Electromagnetic ion cyclotron (EMIC) waves can drive precipitation of tens of keV protons and relativistic electrons, and are a potential candidate for causing radiation belt flux dropouts. In this ...study, we quantitatively analyze three cases of EMIC‐driven precipitation, which occurred near the dusk sector observed by multiple Low‐Earth‐Orbiting (LEO) Polar Operational Environmental Satellites/Meteorological Operational satellite programme (POES/MetOp) satellites. During EMIC wave activity, the proton precipitation occurred from few tens of keV up to hundreds of keV, while the electron precipitation was mainly at relativistic energies. We compare observations of electron precipitation with calculations using quasi‐linear theory. For all cases, we consider the effects of other magnetospheric waves observed simultaneously with EMIC waves, namely, plasmaspheric hiss and magnetosonic waves, and find that the electron precipitation at MeV energies was predominantly caused by EMIC‐driven pitch angle scattering. Interestingly, each precipitation event observed by a LEO satellite extended over a limited L shell region (ΔL ~ 0.3 on average), suggesting that the pitch angle scattering caused by EMIC waves occurs only when favorable conditions are met, likely in a localized region. Furthermore, we take advantage of the LEO constellation to explore the occurrence of precipitation at different L shells and magnetic local time sectors, simultaneously with EMIC wave observations near the equator (detected by Van Allen Probes) or at the ground (measured by magnetometers). Our analysis shows that although EMIC waves drove precipitation only in a narrow ΔL, electron precipitation was triggered at various locations as identified by POES/MetOp over a rather broad region (up to ~4.4 hr MLT and ~1.4 L shells) with similar patterns between satellites.
Key Points
We show three cases of proton and relativistic electron precipitation observed simultaneously with EMIC waves
EMIC‐driven precipitation was observed by POES/MetOp satellites at different locations over a broad L‐MLT region
Each precipitation event extended over ΔL ~ 0.3 on average, showing that wave‐driven pitch angle scattering is localized
Electromagnetic ion cyclotron (EMIC) waves can drive radiation belt depletion and Low‐Earth Orbit satellites can detect the resulting electron and proton precipitation. The ELFIN (Electron Losses and ...Fields InvestigatioN) CubeSats provide an excellent opportunity to study the properties of EMIC‐driven electron precipitation with much higher energy and pitch‐angle resolution than previously allowed. We collect EMIC‐driven electron precipitation events from ELFIN observations and use POES (Polar Orbiting Environmental Satellites) to search for 10s–100s keV proton precipitation nearby as a proxy of EMIC wave activity. Electron precipitation mainly occurs on localized radial scales (∼0.3 L), over 15–24 MLT and 5–8 L shells, stronger at ∼MeV energies and weaker down to ∼100–200 keV. Additionally, the observed loss cone pitch‐angle distribution agrees with quasilinear predictions at ≳250 keV (more filled loss cone with increasing energy), while additional mechanisms are needed to explain the observed low‐energy precipitation.
Plain Language Summary
Electromagnetic ion cyclotron (EMIC) emissions are a type of plasma wave that can be excited in the near‐Earth environment and interact with energetic electrons in the Earth's radiation belts. Through these wave‐particle interactions, electrons can be pushed into the loss cone and lost into the Earth's atmosphere (electron precipitation), where they deposit their energy by interacting with neutral atoms and cold charged particles. EMIC‐driven electron precipitation still needs to be fully characterized and understood. In this work, we use data from the Electron Losses and Fields InvestigatioN (ELFIN) CubeSats, which provide electron fluxes at high energy and pitch‐angle (look direction) resolution at ∼450 km of altitude. Our analysis reveals that precipitation is most efficient for ∼MeV electrons and is accompanied by weaker low‐energy precipitation down to ∼100–200 keV. Given the ELFIN CubeSats spin, we can also study the distribution of the precipitating electrons along different look directions (pitch‐angles). We find that the loss cone shape is well‐reproduced by quasilinear predictions of EMIC‐electron interactions at higher energies (≳250 keV), while quasilinear calculations underestimate the observed low‐energy precipitation.
Key Points
Energetic electron precipitation is observed by Electron Losses and Fields InvestigatioN nearby proton precipitation (a proxy for Electromagnetic ion cyclotron waves) primarily over 15–24 MLT
Precipitation efficiency increases as a function of energy: weak ∼100s keV precipitation is concurrent with intense ∼MeV precipitation
The observed pitch‐angle distribution shows a loss cone filling up with energy, similar to the pitch‐angle profiles from quasilinear theory
With the aim of gathering temporal trends on bacterial epidemiology and resistance from multiple laboratories in China, the CHINET surveillance system was organized in 2005. Antimicrobial ...susceptibility testing was carried out according to a unified protocol using the Kirby-Bauer method or automated systems. Results were analyzed according to Clinical and Laboratory Standards Institute (CLSI) 2014 definitions. Between 2005 and 2014, the number of bacterial isolates ranged between 22 774 and 84 572 annually. Rates of extended-spectrum β-lactamase production among Escherichia coli isolates were stable, between 51.7 and 55.8%. Resistance of E. coli and Klebsiella pneumoniae to amikacin, ciprofloxacin, piperacillin/tazobactam and cefoperazone/sulbactam decreased with time. Carbapenem resistance among K. pneumoniae isolates increased from 2.4 to 13.4%. Resistance of Pseudomonas aeruginosa strains against all of antimicrobial agents tested including imipenem and meropenem decreased with time. On the contrary, resistance of Acinetobacter baumannii strains to carbapenems increased from 31 to 66.7%. A marked decrease of methicillin resistance from 69% in 2005 to 44.6% in 2014 was observed for Staphylococcus aureus. Carbapenem resistance rates in K. pneumoniae and A. baumannii in China are high. Our results indicate the importance of bacterial surveillance studies.
Abstract Diabetes mellitus (DM) adversely affects the number and function of circulating endothelial progenitor cells (EPCs). Consequently, there is also a reduction in the repair mechanism of these ...cells, which is a critical and initiating factor in the development of diabetic vascular disease. The aim of the present study was to analyze miR expression profiles in EPCs from patients with DM and choose the most significantly regulated miR to study its possible role on EPC dysfunction and elucidate its mechanism of action. EPCs were collected from subjects with Type II DM and non-diabetic control subjects. Total RNA was harvested from EPCs, and a total of 5 candidate miRNAs were identified by microarray screening and were quantified by TaqMan real-time PCR. Lentiviral vectors expressing miR-126 and miR-126 inhibitor (anti-miR-126) were transfected into EPCs, and the EPC colony-forming capacity, proliferation activity, migratory activity, differentiation capacity, and apoptotic susceptibility were determined and Western Blotting and mRNA real-time PCR analyses were performed. To study the mechanisms, lentiviral vectors expressing Spred-1 and a short interfering RNA (siRNA) targeting Spred-1 were prepared. Five miRs were aberrantly downregulated in EPCs from DM patients. These miRs included miR-126, miR-21, miR-27a, miR-27b and miR-130a. Anti-miR-126 inhibited EPC proliferation, migration, and enhanced apoptosis. Restored miR-126 expression in EPCs from DM promoted EPC proliferation, migration, and inhibited EPC apoptosis ability. Despite this, miR-126 had no effect on EPC differentiation. miR-126 overexpression significantly downregulated Spred-1 in EPCs. The knockdown of Spred-1 expression in EPCs from DM promoted proliferation, migration, and inhibited apoptosis of the cells. The signal pathway of miR-126 effecting on EPCs is partially mediated through Ras/ERK/VEGF and PI3K/Akt/eNOS regulation. This study provides the first evidence that miR-126 is downregulated in EPCs from diabetic patients, and impairs EPCs-mediated function via its target, Spred-1, and through Ras/ERK/VEGF and PI3K/Akt/eNOS signal pathway.
We present a global survey of energetic electron precipitation from the equatorial magnetosphere due to hiss waves in the plasmasphere and plumes. Using Van Allen Probes measurements, we calculate ...the pitch angle diffusion coefficients at the bounce loss cone, and evaluate the energy spectrum of precipitating electron flux. Our ∼6.5‐year survey shows that, during disturbed times, hiss inside the plasmasphere primarily causes the electron precipitation at L > 4 over 8 h < MLT < 18 h, and hiss waves in plumes cause the precipitation at L > 5 over 8 h < MLT < 14 h and L > 4 over 14 h < MLT < 20 h. The precipitating energy flux increases with increasing geomagnetic activity, and is typically higher in the plasmaspheric plume than the plasmasphere. The characteristic energy of precipitation increases from ∼20 keV at L = 6–∼100 keV at L = 3, potentially causing the loss of electrons at several hundred keV.
Plain Language Summary
Hiss is a plasma wave with a broad frequency range spanning from tens to several thousand Hz, commonly observed in the dayside plasmasphere and plumes of the Earth's magnetosphere, and plays an important role in the loss of energetic electrons. Subject to the interaction with hiss waves, the radiation belt electrons precipitate from the equatorial magnetosphere into the Earth's upper atmosphere, potentially changing the ionospheric conductance and chemistry. Using the measurements of hiss waves and electrons from the ∼6.5‐year data of Van Allen Probes, we perform a global survey of electron precipitation due to hiss waves in the magnetosphere. Our survey indicates that hiss waves mostly cause the energetic electron precipitation in the dayside plasmasphere and in the afternoon sector of the plume. The precipitation is more significant during disturbed geomagnetic conditions than quiet times, and the precipitating flux is higher in the plasmaspheric plume than the plasmasphere. The characteristic energy of precipitating electrons increases with decreasing distance from the Earth. Although the average precipitating electron flux due to hiss is lower than that of chorus, the average energy of precipitation is higher, potentially causing the loss of relativistic electrons in the radiation belts.
Key Points
During disturbed times, hiss waves cause enhanced electron precipitation in the dayside plasmasphere and plume in the afternoon sector
The average total precipitating energy flux due to hiss waves reaches 0.3–1 erg/cm2/s at L > 4.5 and 8 h < MLT < 18 h when AE∗ > 500 nT
Average precipitating flux is higher in the plume than plasmasphere, and the precipitation energy increases with decreasing L shell
Whistler mode chorus waves can scatter plasma sheet electrons into the loss cone and produce the Earth's diffuse aurora. Van Allen Probes observed plasma sheet electron injections and intense chorus ...waves on 24 November 2012. We use quasilinear theory to calculate the precipitating electron fluxes, demonstrating that the chorus waves could lead to high differential energy fluxes of precipitating electrons with characteristic energies of 10–30 keV. Using this method, we calculate the precipitating electron flux from 2012 to 2019 when the Van Allen Probes were near the magnetic equator and perform global surveys of electron precipitation under different geomagnetic conditions. The most significant electron precipitation due to chorus is found from the nightside to dawn sectors over 4 < L < 6.5. The average total precipitating energy flux is enhanced during disturbed conditions, with time‐averaged values reaching ~3–10 erg/cm2/s when AE ≥ 500 nT.
Plain Language Summary
Whistler mode chorus is an electromagnetic emission present in the low‐density region of Earth's magnetosphere. Chorus waves can change the electron distribution in the plasma sheet to cause electron precipitation into Earth's upper atmosphere, leading to the diffuse aurora. We use satellite measurements of waves and electrons to quantify the electron precipitation from the plasma sheet to the upper atmosphere. An event study is presented to demonstrate that intense chorus waves observed near the magnetic equator can cause high energy fluxes of precipitating electrons with characteristic energy of 10–30 keV. To obtain the statistics of the electron precipitation, we calculate the precipitating electron flux from 2012 to 2019 using wave and electron measurements near the magnetic equator. Our survey indicates that chorus waves can cause the precipitation from the nightside to dawn sectors, over an equatorial radial distance of 4–6.5 Earth radii. The energy flux of electron precipitation is enhanced during disturbed geomagnetic conditions compared to quiet conditions. Our study provides the quantification of the empirical electron precipitation from the plasma sheet due to chorus on a global scale.
Key Points
We evaluate the electron precipitation due to whistler mode chorus waves and perform a global survey of the precipitating flux at L < 6.5
The chorus waves cause the precipitation of 1‐ to 100‐keV electrons predominantly from the nightside to dawn sectors over 4 < L < 6.5
Average total precipitating energy flux is enhanced during disturbed conditions, reaching 3–10 erg/cm2/s when AE > 500 nT
We report unusual Electromagnetic Ion Cyclotron (EMIC) waves with a very narrow frequency bandwidth, closely following and approaching the proton gyrofrequency. One interesting case analysis shows ...that magnetosonic waves, anisotropic suprathermal proton distributions, and high frequency EMIC waves are closely related. Magnetosonic waves potentially cause the resonant heating of suprathermal protons and the temperature anisotropy of suprathermal protons (10–100 eV) likely provides free energy for the excitation of high frequency EMIC waves. The statistical analysis shows that this type of EMIC waves has a typical wave amplitude of ~100 pT, left‐handed polarization, and small wave normal angles. Moreover, these low frequency EMIC waves typically occur near the equator in the low‐density regions from dawn to dusk. These newly observed high frequency EMIC waves provide new insights into understanding the generation of EMIC waves and the energy transfer between magnetosonic waves and EMIC waves.
Plain Language Summary
Electromagnetic Ion Cyclotron (EMIC) waves are commonly observed in the Earth's magnetosphere and play an important role in causing the loss of ring current ions and relativistic electrons due to pitch angle scattering. In this study, we report unusual high frequency EMIC waves with frequency very close to the proton gyrofrequency. An interesting case study clearly shows the correlation between magnetosonic waves, the enhancement of suprathermal protons, and high frequency EMIC waves. The protons at suprathermal energies could be heated by magnetosonic waves and the anisotropic distribution of suprathermal protons is likely responsible for the excitation of high frequency EMIC waves. The statistical analysis shows that this type of EMIC waves has a typical wave amplitude of ~100 pT, left‐handed polarization, and small wave normal angles. These newly observed high frequency EMIC waves provide new insights into understanding the generation of EMIC waves and the energy transfer between magnetosonic waves and EMIC waves.
Key Points
Unusually high frequency EMIC waves are observed near the proton gyrofrequency with a very narrow bandwidth
Temperature anisotropy of suprathermal protons in association with magnetosonic waves likely excites high frequency EMIC waves
Statistical results show that high frequency EMIC waves typically occur near the equator in the low‐density regions from dawn to dusk
We investigate relativistic electron precipitation events detected by Polar Environmental Satellites (POES) in low‐Earth orbit in close conjunction with Van Allen Probe A observations of ...electromagnetic ion cyclotron (EMIC) waves near the geomagnetic equator. We show that the occurrence rate of >0.7 MeV electron precipitation recorded by POES during those times strongly increases, reaching statistically significant levels when the minimum electron energy for cyclotron resonance with hydrogen or helium band EMIC waves at the equator decreases below ≃1.0–2.5 MeV, as expected from the quasi‐linear theory. Both hydrogen and helium band EMIC waves can be effective in precipitating MeV electrons. However, >0.7 MeV electron precipitation is more often observed (at statistically significant levels) when the minimum electron energy for cyclotron resonance with hydrogen band waves is low (Emin = 0.6–1.0 MeV), whereas it is more often observed when the minimum electron energy for cyclotron resonance with helium band waves is slightly larger (Emin = 1.0–2.5 MeV). This is indicative of the warm plasma effects for waves approaching the He+ gyrofrequency. We further show that most precipitation events had energies > 0.7–1.0 MeV, consistent with the estimated minimum energy (Emin ∼ 0.6 − 2.5 MeV) of cyclotron resonance with the observed EMIC waves during the majority of these events. However, 4 out of the 12 detected precipitation events cannot be explained by electron quasi‐linear scattering by the observed EMIC waves, and 12 out of 20 theoretically expected precipitation events were not detected by POES, suggesting the possibility of nonlinear effects likely present near the magnetic equator, or warm plasma effects, and/or narrowly localized bursts of EMIC waves.
Key Points
We examine close conjunctions of relativistic electron precipitation observed at Polar Environmental Satellites and electromagnetic ion cyclotron wave measurements by Van Allen Probes
The occurrence rate of MeV electron precipitation becomes statistically significant when cyclotron resonance is possible below 1–2.5 MeV
During most precipitation events, a majority of precipitating electrons likely had energies larger than 0.7 MeV
Whistler mode waves are suggested to play a dual role in precipitation loss and acceleration of energetic electrons in Jovian magnetosphere. Using the combined wave data from Juno and Galileo, we ...constructed global maps of whistler mode waves in the Jovian inner magnetosphere (M‐shell <20). Whistler mode waves are found to be extensively present over M‐shells from 6 to ~13, peaking at ~10, and extend to magnetic latitudes at least up to 50°. Whistler mode wave intensities vary from a few pT to ~100 pT, similar to the intensity level at Earth. The new finding on the latitudinal extension of whistler mode waves indicates their potential effects on electron precipitation over a broad energy range from ~100 eV to several MeV. The newly constructed whistler mode wave spectra are crucial for evaluating the accurate role of whistler mode waves in energetic electron dynamics in the Jovian inner magnetosphere.
Plain Language Summary
Whistler mode waves, a type of natural plasma wave with frequencies below electron cyclotron frequency, are known to play an important role in both loss and acceleration processes of energetic electrons in Jovian magnetosphere. However, the global distribution of whistler mode waves in an extensive region, which is critical for evaluating the effects of whistler mode waves on energetic electrons, is not well known. In the present study, we constructed global maps of whistler mode waves in the Jovian inner magnetosphere using plasma wave data from both Juno and Galileo satellites. Our statistical results show that whistler mode waves are extensively present with an intensity ranging from a few picotesla (pT) to ~100 pT, similar to the intensity level at Earth. In particular, Juno wave data newly reveal that whistler mode waves can extend to magnetic latitudes at least up to 50°, implying that whistler mode waves should be effective in scattering electrons into the upper atmosphere over a broad energy range from ~100 electronvolts to several mega‐electronvolts. Whistler mode wave spectra from Juno also provide crucial information for quantifying the role of whistler mode waves in energetic electron dynamics in the Jovian inner magnetosphere.
Key Points
Whistler mode waves are extensively present in the Jovian inner magnetosphere peaking at M‐shell ~10
Whistler mode waves are observed at magnetic latitudes up to at least ~50°, higher than previously thought
Whistler mode wave distributions from Juno and Galileo are consistent in the overlapped region with an intensity up to ~100 pT
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