scholarly journals Turbulence Upstream and Downstream of Interplanetary Shocks

2021 ◽  
Vol 8 ◽  
Author(s):  
A. Pitňa ◽  
J. Šafránková ◽  
Z. Němeček ◽  
T. Ďurovcová ◽  
A. Kis
Keyword(s):  
Inertial Range ◽  
Shock Propagation ◽  
Interplanetary Shocks ◽  
Fermi Acceleration ◽  
Spatial And Temporal Scales ◽  
Key Characteristics ◽  
Order Of Magnitude ◽  
Inner Parts ◽  
Shock Fronts ◽  
Shed Light

The paper reviews the interaction of collisionless interplanetary (IP) shocks with the turbulent solar wind. The coexistence of shocks and turbulence plays an important role in understanding the acceleration of particles via Fermi acceleration mechanisms, the geoeffectiveness of highly disturbed sheaths following IP shocks and, among others, the nature of the fluctuations themselves. Although our knowledge of physics of upstream and downstream shock regions has been greatly improved in recent years, many aspects of the IP-shock/turbulence interaction are still poorly known, for example, the nature of turbulence, its characteristics on spatial and temporal scales, how it decays, its relation to shock passage and others. We discuss properties of fluctuations ahead (upstream) and behind (downstream) of IP shock fronts with the focus on observations. Some of the key characteristics of the upstream/downstream transition are 1) enhancement of the power in the inertial range fluctuations of the velocity, magnetic field and density is roughly one order of magnitude, 2) downstream fluctuations are always more compressible than the upstream fluctuations, and 3) energy in the inertial range fluctuations is kept constant for a significant time after the passage of the shock. In this paper, we emphasize that–for one point measurements–the downstream region should be viewed as an evolutionary record of the IP shock propagation through the plasma. Simultaneous measurements of the recently launched spacecraft probing inner parts of the Solar System will hopefully shed light on some of these questions.

scholarly journals Shock Propagation and Associated Particle Acceleration in the Presence of Ambient Solar-Wind Turbulence

2021 ◽  
Vol 8 ◽  
Author(s):  
Fan Guo ◽  
Joe Giacalone ◽  
Lulu Zhao
Keyword(s):  
Solar Wind ◽  
Particle Acceleration ◽  
Energetic Particles ◽  
Low Energy ◽  
Shock Propagation ◽  
Interplanetary Shocks ◽  
Solar Wind Turbulence ◽  
Wind Turbulence ◽  
Shock Fronts ◽  
Ambient Solar Wind

The topic of this review paper is on the influence of solar wind turbulence on shock propagation and its consequence on the acceleration and transport of energetic particles at shocks. As the interplanetary shocks sweep through the turbulent solar wind, the shock surfaces fluctuate and ripple in a range of different scales. We discuss particle acceleration at rippled shocks in the presence of ambient solar-wind turbulence. This strongly affects particle acceleration and transport of energetic particles (both ions and electrons) at shock fronts. In particular, we point out that the effects of upstream turbulence is critical for understanding the variability of energetic particles at shocks. Moreover, the presence of pre-existing upstream turbulence significantly enhances the trapping near the shock of low-energy charged particles, including those near the thermal energy of the incident plasma, even when the shock propagates normal to the average magnetic field. Pre-existing turbulence, always present in space plasmas, provides a means for the efficient acceleration of low-energy particles and overcoming the well known injection problem at shocks.

scholarly journals Cluster observations of sudden impulses in the magnetotail caused by interplanetary shocks and pressure increases

2005 ◽  
Vol 23 (2) ◽  
pp. 609-624 ◽  
Author(s):  
K. E. J. Huttunen ◽  
J. Slavin ◽  
M. Collier ◽  
H. E. J. Koskinen ◽  
A. Szabo ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Dynamic Pressure ◽  
Solar Wind Speed ◽  
Interplanetary Shock ◽  
Wind Pressure ◽  
Shock Propagation ◽  
Interplanetary Shocks ◽  
Maximum Variance ◽  
The Magnetic Field

Abstract. Sudden impulses (SI) in the tail lobe magnetic field associated with solar wind pressure enhancements are investigated using measurements from Cluster. The magnetic field components during the SIs change in a manner consistent with the assumption that an antisunward moving lateral pressure enhancement compresses the magnetotail axisymmetrically. We found that the maximum variance SI unit vectors were nearly aligned with the associated interplanetary shock normals. For two of the tail lobe SI events during which Cluster was located close to the tail boundary, Cluster observed the inward moving magnetopause. During both events, the spacecraft location changed from the lobe to the magnetospheric boundary layer. During the event on 6 November 2001 the magnetopause was compressed past Cluster. We applied the 2-D Cartesian model developed by collier98 in which a vacuum uniform tail lobe magnetic field is compressed by a step-like pressure increase. The model underestimates the compression of the magnetic field, but it fits the magnetic field maximum variance component well. For events for which we could determine the shock normal orientation, the differences between the observed and calculated shock propagation times from the location of WIND/Geotail to the location of Cluster were small. The propagation speeds of the SIs between the Cluster spacecraft were comparable to the solar wind speed. Our results suggest that the observed tail lobe SIs are due to lateral increases in solar wind dynamic pressure outside the magnetotail boundary.

The solar semidiurnal variation of cosmic-ray intensity 70 m.w.e. underground

1968 ◽  
Vol 46 (10) ◽  
pp. S839-S843 ◽  
Author(s):  
G. Cini-Castagnoli ◽  
M. A. Dodero ◽  
L. Andreis
Keyword(s):  
Diurnal Variation ◽  
Cosmic Ray ◽  
Fermi Acceleration ◽  
Sidereal Time ◽  
Cosmic Ray Intensity ◽  
Intensity Measurements ◽  
Hourly Data ◽  
Semidiurnal Variation ◽  
Order Of Magnitude ◽  
Different Depths

Cosmic-ray intensity measurements have been carried out during the last year at a depth of 70 m.w.e. in the Monte dei Cappuccini laboratory in Torino, using solid vertical semicubical scintillator telescopes with a total area of 2 m2. Hourly data for 245 days corrected for barometric changes have been analyzed for the solar, apparent sidereal, and antisidereal daily variations whose harmonics are as follows:[Formula: see text]The true sidereal diurnal variation is estimated to have an amplitude of 0.019% with a time of maximum at 1720 h local sidereal time. The solar diurnal variation at different depths underground follows the energy dependence calculated with Axford's theory. The solar semidiurnal variation shows instead a fairly constant value at different μ energies. Its order of magnitude agrees with that expected as a result of Fermi acceleration in collisions of primaries moving in roughly solar and antisolar directions with solar wind inhomogeneities.

scholarly journals Can the dataset of field based recharge estimates in Australia be used to predict recharge in data-poor areas?

2010 ◽  
Vol 7 (4) ◽  
pp. 5647-5684 ◽  
Author(s):  
R. S. Crosbie ◽  
I. D. Jolly ◽  
F. W. Leaney ◽  
C. Petheram
Keyword(s):  
Vegetation Type ◽  
Annual Rainfall ◽  
Effective Management ◽  
Empirical Relationships ◽  
Spatial And Temporal Scales ◽  
Difficult Time ◽  
Average Annual Rainfall ◽  
Order Of Magnitude ◽  
Surface Geology ◽  
The Relationship

Abstract. Effective management of water resources requires that all elements of the water balance be estimated. Groundwater recharge measurements are difficult, time consuming and expensive. In some cases a field study cannot be justified and simple empirical relationships are used to estimate recharge, and often the value chosen is simply a percentage of rainfall. This paper aims to use a data-base of 4386 field based estimates of recharge from 172 studies in Australia to produce simple empirical relationships that relate recharge to nationally available datasets and hence can be used to estimate recharge in data-poor areas in a scientifically defensible way. It was found that the vegetation and soil type were critical determinants in forming relationships between average annual rainfall and average annual recharge. Climate zones and surface geology were not found to be significant determinants in the relationship between rainfall and recharge. The method used to estimate recharge had an impact upon the magnitude of the recharge estimates due to the spatial and temporal scales over which the different methods estimate recharge. Relationships have been developed here between average annual rainfall and average annual recharge for combinations of soil and vegetation type that can be used with only nationally available datasets to provide a recharge estimate. The 95 percent confidence limits about the recharge predicted using these relationships is generally greater than an order of magnitude either side of the relationship developed. This means that if these relationships are used to help determine water allocations then the precautionary principle should limit allocations to less than about 5% of the estimated recharge, if allocations are greater than this a more detailed site specific study is warranted.

Microplastics research at the interface of aquatic and terrestrial systems – Opinion

2021 ◽  
Author(s):  
Julia Prume ◽  
Collin Weber
Keyword(s):  
Complex Systems ◽  
Nutrient Enrichment ◽  
Biofilm Formation ◽  
River Sediments ◽  
System Function ◽  
Comprehensive Understanding ◽  
Spatial And Temporal Scales ◽  
River Waters ◽  
Academic Problem ◽  
Shed Light

<p>Rivers are often pictured as transport routes for plastics and microplastics from land to sea. Indeed, from a geological and geomorphological perspective, the main system function of rivers is the transport of water and sediments. An increasing amount of studies has detected microplastics not only in river waters but also in river sediments, banks and floodplains. The occurrence of microplastics in both aquatic and terrestrial systems raises the question of processes related to microplastics at the two system’s interface. However, in microplastics’ research, aquatic and terrestrial compartments are usually investigated separately from each other. Such a restricted perspective cannot explain reality adequately: Rivers are highly dynamic and complex systems, they are framed by and interact with terrestrial systems on different spatial and temporal scales. This interaction is known with regard to sediment deposition and erosion as well as pollutant or nutrient enrichment. In microplastics’ research, to date, little is known on interface processes such as (potentially bidirectional) horizontal and vertical plastic transport, deposition and erosion as well as remobilization. Little is known on the fate of plastics within both systems and at the interface: fragmentation, leaching and absorption of chemicals, biofilm formation, homoaggregation, heteroaggregation, intake by plant and animal organisms. However, a comprehensive understanding of sources, transport paths, as well as sinks is not only an academic problem but can support political stakeholders to manage pollution by microplastics. Therefore, we suggest to shed light not only on microplastics’ abundance in rivers or soils but also on processes at the interface of aquatic and terrestrial systems. </p>

scholarly journals Non-thermal emission from cosmic rays accelerated in H II regions

2019 ◽  
Vol 630 ◽  
pp. A72 ◽  
Author(s):  
Marco Padovani ◽  
Alexandre Marcowith ◽  
Álvaro Sánchez-Monge ◽  
Fanyi Meng ◽  
Peter Schilke
Keyword(s):  
Cosmic Rays ◽  
Thermal Radiation ◽  
Thermal Emission ◽  
Cosmic Ray ◽  
Local Source ◽  
Relativistic Electrons ◽  
Deep South ◽  
Fermi Acceleration ◽  
First Order ◽  
Order Of Magnitude

Context. Radio observations at metre-centimetre wavelengths shed light on the nature of the emission of H II regions. Usually this category of objects is dominated by thermal radiation produced by ionised hydrogen, namely protons and electrons. However, a number of observational studies have revealed the existence of H II regions with a mixture of thermal and non-thermal radiation. The latter represents a clue as to the presence of relativistic electrons. However, neither the interstellar cosmic-ray electron flux nor the flux of secondary electrons, produced by primary cosmic rays through ionisation processes, is high enough to explain the observed flux densities. Aims. We investigate the possibility of accelerating local thermal electrons up to relativistic energies in H II region shocks. Methods. We assumed that relativistic electrons can be accelerated through the first-order Fermi acceleration mechanism and we estimated the emerging electron fluxes, the corresponding flux densities, and the spectral indexes. Results. We find flux densities of the same order of magnitude of those observed. In particular, we applied our model to the “deep south” (DS) region of Sagittarius B2 and we succeeded in reproducing the observed flux densities with an accuracy of less than 20% as well as the spectral indexes. The model also gives constraints on magnetic field strength (0.3–4 mG), density (1–9 × 104 cm−3), and flow velocity in the shock reference frame (33–50 km s−1) expected in DS. Conclusions. We suggest a mechanism able to accelerate thermal electrons inside H II regions through the first-order Fermi acceleration. The existence of a local source of relativistic electrons can explain the origin of both the observed non-thermal emission and the corresponding spectral indexes.

scholarly journals Musicological discourse of Vesna Mikić (1967-2019): Characteristics, effects, and achievements

New Sound ◽  
2020 ◽  
pp. 139-178
Author(s):  
Biljana Leković
Keyword(s):  
Key Characteristics ◽  
Insight Into ◽  
Shed Light

The aim of this paper is to gain an insight into the entire musicological discourse of Vesna Mikic, to offer its systematization, or, in other words, to shed light on her use of scientific and research procedures, methods and contributions. By analyzing her texts, I will try to define the development train of her musicological thought. Furthermore, I will emphasize the key characteristics regarding her field of research, and the mechanisms they are founded upon. I will also try to define the thematic fields she analyzed, thus demonstrating the valuable achievements of her work.

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