Multi-scale Analysis of Electromagnetic Energy Input using Swarm: Quantifying Key Scales in Magnetosphere-Ionosphere Coupling

2020 ◽  
Author(s):  
Ivan Pakhotin ◽  
Ian Mann ◽  
Kai Xie ◽  
David Knudsen ◽  
Johnathan Burchill
Keyword(s):  
Energy Input ◽  
Energy Content ◽  
Field Measurements ◽  
Electromagnetic Energy ◽  
Small Scale ◽  
Poynting Flux ◽  
Modelling Studies ◽  
New Instrumentation ◽  
Auroral Phenomena ◽  
Electromagnetic Disturbances

<p>Electromagnetic energy transfer in magnetosphere-ionosphere coupling (MIC) is an inherently multiscale process, where the relative contributions of various scale sizes, linked to various auroral phenomena, are largely unknown. While work in previous decades has largely focused on large scales, in recent years with the development of new instrumentation smaller scale electromagnetic disturbances have once again come into focus. Recent work by the authors has demonstrated evidence that small-scale processes appear to be so important as to potentially account for a global interhemispheric asymmetry in ionospheric energy input. This study attempts to statistically quantify the contribution of energy at the small and mesoscales using Poynting flux, calculated using the unprecedented ESA Swarm mission dataset of simultaneous electric and magnetic field measurements at 16 Hz, with statistics now spanning several years. We find important contributions at small scales to the total energy budget, while at the same time noting that there appears to be a limit above which energy content tends to drop off. In the context of previous observations from other spacecraft this may shed light on key small-scale processes happening in and around the auroral acceleration region, in particular discrete arcs and Alfvén wave reflection from the ionosphere, which are important in forming inputs to coupled magnetosphere-ionosphere-thermosphere modelling studies.</p>

scholarly journals Northern preference for terrestrial electromagnetic energy input from space weather

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
I. P. Pakhotin ◽  
I. R. Mann ◽  
K. Xie ◽  
J. K. Burchill ◽  
D. J. Knudsen
Keyword(s):  
Space Weather ◽  
Energy Input ◽  
Rotation Axis ◽  
Electromagnetic Energy ◽  
Magnetic Pole ◽  
Poynting Flux ◽  
Auroral Emissions ◽  
Energy And Momentum ◽  
Swarm Satellite ◽  
Northern And Southern Hemispheres

AbstractTerrestrial space weather involves the transfer of energy and momentum from the solar wind into geospace. Despite recently discovered seasonal asymmetries between auroral forms and the intensity of emissions between northern and southern hemispheres, seasonally averaged energy input into the ionosphere is still generally considered to be symmetric. Here we show, using Swarm satellite data, a preference for electromagnetic energy input at 450 km altitude into the northern hemisphere, on both the dayside and the nightside, when averaged over season. We propose that this is explained by the offset of the magnetic dipole away from Earth’s center. This introduces a larger separation between the magnetic pole and rotation axis in the south, creating different relative solar illumination of northern and southern auroral zones, resulting in changes to the strength of reflection of incident Alfvén waves from the ionosphere. Our study reveals an important asymmetry in seasonally averaged electromagnetic energy input to the atmosphere. Based on observed lower Poynting flux on the nightside this asymmetry may also exist for auroral emissions. Similar offsets may drive asymmetric energy input, and potentially aurora, on other planets.

scholarly journals Northern Preference for Terrestrial Electromagnetic Energy Input from Space Weather

2020 ◽  
Author(s):  
Ivan Pakhotin ◽  
I R Mann ◽  
K Xie ◽  
J Burchill ◽  
D Knudsen
Keyword(s):  
Space Weather ◽  
Energy Input ◽  
Electromagnetic Energy

scholarly journals Can the heterogeneity in stream dissolved organic carbon be explained by contributing landscape elements?

2014 ◽  
Vol 11 (4) ◽  
pp. 1199-1213 ◽  
Author(s):  
A. M. Ågren ◽  
I. Buffam ◽  
D. M. Cooper ◽  
T. Tiwari ◽  
C. D. Evans ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Model Development ◽  
Field Measurements ◽  
Mixing Model ◽  
Residual Analysis ◽  
Residence Times ◽  
Stream Network ◽  
Landscape Elements ◽  
Modelling Studies

Abstract. The controls on stream dissolved organic carbon (DOC) concentrations were investigated in a 68 km2 catchment by applying a landscape-mixing model to test if downstream concentrations could be predicted from contributing landscape elements. The landscape-mixing model reproduced the DOC concentration well throughout the stream network during times of high and intermediate discharge. The landscape-mixing model approach is conceptually simple and easy to apply, requiring relatively few field measurements and minimal parameterisation. Our interpretation is that the higher degree of hydrological connectivity during high flows, combined with shorter stream residence times, increased the predictive power of this whole watershed-based mixing model. The model was also useful for providing a baseline for residual analysis, which highlighted areas for further conceptual model development. The residual analysis indicated areas of the stream network that were not well represented by simple mixing of headwaters, as well as flow conditions during which simple mixing based on headwater watershed characteristics did not apply. Specifically, we found that during periods of baseflow the larger valley streams had much lower DOC concentrations than would be predicted by simple mixing. Longer stream residence times during baseflow and changing hydrological flow paths were suggested as potential reasons for this pattern. This study highlights how a simple landscape-mixing model can be used for predictions as well as providing a baseline for residual analysis, which suggest potential mechanisms to be further explored using more focused field and process-based modelling studies.

scholarly journals Improvement of density models of geological structures by fusion of gravity data and cosmic muon radiographies

2015 ◽  
Vol 5 (1) ◽  
pp. 83-116 ◽  
Author(s):  
K. Jourde ◽  
D. Gibert ◽  
J. Marteau
Keyword(s):  
Gravity Data ◽  
Field Measurements ◽  
Small Scale ◽  
Density Structure ◽  
Spatial Filters ◽  
Muon Tomography ◽  
Mathematical Expressions ◽  
Integration Formulas ◽  
Muon Radiography ◽  
Gravity Measurements

Abstract. This paper examines how the resolution of small-scale geological density models is improved through the fusion of information provided by gravity measurements and density muon radiographies. Muon radiography aims at determining the density of geological bodies by measuring their screening effect on the natural flux of cosmic muons. Muon radiography essentially works like medical X-ray scan and integrates density information along elongated narrow conical volumes. Gravity measurements are linked to density by a 3-D integration encompassing the whole studied domain. We establish the mathematical expressions of these integration formulas – called acquisition kernels – and derive the resolving kernels that are spatial filters relating the true unknown density structure to the density distribution actually recovered from the available data. The resolving kernels approach allows to quantitatively describe the improvement of the resolution of the density models achieved by merging gravity data and muon radiographies. The method developed in this paper may be used to optimally design the geometry of the field measurements to perform in order to obtain a given spatial resolution pattern of the density model to construct. The resolving kernels derived in the joined muon/gravimetry case indicate that gravity data are almost useless to constrain the density structure in regions sampled by more than two muon tomography acquisitions. Interestingly the resolution in deeper regions not sampled by muon tomography is significantly improved by joining the two techniques. The method is illustrated with examples for La Soufrière of Guadeloupe volcano.

Experiments on the stability and transition of wind-driven water surfaces

2001 ◽  
Vol 446 ◽  
pp. 25-65 ◽  
Author(s):  
FABRICE VERON ◽  
W. KENDALL MELVILLE
Keyword(s):  
Surface Current ◽  
Field Measurements ◽  
Surface Flow ◽  
Transition To Turbulence ◽  
Surface Velocity ◽  
Small Scale ◽  
Gas Transfer ◽  
Water Surfaces ◽  
Langmuir Circulations ◽  
The Stability

We present the results of laboratory and field measurements on the stability of wind-driven water surfaces. The laboratory measurements show that when exposed to an increasing wind starting from rest, surface current and wave generation is accompanied by a variety of phenomena that occur over comparable space and time scales. Of particular interest is the generation of small-scale, streamwise vortices, or Langmuir circulations, the clear influence of the circulations on the structure of the growing wave field, and the subsequent transition to turbulence of the surface flow. Following recent work by Melville, Shear & Veron (1998) and Veron & Melville (1999b), we show that the waves that are initially generated by the wind are then strongly modulated by the Langmuir circulations that follow. Direct measurements of the modulated wave variables are qualitatively consistent with geometrical optics and wave action conservation, but quantitative comparison remains elusive. Within the range of parameters of the experiments, both the surface waves and the Langmuir circulations first appear at constant Reynolds numbers of 370 ± 10 and 530 ± 20, respectively, based on the surface velocity and the depth of the laminar shear layer. The onset of the Langmuir circulations leads to a significant increase in the heat transfer across the surface. The field measurements in a boat basin display the same phenomena that are observed in the laboratory. The implications of the measurements for air–sea fluxes, especially heat and gas transfer, and sea-surface temperature, are discussed.

scholarly journals Emergence of small-scale magnetic flux in the quiet Sun

2020 ◽  
Vol 633 ◽  
pp. A67 ◽  
Author(s):  
I. Kontogiannis ◽  
G. Tsiropoula ◽  
K. Tziotziou ◽  
C. Gontikakis ◽  
C. Kuckein ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Morphological Characteristics ◽  
Small Scale ◽  
X Rays ◽  
Coronal Emission ◽  
Quiet Sun ◽  
Temperature Regimes ◽  
Multi Wavelength ◽  
Modelling Studies

Context. We study the evolution of a small-scale emerging flux region (EFR) in the quiet Sun, from its emergence in the photosphere to its appearance in the corona and its decay. Aims. We track processes and phenomena that take place across all atmospheric layers; we explore their interrelations and compare our findings with those from recent numerical modelling studies. Methods. We used imaging as well as spectral and spectropolarimetric observations from a suite of space-borne and ground-based instruments. Results. The EFR appears in the quiet Sun next to the chromospheric network and shows all morphological characteristics predicted by numerical simulations. The total magnetic flux of the region exhibits distinct evolutionary phases, namely an initial subtle increase, a fast increase with a Co-temporal fast expansion of the region area, a more gradual increase, and a slow decay. During the initial stages, fine-scale G-band and Ca II H bright points coalesce, forming clusters of positive- and negative-polarity in a largely bipolar configuration. During the fast expansion, flux tubes make their way to the chromosphere, pushing aside the ambient magnetic field and producing pressure-driven absorption fronts that are visible as blueshifted chromospheric features. The connectivity of the quiet-Sun network gradually changes and part of the existing network forms new connections with the newly emerged bipole. A few minutes after the bipole has reached its maximum magnetic flux, the bipole brightens in soft X-rays forming a coronal bright point. The coronal emission exhibits episodic brightenings on top of a long smooth increase. These coronal brightenings are also associated with surge-like chromospheric features visible in Hα, which can be attributed to reconnection with adjacent small-scale magnetic fields and the ambient quiet-Sun magnetic field. Conclusions. The emergence of magnetic flux even at the smallest scales can be the driver of a series of energetic phenomena visible at various atmospheric heights and temperature regimes. Multi-wavelength observations reveal a wealth of mechanisms which produce diverse observable effects during the different evolutionary stages of these small-scale structures.

scholarly journals Improvement of density models of geological structures by fusion of gravity data and cosmic muon radiographies

2015 ◽  
Vol 4 (2) ◽  
pp. 177-188 ◽  
Author(s):  
K. Jourde ◽  
D. Gibert ◽  
J. Marteau
Keyword(s):  
Gravity Data ◽  
Field Measurements ◽  
Small Scale ◽  
Density Structure ◽  
Spatial Filters ◽  
Muon Tomography ◽  
Mathematical Expressions ◽  
Muon Radiography ◽  
Gravity Measurements ◽  
Kernel Approach

Abstract. This paper examines how the resolution of small-scale geological density models is improved through the fusion of information provided by gravity measurements and density muon radiographies. Muon radiography aims at determining the density of geological bodies by measuring their screening effect on the natural flux of cosmic muons. Muon radiography essentially works like a medical X-ray scan and integrates density information along elongated narrow conical volumes. Gravity measurements are linked to density by a 3-D integration encompassing the whole studied domain. We establish the mathematical expressions of these integration formulas – called acquisition kernels – and derive the resolving kernels that are spatial filters relating the true unknown density structure to the density distribution actually recovered from the available data. The resolving kernel approach allows one to quantitatively describe the improvement of the resolution of the density models achieved by merging gravity data and muon radiographies. The method developed in this paper may be used to optimally design the geometry of the field measurements to be performed in order to obtain a given spatial resolution pattern of the density model to be constructed. The resolving kernels derived in the joined muon–gravimetry case indicate that gravity data are almost useless for constraining the density structure in regions sampled by more than two muon tomography acquisitions. Interestingly, the resolution in deeper regions not sampled by muon tomography is significantly improved by joining the two techniques. The method is illustrated with examples for the La Soufrière volcano of Guadeloupe.

scholarly journals Characterising the surface magnetic fields of T Tauri stars with high-resolution near-infrared spectroscopy

2019 ◽  
Vol 630 ◽  
pp. A99 ◽  
Author(s):  
A. Lavail ◽  
O. Kochukhov ◽  
G. A. J. Hussain
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Large Scale ◽  
Near Infrared ◽  
Field Measurements ◽  
T Tauri Stars ◽  
Small Scale ◽  
Surface Magnetic Field ◽  
T Tauri

Aims. In this paper, we aim to characterise the surface magnetic fields of a sample of eight T Tauri stars from high-resolution near-infrared spectroscopy. Some stars in our sample are known to be magnetic from previous spectroscopic or spectropolarimetric studies. Our goals are firstly to apply Zeeman broadening modelling to T Tauri stars with high-resolution data, secondly to expand the sample of stars with measured surface magnetic field strengths, thirdly to investigate possible rotational or long-term magnetic variability by comparing spectral time series of given targets, and fourthly to compare the magnetic field modulus ⟨B⟩ tracing small-scale magnetic fields to those of large-scale magnetic fields derived by Stokes V Zeeman Doppler Imaging (ZDI) studies. Methods. We modelled the Zeeman broadening of magnetically sensitive spectral lines in the near-infrared K-band from high-resolution spectra by using magnetic spectrum synthesis based on realistic model atmospheres and by using different descriptions of the surface magnetic field. We developped a Bayesian framework that selects the complexity of the magnetic field prescription based on the information contained in the data. Results. We obtain individual magnetic field measurements for each star in our sample using four different models. We find that the Bayesian Model 4 performs best in the range of magnetic fields measured on the sample (from 1.5 kG to 4.4 kG). We do not detect a strong rotational variation of ⟨B⟩ with a mean peak-to-peak variation of 0.3 kG. Our confidence intervals are of the same order of magnitude, which suggests that the Zeeman broadening is produced by a small-scale magnetic field homogeneously distributed over stellar surfaces. A comparison of our results with mean large-scale magnetic field measurements from Stokes V ZDI show different fractions of mean field strength being recovered, from 25–42% for relatively simple poloidal axisymmetric field topologies to 2–11% for more complex fields.

scholarly journals The physical impact of towed demersal fishing gears on soft sediments

2015 ◽  
Vol 73 (suppl_1) ◽  
pp. i5-i14 ◽  
Author(s):  
F. G. O'Neill ◽  
A. Ivanović
Keyword(s):  
Mathematical Modelling ◽  
Large Scale ◽  
Lateral Displacement ◽  
Field Measurements ◽  
Small Scale ◽  
Physical Interaction ◽  
Soft Sediments ◽  
Fishing Gears ◽  
Scale Modelling ◽  
Physical Impact

Abstract An improved understanding of the physical interaction of towed demersal fishing gears with the seabed has been developed in recent years, and there is a clearer view of the underpinning mechanical processes that lead to the modification and alteration of the benthic environment. The physical impact of these gears on soft sediments can be classified broadly as being either geotechnical or hydrodynamic in nature: penetration and piercing of the substrate, lateral displacement of sediment, and the influence of the pressure field transmitted through the sediment can be considered geotechnical, whereas the mobilization of sediment into the water column can be considered hydrodynamic. A number of experimental and numerical approaches have been used to gain better insights of these physical processes. These include small-scale modelling in towing tanks and sand channels; large-scale modelling in the field; measurements behind full-scale towed gears at sea; numerical/mathematical modelling of sediment mechanics; and numerical/mathematical modelling of hydrodynamics. Here, we will review this research, and that in associated fields, and show how it can form the basis of predictive models of the benthic impact of trawl gears.

scholarly journals The thermal structure of the anoxic trough in Lake Untersee, Antarctica

2018 ◽  
Vol 30 (6) ◽  
pp. 333-344 ◽  
Author(s):  
James Bevington ◽  
Christopher P. McKay ◽  
Alfonso Davila ◽  
Ian Hawes ◽  
Yukiko Tanabe ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Solar Radiation ◽  
Water Temperature ◽  
Energy Input ◽  
Thermal Structure ◽  
Field Measurements ◽  
Maximum Depth ◽  
Antarctic Lake ◽  
Thermal Maximum ◽  
Anoxic Basin

AbstractLake Untersee is a perennially ice-covered Antarctic lake that consists of two basins. The deepest basin, next to the Anuchin Glacier is aerobic to its maximum depth of 160 m. The shallower basin has a maximum depth of 100 m, is anoxic below 80 m, and is shielded from convective currents. The thermal profile in the anoxic basin is unusual in that the water temperature below 50 m is constant at 4°C but rises to 5°C between 70 m and 80 m depth, then drops to 3.7°C at the bottom. Field measurements were used to conduct a thermal and stability analysis of the anoxic basin. The shape of the thermal maximum implies two discrete locations of energy input, one of 0.11 W m-2 at 71 m depth and one of 0.06 W m-2 at 80 m depth. Heat from microbial activity cannot account for the required amount of energy at either depth. Instead, absorption of solar radiation due to an increase in water opacity at these depths can account for the required energy input. Hence, while microbial metabolism is not an important source of heat, biomass increases opacity in the water column resulting in greater absorption of sunlight.

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