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Solitary waves and enhanced incoherent scatter ion lines
Umeå University, Faculty of Science and Technology, Department of Physics. (The Swedish Institute of Space Physics, Kiruna)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis addresses solitary waves and their significance for auroral particle acceleration, coronal heating and incoherent scatter radar spectra. Solitary waves are formed due to a balance of nonlinear and dispersive effects. There are several nonlinearities present in ideal magnetohydrodynamics (MHD) and dispersion can be introduced by including theHall termin the generalised Ohm’s law. The resulting system of equations comprise the classical ideal MHD waves, whistlers, drift waves and solitarywave solutions. The latter reside in distinct regions of the phase space spanned by the speed and the angle (to the magnetic field) of the propagating wave. Within each region, qualitatively similar solitary structures are found. In the limit of neglected electron intertia, the solitary wave solutions are confined to two regions of slow and fast waves, respectively. The slow (fast) structures are associated with density compressions (rarefactions) and positive (negative) electric potentials. Such negative potentials are shown to accelerate electrons in the auroral region (solar corona) to tens (hundreds) of keV. The positive electric potentials could accelerate solar wind ions to velocities of 300–800 km/s. The structure widths perpendicular to themagnetic field are in the Earth’s magnetosphere (solar corona) of the order of 1–100 km (m). This thesis also addresses a type of incoherent scatter radar spectra, where the ion line exhibits a spectrally uniform power enhancement with the up- and downshifted shoulder and the spectral region in between enhanced simultaneously and equally. The power enhancements are one order of magnitude above the thermal level and are often localised to an altitude range of less than 20 km at or close to the ionospheric F region peak. The observations are well-described by a model of ion-acoustic solitary waves propagating transversely across the radar beam. Two cases of localised ion line enhancements are shown to occur in conjunction with auroral arcs drifting through the radar beam. The arc passages are associated with large gradients in ion temperature, which are shown to generate sufficiently high velocity shears to give rise to growing Kelvin-Helmholtz (K-H) instabilities. The observed ion line enhancements are interpreted in the light of the low-frequency turbulence associated with these instabilities.

Abstract [sv]

Denna avhandling handlar om solitära vågor och deras roll i norrskensacceleration och koronaupphettning, samt deras signatur i spektra uppmätta med inkoherent spridningsradar. Solitära vågor bildas genom en balans mellan ickelinjära och dispersiva effekter. Ickelinjäriteter finns det gott om i ideal magnetohydrodynamik (MHD) och dispersion kan införas genom att inkludera Halltermen i den generaliserade Ohms lag. Det resulterande ekvationssystemet omfattar de klassiska vågorna inom ideal MHD, visslare, driftvågor och solitära vågor. De sistnämnda återfinns i väldefinierade områden i fasrummet som spänns upp av farten och vinkeln (mot magnetfältet) för den propagerande vågen. Inom varje sådant område återfinns kvalitativt lika solitära våglösningar. Om man försummar elektronernas tröghet begränsas de solitära våglösningarna till två områden med långsamma respektive snabba vågor. De långsamma (snabba) strukturerna är associerade med täthets-kompressioner (förtunningar) och positiva (negativa) elektriska potentialer. De negativa potentialerna visas kunna accelerera elektroner i norrskensområdet (solens korona) till tiotals (hundratals) keV medan de positiva potentialerna accelererar solvindsjoner till hastigheter på 300–800 km/s. Strukturbredderna vinkelrät mot magnetfältet är i jordens magnetosfär (solens korona) av storleksordningen 1–100 km (m). Denna avhandling tar även upp en typ av inkoherent spridningsradarspektra, där jonlinjen uppvisar en spektralt uniform förstärkning. Detta innebär att den upp- och nedskiftade skuldran och spektralbandet däremellan förstärks simultant och i lika hög grad. Effektförstärkningen är en storleksordning över den termiska nivån och är ofta lokaliserad till ett höjd-intervall av mindre än 20 km nära jonosfärens F-skiktstopp. Observationerna beskrivs väl av en modell med solitära vågor som propagerar transversellt genom radarstrålen. Två fall av lokaliserade jonlinjeförstärkningar visas sammanfalla med att norrskensbågar driver genom radarstrålen. I samband med bågarnas passage uppmäts stora gradienter i jontemperatur, vilket visas skapa tillräckligt kraftiga hastighetsskjuvningar för att Kelvin-Helmholtz-instabiliteter ska tillåtas växa. De observerade jonlinjeförstärkningarna tolkas i skenet av den lågfrekventa turbulensen som är kopplad till dessa instabiliteter.

Place, publisher, year, edition, pages
Kiruna: Institutet för rymdfysik, Umeå universitet , 2011. , 51 p.
Series
IRF Scientific Report, ISSN 0284-1703 ; 301
Keyword [en]
plasma waves and instabilities, nonlinear phenomena, solitons and solitary waves, ionosphere, Sun: corona, incoherent scatter radar, MHD
Keyword [sv]
plasmavågor och instabiliteter, ickelinjära fenomen, solitoner och solitära vågor, jonosfär, solen: korona, inkoherent spridningsradar, MHD
National Category
Fusion, Plasma and Space Physics Fusion, Plasma and Space Physics Fusion, Plasma and Space Physics Other Physics Topics
Research subject
Physics; Space and Plasma Physics
Identifiers
URN: urn:nbn:se:umu:diva-42955ISBN: 978-91-977255-7-6OAI: oai:DiVA.org:umu-42955DiVA: diva2:410884
Public defence
2011-05-13, Aulan, Institutet för rymdfysik, Rymdcampus 1, Kiruna, 10:00 (English)
Opponent
Supervisors
Available from: 2011-04-20 Created: 2011-04-15 Last updated: 2011-04-19Bibliographically approved
List of papers
1. Dispersive MHD waves and alfvenons in charge non-neutral plasmas
Open this publication in new window or tab >>Dispersive MHD waves and alfvenons in charge non-neutral plasmas
2008 (English)In: Nonlinear processes in geophysics, ISSN 1023-5809, E-ISSN 1607-7946, Vol. 15, no 4, 681-693 p.Article in journal (Refereed) Published
Abstract [en]

Dispersive properties of linear and nonlinear MHD waves, including shear, kinetic, electron inertial Alfv´en, and slow and fast magnetosonic waves are analyzed using both analytical expansions and a novel technique of dispersion diagrams. The analysis is extended to explicitly include space charge effects in non-neutral plasmas. Nonlinear soliton solutions, here called alfvenons, are found to represent either convergent or divergent electric field structures with electric potentials and spatial dimensions similar to those observed by satellites in auroral regions. Similar solitary structures are postulated to be created in the solar corona, where fast alfvenons can provide acceleration of electrons to hundreds of keV during flares. Slow alfvenons driven by chromospheric convection produce positive potentials that can account for the acceleration of solar wind ionsto 300–800 km/s. New results are discussed in the context of observations and other theoretical models for nonlinear Alfv´en waves in space plasmas.

Identifiers
urn:nbn:se:umu:diva-42824 (URN)
Available from: 2011-04-14 Created: 2011-04-13 Last updated: 2011-04-19Bibliographically approved
2. Electric potentials and energy fluxes available for particle acceleration by alfvenons in the solar corona
Open this publication in new window or tab >>Electric potentials and energy fluxes available for particle acceleration by alfvenons in the solar corona
2008 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 680, no 2, L153-L156 p.Article in journal (Refereed) Published
Abstract [en]

We show that solitary wave solutions of the one- and two-fluid MHD equations, here called alfvenons, represent two types of electric field structures with negative or positive potentials that can explain the acceleration of particles in the solar corona. Negative potentials are created self-consistently by fast alfvenons and can reach hundreds of kilovolts, which could accelerate the electrons that produce X-ray emissions during flares. Slow alfvenons create positive potential structures of a few kV that accelerate solar wind ions. These alfvenons can be powered by irregular plasma flows in the photosphere and chromosphere, as well as by time-varying magnetic fields during reconnection events at the tops of coronal loops. Similar alfvenon structures are observed in the terrestrial magnetosphere, where they accelerate particles related to aurorae.

Keyword
acceleration of particles, MHD, Sun: corona, Sun: flares, Sun: X-rays, gamma rays
Identifiers
urn:nbn:se:umu:diva-42825 (URN)10.1086/589878 (DOI)
Available from: 2011-04-14 Created: 2011-04-13 Last updated: 2011-04-19Bibliographically approved
3. [Reply to comment on heating of the solar corona by dissipative Alfvén solitons]
Open this publication in new window or tab >>[Reply to comment on heating of the solar corona by dissipative Alfvén solitons]
2007 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 99, no 8, 089502(1)- p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
The American Physical Society, 2007
Identifiers
urn:nbn:se:umu:diva-8760 (URN)10.1103/PhysRevLett.99.089502 (DOI)
Note
Phys. Rev. Lett. 96, 175003 (2006) [4 pages] Heating of the Solar Corona by Dissipative Alfvén Solitons, Stasiewicz, Kristof. DOI: 10.1103/PhysRevLett.96.175003. Comment on "Heating of the Solar Corona by Dissipative Alfvén Solitons" Vranjes, J.; Poedts, S.; Pandey, B. P. Physical Review Letters, vol. 98, Issue 4, id. 049501. DOI: 10.1103/PhysRevLett.98.049501Available from: 2011-04-14 Created: 2008-02-10 Last updated: 2011-04-19Bibliographically approved
4. Ion-acoustic solitary waves and spectrally uniform scattering cross section enhancements
Open this publication in new window or tab >>Ion-acoustic solitary waves and spectrally uniform scattering cross section enhancements
2010 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 28, no 6, 1299-1306 p.Article in journal (Refereed) Published
Abstract [en]

Spectra measured by incoherent scatter radars are formed predominantly by scattering of the incident signal off ion-acoustic and Langmuir waves in the ionosphere. Occasionally, the upshifted and/or downshifted lines produced by the ion-acoustic waves are enhanced well above thermal levels and referred to as naturally enhanced ion-acoustic lines. In this paper, we study another kind of enhancement, which is spectrally uniform over the whole ion-line, i.e. the upand downshifted shoulder and the spectral valley in between. Based on observations made with the EISCAT Svalbard radar (ESR) facility, we investigate the transient and spectrally uniform power enhancements, which can be explained by ionacoustic solitary waves. We use a theory of nonlinear waves in a magnetized plasma to determine the properties of such waves and evaluate their effects on scattered signals easured by ESR.We suggest a new mechanism that can explain backscattered power enhancements by one order of magnitude above the thermal level and show that it is consistent with observations.

Place, publisher, year, edition, pages
Copernicus Publications, 2010
Keyword
Ionosphere (Auroral ionosphere, Plasma waves and instabilities), Space plasma physics (Nonlinear phenomena)
Identifiers
urn:nbn:se:umu:diva-42826 (URN)10.5194/angeo-28-1299-2010 (DOI)
Available from: 2011-04-14 Created: 2011-04-13 Last updated: 2011-04-19Bibliographically approved
5. Soliton-induced spectrally uniform ion line power enhancements at the ionospheric F region peak
Open this publication in new window or tab >>Soliton-induced spectrally uniform ion line power enhancements at the ionospheric F region peak
2012 (English)In: Earth Planets and Space, ISSN 1343-8832, E-ISSN 1880-5981, Vol. 64, no 7, 605-611 p.Article in journal (Refereed) Published
Abstract [en]

We present European incoherent scatter (EISCAT) observations of spectrally uniform ion line power enhancements (SUIPE), where the up- and downshifted shoulder and the spectral valley between them are enhanced simultaneously and equally. We have identified 48 cases of this type of ion line enhancements in data from the EISCAT Svalbard radar taken during the International Polar Year (extending from March 2007 to the end of February 2008). The SUIPEs are observed at altitudes between 210 km and 280 km with a standard deviation of 9% of the average occurrence height 230 km. The power enhancements are one order of magnitude above the thermal level. The SUIPEs occur at the ionospheric F region peak with 85% of the cases located within 10 km of the peak. The occurrence shows a clear preference for magnetically disturbed conditions, with the likelihood of occurrence increasing with increasing K index. A majority of the events occur in the magnetic evening to pre-midnight sector.

Place, publisher, year, edition, pages
Tokyo: Terra scientific publishing company, 2012
Keyword
auroral ionosphere, radar observations, plasma waves and instabilities, solitons and solitary waves
National Category
Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:umu:diva-42827 (URN)10.5047/eps.2012.02.005 (DOI)000308133500005 ()
External cooperation:
Available from: 2011-04-14 Created: 2011-04-13 Last updated: 2016-09-12Bibliographically approved
6. Incoherent scatter ion line enhancements and auroral arc-induced Kelvin-Helmholtz turbulence
Open this publication in new window or tab >>Incoherent scatter ion line enhancements and auroral arc-induced Kelvin-Helmholtz turbulence
Show others...
2015 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 122, 119-128 p.Article in journal (Refereed) Published
Abstract [en]

We present two cases of incoherent-scatter ion line enhancements in conjunction with auroral arcs drifting through the radar beam. The up- and downshifted ion line shoulders as well as the spectral region between them are enhanced equally and simultaneously. The power enhancements are one order of magnitude above the thermal level and are concentrated in less than 15 km wide altitude ranges at the ionospheric F region peak. The auroral arc passages are preceded by significantly enhanced ion temperatures in the E region, which are shown to generate high velocity shears. We use a Hall MHD model of velocity shears perpendicular to the geomagnetic field and show that a Kelvin-Helmholtz instability will grow for the two presented cases. We assess the possibility that the subsequently generated low frequency turbulence can explain the observed spectrally uniform ion line power enhancements.

Place, publisher, year, edition, pages
Oxford: Pergamon Press, 2015
Keyword
auroral ionosphere, radar observations, plasma waves and instabilities
National Category
Geochemistry Geophysics Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:umu:diva-42828 (URN)10.1016/j.jastp.2014.10.018 (DOI)000348627300013 ()
External cooperation:
Available from: 2011-04-14 Created: 2011-04-13 Last updated: 2016-09-06Bibliographically approved

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