526 research outputs found
The global structure and time evolution of dayside magnetopause surface eigenmodes
Theoretical work and recent observations suggest that the dayside magnetopause may support its own eigenmode, consisting of propagating surface waves which reflect at the northern and southern ionospheres. These magnetopause surface eigenmodes (MSEs) are a potential source of magnetospheric ultralowâfrequency (ULF) waves with frequencies less than 2âmHz. Here we use the Space Weather Modeling Framework to study the magnetospheric response to impulsive solar wind dynamic pressure increases. Waves with 1.8âmHz frequency are excited whose global properties are largely consistent with theoretical predictions for MSE and cannot be explained by other known ULF wave modes. These simulation results lead to two key findings: (1) MSE can be sustained in realistic magnetic field geometries with nonzero flow shear and finite current layer thickness at the magnetopause and (2) MSE can seed the growth of tailward propagating surface waves via the KelvinâHelmholtz instability.Key PointsDayside ULF response to pulse consistent with magnetopause surface eigenmodeMagnetopause surface eigenmodes are a potential source of ULF waves below 2âmHzMagnetopause surface eigenmodes seed tailward propagating surface wave growthPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111803/1/grl52799.pd
Massless, String Localized Quantum Fields for Any Helicity
For any massless, irreducible representation of the covering of the proper,
orthochronous Poincar\'e group we construct covariant, free quantum fields that
generate the representation space from the vacuum and are localized in
semi-infinite strings in the sense of commutation or anti-commutation of the
field operators at space-like separation of the strings.Comment: Minor corrections. To be published in Journal of Mathematical Physic
In Situ Observations of a Magnetosheath High-Speed Jet Triggering Magnetopause Reconnection
Magnetosheath highâspeed jetsâlocalized dynamic pressure enhancements typically of âŒ1 Earth radius in sizeâimpact the dayside magnetopause several times per hour. Here we present the first in situ measurements suggesting that such an impact triggered magnetopause reconnection. We use observations from the five Time History of Events and Macroscale Interactions during Substorms spacecraft in a stringâofâpearls configuration on 7 August 2007. The spacecraft recorded magnetopause inâandâout motion during an impact of a magnetosheath jet (VNâŒâ300 km/s along the magnetopause normal direction). There was no evidence for reconnection for the preimpact crossing, yet three probes observed reconnection after the impact. We infer that the jet impact compressed the originally thick (60â70 di), high magnetic shear (140â160° magnetopause until it was thin enough for reconnection to occur. Magnetosheath highâspeed jets could therefore act as a driver for bursty dayside reconnection
Combining thermodynamic simulations, element and surface analytics to study U(VI) retention in corroded cement monokiths upon >20 years of leaching
On the alignment of velocity and magnetic fields within magnetosheath jets
Jets in the subsolar magnetosheath are localized enhancements in dynamic pressure that are able to propagate all the way from the bow shock to the magnetopause. Due to their excess velocity with respect to their environment, they push slower ambient plasma out of their way, creating a vortical plasma motion in and around them. Simulations and case study results suggest that jets also modify the magnetic field in the magnetosheath on their passage, aligning it more with their velocity. Based on Magnetospheric Multi-scale (MMS) jet observations and corresponding superposed epoch analyses of the angles phi between the velocity and magnetic fields, we can confirm that this suggestion is correct. However, while the alignment is more significant for faster than for slower jets, and for jets observed close to the bow shock, the overall effect is small: typically, reductions in phi of around 10 degrees are observed at jet core regions, where the jets' velocities are largest. Furthermore, time series of phi pertaining to individual jets significantly deviate from the superposed epoch analysis results. They usually exhibit large variations over the entire range of phi: 0 to 90 degrees. This variability is commonly somewhat larger within jets than outside them, masking the systematic decrease in phi at core regions of individual jets
Magnetosheath High-Speed Jets: Internal Structure and InteractionWith Ambient Plasma
National Aeronautics and Space Administration (NASA). Grant Number: NNG04EB99C; Ăsterreichische Forschungsförderungsgesellschaft (FFG); Austrian Academy of Sciences and the Austrian Space Applications Programme. Grant Number: FFG/ASAP-844377; NASA. Grant Numbers: NNX17AI45G, NAS5-02099; Austrian Science Fund (FWF). Grant Number: P 28764-N2
Shocklets and Short Large Amplitude Magnetic Structures (SLAMS) in the high Mach foreshock of Venus
Shocklets and short large-amplitude magnetic structures (SLAMS) are steepened magnetic fluctuations commonly found in Earth's upstream foreshock. Here we present Venus Express observations from the 26th of February 2009 establishing their existence in the steady-state foreshock of Venus, building on a past study which found SLAMS during a substantial disturbance of the induced magnetosphere. The Venusian structures were comparable to those reported near Earth. The 2 Shocklets had magnetic compression ratios of 1.23 and 1.34 with linear polarization in the spacecraft frame. The 3 SLAMS had ratios between 3.22 and 4.03, two of which with elliptical polarization in the spacecraft frame. Statistical analysis suggests SLAMS coincide with unusually high solar wind AlfvĂ©n mach-number at Venus (12.5, this event). Thus, while we establish Shocklets and SLAMS can form in the stable Venusian foreshock, they may be rarer than at Earth. We estimate a lower limit of their occurrence rate of âł14%
Colloid/nanoparticle formation and mobility in the context of deep geological nuclear waste disposal (project KOLLORADO-1; final report)
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