Title
Statistics of Langmuir waves associated with type III solar radio bursts / Sonja Vidojević.
Creator
Vidojević, Sonja.
Copyright date
2012
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Autorstvo-Nekomercijalno-Bez prerade 3.0 Srbija (CC BY-NC-ND 3.0)
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Language
English
Cobiss-ID
Theses Type
Doktorska disertacija
description
Datum odbrane: 24. 9. 2012.
Academic Expertise
Prirodno-matematičke nauke
Academic Title
-
Publisher
[S. Vidojević]
description
Astronomy and astrophysics
Abstract (en)
Interplanetary electron beams, produced by solar flares, are unstable in the
solar wind and generate Langmuir waves at the local plasma frequency, fp. These waves
are then converted into the so-called type III radio bursts which are freely propagating
electromagnetic emissions at fp or its harmonic. The type IIIs are therefore observed as
drifting emissions from high to low frequencies, in the kilometric wavelengths range. Since
the first theoretical explanation by Ginzburg and Zhelezniakov (1958a), several refined
models have attempted to describe in details the physical processes at the origin of type
III bursts. The mechanisms of “Bump-on-tail” instabilities, Langmuir waves generations,
conversion of these Langmuir waves into radio emissions throughout nonlinear wave-wave
interactions etc, have been studied in detail. Of particular interest from the observational
point of view are the so called in situ type III bursts for which the electron beam, at
the origin of the emission and traveling along open interplanetary magnetic field lines, is
observed directly in situ by a spacecraft, together with the local Langmuir waves and the
resulting radio emissions. Until now only a few of these in situ type IIIs have been reported
in the literature.
The first research study performed in this thesis was to examine the first 16 years of
radio, waves and particles data recorded by the Wind spacecraft in the Solar Wind and
to look for in situ type IIIs. Applying rigorous and careful criteria, this examination has
yielded to a data set of 36 high-quality events. With such a numerous data set, which is
statistically representative of the studied phenomenon, it is now possible to constrain observationally
and with a better confidence the type III generation models. After having built
our statistical dataset, we have studied, for each of the events, the precise shapes of the
Langmuir wave power distributions, observed in the spectral domain. We have fitted these
observed distributions by a Pearson’s system of probability distributions and have shown
that the probability distributions of the logarithm of the Langmuir waves power spectral
density belong to three “main” types of Pearson’s probability distributions: type I, type
IV and type VI. In addition we have modeled the effects of the instrumental integration
time of the Wind radio receivers on the observed Langmuir wave power distributions. By
combining our observations with our models we have shown that it was not possible to conclude
definitively, that the distribution of the Langmuir waves energy in the real temporal
domain is lognormal, as it is predicted in some theories as the Stochastic Growth Theory
by Robinson (1992).
In the last part of the thesis, we have shown how our high-quality data set of 36 in situ
type III events can be used for further studies that could allow to constrain the theoretical
models even better. For instance we have investigated the correlation between the Langmuir
waves power and the energy of impulsive electron or with the power of the radio emissions
themselves
Abstract (fr)
Les faisceaux d’électrons interplanétaires, produits par les éruptions solaires, sont instables
dans le vent solaire et génèrent des ondes de Langmuir à la fréquence plasma locale, fp.
Ces ondes sont ensuite converties en ce qu’on appelle les sursauts radio de type III qui sont
des émissions électromagnétiques se propageant librement à fp ou leurs harmoniques. Les
type IIIs sont donc observés comme des émissions dérivant des hautes aux basses fréquences,
dans la gamme de longueurs d’onde kilométrique. Depuis la première explication théorique
par Ginzburg and Zhelezniakov (1958a), plusieurs modèles détaillés ont été proposés pour
décrire en détail les processus physiques à l’origine des sursauts de type III. Les mécanismes
d’instabilités “Bump-on-tail”, les générations d’ondes de Langmuir, la conversion de
ces ondes de Langmuir en émissions radio à travers les interactions non linéaires onde-onde
etc, ont été étudiées en détail. Les type III in situ, pour lesquels le faisceau d’électron, à
l’origine de l’émission et qui voyage le long des lignes de champ magnétique interplanétaire
ouvertes, sont observées directement in situ par un spacecraft, avec les ondes de Langmuir
locales et les émissions de radio qui en résultent, sont particulièrement intéressants. Jusqu’à
présent, seuls quelques-uns de ces type III in situ ont été rapportés dans la littérature.
La première étude réalisée dans le cadre de cette thèse a été d’examiner les 16 premières
années de données ondes et particules enregistrées par le satellite Wind dans le vent solaire
et de chercher les type III in situ. L’application de critères rigoureux pendant cet examen
a fournit un ensemble, de données de 36 événements de garnde qualité. Avec un tel
ensemble, statistiquement représentatif du phénomène étudié, il est désormais possible de
mieux contraindre les modèles de génération de type III. Après avoir construit notre base de
données statistiques, nous avons étudié, pour chacun de ces événements, les formes précises
des distributions de puissance des ondes Langmuir, observées dans le domaine spectral.
Nous avons modélisé ces distributions avec un système de distributions de probabilités de
type Pearson. Nous avons montré que les distributions de probabilité du logarithme de la
densité de puissance spectrale des ondes de Langmuir appartiennent à trois types ”principaux”
de distributions de Pearson : type I, type IV et type VI. En outre, nous avons
simulé les effets du d’intégration et de la fonction de transfert instrumentale des récepteurs
radio de Wind sur les distributions de puissance des ondes de Langmuir observées. En
combinant nos observations avec nos simulations, nous avons montré qu’il n’était pas possible
de conclure de façon définitive, que la distribution de l’énergie des ondes de Langmuir
dans le domaine temporel réel est log-normale, comme prévu par certaines théories de type
“croissance stochastique” (Robinson, 1992).
Dans la dernière partie de la thèse, nous avons montré comment notre base de données
constituée par les 36 événements de type III in situ peut être utilisée pour d’autres études
permettant d’encore mieux contraindre les modèles théoriques. Par exemple, nous avons
étudié la corrélation entre la puissance des ondes de Langmuir et l’énergie des électrons
impulsifs ou bien encore la puissance des émissions de radio elles-mêmes.
Abstract (sr)
Međuplanetski snopovi elektrona proizvedeni u Sunčevim erupcijama nestabilni
su u Sunčevom vetru i proizvode Lengmirove talase na plazmenoj frekvenciji, fp. Ovi
talasi se zatim konvertuju u takozvane radio-erupcije tipa III – elektromagnetno zračenje
koje se slobodno prostire na fp ili na prvom harmoniku. Erupcije tipa III se posmatraju kao
zračenje koje se pomera od visokih ka niskim frekvencijama u kilometarskom opsegu. Posle
prvog teorijskog objašnjenja koje su dali Ginzburg i Železnjakov 1958. godine (Ginzburg
and Zhelezniakov, 1958a), sa nekoliko poboljšanih modela izvršen je pokušaj da se detaljno
opišu fizički procesi od kojih potiču erupcije tipa III. Nestabilnost usled “izbočine na repu”
(“Bump-on-tail”, eng.) raspodele po brzinama čestica, generisanje Lengmirovih talasa, konverzija
Lengmirovih talasa u radio-zračenje putem nelinearnih talasno-talasnih interakcija
itd, su mehanizmi koji su detaljno proučavani. Sa posmatračkog stanovišta, od posebnog
interesa su takozvane erupcije tipa III za koje je snop elektrona, koji se kreće duž linija sila
magnetnog polja, posmatran pomoću satelita na mestu izvora emitovanja direktno–in situ
zajedno sa Lengmirovim talasima i rezultujućom radio-emisijom. Samo nekoliko erupcija
tipa III posmatranih in situ je do sada proučeno i opisano u literaturi.
Prvi zadatak u ovoj disertaciji je bio da se ispitaju posmatranja čestica, radio i elektrostatičkog
zračenja Sunčevog vetra zabeleženih pomoću satelita Wind in situ tokom prvih
16 godina i da se izdvoje erupcije tipa III. Primenjujući pažljivo odabrane stroge kriterijume,
dobijen je skup od 36 događaja visokog kvaliteta. Sa ovako brojnim skupom posmatranja
koji je statistički reprezentativan za posmatranu pojavu, sada je sa većim poverenjem
moguće postaviti posmatračka ograničenja na modele generisanja erupcija tipa III. Nakon
izdvajanja statističkog skupa, za svaki od dogaljaja je precizno određen oblik raspodele
snage Lengmirovih talasa posmatrane u spektralnom domenu. Ova posmatranja su modelovana
sistemom Pirsonovih raspodela verovatnoće i pokazano je da raspodela verovatnoće
logaritama spektralne gustine snage Lengmirovih talasa pripada trima “glavnim” tipovima
Pirsonovih raspodela verovatnoće: tipu I, tipu IV i tipu VI. Dodatno su modelovani instrumentski
efekti vremena integracije radio-prijemnika satelita Wind na posmatrane raspodele
snage Lengmirovih talasa. Kombinujući posmatranja i naše modele, pokazali smo da nije
moguće izvesti definitivan zaključak da je raspodela energije Lengmirovih talasa u realnom
vremenu log-normalna što predviđaju neke teorije kao što je Robinsonova teorija stohastičkog
rasta (Robinson, 1992).
U poslednjem delu disertacije, pokazali smo kako naš skup in situ posmatranja visokog
kvaliteta od 36 događaja tipa III može da se koristi u budućim studijama kojima bi se još
bolje postavila ograničenja na teorijske modele. Mi smo, na primer, ispitali korelaciju snage
Lengmirovih talasa sa energijom brzih elektrona i sa snagom radio-zračenja.
Authors Key words
Solar wind; Langmuir waves; Electron beam; Type III radio bursts.
Authors Key words
Sunčev vetar; Lengmirovi talasi; Snop elektrona; Radio erupcije tipa III.
Classification
a523.62-726-78(043.3)
Type
Tekst
Abstract (en)
Interplanetary electron beams, produced by solar flares, are unstable in the
solar wind and generate Langmuir waves at the local plasma frequency, fp. These waves
are then converted into the so-called type III radio bursts which are freely propagating
electromagnetic emissions at fp or its harmonic. The type IIIs are therefore observed as
drifting emissions from high to low frequencies, in the kilometric wavelengths range. Since
the first theoretical explanation by Ginzburg and Zhelezniakov (1958a), several refined
models have attempted to describe in details the physical processes at the origin of type
III bursts. The mechanisms of “Bump-on-tail” instabilities, Langmuir waves generations,
conversion of these Langmuir waves into radio emissions throughout nonlinear wave-wave
interactions etc, have been studied in detail. Of particular interest from the observational
point of view are the so called in situ type III bursts for which the electron beam, at
the origin of the emission and traveling along open interplanetary magnetic field lines, is
observed directly in situ by a spacecraft, together with the local Langmuir waves and the
resulting radio emissions. Until now only a few of these in situ type IIIs have been reported
in the literature.
The first research study performed in this thesis was to examine the first 16 years of
radio, waves and particles data recorded by the Wind spacecraft in the Solar Wind and
to look for in situ type IIIs. Applying rigorous and careful criteria, this examination has
yielded to a data set of 36 high-quality events. With such a numerous data set, which is
statistically representative of the studied phenomenon, it is now possible to constrain observationally
and with a better confidence the type III generation models. After having built
our statistical dataset, we have studied, for each of the events, the precise shapes of the
Langmuir wave power distributions, observed in the spectral domain. We have fitted these
observed distributions by a Pearson’s system of probability distributions and have shown
that the probability distributions of the logarithm of the Langmuir waves power spectral
density belong to three “main” types of Pearson’s probability distributions: type I, type
IV and type VI. In addition we have modeled the effects of the instrumental integration
time of the Wind radio receivers on the observed Langmuir wave power distributions. By
combining our observations with our models we have shown that it was not possible to conclude
definitively, that the distribution of the Langmuir waves energy in the real temporal
domain is lognormal, as it is predicted in some theories as the Stochastic Growth Theory
by Robinson (1992).
In the last part of the thesis, we have shown how our high-quality data set of 36 in situ
type III events can be used for further studies that could allow to constrain the theoretical
models even better. For instance we have investigated the correlation between the Langmuir
waves power and the energy of impulsive electron or with the power of the radio emissions
themselves
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