.; Goldsten, J.; Peplowski, P. N.; Korth, H.; Slavin, J. A.; Krimigis, S. M.; Anderson, B. J.; Ho, G. C.; McNutt, R. L.; Raines, J. M.; Schriver, D.; Solomon, Sean C.

doi:10.1002/2015ja021778

Cited by 29 publications

(42 citation statements)

References 35 publications

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“…In previous observations, energetic electron events were prominently observed on the dawnside magnetosphere of Mercury [e.g., Baker et al, 2016;Ho et al, 2016;Lindsay et al, 2016]. This feature is more prominent during the Mercury's magnetospheric active periods but is not clear in the quiet times.…”

Section: Conclusion and Discussionmentioning

confidence: 86%

“…Energetic electron events possibly associated with dipolarizations at Mercury were first reported with Mariner 10 observations in the 1970s [e.g., Christon et al, 1979;Christon, 1987;Slavin et al, 1997]. MESSENGER measurements have provided more comprehensive investigations of the energetic electron distributions, which have displayed clear dawn-dusk asymmetries with more energetic electron events detected in the dawnside of the magnetosphere [e.g., Baker et al, 2016;Ho et al, 2016;Lindsay et al, 2016]. Further, Lindsay et al [2016] found that the MESSENGER X-ray Spectrometer (XRS) observed a dawnside maximum in X-ray emissions from Mercury's surface.…”

Section: Introductionmentioning

confidence: 99%

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MESSENGER observations of the energization and heating of protons in the near‐Mercury magnetotail

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Raines

et al. 2017

Geophysical Research Letters

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The energization and heating processes for protons in the near‐Mercury tail are examined with MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) observations. In a case study, suprathermal proton particle flux (STPF) and proton temperature are observed to be clearly enhanced during near‐Mercury substorm dipolarizations, indicating the proton energization and heating processes. STPF and proton temperature distributions in near‐Mercury central plasma sheets display dawn‐dusk asymmetries, with higher values in the dawnside plasma sheet, i.e., postmidnight, than in the duskside, i.e., premidnight. Further investigations reveal that these asymmetries are more prominent during active periods in Mercury's magnetosphere, as compared to quiet periods. Magnetic field variations in the ZMSM component display a similar feature, with variations being more prominent on the dawnside than the duskside during active periods. We propose that the dawn‐dusk asymmetry in the distributions of protons could be due to the fact that more substorm dipolarizations were initiated on the dawnside of Mercury's magnetotail.

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Section: Conclusion and Discussionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

MESSENGER observations of the energization and heating of protons in the near‐Mercury magnetotail

Sun

Raines

et al. 2017

Geophysical Research Letters

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“…Thus, it would be expected that more fast flows brake and initiate substorm onset on the postmidnight sector at Mercury, which is different from the well determined premidnight onset locations of substorm at Earth [e.g., Liou et al ., ; Frey et al ., ]. Energetic electrons in Mercury's magnetosphere are more frequently detected on the premidnight sector than on the postmidnight sector [ Lawrence et al ., ; Baker et al ., ; Ho et al ., ; Lindsay et al ., ]. This is commonly believed to be due to the dawnward drift of electrons in the magnetosphere of Mercury.…”

Section: Discussionmentioning

confidence: 99%

Spatial distribution of Mercury's flux ropes and reconnection fronts: MESSENGER observations

et al. 2016

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We perform a statistical study of flux ropes and reconnection fronts based on MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) magnetic field and plasma observations to study the implications for the spatial distribution of reconnection sites in Mercury's near magnetotail. The results show important differences of temporal and spatial distributions as compared to Earth. We have surveyed the plasma sheet crossings between −2 RM and −3 RM downtail from the planet, i.e., the location of Near‐Mercury Neutral Line (NMNL). Plasma sheets were defined to be regions with β ≥ 0.5. Using this definition, 39 flux ropes and 86 reconnection fronts were identified in the plasma sheet. At Mercury, the distributions of flux ropes and reconnection fronts show clear dawn‐dusk asymmetry with much higher occurrence rate on the dawnside plasma sheet than on the duskside. This suggests that magnetic reconnection in Mercury's magnetotail occurs more frequently in the dawnside than in the duskside plasma sheet, which is different than the observations in Earth's magnetotail showing more reconnection signatures in the duskside plasma sheet. The distribution of plasma sheet thickness shows that plasma sheet near the midnight is the thinnest part and does not show obvious asymmetry. Thus, the reasons that cause magnetic reconnection to preferentially occur on the dawnside of the magnetotail at Mercury may not be the plasma sheet thickness and require further study. The peak occurrence rates of flux ropes and reconnection fronts in Mercury's plasma sheet are ~ 60 times higher than that of Earth's values, which we interpret to be due to the highly variable magnetospheric conditions at Mercury. Such higher occurrence rate of magnetic reconnection would generate more plasma flows in the dawnside plasma sheet than in the duskside. These plasma flows would mostly brake and initiate the substorm dipolarization on the postmidnight sector at Mercury rather than the premidnight susbtorm onset location at Earth.

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“…This period is after the GRS flight software update that improved the sensitivity to energetic electrons. This period also includes a new phase of the MESSENGER orbital mission starting in April 2012 when the apoapsis of the spacecraft orbit was reduced from 15,000 km to ~10,000 km, reducing the orbital period from 12 to 8 hr (Baker et al, 2016; Lawrence et al, 2015). Note that the GRS flight software reconfiguration also included the addition of the high time‐resolution (10 ms) mode for measurements of energetic electrons.…”

Section: Ee Observationsmentioning

confidence: 99%

“…The Lawrence et al (2015) study identified over 2,700 electron burst events and showed their temporal, spatial, and spectral behavior. In a subsequent study, Baker et al (2016) investigated the most intense EE events among the GRS high‐resolution measurements and found signatures of accelerated electrons being injected from the near‐tail region and forming quasi‐trapped populations. Gershman et al (2015) also observed that during solar energetic particle events, there are enhanced electron fluxes within the central plasma sheet that are indicative of an apparent trapped electron population at low latitudes in the magnetotail.…”

Section: Introductionmentioning

confidence: 99%

Statistical Study of Mercury's Energetic Electron Events as Observed by the Gamma‐Ray and Neutron Spectrometer Instrument Onboard MESSENGER

et al. 2018

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We present results from a statistical analysis of Mercury's energetic electron (EE) events as observed by the gamma‐ray and neutron spectrometer instrument onboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. The main objective of this study is to investigate possible anisotropic behavior of EE events using multiple data sets from MESSENGER instruments. We study the data from the neutron spectrometer (NS) and the gamma‐ray spectrometer anticoincidence shield (ACS) because they use the same type of borated plastic scintillator and, hence, they have very similar response functions, and their large surface areas make them more sensitive to low‐intensity EE events than MESSENGER's particle instrumentation. The combined analysis of NS and ACS data reveals two different classes of energetic electrons: “Standard” events and “ACS‐enhanced” events. Standard events, which comprise over 90% of all events, have signal sizes that are the same in both the ACS and NS. They are likely gyrating particles about Mercury's magnetic field following a 90° pitch angle distribution and are located in well‐defined latitude and altitude regions within Mercury's magnetosphere. ACS‐enhanced events, which comprise less than 10% of all events, have signal sizes in the ACS that are 10 to 100 times larger than those observed by the NS. They follow a beam‐like distribution and are observed both inside and outside Mercury's magnetosphere with a wider range of latitudes and altitudes than Standard events. The difference between the Standard and ACS‐enhanced event characteristics suggests distinct underyling acceleration mechanisms.

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Intense energetic electron flux enhancements in Mercury's magnetosphere: An integrated view with high‐resolution observations from MESSENGER

Cited by 29 publications

References 35 publications

MESSENGER observations of the energization and heating of protons in the near‐Mercury magnetotail

MESSENGER observations of the energization and heating of protons in the near‐Mercury magnetotail

Spatial distribution of Mercury's flux ropes and reconnection fronts: MESSENGER observations

Statistical Study of Mercury's Energetic Electron Events as Observed by the Gamma‐Ray and Neutron Spectrometer Instrument Onboard MESSENGER

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